text:
Hafizullah Amin

Hafizullah Amin (حفيظ الله امين; 1 August 1929 – 27 December 1979) was an Afghan communist head of state, who served in that position for a little over three months, from September 1979 until his assassination. He organized the Saur Revolution of 1978 and co-founded the Democratic Republic of Afghanistan (DRA), ruling Afghanistan as General Secretary of the People's Democratic Party.

Born in the town of Paghman in Kabul Province, Amin studied at Kabul University and started his career as a teacher before he twice went to the United States to study. During this time, Amin became attracted to Marxism and became involved in radical student movements at the University of Wisconsin. Upon his return to Afghanistan, he used his teaching position to spread socialist ideologies to students, and he later joined the People's Democratic Party of Afghanistan (PDPA), a new far-left organization co-founded by Nur Muhammad Taraki and Babrak Karmal. He ran as a candidate in the 1965 parliamentary election but failed to secure a seat, but in 1969 became the only Khalqist elected to parliament, increasing his standing within the party.

Amin was the main organizer of the April 1978 Saur Revolution, which overthrew the government of Mohammad Daoud Khan and formed a pro-Soviet state based on socialist ideals. Being second in chief of the Democratic Republic, Amin soon became the regime's strongman, the main architect of the state's programs including mass persecution of those deemed counter-revolutionary. A growing personal struggle with General Secretary Taraki eventually led to Amin wrestling power away then successfully deposing him and later ordering his execution; on 16 September 1979, Amin named himself Chairman of the Council of Ministers (head of government), Chairman of the Revolutionary Council (head of state), and General Secretary of the PDPA Central Committee (supreme leader).

Amin's short-lived leadership featured controversies from beginning to end. His government failed to solve the problem of the population revolting against the regime as the situation rapidly worsened and army desertions and defections continued. He tried to change things with friendly overtures to the United States, however his reputation in Washington was tarnished by his role in the assassination of Adolph Dubs. Some Afghans, especially those from minority ethnic groups such as the Hazaras, held Amin responsible for the regime's harshest measures, such as ordering thousands of executions, more than 7,000 of which were from the Hazara minority. Thousands of people disappeared without trace during his time in office. The Soviet Union under Leonid Brezhnev was dissatisfied with and mistrusted Amin; they intervened in Afghanistan, invoking the 1978 Twenty-Year Treaty of Friendship between Afghanistan and the Soviet Union. Soviet operatives assassinated Amin at the Tajbeg Palace on 27 December 1979 as part of Operation Storm-333, kickstarting the 10-year Soviet–Afghan War; he had ruled for a little more than three months.

Early life and career
Hafizullah Amin was born to a Kharōṭī Ghilzai Pashtun family in the Qazi Khel village in Paghman on 1 August 1929. His father, a civil servant, died in 1937 when he was 8. Thanks to his brother Abdullah, a primary school teacher, Amin was able to attend both primary and secondary school, which in turn allowed him to attend Kabul University (KU). After studying mathematics there, he also graduated from the Darul Mualimeen Teachers College in Kabul, and became a teacher. Amin later became vice-principal of the Darul Mualimeen College, and then principal of the prestigious Avesina High School, and in 1957 left Afghanistan for Columbia University in New York City, where he earned MA in education. It was at Columbia that Amin became attracted to Marxism, and in 1958 he became a member of the university's Socialist Progressive Club. When he returned to Afghanistan, Amin became a teacher at Kabul University, and later, for the second time, the principal of Avesina High School. During this period Amin became acquainted with Nur Muhammad Taraki, a communist. Around this time, Amin quit his position as principal of Avesina High School to become principal of the Darul Mualimeen College.

It is alleged that Amin became radicalised during his second stay in the United States in 1962, when he enrolled in a work-study group at the University of Wisconsin. Amin studied in the doctoral programme at the Columbia University Teachers College, but started to neglect his studies in favour of politics; in 1963 he became head of the Afghan students' association at the college. The association was funded by the Asia Foundation, known to be a CIA pass-through group, or front. When he returned to Afghanistan in the mid-1960s, the route flew to Afghanistan by way of Moscow. There, Amin met the Afghan ambassador to the Soviet Union, his old friend Ali Ahmad Popel, a previous Afghan Minister of Education. During his short stay, Amin became even more radicalised. Some people, Nabi Misdaq for instance, do not believe he travelled through Moscow, but rather West Germany and Lebanon. By the time he had returned to Afghanistan, the Communist People's Democratic Party of Afghanistan (PDPA) had already held its founding congress, which was in 1965. Amin ran as a candidate for the PDPA in the 1965 parliamentary election, and lost by a margin of less than fifty votes. In 1966, when the PDPA Central Committee was expanded, Amin was elected as a non-voting member, and in the spring of 1967 he gained full membership. Amin's standing in the Khalq faction of the PDPA increased when he was the only Khalqist elected to parliament in the 1969 parliamentary election. When the PDPA split along factional lines in 1967, between Khalqists led by Nur and Parchamites led by Babrak Karmal, Amin joined the Khalqists. As a member of parliament, Amin tried to win over support from the Pashtun people in the armed forces. According to a biography about Amin, he used his position as member of parliament to fight against imperialism, feudalism, and Reactionary tendencies, and fought against the "rotten" regime, the monarchy. Amin himself said that he used his membership in parliament to pursue the class struggle against the bourgeoisie. Relations between Khalqists and Parchamites deteriorated during this period. Amin, the only Khalq member of parliament, and Babrak Karmal, the only Parcham member of parliament, did not cooperate with each other. Amin would later, during his short stint in power, mention these events with bitterness. Following the arrest of fellow PDPA members Dastagir Panjsheri and Saleh Mohammad Zeary in 1969, Amin became one of the party's leading members, and was still a pre-eminent party member by the time of their release in 1973.

The Daoud era
From 1973 until the PDPA unification in 1977, Amin was second only to Taraki in the Khalqist PDPA. When the PDPA ruled Afghanistan, their relationship was referred to as a disciple (Amin) following his mentor (Taraki). This official portrayal of the situation was misleading; their relationship was more work-oriented. Taraki needed Amin's "tactical and strategic talents"; Amin's motivations are more uncertain, but it is commonly believed that he associated with Taraki to protect his own position. Amin had attracted many enemies during his career, the most notable being Karmal. According to the official version of events, Taraki protected Amin from party members or others who wanted to hurt the PDPA and the country. When Mohammed Daoud Khan ousted the monarchy, and established the Republic of Afghanistan, the Khalqist PDPA offered its support for the new regime if it established a National Front which presumably included the Khalqist PDPA itself. The Parchamite PDPA had already established an alliance with Daoud at the beginning of his regime, and Karmal called for the dissolution of the Khalqist PDPA. Karmal's call for dissolution only worsened relations between the Khalqist and Parchamite PDPA. However, Taraki and Amin were lucky; Karmal's alliance actually hurt the Parchamites' standing in Afghan politics. Some communists in the armed forces became disillusioned with the government of Daoud, and turned to the Khalqist PDPA because of its apparent independence. Parchamite association with the Daoud government indirectly led to the Khalqist-led PDPA coup of 1978, popularly referred to as the Saur Revolution. From 1973 until the 1978 coup, Amin was responsible for organising party work in the Afghan armed forces. According to the official version, Amin "met patriotic liaison officers day or night, in the desert or the mountains, in the fields or the forests, enlightening them on the basis of the principles of the working class ideology." Amin's success in recruiting military officers lay in the fact that Daoud "betrayed the left" soon after taking power. When Amin began recruiting military officers for the PDPA, it was not difficult for him to find disgruntled military officers. In the meantime, relations between the Parchamite and Khalqist PDPA deteriorated; in 1973 it was rumoured that Major Zia Mohammadzai, a Parchamite and head of the Republican Guard, planned to assassinate the entire Khalqist leadership. The plan, if true, failed because the Khalqists found out about it. The assassination attempt proved to be a further blow to relations between the Parchamites and Khalqists. The Parchamites deny that they ever planned to assassinate the Khalqist leadership, but historian Beverley Male argues that Karmal's subsequent activities give credence to the Khalqist view of events. Because of the Parchamite assassination attempt, Amin pressed the Khalqist PDPA to seize power in 1976 by ousting Daoud. The majority of the PDPA leadership voted against such a move. The following year, in 1977, the Parchamites and Khalqists officially reconciled, and the PDPA was unified. The Parchamite and Khalqist PDPAs, which had separate general secretaries, politburos, central committees and other organisational structures, were officially unified in the summer of 1977. One reason for unification was that the international communist movement, represented by the Communist Party of India, Iraqi Communist Party and the Communist Party of Australia, called for party unification.

Saur Revolution
On 18 April 1978 Mir Akbar Khyber, the chief ideologue of the Parcham faction, was killed; he was commonly believed to have been assassinated by the Daoud government. Khyber's assassination initiated a chain of events which led to the PDPA taking power eleven days later, on 27 April. The assassin was never caught, but Anahita Ratebzad, a Parchamite, believed that Amin had ordered the assassination. Khyber's funeral evolved into a large anti-government demonstration. Daoud, who did not understand the significance of the events, began a mass arrest of PDPA members seven days after Khyber's funeral. Amin, who organised the subsequent revolution against Daoud, was one of the last Central Committee members to be arrested by the authorities. His late arrest can be considered as proof of the regime's lack of information; Amin was the leading revolutionary party organiser. The government's lack of awareness was proven by the arrest of Taraki – Taraki's arrest was the pre-arranged signal for the revolution to commence. When Amin found out that Taraki had been arrested, he ordered the revolution to begin at 9 am on 27 April. Amin, in contrast to Taraki, was not imprisoned, but instead put under house arrest. His son, Abdur Rahman, was still allowed freedom of movement. The revolution was successful, thanks to overwhelming support from the Afghan military; for instance, it was supported by Defence Minister Ghulam Haidar Rasuli, Aslam Watanjar the commander of the ground forces, and the Chief of Staff of the Afghan Air Force, Abdul Qadir.

Khalq–Parcham break
After the Saur revolution, Taraki was appointed Chairman of the Presidium of the Revolutionary Council and Chairman of the Council of Ministers, and retained his post as PDPA general secretary. Taraki initially formed a government which consisted of both Khalqists and Parchamites; Karmal became Deputy Chairman of the Revolutionary Council while Amin became Minister of Foreign Affairs and a Deputy Prime Minister, and Mohammad Aslam Watanjar became a Deputy Prime Minister. The two Parchamites Abdul Qadir and Mohammad Rafi became Minister of National Defence and Minister of Public Works respectively. According to Angel Rasanayagam, the appointment of Amin, Karmal and Watanjar as Deputy Prime Ministers led to the establishment of three cabinets; the Khalqists were answerable to Amin, the Parchamites were answerable to Karmal, and the military officers (who were Parchamites) were answerable to Watanjar. The first conflict between the Khalqists and Parchamites arose when the Khalqists wanted to give PDPA Central Committee membership to the military officers who participated in the Saur Revolution. Amin, who had previously opposed the appointment of military officers to the PDPA leadership, switched sides; he now supported their elevation. The PDPA Politburo voted in favour of giving membership to the military officers; the victors (the Khalqists) portrayed the Parchamites as opportunists, implying that the Parchamites had ridden the revolutionary wave, but not actually participated in the revolution. To make matters worse for the Parchamites, the term Parcham was, according to Taraki, a word synonymous with factionalism.

"There is only one leading force in the country - Hafizullah Amin. In the Politburo, everybody fears Amin." On 27 June 1978, three months after the revolution, Amin managed to outmaneuver the Parchamites at a Central Committee meeting. The meeting decided that the Khalqists had exclusive rights to formulate and decide policy, a policy which left the Parchamites impotent. Karmal was exiled, but was able to establish a network with the remaining Parchamites in government. A coup to overthrow Amin was planned for September. Its leading members in Afghanistan were Qadir, the defence minister, and Army Chief of Staff General Shahpur Ahmedzai. The coup was planned for 4 September, on the Festival of Eid, because soldiers and officers would be off duty. The conspiracy failed when the Afghan ambassador to India told the Afghan leadership about the plan. A purge was initiated, and Parchamite ambassadors were recalled; few returned, for example Karmal and Mohammad Najibullah both stayed in their assigned countries.

Amin–Taraki break
The Afghan people revolted against the PDPA government when the government introduced several socialist reforms, including land reforms. By early 1979, twenty-five out of Afghanistan's twenty-eight provinces were unsafe because of armed resistance against the government. On 29 March 1979, the Herat uprising began; the uprising turned the revolt into an open war between the Afghan government and anti-regime resistance. It was during this period that Amin became Kabul's strongman. Shortly after the Herat uprising had been crushed, the Revolutionary Council convened to ratify the new Five-Year Plan, the Afghan–Soviet Friendship Treaty, and to vote on whether or not to reorganise the cabinet and to enhance the power of the executive (the Chairman of the Revolutionary Council). While the official version of events said that all issues were voted on democratically at the meeting, the Revolutionary Council held another meeting the following day to ratify the new Five-Year Plan and to discuss the reorganisation of the cabinet.

Alexander Puzanov, the Soviet ambassador to Afghanistan, was able to persuade Aslam Watanjar, Sayed Mohammad Gulabzoy and Sherjan Mazdoryar to become part of a conspiracy against Amin. These three men put pressure on Taraki, who by this time believed that "he really was the 'great leader'", to sack Amin from office. It is unknown if Amin knew anything about the conspiracy against him, but it was after the cabinet reorganisation that he talked about his dissatisfaction. On 26 March the PDPA Politburo and the Council of Ministers approved the extension of the powers of the executive branch, and the establishment of the Homeland Higher Defence Council (HHDC) to handle security matters. Many analysts of the day regarded Amin's appointment as Prime Minister as an increase in his powers at the expense of Taraki. However, the reorganisation of the cabinet and the strengthening of Taraki's position as Chairman of the Revolutionary Council, had reduced the authority of the Prime Minister. The Prime Minister was, due to the strengthening of the executive, now appointed by the Chairman of the Revolutionary Council. While Amin could appoint and dismiss new ministers, he needed Taraki's consent to actually do so. Another problem for Amin was that while the Council of Ministers was responsible to the Revolutionary Council and its chairman, individual ministers were only responsible to Taraki. When Amin became Prime Minister, he was responsible for planning, finance and budgetary matters, the conduct of foreign policy, and for order and security. The order and security responsibilities had been taken over by the HHDC, which was chaired by Taraki. While Amin was HHDC Deputy chairman, the majority of HHDC members were members of the anti-Amin faction. For instance, the HHDC membership included Watanjar the Minister of National Defence, Interior Minister Mazdoryar, the President of the Political Affairs of the Armed Forces Mohammad Iqbal, Mohammad Yaqub, the Chief of the General Staff, the Commander of the Afghan Air Force Nazar Mohammad and Assadullah Sarwari the head of ASGA, the Afghan secret police. The order of precedence had been institutionalised, whereby Taraki was responsible for defence and Amin responsible for assisting Taraki in defence related matters. Amin's position was given a further blow by the democratisation of the decision-making process, which allowed its members to contribute; most of them were against Amin. Another problem for Amin was that the office of HHDC Deputy chairman had no specific functions or powers, and the appointment of a new defence minister who opposed him drastically weakened his control over the Ministry of National Defence. The reorganisation of ministers was a further blow to Amin's position; he had lost control of the defence ministry, the interior ministry and the ASGA. Amin still had allies at the top, many of them in strategically important positions, for instance, Yaqub was his brother-in-law and the Security Chief in the Ministry of Interior was Sayed Daoud Taroon, who was also later appointed to the HHDC as an ordinary member in April. Amin succeeded in appointing two more of his allies to important positions; Mohammad Sediq Alemyar as Minister of Planning and Khayal Mohammad Katawazi as Minister of Information and Culture; and Faqir Mohammad Faqir was appointed Deputy Prime Minister in April 1978. Amin's political position was not secure when Alexei Yepishev, the Head of the Main Political Directorate of the Soviet Army and Navy, visited Kabul. Yepishev met personally with Taraki on 7 April, but never met with Amin. The Soviets were becoming increasingly worried about Amin's control over the Afghan military. Even so, during Yepishev's visit Amin's position was actually strengthened; Taroon was appointed Taraki's aide-de-camp.

Soon after, at two cabinet meetings, the strengthening of the executive powers of the Chairman of the Revolutionary Council was proven. Even though Amin was Prime Minister, Taraki chaired the meetings instead of him. Amin's presence at these two meetings was not mentioned at all, and it was made clear that Taraki, through his office as Chairman of the Revolutionary Council, also chaired the Council of Ministers. Another problem facing Amin was Taraki's policy of autocracy; he tried to deprive the PDPA Politburo of its powers as a party and state decision-making organ. The situation deteriorated when Amin personally warned Taraki that "the prestige and popularity of leaders among the people has no common aspect with a personality cult."

Factionalism within the PDPA made it ill-prepared to handle the intensified counter-revolutionary activities in the country. Amin tried to win support for the communist government by depicting himself as a devout Muslim. Taraki and Amin blamed different countries for helping the counter-revolutionaries; Amin attacked the United Kingdom and the British Broadcasting Corporation (BBC) and played down American and Chinese involvement, while Taraki blamed American imperialism and Iran and Pakistan for supporting the uprising. Amin's criticism of the United Kingdom and the BBC fed on the traditional anti-British sentiments held by rural Afghans. In contrast to Taraki, "Amin bent over backwards to avoid making hostile reference to", China, the United States or other foreign governments. Amin's cautious behavior was in deep contrast to the Soviet Union's official stance on the situation; it seemed, according to Beverley Male, that the Soviet leadership tried to force a confrontation between Afghanistan and its enemies. Amin also tried to appease the Shia communities by meeting with their leaders; despite this, a section of the Shia leadership called for the continuation of the resistance. Subsequently, a revolt broke out in a Shia populated district in Kabul; this was the first sign of unrest in Kabul since the Saur Revolution. To add to the government's problems, Taraki's ability to lead the country was questioned – he was a heavy drinker and was not in good health. Amin on the other hand was characterised in this period by portrayals of strong self-discipline. In the summer of 1979 Amin began to disassociate himself from Taraki. On 27 June Amin became a member of the PDPA Politburo, the leading decision-making body in Afghanistan.

Rise to power
In-mid July the Soviets made their view official when Pravda wrote an article about the situation in Afghanistan; the Soviets did not wish to see Amin become leader of Afghanistan. This triggered a political crisis in Afghanistan, as Amin initiated a policy of extreme repression, which became one of the main reasons for the Soviet intervention later that year. On 28 July, a vote in the PDPA Politburo approved Amin's proposal of creating a collective leadership with collective decision-making; this was a blow to Taraki, and many of his supporters were replaced by pro-Amin PDPA members. Ivan Pavlovsky, the Commander of the Soviet Ground Forces, visited Kabul in mid-August to study the situation in Afghanistan. Amin, in a speech just a few days after Pavlovsky's arrival, said that he wanted closer relations between Afghanistan and the People's Republic of China; in the same speech he hinted that he had reservations about Soviet meddling in Afghanistan. He likened Soviet assistance to Afghanistan with Vladimir Lenin's assistance to the Hungarian Soviet Republic in 1919. Taraki, a delegate to the conference held by the Non-Aligned Movement in Havana, met personally with Andrei Gromyko, the Soviet Minister of Foreign Affairs, to discuss the Afghanistan situation on 9 September. Shah Wali, the Minister of Foreign Affairs, who was a supporter of Amin, did not participate in the meeting. This, according to Beverley Male, "suggested that some plot against Amin was in preparation".

Taraki was instructed to stop-over in Moscow, where the Soviet leaders urged him to remove Amin from power as per the KGB's decision, because Amin posed danger. Amin's trusted aid, Daoud Taroon, informed Amin of the meeting and the KGB's plan. In Kabul, Taraki's aides, the Gang of Four (consisting of Watanjar, Mazdoryar, Gulabzoi and Sarwari), planned to assassinate Amin but failed as Amin was informed of their plot. Within hours of Taraki's return to Kabul on 11 September, Taraki convened the cabinet "ostensibly to report on the Havana Summit". Instead of reporting on the summit, Taraki tried to dismiss Amin as Prime Minister. Amin, aware of the murder plot, demanded the Gang of Four to be removed from their posts, but Taraki laughed it off. Taraki sought to neutralise Amin's power and influence by requesting that he serve overseas as an ambassador. Amin turned down the proposal, shouting "You are the one who should quit! Because of drink and old age you have taken leave of your senses."

On 13 September, Taraki invited Amin to the presidential palace for lunch with him and the Gang of Four. Amin turned down the offer, stating he would prefer their resignation rather than lunching with them. Soviet ambassador Puzanov persuaded Amin to make the visit to the Presidential Palace along with Taroon, the Chief of Police, and Nawab Ali, an intelligence officer. Inside the palace on 14 September, bodyguards within the building opened fire on the visitors. Taroon was killed but Amin only sustained an injury and escaped. Amin drove to the Ministry of Defence building, put the Army on high alert and ordered Taraki's arrest. At 6:30 pm tanks from the 4th Armoured Corps entered the city and stood at government buildings. Shortly afterwards, Amin returned to the palace with a contingent of Army officers, and placed Taraki under arrest. The Gang of Four, however, had "disappeared" and sought refuge in the Soviet Embassy.

After Taraki's arrest, the Soviets tried to rescue Taraki (or, according to other sources, kidnap Amin) via the embassy or Bagram Air Base but the strength of Amin's officers repelled their decision to make a move. Amin was told by the Soviets not to punish Taraki and strip him and his comrades of their positions, but Amin ignored them. Amin reportedly discussed the incident with Leonid Brezhnev, and indirectly asked for the permission to kill Taraki, to which Brezhnev replied that it was his choice. Amin, who now believed he had the full support of the Soviets, ordered the death of Taraki. It is believed Taraki was suffocated with pillows on 8 October 1979. The Afghan media would report that the ailing Taraki had died, omitting any mention of his murder. Taraki's murder shocked and upset Brezhnev.

Domestic policies
Following Taraki's fall from power, Amin was elected Chairman of the Presidum of the Revolutionary Council and General Secretary of the PDPA Central Committee by the PDPA Politburo. The election of Amin as PDPA General Secretary and the removal of Taraki from all party posts was unanimous. The only members of the cabinet replaced when Amin took power were the Gang of Four – Beverley Male saw this as "a clear indication that he had their [the ministers'] support". Amin's rise to power was followed by a policy of moderation, and attempts to persuade the Afghan people that the regime was not anti-Islamic. Amin's government began to invest in the reconstruction, or reparation, of mosques. He also promised the Afghan people freedom of religion. Religious groups were given copies of the Quran, and Amin began to refer to Allah in speeches. He even claimed that the Saur Revolution was "totally based on the principles of Islam". The campaign proved to be unsuccessful, and many Afghans held Amin responsible for the regime's totalitarian behavior. Amin's rise to power was officially endorsed by the Jamiatul Ulama on 20 September 1979. Their endorsement led to the official announcement that Amin was a pious Muslim – Amin thus scored a point against the counter-revolutionary propaganda which claimed the communist regime was atheist. Amin also tried to increase his popularity with tribal groups, a feat Taraki had been unable or unwilling to achieve. In a speech to tribal elders Amin was defensive about the Western way he dressed; an official biography was published which depicted Amin in traditional Pashtun clothes. During his short stay in power, Amin became committed to establishing a collective leadership; when Taraki was ousted, Amin promised "from now on there will be no one-man government..."

Attempting to pacify the population, Amin released a list of 18,000 people who had been executed, and blamed the executions on Taraki. The total number of arrested during Taraki's and Amin's combined reign number between 17,000 and 45,000. Amin was not liked by the Afghan people. During his rule, opposition to the communist regime increased, and the government lost control of the countryside. The state of the Afghan military deteriorated; due to desertions the number of military personnel in the Afghan army decreased from 100,000 in the immediate aftermath of the Saur Revolution, to somewhere between 50,000 and 70,000. Another problem Amin faced was the KGB's penetration of the PDPA, the military and the government bureaucracy. While Amin's position in Afghanistan was becoming more perilous by the day, his enemies who were exiled in the Soviet Union and the Eastern Bloc were agitating for his removal. Babrak Karmal, the Parchamite leader, met several leading Eastern Bloc figures during this period, and Mohammad Aslam Watanjar, Sayed Mohammad Gulabzoy and Assadullah Sarwari wanted to exact revenge upon Amin.

Foreign policy
In July of 1979, Hafizullah Amin announced that the DRA was not bound by old treaties with Iran regarding the distribution of water from the Helmand River. Iran interpreted this as Afghanistan using Soviet backing to assert themselves in the region. When Amin became leader, he tried to reduce Afghanistan's dependence on the Soviet Union. The Soviets were concerned when they received reports that Amin had met personally with Gulbuddin Hekmatyar, one of the leading anti-communists in Afghanistan. His general untrustworthiness and his unpopularity amongst Afghans made it more difficult for Amin to find new "foreign patrons". Amin's involvement in the death of Adolph Dubs, the American Ambassador to Afghanistan, strained his relations with the United States. He tried to improve relations by reestablishing contact, met with three different American chargé d'affaires, and was interviewed by an American correspondent. But this did not improve Afghanistan's standing in the eyes of the United States Government. After the third meeting with Amin, J. Bruce Amstutz, the American Ambassador to Afghanistan from 1979 to 1980, believed the wisest thing to do was to maintain "a low profile, trying to avoid issues, and waiting to see what happens". In early December 1979, the Ministry of Foreign Affairs proposed a joint summit meeting between Amin and Muhammad Zia-ul-Haq, the President of Pakistan. The Pakistani Government, accepting a modified version of the offer, agreed to send Agha Shahi, the Pakistani foreign minister, to Kabul for talks. In the meanwhile, the Inter-Services Intelligence (ISI), Pakistani's secret police, continued to train Mujahideen fighters who opposed Amin's regime.

Afghan-Soviet relations
Contrary to popular belief, the Soviet leadership headed by Leonid Brezhnev, Alexei Kosygin and the Politburo, were not eager to send troops to Afghanistan. The Soviet Politburo decisions were guided by a Special Commission on Afghanistan, which consisted of Yuri Andropov the KGB chairman, Andrei Gromyko the Minister of Foreign Affairs, Defence Minister Dmitriy Ustinov, and Boris Ponomarev, the head of the International Department of the Central Committee. The Politburo was opposed to the removal of Taraki and his subsequent murder. According to Brezhnev, the General Secretary of the Central Committee of the Communist Party of the Soviet Union, "Events developed so swiftly in Afghanistan that essentially there was little opportunity to somehow interfere in them. Right now our mission is to determine our further actions, so as to preserve our position in Afghanistan and to secure our influence there." Although Afghan–Soviet relations deteriorated during Amin's short stint in power, he was invited on an official visit to Moscow by Alexander Puzanov, the Soviet ambassador to Afghanistan, because of the Soviet leadership's satisfaction with his party and state-building policy. Not everything went as planned, and Andropov talked about "the undesirable turn of events" taking place in Afghanistan under Amin's rule. Andropov also brought up the ongoing political shift in Afghanistan under Amin; the Soviets were afraid that Amin would move Afghanistan's foreign policy from a pro-Soviet position to a pro-United States position. By early-to-mid December 1979, the Soviet leadership had established an alliance with Babrak Karmal and Assadullah Sarwari.

Amin kept a portrait of Joseph Stalin on his desk. When Soviet officials criticized him of his brutality, Amin replied "Comrade Stalin showed us how to build socialism in a backward country."

As it turned out, the relationship between Puzanov and Amin broke down. Amin started a smear campaign to discredit Puzanov. This in turn led to an assassination attempt against Amin, in which Puzanov participated. The situation was worsened by the KGB accusing Amin of misrepresenting the Soviet position on Afghanistan in the PDPA Central Committee and the Revolutionary Council. The KGB also noted an increase in anti-Soviet agitation by the government during Amin's rule, and harassment against Soviet citizens increased under Amin. A group of senior politicians reported to the Soviet Central Committee that it was necessary to do "everything possible" to prevent a change in political orientation in Afghanistan. However, the Soviet leadership did not advocate intervention at this time, and instead called for increasing its influence in the Amin leadership to expose his "true intentions". A Soviet Politburo assessment referred to Amin as "a power-hungry leader who is distinguished by brutality and treachery". Amongst the many sins they alleged were his "insincerity and duplicity" when dealing with the Soviet Union, creating fictitious accusations against PDPA-members who opposed him, indulging in a policy of nepotism, and his tendency to conduct a more "balanced policy" towards First World countries. According to the former senior Soviet diplomat, Oleg Grinevsky, the KGB was becoming increasingly convinced that Amin couldn't be counted on to effectively deal with the insurgency and preserve the survival of the Afghan Marxist state.

By the end of October the Special Commission on Afghanistan, which consisted of Andropov, Gromyko, Ustinov and Ponomarev, wanted to end the impression that the Soviet government supported Amin's leadership and policy. The KGB's First Chief Directorate was put under orders that something had to be done about Afghanistan, and several of its personnel were assembled to deal with the task. Andropov fought hard for Soviet intervention, saying to Brezhnev that Amin's policies had destroyed the military and the government's capabilities to handle the crisis by use of mass repression. The plan, according to Andropov, was to assemble a small force to intervene and remove Amin from power and replace him with Karmal. The Soviet Union declared its plan to intervene in Afghanistan on 12 December 1979; large numbers of Soviet airborne troops landed in Kabul on 25 December, with the approval of Amin who miscalculated their intentions. Soviet leadership initiated Operation Storm-333 (the first phase of the intervention) on 27 December 1979.

Attempted poisoning by Amin's chef
The leadership of the USSR had no need for Amin to remain alive. Andropov's special representative in Afghanistan, General Boris Ivanov, recommended for Amin to attend a conciliatory dinner with his political mentor, who had become an enemy of Amin, so that Amin's chef could poison Amin. However, Amin survived the poisoning after being treated by doctors at the Soviet embassy, who did not know that "special reconnaissance officers" were trying to kill Amin. Since Amin, who was very loyal to the USSR, had survived two attempted assassinations that had been approved by the USSR, the decision was made to eliminate him through a bloody coup at Amin's residence, the Taj Beck Palace.

Death
Amin trusted the Soviet Union until the very end, despite the deterioration of official relations, and was unaware that the tide in Moscow had turned against him since he ordered Taraki's death. When the Afghan intelligence service handed Amin a report that the Soviet Union would invade the country and topple him, Amin claimed that the report was a product of imperialism. His view can be explained by the fact that the Soviet Union, after several months, finally gave in to Amin's demands and sent troops into Afghanistan to secure the PDPA government. Contrary to common Western belief, Amin was informed of the Soviet decision to send troops into Afghanistan. General Tukharinov, commander of the 40th Army, met with Afghan Major General Babadzhan to talk about Soviet troop movements before the Soviet army's intervention. On 25 December, Dmitry Ustinov issued a formal order, stating that "[t]he state frontier of the Democratic Republic of Afghanistan is to be crossed on the ground and in the air by forces of the 40th Army and the Air Force at 1500 hrs on 25 December". This was the formal beginning of the Soviet intervention in Afghanistan.

Concerned for his safety, on 20 December Amin moved from the Presidential Palace, located in the centre of Kabul, to the Tajbeg Palace, which had previously been the headquarters of the Central Corps of the Afghan Army. The palace was formidable, with walls strong enough to withstand artillery fire. According to Rodric Braithwaite, "its defences had been carefully and intelligently organised". All roads to the palace had been mined, with the exception of one, which had heavy machine guns and artillery positioned to defend it. To make matters worse for the Soviets, the Afghans had established a second line of defence which consisted of seven posts, "each manned by four sentries armed with a machine gun, a mortar, and automatic rifles". The external defences of the palace were handled by the Presidential Guard, which consisted of 2,500 troops and three T-54 tanks. Several Soviet commanders involved in the assassination of Amin thought the plan to attack the palace was "crazy". Although the military had been informed by the Soviet leadership through their commanders, Yuri Drozdov and Vasily Kolesnik, that the leader was a "CIA agent" who had betrayed the Saur Revolution, many Soviet soldiers hesitated; despite what their commanders had told them, it seemed implausible that Amin, the leader of the PDPA government, was an American double agent. Despite several objections, the plan to assassinate Amin went ahead.

Before resorting to killing Amin by brute force, the Soviets had tried to poison him as early as 13 December (but nearly killed his nephew instead) and to kill him with a sniper shot on his way to work (this proved impossible as the Afghans had improved their security measures). They even tried to poison Amin just hours before the assault on the Presidential Palace on 27 December. Amin had organised a lunch for party members to show guests his palace and to celebrate Ghulam Dastagir Panjsheri's return from Moscow. Panjsheri's return improved the mood even further; he boasted that he and Gromyko always kept in contact with each other. During the meal, Amin and several of his guests lost consciousness as they had been poisoned. Amin survived his encounter with death, because the carbonation of the Coca-Cola he was drinking diluted the toxic agent. Mikhail Talybov, a KGB agent, was given responsibility for the poisonings.

The assault on the palace began shortly afterward. During the attack Amin still believed the Soviet Union was on his side, and told his adjutant, "The Soviets will help us". The adjutant replied that it was the Soviets who were attacking them; Amin initially replied that this was a lie. Only after he tried but failed to contact the Chief of the General Staff, he muttered, "I guessed it. It's all true". There are various accounts of how Amin died, but the exact details have never been confirmed. Amin was either killed by a deliberate attack or died by a "random burst of fire". Amin's son was fatally wounded and died shortly after. His daughter was wounded, but survived. It was Gulabzoy who had been given orders to kill Amin and Watanjar who later confirmed his death. The men of Amin's family were all executed either immediately or shortly thereafter (his brother Abdullah and nephew Asadullah were executed in June 1980) The women including his daughter were imprisoned at Pul-e-Charkhi prison until being released by President Najibullah in early 1992. After Amin's death on 27 December 1979, Radio Kabul broadcast Babrak Karmal's pre-recorded speech to the Afghan people, saying: "Today the torture machine of Amin has been smashed". Karmal was installed by the Soviets as the new leader while the Soviet Army began its intervention in Afghanistan that would last for nine years.

Post-death
On 2 January 1980 on the PDPA's 15th anniversary, Karmal who was now the new General Secretary called Amin a "conspirator, professional criminal and recognised spy of the U.S.", as reported in the Kabul New Times. Anahita Ratebzad, the education minister, said about Amin:

 * ...this wrathy, cruel and criminal murderer who had made terror and suppression and crushing of every opposition force part and parcel of his way of rule, and started every day with new acts of destruction, putting opponents of his bloody regime, group by group, to places of torture, jails, and slaughterhouses.

Quotes
"'Did Stalin make the revolution in white gloves?'" — Hafizullah Amin when questioned on his extreme ways of building a new country.

"Comrade Stalin showed us how to build socialism in a backward country; it's painful to begin with, but afterwards everything turns out just fine"

— Hafizullah Amin's response to Soviet criticism

title: Hafizullah Amin


text:
Hubris

Hubris, or less frequently hybris , describes a personality quality of extreme or excessive pride or dangerous overconfidence and complacency, often in combination with (or synonymous with) arrogance. The term arrogance comes from the Latin , meaning "to feel that one has a right to demand certain attitudes and behaviors from other people". To arrogate means "to claim or seize without justification... To make undue claims to having", or "to claim or seize without right... to ascribe or attribute without reason". The term pretension is also associated with the term hubris, but is not synonymous with it.

According to studies, hubris, arrogance, and pretension are related to the need for victory (even if it does not always mean winning) instead of reconciliation, which "friendly" groups might promote. Hubris is usually perceived as a characteristic of an individual rather than a group, although the group the offender belongs to may suffer collateral consequences from wrongful acts. Hubris often indicates a loss of contact with reality and an overestimation of one's own competence, accomplishments, or capabilities. The adjectival form of the noun hubris/hybris is hubristic/hybristic.

The term hubris originated in Ancient Greek, where it had several different meanings depending on the context. In legal usage, it meant assault or sexual crimes and theft of public property, and in religious usage it meant emulation of divinity or transgression against a god.

Ancient Greek origin
In ancient Greek, hubris referred to "outrage": actions that violated natural order, or which shamed and humiliated the victim, sometimes for the pleasure or gratification of the abuser.

Mythological usage
Hesiod and Aeschylus used the word "hubris" to describe transgressions against the gods. A common way that hubris was committed was when a mortal claimed to be better than a god in a particular skill or attribute. Claims like these were rarely left unpunished, and so Arachne, a talented young weaver, was transformed into a spider when she said that her skills exceeded those of the goddess Athena, even though her claim was true. Additional examples include Icarus, Phaethon, Salmoneus, Niobe, Cassiopeia, Tantalus, and Tereus.

The goddess Hybris is described in the Encyclopædia Britannica Eleventh Edition as having "insolent encroachment upon the rights of others".

These events were not limited to myth, and certain figures in history were considered to have been punished for committing hubris through their arrogance. One such person was king Xerxes as portrayed in Aeschylus's play The Persians, and who allegedly threw chains to bind the Hellespont sea as punishment for daring to destroy his fleet.

What is common in all of these examples is the breaching of limits, as the Greeks believed that the Fates (Μοῖραι) had assigned each being with a particular area of freedom, an area that even the gods could not breach.

Legal usage
In ancient Athens, hubris was defined as the use of violence to shame the victim (this sense of hubris could also characterize rape). In legal terms, hubristic violations of the law included what might today be termed assault-and-battery, sexual crimes, or the theft of public or sacred property. In some contexts, the term had a sexual connotation. Shame was frequently reflected upon the perpetrator, as well.

Crucial to this definition are the ancient Greek concepts of honour (τιμή, timē) and shame (αἰδώς, aidōs). The concept of honour included not only the exaltation of the one receiving honour, but also the shaming of the one overcome by the act of hubris. This concept of honour is akin to a zero-sum game. Rush Rehm simplifies this definition of hubris to the contemporary concept of "insolence, contempt, and excessive violence".

Two well-known cases are found in the speeches of Demosthenes, a prominent statesman and orator in ancient Greece. These two examples occurred when first Midias punched Demosthenes in the face in the theatre (Against Midias), and second when (in Against Conon) a defendant allegedly assaulted a man and crowed over the victim. Yet another example of hubris appears in Aeschines' Against Timarchus, where the defendant, Timarchus, is accused of breaking the law of hubris by submitting himself to prostitution and anal intercourse. Aeschines brought this suit against Timarchus to bar him from the rights of political office and his case succeeded. Aristotle defined hubris as shaming the victim, not because of anything that happened to the committer or might happen to the committer, but merely for that committer's own gratification: "to cause shame to the victim, not in order that anything may happen to you, nor because anything has happened to you, but merely for your own gratification. Hubris is not the requital of past injuries; this is revenge. As for the pleasure in hubris, its cause is this: naive men think that by ill-treating others they make their own superiority the greater."

Early Christianity
In the Septuagint, the "hubris is overweening pride, superciliousness or arrogance, often resulting in fatal retribution or nemesis". The word hubris as used in the New Testament parallels the Hebrew word pesha, meaning "transgression". It represents a pride that "makes a man defy God", sometimes to the degree that he considers himself an equal.

Modern usage
In its modern usage, hubris denotes overconfident pride combined with arrogance. Hubris is also referred to as "pride that blinds" because it often causes a committer of hubris to act in foolish ways that belie common sense.

Hubris has also been presented as a positive trait: Larry Wall promoted "the three great virtues of a programmer: laziness, impatience, and hubris".

Arrogance
The Oxford English Dictionary defines "arrogance" in terms of "high or inflated opinion of one's own abilities, importance, etc., that gives rise to presumption or excessive self-confidence, or to a feeling or attitude of being superior to others [...]." Adrian Davies sees arrogance as more generic and less severe than hubris.

license: Creative Commons - Attribution Share-Alike - https://creativecommons.org/licenses/by-sa/4.0/

title: Hubris


text:
Heavy water

Heavy water (deuterium oxide, ', ') is a form of water whose hydrogen atoms are all deuterium ( or D, also known as heavy hydrogen) rather than the common hydrogen-1 isotope (, also called protium) that makes up most of the hydrogen in normal water. The presence of the heavier isotope gives the water different nuclear properties, and the increase in mass gives it slightly different physical and chemical properties when compared to normal water.

Deuterium is a heavy hydrogen isotope. Heavy water contains deuterium atoms and is used in nuclear reactors. Semiheavy water (HDO) is more common than pure heavy water, while heavy-oxygen water is denser but lacks unique properties. Tritiated water is radioactive due to tritium content.

Heavy water has different physical properties from regular water, such as being 10.6% denser and having a higher melting point. Heavy water is less dissociated at a given temperature, and it does not have the slightly blue color of regular water. While it has no significant taste difference, it can taste slightly sweet. Heavy water affects biological systems by altering enzymes, hydrogen bonds, and cell division in eukaryotes. It can be lethal to multicellular organisms at concentrations over 50%. However, some prokaryotes like bacteria can survive in a heavy hydrogen environment. Heavy water can be toxic to humans, but a large amount would be needed for poisoning to occur.

Deuterated water (HDO) occurs naturally in normal water and can be separated through distillation, electrolysis, or chemical exchange processes. The most cost-effective process for producing heavy water is the Girdler sulfide process. Heavy water is used in various industries and is sold in different grades of purity. Some of its applications include nuclear magnetic resonance, infrared spectroscopy, neutron moderation, neutrino detection, metabolic rate testing, neutron capture therapy, and the production of radioactive materials such as plutonium and tritium.

Composition
The deuterium nucleus consists of a neutron and a proton; the nucleus of a protium (normal hydrogen) atom consists of just a proton. The additional neutron makes a deuterium atom roughly twice as heavy as a protium atom.

A molecule of heavy water has two deuterium atoms in place of the two protium atoms of ordinary water. The term heavy water as defined by the IUPAC Gold Book can also refer to water in which a higher than usual proportion of hydrogen atoms are deuterium. For comparison, Vienna Standard Mean Ocean Water (the "ordinary water" used for a deuterium standard) contains about 156 deuterium atoms per million hydrogen atoms; that is, 0.0156% of the hydrogen atoms are $2$H. Thus heavy water as defined by the Gold Book includes semiheavy water (hydrogen-deuterium oxide, HDO) and other mixtures of, , and HDO in which the proportion of deuterium is greater than usual. For instance, the heavy water used in CANDU reactors is a highly enriched water mixture that is mostly deuterium oxide, but also some hydrogen-deuterium oxide and a smaller amount of ordinary water. It is 99.75% enriched by hydrogen atom-fraction; that is, 99.75% of the hydrogen atoms are of the heavy type; however, heavy water in the Gold Book sense need not be so highly enriched. The weight of a heavy water molecule, however, is not very different from that of a normal water molecule, because about 89% of the mass of the molecule comes from the single oxygen atom rather than the two hydrogens.

Heavy water is not radioactive. In its pure form, it has a density about 11% greater than water but is otherwise physically and chemically similar. Nevertheless, the various differences in deuterium-containing water (especially affecting the biological properties) are larger than in any other commonly occurring isotope-substituted compound because deuterium is unique among heavy stable isotopes in being twice as heavy as the lightest isotope. This difference increases the strength of water's hydrogen–oxygen bonds, and this in turn is enough to cause differences that are important to some biochemical reactions. The human body naturally contains deuterium equivalent to about five grams of heavy water, which is harmless. When a large fraction of water (> 50%) in higher organisms is replaced by heavy water, the result is cell dysfunction and death.

Heavy water was first produced in 1932, a few months after the discovery of deuterium. With the discovery of nuclear fission in late 1938, and the need for a neutron moderator that captured few neutrons, heavy water became a component of early nuclear energy research. Since then, heavy water has been an essential component in some types of reactors, both those that generate power and those designed to produce isotopes for nuclear weapons. These heavy water reactors have the advantage of being able to run on natural uranium without using graphite moderators that pose radiological and dust explosion hazards in the decommissioning phase. The graphite moderated Soviet RBMK design tried to avoid using either enriched uranium or heavy water (being cooled with ordinary water instead) which produced the positive void coefficient that was one of a series of flaws in reactor design leading to the Chernobyl disaster. Most modern reactors use enriched uranium with ordinary water as the moderator.

Semiheavy water
Semiheavy water, HDO, exists whenever there is water with light hydrogen (protium, ) and deuterium (D or ) in the mix. This is because hydrogen atoms ($2$H and $−1$H) are rapidly exchanged between water molecules. Water containing 50% and 50%  in its hydrogen, is actually about 50% HDO and 25% each of  and, in dynamic equilibrium. In normal water, about 1 molecule in 3,200 is HDO (one hydrogen in 6,400 is ), and heavy water molecules only occur in a proportion of about 1 molecule in 41 million (i.e. one in 6,400$−1$). Thus semiheavy water molecules are far more common than "pure" (homoisotopic) heavy water molecules.

Heavy-oxygen water
Water enriched in the heavier oxygen isotopes oxygen-17 and oxygen-18 is also commercially available. It is "heavy water" as it is denser than normal water ( is approximately as dense as, is about halfway between  and )—but is rarely called heavy water, since it does not contain the excess deuterium that gives D$2$O its unusual nuclear and biological properties. It is more expensive than D$1$O due to the more difficult separation of $2$O and $2$O. H$2$$2$O is also used for production of fluorine-18 in radiopharmaceuticals and radiotracers, and positron emission tomography. Small amounts of and  are naturally present in water, and most processes enriching heavy water also enrich heavier isotopes of oxygen as a side-effect. This is undesirable if the heavy water is to be used as a neutron moderator in nuclear reactors, as can undergo neutron capture, followed by emission of an alpha particle, producing radioactive. However, doubly labeled water, containing both a heavy oxygen and hydrogen, is useful as a non-radioactive isotopic tracer.

Compared to the isotopic change of hydrogen atoms, the isotopic change of oxygen has a smaller effect on the physical properties.

Tritiated water
Tritiated water contains tritium ($17$H) in place of protium ($18$H) or deuterium ($18$H). Since tritium is radioactive, tritiated water is also radioactive.

Physical properties
The physical properties of water and heavy water differ in several respects. Heavy water is less dissociated than light water at given temperature, and the true concentration of D$2$ ions is less than ions would be for light water at the same temperature. The same is true of OD$18$ vs. ions. For heavy water Kw D$3$O (25.0 °C) = 1.35 × 10$1$, and [D$2$] must equal [OD$2$] for neutral water. Thus pKw D$2$O = p[OD$2$] + p[D$+$] = 7.44 + 7.44 = 14.87 (25.0 °C), and the p[D$−$] of neutral heavy water at 25.0 °C is 7.44.

The pD of heavy water is generally measured using pH electrodes giving a pH (apparent) value, or pHa, and at various temperatures a true acidic pD can be estimated from the directly pH meter measured pHa, such that pD+ = pHa (apparent reading from pH meter) + 0.41. The electrode correction for alkaline conditions is 0.456 for heavy water. The alkaline correction is then pD+ = pH$2$(apparent reading from pH meter) + 0.456. These corrections are slightly different from the differences in p[D+] and p[OD-] of 0.44 from the corresponding ones in heavy water.

Heavy water is 10.6% denser than ordinary water, and heavy water's physically different properties can be seen without equipment if a frozen sample is dropped into normal water, as it will sink. If the water is ice-cold the higher melting temperature of heavy ice can also be observed: it melts at 3.7 °C, and thus does not melt in ice-cold normal water.

A 1935 experiment reported not the "slightest difference" in taste between ordinary and heavy water. However, a more recent study confirmed anecdotal observation that heavy water tastes slightly sweet to humans, with the effect mediated by the TAS1R2/TAS1R3 taste receptor. Rats given a choice between distilled normal water and heavy water were able to avoid the heavy water based on smell, and it may have a different taste. Some people report that minerals in water affect taste, e.g. potassium lending a sweet taste to hard water, but there are many factors of a perceived taste in water besides mineral contents.

Heavy water lacks the characteristic blue color of light water; this is because the molecular vibration harmonics, which in light water cause weak absorption in the red part of the visible spectrum, are shifted into the infrared and thus heavy water does not absorb red light.

No physical properties are listed for "pure" semi-heavy water because it is unstable as a bulk liquid. In the liquid state, a few water molecules are always in an ionized state, which means the hydrogen atoms can exchange among different oxygen atoms. Semi-heavy water could, in theory, be created via a chemical method, but it would rapidly transform into a dynamic mixture of 25% light water, 25% heavy water, and 50% semi-heavy. However, if it were made in the gas phase and directly deposited into a solid, semi-heavy water in the form of ice could be stable. This is due to collisions between water vapor molecules being almost completely negligible in the gas phase at standard temperatures, and once crystallized, collisions between the molecules cease altogether due to the rigid lattice structure of solid ice.

History
The US scientist and Nobel laureate Harold Urey discovered the isotope deuterium in 1931 and was later able to concentrate it in water. Urey's mentor Gilbert Newton Lewis isolated the first sample of pure heavy water by electrolysis in 1933. George de Hevesy and Erich Hofer used heavy water in 1934 in one of the first biological tracer experiments, to estimate the rate of turnover of water in the human body. The history of large-quantity production and use of heavy water, in early nuclear experiments, is described below.

Emilian Bratu and Otto Redlich studied the autodissociation of heavy water in 1934.

Effect on biological systems
Different isotopes of chemical elements have slightly different chemical behaviors, but for most elements the differences are far too small to have a biological effect. In the case of hydrogen, larger differences in chemical properties among protium, deuterium, and tritium occur because chemical bond energy depends on the reduced mass of the nucleus–electron system; this is altered in heavy-hydrogen compounds (hydrogen-deuterium oxide is the most common) more than for heavy-isotope substitution involving other chemical elements. The isotope effects are especially relevant in biological systems, which are very sensitive to even the smaller changes, due to isotopically influenced properties of water when it acts as a solvent.

To perform their tasks, enzymes rely on their finely tuned networks of hydrogen bonds, both in the active center with their substrates and outside the active center, to stabilize their tertiary structures. As a hydrogen bond with deuterium is slightly stronger than one involving ordinary hydrogen, in a highly deuterated environment, some normal reactions in cells are disrupted.

Particularly hard-hit by heavy water are the delicate assemblies of mitotic spindle formations necessary for cell division in eukaryotes. Plants stop growing and seeds do not germinate when given only heavy water, because heavy water stops eukaryotic cell division. Tobacco does not germinate, but wheat does. The deuterium cell is larger and is a modification of the direction of division. The cell membrane also changes, and it reacts first to the impact of heavy water. In 1972, it was demonstrated that an increase in the percentage of deuterium in water reduces plant growth. Research conducted on the growth of prokaryote microorganisms in artificial conditions of a heavy hydrogen environment showed that in this environment, all the hydrogen atoms of water could be replaced with deuterium. Experiments showed that bacteria can live in 98% heavy water. Concentrations over 50% are lethal to multicellular organisms, however a few exceptions are known: plant species such as switchgrass (Panicum virgatum) which is able to grow on 50% D2O; Arabidopsis thaliana (70% D$−15$O); Vesicularia dubyana (85% D2O); Funaria hygrometrica (90% D$+$O); and the anhydrobiotic species of nematode Panagrolaimus superbus (nearly 100% D$−$O).

A comprehensive study of heavy water on the fission yeast Schizosaccharomyces pombe showed that the cells displayed an altered glucose metabolism and slow growth at high concentrations of heavy water. In addition, the cells activated the heat-shock response pathway and the cell integrity pathway, and mutants in the cell integrity pathway displayed increased tolerance to heavy water. Despite its toxicity at high levels, heavy water has been observed to extend lifespan of certain yeasts by up to 85%, with the hypothesized mechanism being the reduction of reactive oxygen species turnover.

Heavy water affects the period of circadian oscillations, consistently increasing the length of each cycle. The effect has been demonstrated in unicellular organisms, green plants, isopods, insects, birds, mice, and hamsters. The mechanism is unknown.

Like ethanol, heavy water temporarily changes the relative density of cupula relative to the endolymph in the vestibular organ, causing positional nystagmus, illusions of bodily rotations, dizziness, and nausea. However, the direction of nystagmus is in the opposite direction of ethanol, since it is denser than water, not lighter.

Effect on animals
Experiments with mice, rats, and dogs have shown that a degree of 25% deuteration causes (sometimes irreversible) sterility, because neither gametes nor zygotes can develop. High concentrations of heavy water (90%) rapidly kill fish, tadpoles, flatworms, and Drosophila. Mice raised from birth with 30% heavy water have 25% deuteration in body fluid and 10% in brains. They are normal except for sterility. Deuteration during pregnancy induces fetal abnormality. Higher deuteration in body fluid causes death. Mammals (for example, rats) given heavy water to drink die after a week, at a time when their body water approaches about 50% deuteration. The mode of death appears to be the same as that in cytotoxic poisoning (such as chemotherapy) or in acute radiation syndrome (though deuterium is not radioactive), and is caused by deuterium's action in generally inhibiting cell division. It is more toxic to malignant cells than normal cells, but the concentrations needed are too high for regular use. As may occur in chemotherapy, deuterium-poisoned mammals die of a failure of bone marrow (producing bleeding and infections) and of intestinal-barrier functions (producing diarrhea and loss of fluids).

Despite the problems of plants and animals in living with too much deuterium, prokaryotic organisms such as bacteria, which do not have the mitotic problems induced by deuterium, may be grown and propagated in fully deuterated conditions, resulting in replacement of all hydrogen atoms in the bacterial proteins and DNA with the deuterium isotope. This leads to a process of bootstrapping. With prokaryotes producing fully deuterated glucose, fully deuterated Escherichia coli and Torula were raised, and they could produce even more complex fully deuterated chemicals. Molds like Aspergillus could not replicate under fully deuterated conditions.

In higher organisms, full replacement with heavy isotopes can be accomplished with other non-radioactive heavy isotopes (such as carbon-13, nitrogen-15, and oxygen-18), but this cannot be done for deuterium. This is a consequence of the ratio of nuclear masses between the isotopes of hydrogen, which is much greater than for any other element.

Deuterium oxide is used to enhance boron neutron capture therapy, but this effect does not rely on the biological or chemical effects of deuterium, but instead on deuterium's ability to moderate (slow) neutrons without capturing them. 2021 experimental evidence indicates that systemic administration of deuterium oxide (30% drinking water supplementation) suppresses tumor growth in a standard mouse model of human melanoma, an effect attributed to selective induction of cellular stress signaling and gene expression in tumor cells.

Toxicity in humans
Because it would take a very large amount of heavy water to replace 25% to 50% of a human being's body water (water being in turn 50–75% of body weight ) with heavy water, accidental or intentional poisoning with heavy water is unlikely to the point of practical disregard. Poisoning would require that the victim ingest large amounts of heavy water without significant normal water intake for many days to produce any noticeable toxic effects.

Oral doses of heavy water in the range of several grams, as well as heavy oxygen $2$O, are routinely used in human metabolic experiments. (See doubly labeled water testing.) Since one in about every 6,400 hydrogen atoms is deuterium, a 50 kg human containing 32 kg of body water would normally contain enough deuterium (about 1.1 g) to make 5.5 g of pure heavy water, so roughly this dose is required to double the amount of deuterium in the body.

A loss of blood pressure may partially explain the reported incidence of dizziness upon ingestion of heavy water. However, it is more likely that this symptom can be attributed to altered vestibular function. Heavy water, like ethanol, causes temporary difference in density of cupula and endolymph, which confuses the vestibulo–ocular reflex and causes motion sickness symptoms.

Heavy water radiation contamination confusion
Although many people associate heavy water primarily with its use in nuclear reactors, pure heavy water is not radioactive. Commercial-grade heavy water is slightly radioactive due to the presence of minute traces of natural tritium, but the same is true of ordinary water. Heavy water that has been used as a coolant in nuclear power plants contains substantially more tritium as a result of neutron bombardment of the deuterium in the heavy water (tritium is a health risk when ingested in large quantities).

In 1990, a disgruntled employee at the Point Lepreau Nuclear Generating Station in Canada obtained a sample (estimated as about a "half cup") of heavy water from the primary heat transport loop of the nuclear reactor, and loaded it into a cafeteria drink dispenser. Eight employees drank some of the contaminated water. The incident was discovered when employees began leaving bioassay urine samples with elevated tritium levels. The quantity of heavy water involved was far below levels that could induce heavy water toxicity, but several employees received elevated radiation doses from tritium and neutron-activated chemicals in the water. This was not an incident of heavy water poisoning, but rather radiation poisoning from other isotopes in the heavy water.

Some news services were not careful to distinguish these points, and some of the public were left with the impression that heavy water is normally radioactive and more severely toxic than it actually is. Even if pure heavy water had been used in the water cooler indefinitely, it is not likely the incident would have been detected or caused harm, since no employee would be expected to get much more than 25% of their daily drinking water from such a source.

Production
On Earth, deuterated water occurs naturally in normal water at a proportion of about 1 molecule in 3,200. This means that 1 in 6,400 hydrogen atoms in water is deuterium, which is 1 part in 3,200 by weight (hydrogen weight). The HDO may be separated from normal water by distillation or electrolysis and also by various chemical exchange processes, all of which exploit a kinetic isotope effect, with the partial enrichment also occurring in natural bodies of water under particular evaporation conditions. (For more information about the isotopic distribution of deuterium in water, see Vienna Standard Mean Ocean Water.) In theory, deuterium for heavy water could be created in a nuclear reactor, but separation from ordinary water is the cheapest bulk production process.

The difference in mass between the two hydrogen isotopes translates into a difference in the zero-point energy and thus into a slight difference in the speed of the reaction. Once HDO becomes a significant fraction of the water, heavy water becomes more prevalent as water molecules trade hydrogen atoms very frequently. Production of pure heavy water by distillation or electrolysis requires a large cascade of stills or electrolysis chambers and consumes large amounts of power, so the chemical methods are generally preferred.

The most cost-effective process for producing heavy water is the dual temperature exchange sulfide process (known as the Girdler sulfide process) developed in parallel by Karl-Hermann Geib and Jerome S. Spevack in 1943. An alternative process, patented by Graham M. Keyser, uses lasers to selectively dissociate deuterated hydrofluorocarbons to form deuterium fluoride, which can then be separated by physical means. Although the energy consumption for this process is much less than for the Girdler sulfide process, this method is currently uneconomical due to the expense of procuring the necessary hydrofluorocarbons.

As noted, modern commercial heavy water is almost universally referred to, and sold as, deuterium oxide. It is most often sold in various grades of purity, from 98% enrichment to 99.75–99.98% deuterium enrichment (nuclear reactor grade) and occasionally even higher isotopic purity.

Argentina
Argentina was the main producer of heavy water, using an ammonia/hydrogen exchange based plant supplied by Switzerland's Sulzer company. It was also a major exporter to Canada, Germany, the US and other countries. The heavy water production facility located in Arroyito was the world's largest heavy water production facility. Argentina produced 200 ST of heavy water per year in 2015 using the monothermal ammonia-hydrogen isotopic exchange method. Since 2017, the Arroyito plant has not been operational.

Soviet Union
In October 1939, Soviet physicists Yakov Borisovich Zel'dovich and Yulii Borisovich Khariton concluded that heavy water and carbon were the only feasible moderators for a natural uranium reactor, and in August 1940, along with Georgy Flyorov, submitted a plan to the Russian Academy of Sciences calculating that 15 tons of heavy water were needed for a reactor. With the Soviet Union having no uranium mines at the time, young Academy workers were sent to Leningrad photographic shops to buy uranium nitrate, but the entire heavy water project was halted in 1941 when German forces invaded during Operation Barbarossa.

By 1943, Soviet scientists had discovered that all scientific literature relating to heavy water had disappeared from the West, which Flyorov in a letter warned Soviet leader Joseph Stalin about, and at which time there was only 2–3 kg of heavy water in the entire country. In late 1943, the Soviet purchasing commission in the U.S. obtained 1 kg of heavy water and a further 100 kg in February 1945, and upon World War II ending, the NKVD took over the project.

In October 1946, as part of the Russian Alsos, the NKVD deported to the Soviet Union from Germany the German scientists who had worked on heavy water production during the war, including Karl-Hermann Geib, the inventor of the Girdler sulfide process. These German scientists worked under the supervision of German physical chemist Max Volmer at the Institute of Physical Chemistry in Moscow with the plant they constructed producing large quantities of heavy water by 1948.

United States
During the Manhattan Project the United States constructed three heavy water production plants as part of the P-9 Project at Morgantown Ordnance Works, near Morgantown, West Virginia; at the Wabash River Ordnance Works, near Dana and Newport, Indiana; and at the Alabama Ordnance Works, near Childersburg and Sylacauga, Alabama. Heavy water was also acquired from the Cominco plant in Trail, British Columbia, Canada. The Chicago Pile-3 experimental reactor used heavy water as a moderator and went critical in 1944. The three domestic production plants were shut down in 1945 after producing around 81,470lb of product. The Wabash plant resumed heavy water production in 1952.

In 1953, the United States began using heavy water in plutonium production reactors at the Savannah River Site. The first of the five heavy water reactors came online in 1953, and the last was placed in cold shutdown in 1996. The reactors were heavy water reactors so that they could produce both plutonium and tritium for the US nuclear weapons program.

The U.S. developed the Girdler sulfide chemical exchange production process—which was first demonstrated on a large scale at the Dana, Indiana plant in 1945 and at the Savannah River Site in 1952.

India
India is one of the world's largest producers of heavy water through its Heavy Water Board. It exports heavy water to countries including the Republic of Korea, China, and the United States.

Empire of Japan
In the 1930s, it was suspected by the United States and Soviet Union that Austrian chemist Fritz Johann Hansgirg built a pilot plant for the Empire of Japan in Japanese ruled northern Korea to produce heavy water by using a new process he had invented.

Norway
In 1934, Norsk Hydro built the first commercial heavy water plant at Vemork, Tinn, eventually producing 4 kg per day. From 1940 and throughout World War II, the plant was under German control, and the Allies decided to destroy the plant and its heavy water to inhibit German development of nuclear weapons. In late 1942, a planned raid called Operation Freshman by British airborne troops failed, both gliders crashing. The raiders were killed in the crash or subsequently executed by the Germans.

On the night of 27 February 1943 Operation Gunnerside succeeded. Norwegian commandos and local resistance managed to demolish small, but key parts of the electrolytic cells, dumping the accumulated heavy water down the factory drains.

On 16 November 1943, the Allied air forces dropped more than 400 bombs on the site. The Allied air raid prompted the Nazi government to move all available heavy water to Germany for safekeeping. On 20 February 1944, a Norwegian partisan sank the ferry M/F Hydro carrying heavy water across Lake Tinn, at the cost of 14 Norwegian civilian lives, and most of the heavy water was presumably lost. A few of the barrels were only half full, hence buoyant, and may have been salvaged and transported to Germany.

Recent investigation of production records at Norsk Hydro and analysis of an intact barrel that was salvaged in 2004 revealed that although the barrels in this shipment contained water of pH 14—indicative of the alkaline electrolytic refinement process—they did not contain high concentrations of D$−$O. Despite the apparent size of the shipment, the total quantity of pure heavy water was quite small, most barrels only containing 0.5–1% pure heavy water. The Germans would have needed about 5 tons of heavy water to get a nuclear reactor running. The manifest clearly indicated that there was only half a ton of heavy water being transported to Germany. Hydro was carrying far too little heavy water for one reactor, let alone the 10 or more tons needed to make enough plutonium for a nuclear weapon. The German nuclear weapons program was much less advanced than the Manhattan Project, and no reactor constructed in Nazi Germany came close to reaching criticality. No amount of heavy water would have changed that.

Israel admitted running the Dimona reactor with Norwegian heavy water sold to it in 1959. Through re-export using Romania and Germany, India probably also used Norwegian heavy water.

Sweden
During the second World War, the company Fosfatbolaget in Ljungaverk, Sweden, produced 2,300 liters per year of heavy water. The heavy water was then sold both to Germany and to the Manhattan Project for the price of 1,40 SEK per gram of heavy water.

Canada
As part of its contribution to the Manhattan Project, Canada built and operated a 1000 to 1200 lb per month (design capacity) electrolytic heavy water plant at Trail, British Columbia, which started operation in 1943.

The Atomic Energy of Canada Limited (AECL) design of power reactor requires large quantities of heavy water to act as a neutron moderator and coolant. AECL ordered two heavy water plants, which were built and operated in Atlantic Canada at Glace Bay, Nova Scotia (by Deuterium of Canada Limited) and Point Tupper, Richmond County, Nova Scotia (by Canadian General Electric). These plants proved to have significant design, construction and production problems. The Glace Bay plant reached full production in 1984 after being taken over by AECL in 1971. The Point Tupper plant reached full production in 1974 and AECL purchased the plant in 1975. Design changes from the Point Tupper plant were carried through as AECL built the Bruce Heavy Water Plant (44.1854°N, -81.3618°W), which it later sold to Ontario Hydro, to ensure a reliable supply of heavy water for future power plants. The two Nova Scotia plants were shut down in 1985 when their production proved unnecessary.

The Bruce Heavy Water Plant (BHWP) in Ontario was the world's largest heavy water production plant with a capacity of 1600 tonnes per year at its peak (800 tonnes per year per full plant, two fully operational plants at its peak). It used the Girdler sulfide process to produce heavy water, and required 340,000 tonnes of feed water to produce one tonne of heavy water. It was part of a complex that included eight CANDU reactors, which provided heat and power for the heavy water plant. The site was located at Douglas Point/Bruce Nuclear Generating Station near Tiverton, Ontario, on Lake Huron where it had access to the waters of the Great Lakes.

AECL issued the construction contract in 1969 for the first BHWP unit (BHWP A). Commissioning of BHWP A was done by Ontario Hydro from 1971 through 1973, with the plant entering service on 28 June 1973, and design production capacity being achieved in April 1974. Due to the success of BHWP A and the large amount of heavy water that would be required for the large numbers of upcoming planned CANDU nuclear power plant construction projects, Ontario Hydro commissioned three additional heavy water production plants for the Bruce site (BHWP B, C, and D). BHWP B was placed into service in 1979. These first two plants were significantly more efficient than planned, and the number of CANDU construction projects ended up being significantly lower than originally planned, which led to the cancellation of construction on BHWP C & D. In 1984, BHWP A was shut down. By 1993 Ontario Hydro had produced enough heavy water to meet all of its anticipated domestic needs (which were lower than expected due to improved efficiency in the use and recycling of heavy water), so they shut down and demolished half of the capacity of BHWP B. The remaining capacity continued to operate in order to fulfil demand for heavy water exports until it was permanently shut down in 1997, after which the plant was gradually dismantled and the site cleared.

AECL is currently researching other more efficient and environmentally benign processes for creating heavy water. This is relevant for CANDU reactors since heavy water represented about 15–20% of the total capital cost of each CANDU plant in the 1970s and 1980s.

Iran
Since 1996 a plant for production of heavy water was being constructed at Khondab near Arak. On 26 August 2006, Iranian President Ahmadinejad inaugurated the expansion of the country's heavy-water plant. Iran has indicated that the heavy-water production facility will operate in tandem with a 40 MW research reactor that had a scheduled completion date in 2009. Iran produced deuterated solvents in early 2011 for the first time. The core of the IR-40 is supposed to be re-designed based on the nuclear agreement in July 2015.

Iran is permitted to store only 130 t of heavy water. Iran exports excess production, making Iran the world's third largest exporter of heavy water. In 2023, Iran sells heavy water; customers have proposed a price over 1,000 dollars per liter.

Pakistan
In Pakistan, there are two heavy water production sites that are based in Punjab. Commissioned in 1997–98, the Khushab Nuclear Complex is a central element of Pakistan's stockpile program for production of weapon-grade plutonium, deuterium, and tritium for advanced compact warheads (i.e. thermonuclear weapons). Another heavy water facility for producing the heavy water is located in Multan, that it sells to nuclear power plants in Karachi and Chashma.

In early 1980s, Pakistan succeeded in acquiring a tritium purification and storage plant and deuterium and tritium precursor materials from two former East German firms. Unlike India and Iran, the heavy water produced by Pakistan is not exported nor available for purchase to any nation and is solely used for its weapons complex and energy generation at its local nuclear power plants.

Other countries
Romania produced heavy water at the now-decommissioned Drobeta Girdler sulfide plant for domestic and export purposes. France operated a small plant during the 1950s and 1960s.

Nuclear magnetic resonance
Deuterium oxide is used in nuclear magnetic resonance spectroscopy when using water as solvent if the nuclide of interest is hydrogen. This is because the signal from light-water ($+$H$+$O) solvent molecules would overwhelm the signal from the molecule of interest dissolved in it. Deuterium has a different magnetic moment and therefore does not contribute to the $a$H-NMR signal at the hydrogen-1 resonance frequency.

For some experiments, it may be desirable to identify the labile hydrogens on a compound, that is hydrogens that can easily exchange away as H$2$ ions on some positions in a molecule. With addition of D$2$O, sometimes referred to as a D$2$O shake, labile hydrogens exchange between the compound of interest and the solvent, leading to replacement of those specific $2$H atoms in the compound with $2$H. These positions in the molecule then do not appear in the $2$H-NMR spectrum.

Organic chemistry
Deuterium oxide is often used as the source of deuterium for preparing specifically labelled isotopologues of organic compounds. For example, C-H bonds adjacent to ketonic carbonyl groups can be replaced by C-D bonds, using acid or base catalysis. Trimethylsulfoxonium iodide, made from dimethyl sulfoxide and methyl iodide can be recrystallized from deuterium oxide, and then dissociated to regenerate methyl iodide and dimethyl sulfoxide, both deuterium labelled. In cases where specific double labelling by deuterium and tritium is contemplated, the researcher must be aware that deuterium oxide, depending upon age and origin, can contain some tritium.

Infrared spectroscopy
Deuterium oxide is often used instead of water when collecting FTIR spectra of proteins in solution. H$2$O creates a strong band that overlaps with the amide I region of proteins. The band from D$18$O is shifted away from the amide I region.

Neutron moderator
Heavy water is used in certain types of nuclear reactors, where it acts as a neutron moderator to slow down neutrons so that they are more likely to react with the fissile uranium-235 than with uranium-238, which captures neutrons without fissioning. The CANDU reactor uses this design. Light water also acts as a moderator, but because light water absorbs more neutrons than heavy water, reactors using light water for a reactor moderator must use enriched uranium rather than natural uranium, otherwise criticality is impossible. A significant fraction of outdated power reactors, such as the RBMK reactors in the USSR, were constructed using normal water for cooling but graphite as a moderator. However, the danger of graphite in power reactors (graphite fires in part led to the Chernobyl disaster) has led to the discontinuation of graphite in standard reactor designs.

The breeding and extraction of plutonium can be a relatively rapid and cheap route to building a nuclear weapon, as chemical separation of plutonium from fuel is easier than isotopic separation of U-235 from natural uranium. Among current and past nuclear weapons states, Israel, India, and North Korea first used plutonium from heavy water moderated reactors burning natural uranium, while China, South Africa and Pakistan first built weapons using highly enriched uranium.

The Nazi nuclear program, operating with more modest means than the contemporary Manhattan Project and hampered by many leading scientists having been driven into exile (many of them ending up working for the Manhattan Project), as well as continuous infighting, wrongly dismissed graphite as a moderator due to not recognizing the effect of impurities. Given that isotope separation of uranium was deemed too big a hurdle, this left heavy water as a potential moderator. Other problems were the ideological aversion regarding what propaganda dismissed as "Jewish physics" and the mistrust between those who had been enthusiastic Nazis even before 1933 and those who were Mitläufer or trying to keep a low profile. In part due to allied sabotage and commando raids on Norsk Hydro (then the world's largest producer of heavy water) as well as the aforementioned infighting, the German nuclear program never managed to assemble enough uranium and heavy water in one place to achieve criticality despite possessing enough of both by the end of the war.

In the U.S., however, the first experimental atomic reactor (1942), as well as the Manhattan Project Hanford production reactors that produced the plutonium for the Trinity test and Fat Man bombs, all used pure carbon (graphite) neutron moderators combined with normal water cooling pipes. They functioned with neither enriched uranium nor heavy water. Russian and British plutonium production also used graphite-moderated reactors.

There is no evidence that civilian heavy water power reactors—such as the CANDU or Atucha designs—have been used to produce military fissile materials. In nations that do not already possess nuclear weapons, nuclear material at these facilities is under IAEA safeguards to discourage any diversion.

Due to its potential for use in nuclear weapons programs, the possession or import/export of large industrial quantities of heavy water are subject to government control in several countries. Suppliers of heavy water and heavy water production technology typically apply IAEA (International Atomic Energy Agency) administered safeguards and material accounting to heavy water. (In Australia, the Nuclear Non-Proliferation (Safeguards) Act 1987.) In the U.S. and Canada, non-industrial quantities of heavy water (i.e., in the gram to kg range) are routinely available without special license through chemical supply dealers and commercial companies such as the world's former major producer Ontario Hydro.

Neutrino detector
The Sudbury Neutrino Observatory (SNO) in Sudbury, Ontario uses 1,000 tonnes of heavy water on loan from Atomic Energy of Canada Limited. The neutrino detector is 6800 ft underground in a mine, to shield it from muons produced by cosmic rays. SNO was built to answer the question of whether or not electron-type neutrinos produced by fusion in the Sun (the only type the Sun should be producing directly, according to theory) might be able to turn into other types of neutrinos on the way to Earth. SNO detects the Cherenkov radiation in the water from high-energy electrons produced from electron-type neutrinos as they undergo charged current (CC) interactions with neutrons in deuterium, turning them into protons and electrons (however, only the electrons are fast enough to produce Cherenkov radiation for detection).

SNO also detects neutrino electron scattering (ES) events, where the neutrino transfers energy to the electron, which then proceeds to generate Cherenkov radiation distinguishable from that produced by CC events. The first of these two reactions is produced only by electron-type neutrinos, while the second can be caused by all of the neutrino flavors. The use of deuterium is critical to the SNO function, because all three "flavours" (types) of neutrinos may be detected in a third type of reaction as well, neutrino-disintegration, in which a neutrino of any type (electron, muon, or tau) scatters from a deuterium nucleus (deuteron), transferring enough energy to break up the loosely bound deuteron into a free neutron and proton via a neutral current (NC) interaction.

This event is detected when the free neutron is absorbed by 35Cl− present from NaCl deliberately dissolved in the heavy water, causing emission of characteristic capture gamma rays. Thus, in this experiment, heavy water not only provides the transparent medium necessary to produce and visualize Cherenkov radiation, but it also provides deuterium to detect exotic mu type (μ) and tau (τ) neutrinos, as well as a non-absorbent moderator medium to preserve free neutrons from this reaction, until they can be absorbed by an easily detected neutron-activated isotope.

Metabolic rate and water turnover testing in physiology and biology
Heavy water is employed as part of a mixture with H$2$$1$O for a common and safe test of mean metabolic rate in humans and animals undergoing their normal activities.The elimination rate of deuterium alone is a measure of body water turnover. This is highly variable between individuals and depends on environmental conditions as well as subject size, sex, age and physical activity.

Tritium production
Tritium is the active substance in self-powered lighting and controlled nuclear fusion, its other uses including autoradiography and radioactive labeling. It is also used in nuclear weapon design for boosted fission weapons and initiators. Tritium undergoes beta decay into helium-3, which is a stable, but rare, isotope of helium that is itself highly sought after. Some tritium is created in heavy water moderated reactors when deuterium captures a neutron. This reaction has a small cross-section (probability of a single neutron-capture event) and produces only small amounts of tritium, although enough to justify cleaning tritium from the moderator every few years to reduce the environmental risk of tritium escape. Given that helium-3 is a neutron poison with orders of magnitude higher capture cross section than any component of heavy or tritiated water, its accumulation in a heavy water neutron moderator or target for tritium production must be kept to a minimum.

Producing a lot of tritium in this way would require reactors with very high neutron fluxes, or with a very high proportion of heavy water to nuclear fuel and very low neutron absorption by other reactor material. The tritium would then have to be recovered by isotope separation from a much larger quantity of deuterium, unlike production from lithium-6 (the present method), where only chemical separation is needed.

Deuterium's absorption cross section for thermal neutrons is 0.52 millibarn (5.2 × 10$2$ m$1$; 1 barn = 10$+$ m$2$), while those of oxygen-16 and oxygen-17 are 0.19 and 0.24 millibarn, respectively. $2$O makes up 0.038% of natural oxygen, making the overall cross section 0.28 millibarns. Therefore, in D$1$O with natural oxygen, 21% of neutron captures are on oxygen, rising higher as $2$O builds up from neutron capture on $1$O. Also, $2$O may emit an alpha particle on neutron capture, producing radioactive carbon-14.

title: Heavy water