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A History of Japan: From Mythology to Nationhood/The American Occupation of Japan

At the end of World War II, Japan was occupied by the Allied Powers, led by the United States with contributions from Australia, India, New Zealand and the United Kingdom. This foreign presence marked the first time in its history that the island nation had been occupied by a foreign power. The San Francisco Peace Treaty, signed on September 8, 1951, marked the end of the Allied occupation, and subsequent to its coming into force on April 28, 1952, Japan was once again an independent country.

Post-Surrender
On V-J Day, United States President Harry Truman appointed General Douglas MacArthur as Supreme Commander of the Allied Powers (SCAP), to supervise the occupation of Japan. During the war, the Allied Powers had planned to divide Japan amongst themselves for the purposes of occupation, as was done for the occupation of Germany. Under the final plan, however, SCAP was given direct control over the main islands of Japan (Honshū, Hokkaidō, Shikoku and Kyūshū) and the immediately surrounding islands, while outlying possessions were divided between the Allied Powers as follows:

 * Soviet Union: North Korea (not a full occupation), Sakhalin, and the Kuril Islands.
 * United States: South Korea (not a full occupation), Okinawa, the Amami Islands, the Ogasawara Islands and Japanese possessions in Micronesia.
 * China: Taiwan and Penghu.

It is unclear why the occupation plan was changed. Common theories include the increased power of the United States following development of the atomic bomb, Truman's greater distrust of the Soviet Union when compared with Roosevelt, and an increased desire to contain Soviet expansion in the Far East after the Yalta Conference.

The Soviet Union had some intentions of occupying Hokkaidō. Had this occurred, there might have been the foundation of a communist "Democratic People's Republic of Japan" in the Soviet zone of occupation. However, unlike the Soviet occupations of East Germany and North Korea, these plans were frustrated by the opposition of President Truman.

The Far Eastern Commission and Allied Council For Japan were also established to supervise the occupation of Japan.

Japanese officials left for Manila on August 19 to meet MacArthur and to be briefed on his plans for the occupation. On August 28, 150 U.S. personnel flew to Atsugi, Kanagawa Prefecture. They were followed by The "USS Missouri, whose accompanying vessels landed the US 4th Marine Division on the southern coast of Kanagawa. Other Allied personnel followed.

MacArthur arrived in Tokyo on August 30, and immediately decreed several laws: No Allied personnel were to assault Japanese people. No Allied personnel were to eat the scarce Japanese food. Flying the Hinomaru or "Rising Sun" flag was initially severely restricted (although individuals and prefectural offices could apply for permission to fly it). The restriction was partially lifted in 1948 and completely lifted the following year. The Hinomaru was the de facto albeit not de jure flag throughout World war II and the occupation period.

On September 2, Japan formally surrendered with the signing of the Japanese Instrument of Surrender. On September 6, US President Harry S. Truman approved a document titled "US Initial Post-Surrender Policy for Japan". The document set two main objectives for the occupation: (1) eliminating Japan's war potential and (2) turning Japan into a western style nation with pro-American orientation. Allied (primarily American) forces were set up to supervise the country, and "for eighty months following its surrender in 1945, Japan was at the mercy of an army of occupation, its people subject to foreign military control." At the head of the Occupation administration was General MacArthur who was technically supposed to defer to an advisory council set up by the Allied powers, but in practice did everything himself. As a result, this period was one of significant American influence, having been already identified in 1951, that "for six years the United States has had a freer hand to experiment with Japan than any other country in Asia, or indeed in the entire world."

MacArthur's first priority was to set up a food distribution network; following the collapse of the ruling government and the wholesale destruction of most major cities, virtually everyone was starving. Even with these measures, millions of people were still on the brink of starvation for several years after the surrender. As expressed by Kawai Kazuo, "Democracy cannot be taught to a starving people,"

Initially the US government provided emergency food relief through GARIOA funds. In fiscal year 1946, this aid amounted to US$92 million in loans. From April 1946, in the guise of LARA, private relief organizations were also permitted to provide relief. Once the food network was in place, at a cost of up to US$1 million per day, MacArthur set out to win the support of Hirohito. The two men met for the first time on September 27; the photograph of the two together is one of the most famous in Japanese history. However, many were shocked that MacArthur wore his standard duty uniform with no tie instead of his dress uniform when meeting the emperor. MacArthur may have done this on purpose, to send a message as to what he considered the emperor's status to be. With the sanction of Japan's reigning monarch, MacArthur had the ammunition he needed to begin the real work of the occupation. While other Allied political and military leaders pushed for Hirohito to be tried as a war criminal, MacArthur resisted such calls and rejected the claims of members of the imperial family such as Prince Mikasa and Prince Higashikuni and intellectuals like Tatsuji Miyoshi who asked for the emperor's abdication, arguing that any such prosecution would be overwhelmingly unpopular with the Japanese people.

By the end of 1945, more than 350,000 U.S. personnel were stationed throughout Japan. By the beginning of 1946, replacement troops began to arrive in the country in large numbers and were assigned to MacArthur's Eighth Army, headquartered in Tokyo's Dai-Ichi building. Of the main Japanese islands, Kyūshū was occupied by the 24th Infantry Division, with some responsibility for Shikoku. Honshū was occupied by the First Cavalry Division. Hokkaidō was occupied by the 11th Airborne Division.

The official British Commonwealth Occupation Force (BCOF), composed of Australian, British, Indian and New Zealand personnel, was deployed on February 21, 1946. While U.S. forces were responsible for overall military government, BCOF was responsible for supervising demilitarization and the disposal of Japan's war industries. BCOF was also responsible for occupation of several western prefectures and had its headquarters at Kure. At its peak, the force numbered about 40,000 personnel. During 1947, BCOF began to decrease its activities in Japan, and officially wound up in 1951.

Japanese Reaction to the start of the Occupation
Hirohito’s surrender broadcast was a shock to Japanese citizens. After years of propaganda which had told them about Japan’s military might and the inevitability of victory, the suddenness of the revelation was a shock. But for many people, these were only secondary concerns since they were also facing starvation and homelessness.

Post-war Japan was chaotic. The air raids on urban centers left millions displaced and food shortages, created by bad harvests and the demands of the war, worsened when the importation of food from Korea, Taiwan, and China ceased. Repatriation of Japanese living in other parts of Asia only aggravated the problems in Japan as these displaced people put more strain on already scarce resources. Over 5.1 million Japanese returned to Japan in the fifteen months following October 1, 1945. Alcohol and drug abuse became major problems. Deep exhaustion, declining morale and despair was so widespread that it was termed the "kyodatsu condition." Inflation was rampant and many people turned to the black market for even the most basic goods. Prostitution also increased considerably.

The phrase "shikata ga nai", or "nothing can be done about it," was commonly used in both Japanese and American press to encapsulate the Japanese public's resignation to the harsh conditions endured while under occupation. However, not everyone reacted the same way to the hardships of the postwar period. While some succumbed to the difficulties, many more were resilient. As the country regained its footing, they were able to bounce back as well.

Disarmament
Japan's postwar constitution, adopted under Allied supervision, included a "Peace Clause" (Article 9), which renounced war and banned Japan from maintaining any armed forces. This was intended to prevent the country from ever becoming an aggressive military power again. However, within a decade, America was pressuring Japan to rebuild its army as a bulwark against Communism in Asia after the Chinese Civil War and the Korean War, and Japan established Self-Defense Forces. Traditionally, Japan's military spending has been restricted to about 1% of its GNP though this is by popular practice, not law, and has fluctuated up and down from this figure. Recently, past Prime Ministers Junichiro Koizumi and Shinzo Abe, and other politicians have tried to repeal or amend the clause. Although the intention of the American Occupation was to demilitarize the Japanese, due to the subsequent Asian threat of communism, and at American urging, the Japanese military was slowly restored to considerable strength. Japan currently has the seventh largest military budget in the world.

Liberalization
The Occupation was not the simple experiment in democracy it is often portrayed to be. With the intensification of the Cold War, SCAP reined in its reform initiatives. From late 1947, US Priorities shifted perceptibly from liberal social change to internal political stability and economic recovery. Demilitarisation and democratization lost momentum and then seemed to stall. Economic deconcentration, for example, was left uncompleted as GHQ responded to new imperatives. American authorities encouraged business practices and industrial policies that have since become sources of contention between Japan and its major trade partners, notably the United States." During the Occupation, GHQ/SCAP successfully (if not entirely) abolished many of the financial coalitions known as the Zaibatsu, which had previously monopolized industry. Along with the later American change of heart, however (due in part to the need for an economically stronger Japan in the face of a perceived Soviet threat), these economic reforms were also hampered by the wealthy and influential Japanese who obviously stood to lose a great deal. As such, there were those who consequently resisted any attempts at reform, claiming that the zaibatsu were required for Japan to compete internationally, and looser industrial groupings known as keiretsu evolved. A major land reform was also conducted, led by Wolf Ladejinsky of General Douglas MacArthur's SCAP staff. However, Ladejinsky has stated that the real architect of reform was Socialist Hiro Wada, former Japanese Minister of Agriculture. Between 1947 and 1949, approximately 5,800,000 acres of land (23,500 km2) (approximately 38% of Japan's cultivated land) were purchased from the landlords under the government's reform program and resold at extremely low prices (after inflation) to the farmers who worked them. By 1950, three million peasants had acquired land, dismantling a power structure that the landlords had long dominated.

Democratization
In 1946, the Diet ratified a new Constitution of Japan that followed closely a 'model copy' prepared by the GHQ/SCAP (namely the organization headed by Gen. MacArthur that was responsible for conducting the Occupation), and was promulgated as an amendment to the old Prussian-style Meiji Constitution. "The political project drew much of its inspiration from the US Bill of Rights, New Deal social legislation, the liberal constitutions of several European states and even the Soviet Union... (It) transferred sovereignty from the Emperor to the people in an attempt to depoliticize the Throne and reduce it to the status of a state symbol. Included in the revised charter was the famous 'no war', 'no arms' Article Nine, which outlawed belligerency as an instrument of state policy and the maintenance of a standing army. The 1947 Constitution also enfranchised women, guaranteed fundamental human rights, strengthened the powers of Parliament and the Cabinet, and decentralized the police and local government." On December 15, 1945 the Shinto Directive was issued abolishing Shinto as a state religion and prohibiting some of its teachings and rites that were deemed to be militaristic or ultra-nationalistic. On April 10, 1946, an election that saw 78.52% voter turnout among men and 66.97% among women gave Japan its first modern prime minister, Shigeru Yoshida.

Trade Union Act
In 1945 the Diet passed Japan's first ever trade union law protecting the rights of workers to form or join a union, to organize and take industrial action. There had been pre-war attempts to do so, but none that were successfully passed until the Allied occupation. A new Trade Union law was passed on June 1 1949, which remains in place to the present day. According to Article 1 of the Act, the purpose of the act is to "elevate the status of workers by promoting their being on equal standing with the employer".

Labor Standards Act
The Labor Standards Act was enacted on 7 April, 1947 to govern working conditions in Japan. According to Article 1 of the Act, its goal is to ensure that "Working conditions shall be those which should meet the needs of workers who live lives worthy of human beings." While it was created while Japan was under occupation, the origins of the act have nothing to do with the occupation forces. It appears to have been the brainchild of Kosaku Teramoto, a former member of the Thought Police, who had become the head of the Labor Standards section of the Welfare Ministry.

Education reform
Before and during the war, Japanese education was based on the German system, with "Gymnasium" (selective grammar schools) and universities to train students after primary school. During the occupation, Japan's secondary education system was changed to incorporate three-year junior high schools and senior high schools similar to those in the U.S.: junior high became compulsory but senior high remained optional. The Imperial Rescript on Education was repealed, and the Imperial University system reorganized. The longstanding issue of Japanese script reform, which had been planned for decades but continuously opposed by more conservative elements, was also resolved during this time. The Japanese written system was drastically reorganized with the Tōyō kanji-list in 1946, predecessor of today's Jōyō kanji, and orthography was greatly altered to reflect spoken usage.

Purging of war criminals
While these other reforms were taking place, various military tribunals, most notably the International Military Tribunal for the Far East in Ichigaya, were trying Japan's war criminals and sentencing many to death and imprisonment. However, many suspects such as Tsuji Masanobu, Nobusuke Kishi, Yoshio Kodama and Ryoichi Sasakawa were never judged, while the Showa Emperor, all members of the imperial family implicated in the war such as Prince Chichibu, Prince Asaka, Prince Hiroyasu Fushimi, Prince Higashikuni and Prince Takeda, and all members of Unit 731 were given immunity from criminal prosecution by General MacArthur.

Before the war crimes trials actually convened, the SCAP, the IPS and Shōwa officials worked behind the scenes not only to prevent the imperial family from being indicted, but also to slant the testimony of the defendants to ensure that no one implicated the Emperor. High officials in court circles and the Shōwa government collaborated with Allied GHQ in compiling lists of prospective war criminals, while the individuals arrested as Class A suspects and incarcerated in Sugamo prison solemnly vowed to protect their sovereign against any possible taint of war responsibility. Thus, "months before the Tokyo tribunal commenced, MacArthur's highest subordinates were working to attribute ultimate responsibility for Pearl Harbor to Hideki Tōjō" by allowing "the major criminal suspects to coordinate their stories so that the Emperor would be spared from indictment."

For historian John W. Dower, "Even Japanese peace activists who endorse the ideals of the Nuremberg and Tokyo charters, and who have labored to document and publicize Japanese atrocities, cannot defend the American decision to exonerate the emperor of war responsibility and then, in the chill of Cold war, release and soon afterwards openly embrace accused right-wing war criminals like the later prime minister Kishi Nobusuke".

In retrospect, apart from the military officer corps, the purge of alleged militarists and ultranationalists that was conducted under the Occupation had relatively small impact on the long-term composition of men of influence in the public and private sectors. The purge initially brought new blood into the political parties, but this was offset by the return of huge numbers of formally purged conservative politicians to national as well as local politics in the early 1950s. In the bureaucracy, the purge was negligible from the outset... In the economic sector, the purge similarly was only mildly disruptive, affecting less than sixteen hundred individuals spread among some four hundred companies. Everywhere one looks, the corridors of power in postwar Japan are crowded with men whose talents had already been recognized during the war years, and who found the same talents highly prized in the "new" Japan.

Rape
While many Japanese civilians feared that the Allied troops were likely to rape Japanese women, the incidence of rape committed by members of the occupation force was low. Its incidence did increase after the criminalization of prostitution, however. Michael S. Molasky reports that while rape and other violent crime was widespread in naval ports like Yokosuka and Yokohama during the first few weeks of occupation, according to Japanese police reports, the number of incidents declined shortly after and were not common on mainland Japan throughout the rest of occupation.

According to Toshiyuki Tanaka, 76 cases of rape or rape-murder were reported on Okinawa during the first five years of occupation. However, this is probably not the true figure, as most cases went unreported.

Censorship
After the surrender of Japan in 1945, the Supreme Commander of the Allied Powers abolished all forms of censorship and controls on Freedom of Speech, which was also integrated into Article 21 of the 1947 Constitution of Japan. However, press censorship remained a reality in the post-war era, especially in matters of pornography, and in political matters deemed subversive by the American government during the occupation of Japan.

The Allied occupation forces suppressed news of criminal activities such as rape; on September 10, 1945 SCAP "issued press and pre-censorship codes outlawing the publication of all reports and statistics 'inimical to the objectives of the Occupation'."

Comfort women
With the acceptance of the Allied occupation authorities the Japanese organized a brothel system for the benefit of the more than 300,000 occupation troops. "The strategy was, through the special work of experienced women, to create a breakwater to protect regular women and girls."

In December 1945 a senior officer with the Public Health and Welfare Division of the occupation's General Headquarters wrote regarding the typical prostitute:
 * "The girl is impressed into contracting by the desperate financial straits of her parents and their urging, occasionally supplemented by her willingness to make such a sacrifice to help her family," he wrote. "It is the belief of our informants, however, that in urban districts the practice of enslaving girls, while much less prevalent than in the past, still exists."

"The worst victims... were the women who, with no previous experience, answered the ads calling for 'Women of the New Japan,"'

When MacArthur finally closed the brothels on March 25, 1946, it is estimated that more than 25% of the U.S. troops had sexually transmitted diseases.

Industrial disarmament
To further remove Japan as a potential future threat to the U.S., the Far Eastern Commission decided that Japan was to be partly de-industrialized. The necessary dismantling of Japanese industry was foreseen to have been achieved when Japanese standards of living had been reduced to those existing in Japan the period 1930 - 1934. In the end the adopted program of de-industrialisation in Japan was implemented to a lesser degree than the similar U.S. "industrial disarmament" program in Germany. In view of the cost to American taxpayers for emergency food aid to Japan, in April 1948 the Johnston Committee Report recommended that the economy of Japan should instead be reconstructed. The report included suggestions for reductions in war reparations, and a relaxation of the "economic deconcentration" policy. For the fiscal year of 1949 funds were moved from the GARIOA budget into an Economic Rehabilitation in Occupied Areas (EROA) programme, to be used for the import of materials needed for economic reconstruction.

Expulsions
The defeat of the Japanese Empire meant reversal of its previous annexations-Taiwan and Manchuria returned to China, while Korea regained its independence.

The Soviet Union claimed South Sakhalin and the Kuril Islands, with 400,000 Japanese fleeing or expelled. Similar actions happened in Taiwan and Manchuria after their return to China, while independent Korea saw flight of over 800,000 Japanese settlers—fearing reprisals for Japanese war crimes and decades of looting of the peninsula by settlers.

Soviet Attacks
In a bid to occupy as much Japanese territory as possible, Soviet troops continued offensive military operations after the Japanese surrender, causing large scale civilian casualties.

Politics
Unlike the case in Germany, Japan retained a native government throughout the occupation, although its de facto authority was strictly limited at first and senior figures in the government such as the Prime Minister effectively served at the leisure of the occupational authorities prior to the first post-war elections being held.

Political parties had begun to revive almost immediately after the occupation began. Left-wing organizations, such as the Japan Socialist Party and the Japan Communist Party, having being banned by the Fascists, quickly reestablished themselves, as did various conservative parties. The old Seiyukai and Rikken Minseito came back as, respectively, the Liberal Party (Nihon Jiyuto) and the Japan Progressive Party (Nihone Shimpoto). The first postwar elections were held in 1946 (women were given the franchise for the first time), and the Liberal Party's vice president, Yoshida Shigeru (1878–1967), became prime minister. For the 1947 elections, anti-Yoshida forces left the Liberal Party and joined forces with the Progressive Party to establish the new Japan Democratic Party (Minshuto). This divisiveness in conservative ranks gave a plurality to the Japan Socialist Party, which was allowed to form a cabinet, which lasted less than a year. Thereafter, the socialist party steadily declined in its electoral successes. After a short period of Democratic Party administration, Yoshida returned in late 1948 and continued to serve as prime minister until 1954. However, because of a heart failure Yoshida was replaced by Shinto in 1955.

End of the occupation
In 1949, MacArthur made a sweeping change in the SCAP power structure that greatly increased the power of Japan's native rulers, and the occupation began to draw to a close. The San Francisco Peace Treaty, signed on September 8, 1951, marked the end of the Allied occupation, and when it went into effect on April 28, 1952, Japan was once again an independent state (with the exceptions of Okinawa, which remained under U.S. control until 1972, and Iwo Jima, which remained under US control until 1968). Even though some 31,000 U.S. military personnel remain in Japan today, they are there at the invitation of the Japanese government under the terms of the Treaty of Mutual Cooperation and Security between the United States and Japan (1960) and not as an occupying force.


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A History of Japan: From Mythology to Nationhood/The Warring States Period

The Sengoku period (戦国時代 Sengoku Jidai) or Warring States period in Japanese history was a time of social upheaval, political intrigue, and nearly constant military conflict that lasted roughly from the middle of the 15th century to the beginning of the 17th century. The name "Sengoku" was adopted by Japanese historians in reference to the Warring States period in Chinese history which preceded the unification of China. Likewise, the Sengoku period in Japan would eventually lead to the unification of political power under the Tokugawa shogunate. Although the Ashikaga shogunate had retained the structure of the Kamakura bakufu and instituted a warrior government based on the same social economic rights and obligations established by the Hōjō with the Jōei Code in 1232, it failed to win the loyalty of many daimyo, especially those whose domains were far from Kyoto. As trade with China grew, the economy developed, and the use of money became widespread as markets and commercial cities appeared. This, combined with developments in agriculture and small-scale trading, led to the desire for greater local autonomy throughout all levels of the social hierarchy. As early as the beginning of the 15th century, suffering and misery caused by natural disasters such as earthquakes and famines often served to trigger armed uprisings by farmers weary of debt and taxes. The Ōnin War (1467–1477), a conflict rooted in economic distress and brought on by a dispute over shogunal succession, is generally regarded as the onset of the Sengoku period. The "eastern" army of the Hosokawa family and its allies clashed with the "western" army of the Yamana, and fighting in and around Kyoto lasted for nearly 11 years, after which it spread to outlying provinces.

Gekokujō
The upheaval resulted in the further weakening of central authority, and throughout Japan regional lords, or daimyo, rose to fill the vacuum. In the course of this power shift, well established clans such as the Takeda and the Imagawa, who had ruled under the authority of both the Kamakura and Muromachi bakufu, were able to expand their spheres of influence. There were many, however, whose positions eroded and were eventually usurped by more capable underlings. This phenomenon of social meritocracy, in which capable subordinates rejected the status quo and forcefully overthrew an emaciated aristocracy became known as gekokujō (下克上?), which literally means "the underling conquers the overlord." One of the earliest instances of this phenomenon was Hōjō Sōun, who rose from relatively humble origins and eventually seized power in Izu province in 1493. Building on the accomplishments of Sōun, the Late Hōjō clan remained a major power in the Kantō region until its subjugation by Toyotomi Hideyoshi late in the Sengoku period. Other notable examples include the supplanting of the Hosokawa clan by the Miyoshi, the Shiba clan by the Oda clan, and the Toki by the Saito. Well organized religious groups also gained political power at this time by uniting farmers in resistance and rebellion against the rule of the daimyo. The monks of the Buddhist True Pure Land sect formed numerous Ikkō-ikki, the most successful of which, in Kaga Province, remained independent for nearly 100 years.

Rise of Oda Nobunaga
During the last half of the 16th century, a number of different daimyo became strong enough either to manipulate the Muromachi bakufu to their own advantage or to overthrow it altogether. One attempt to overthrow the bakufu was made in 1560 by Imagawa Yoshimoto, whose march towards the capital came to an ignominious end at the hands of Oda Nobunaga in the Battle of Okehazama. In 1562, The Tokugawa clan who was adjacent to the east of Nobunaga's territory became independent of the Imagawa clan, and allied with Nobunaga. The eastern part of the territory of Nobunaga's was not invaded by this alliance. And, he moves the army to the west. In 1565, an alliance of the Matsunaga and Miyoshi clans attempted a coup by assassinating Ashikaga Yoshiteru, the 13th Ashikaga shogun. Internal squabbling, however, prevented them from acting swiftly to legitimatize their claim to power, and it was not until 1568 that they managed to install Yoshiteru's cousin, Ashikaga Yoshihide, as the next Shogun. Failure to enter Kyoto and gain recognition from the imperial court, however, had left the succession in doubt, and a group of bakufu retainers led by Hosokawa Fujitaka negotiated with Nobunaga to gain support for Yoshiteru's younger brother, Yoshiaki.

Nobunaga, who had prepared over a period of years for just such an opportunity by establishing an alliance with the Asai clan in northern Ōmi Province and then conquering the neighboring province of Mino Province, now marched toward Kyoto. After routing the Rokkaku clan in southern Omi, Nobunaga forced the Matsunaga to capitulate and the Miyoshi to withdraw to Settsu. He then entered the capital, where he successfully gained recognition from the emperor for Yoshiaki, who became the 15th Ashikaga shogun.

Nobunaga had no intention, however, of serving the Muromachi bakufu, and instead now turned his attention to tightening his grip on the Kansai region. Resistance in the form of rival daimyo, intransigent Buddhist monks, and hostile merchants was eliminated swiftly and mercilessly, and Nobunaga quickly gained a reputation as a ruthless, unrelenting adversary. In support of his political and military moves, he instituted economic reform, removing barriers to commerce by invalidating traditional monopolies held by shrines and guilds and promoting initiative by instituting free markets known as rakuichi-rakuza.

By 1573 he had destroyed the alliance of Asakura clan and Azai clans that threatened his northern flank, obliterated the militant Tendai Buddhists monastic center at Mount Hiei near Kyoto, and also had managed to avoid a potentially debilitating confrontation with Takeda Shingen, who had suddenly taken ill and died just as his army was on the verge of defeating the Tokugawa and invading Oda's domain on its way to Kyoto.

Even after Shingen's death, there remained several daimyo powerful enough to resist Nobunaga, but none were situated close enough to Kyoto to pose a threat politically, and it appeared that unification under the Oda banner was a matter of time.

Nobunaga's enemies were not only other Sengoku daimyō but also adherents of a Jōdo Shinshu sect of Buddhism who attended Ikkō-ikki. Their leader was Kennyo. He endured though Nobunaga kept attacking his fortress for ten years. Nobunaga expelled Kennyo in the eleventh year, but, by a riot caused by Kennyo, Nobunaga's territory took the big damage. This long war was called Ishiyama Hongan-ji War.

To suppress the Buddhism, Nobunaga supported Christianity. And, a lot of cultures were introduced to Japan by the missionary from Europe. Those things include new foods, new drawing methods, astronomy, geography, medical science, and new printing techniques.

Unification of Japan
After nearly a century and a half of political instability and warfare, Japan was on the verge of unification by Oda Nobunaga, who had emerged from obscurity in the province of Owari (present-day Aichi Prefecture) to dominate central Japan, when in 1582 Nobunaga himself fell victim to the treachery of one of his own generals, Akechi Mitsuhide. This in turn provided Toyotomi Hideyoshi, who had risen through the ranks from ashigaru (footsoldier) to become one of Nobunaga's most trusted generals, with the opportunity to establish himself as Nobunaga's successor. Hideyoshi eventually consolidated his control over the remaining daimyo and, although he was ineligible for the title of Seii Taishogun because of his common birth, ruled as Kampaku. He would later name his nephew, Toyotomi Hidetsugu, as Kampaku in 1592 following the death of Hideyoshi's half-brother, Toyotomi Hidenaga.

In the same year, Hideyoshi would launch his campaigns into Korea, now known as the Imjin War. The conflict would last from 1592 until 1598, with a brief truce in 1596. It would result in the Japanese failing to secure the peninsula.

At home, Hideyoshi and Hidetsugu's relationship had begun to deteriorate. Hidetsugu was accused of committing many murders that were deemed unjust. In 1595, he was accused of plotting a coup and later was ordered by Hideyoshi to commit seppuku on Mount Koya. Hidetsugu's family was later executed upon Hideyoshi's ordered, which was very controversial among daimyo. Hidetsugu and his family's deaths eventually led to the dissolution of the Toyotomi clan's authority post-Sekigahara.

When, in 1598, Hideyoshi died without leaving a capable successor, the country was once again thrust into political turmoil, and this time it was Tokugawa Ieyasu who took advantage of the opportunity.

Sekigahara, Creation of the Edo Shogunate, and Osaka
Before Hideyoshi's death, he assigned Tokugawa Ieyasu of the Kantō region, Ukita Hideie of Bizen and Mimasaka, Maeda Toshiie of Kaga and Etchū, Uesugi Kagekatsu of Yonezawa, Mōri Terumoto of Choshu, and Kobayakawa Takakage of Chikuzen to the Council of Five Elders. The council effectively ruled as regents to Hideyoshi's son and heir, Toyotomi Hideyori. However, following Hideyoshi's death in 1598, the council's relationship began to decline and by 1599, after the death of the "neutral" Maeda Toshiie, the conflicts had begun. Two factions then arose; the Bunchiha, which favored a civil service in Japan and the Bundanha, which favored a military government.

Ieyasu's influence was very large and was effectively a hegemony. He had organized many political marriages, securing alliances throughout Japan, including his son, Tadateru, to Date Masamune's daughter, Irohahime. This angered many council members, who believed that the marriages required approval from the council. The daimyō of Sawayama Castle, Ishida Mitsunari, then formed an alliance comprised of those opposed to the Tokugawa and were staunch Toyotomi chauvinists. Mitsunari eventually gained the support of Hideie, Kagekatsu, and Terumoto. Terumoto decided to stay within Osaka Castle, so field command was placed under Mitsunari. A factional dispute later arose between Ishida Mitsunari and several other generals under the Toyotomi banner, including Kato Kiyomasa of the Kumamoto domain. This allowed Tokugawa Ieyasu to persuade many daimyo to confront Mitsunari opposition to Ieyasu. In 1600, Uesugi Kagekatsu openly defied Tokugawa Ieyasu by building a castle in Aizu. Ieyasu had then demanded that Kagekatsu explained his actions, to which Kagekatsu refused. Kagekatsu had done this to distract Ieyasu to allow Mitsunari to enact his plan. However, Ieyasu had predicted this, and instead of personally leading a force against Kagekatsu, he had Mogami Yoshiaki and Date Masamune continue conflict against Kagekatsu in Tohoku.

Meanwhile, Ishida Mitsunari had finally launched his campaign. On 27 August, he began his siege of Fushimi Castle. He had hoped for a quick victory, but it turned into a ten day siege. The castle fell on 8 September and its defenders committed suicide. While Mitsunari achieved victory, he had lost the crucial time that was needed to secure an overall success in the campaign against Ieyasu. Mitsunari had hoped to use Gifu Castle as a point to delay the Tokugawa clan's advances. However, the castle fell to Ii Naomasa and Fukushima Masanori on 30 September. When realizing Tokugawa Ieyasu was marching towards Osaka Castle, Mitsunari revised his plans, and began to desire a direct confrontation at Sekigahara.

On 21 October, the battle of Sekigahara had begun. Ishida Mitsunari and his side comprised the Western Army, while Tokugawa Ieyasu and his side comprised the Eastern army. The battle had eventually stalemated, with both sides racking up casualties. Kobayakawa Hideaki, Toyotomi Hideyoshi's nephew, who had only accompanied Mitsunari with the intent of betrayal, finally defected to the Tokugawa clan's side. His force would begin to attack the positions of Otani Yoshitsugu, who'd eventually asked a retainer to behead him. After Hideaki's betrayal, the Western Army's front began to collapse. Meanwhile, Ii Naomasa was wounded in while chasing troops under the Shimazu clan. With no reinforcements incoming, the Western Army had been destroyed. However, Mitsunari was able to escape from the battlefield. He was later found and executed on 6 November.

In 1603, Emperor Go-Yozei bestowed the position of shogun to Tokugawa Ieyasu. This created the Tokugawa Shogunate, which is notable for its stability and peace. Ieyasu would later resign in 1605 in favor of his son, Tokugawa Hidetada. However, he still held control over the government.

However, Ieyasu still had one more major opponent, Toyotomi Hideyori. After tension between the two escalated in 1614, Ieyasu gathered a force of 160,000 and marched on Osaka Castle. This began the first phase of the siege of Osaka, the winter siege. Bombardment of the castle was heavy, but Osaka did not surrender. An uneasy treaty was then established between the two sides, but conflict began the next year once again. With the loss of the Battle of Tennoji, Osaka Castle on fire, and Sanada Yukimura's death, Hideyori and his mother committed seppuku as the castle burned around them. After their death's were announced, many other nobles committed suicide and the castle eventually surrendered, ending the Toyotomi clan and ending any major challenge to the Tokugawa's reign.

Tokugawa Ieyasu died on June 1, 1616 at the age of 73, becoming the last great unifier to die.

The Great Unifiers of Japan

 * Oda Nobunaga
 * Toyotomi Hideyoshi
 * Tokugawa Ieyasu

Other daimyo

 * Azai Nagamasa
 * Chōsokabe Motochika
 * Date Masamune
 * Hōjō Sōun
 * Ii Naotora
 * Imagawa Yoshimoto
 * Maeda Toshiie
 * Miyoshi Nagayoshi
 * Mōri Motonari
 * Ōtomo Sōrin
 * Saitō Dōsan
 * Sanada Masayuki
 * Shimazu Yoshihiro
 * Tachibana Muneshige
 * Tachibana Ginchiyo
 * Takeda Shingen
 * Uesugi Kenshin
 * Ukita Hideie

Other notable individuals

 * Akechi Mitsuhide
 * Fukushima Masanori
 * Fūma Kotarō
 * Hattori Hanzō
 * Honda Tadakatsu
 * Ii Naomasa
 * Ishida Mitsunari
 * Kato Kiyomasa
 * Maeda Keiji
 * Miyamoto Musashi
 * Mori Ranmaru
 * Naoe Kanetsugu
 * Oda Nobutada
 * Saika Magoichi
 * Sanada Yukimura
 * Sasaki Kojirō
 * Shibata Katsuie
 * Shima Sakon

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


text:
Cookbook:Cuisine of Uruguay

| South American Cuisines

 * Alfajores
 * Arroz con leche
 * Bizcochos uruguayos
 * Bolas de Fraile
 * Chivito
 * Choripan
 * Coquitos
 * Croquetas de Arroz
 * Croquetas de Papa
 * Ensalada Rusa
 * Ensalada de Fruta Fruit Salad with Orange Soda
 * Faina
 * Fideos con tuco
 * Gnocchis
 * Guiso de Lentejas
 * Mate
 * Milanesa
 * Pascualina
 * Pasta Frola
 * Pasta puttanesca
 * Polenta rellena
 * Matambre relleno
 * Mondongo
 * Tomates Rellenos
 * Tortas Fritas

title: Cookbook:Cuisine of Uruguay


text:
Basic Physics of Nuclear Medicine/Attenuation of Gamma-Rays

We covered the interaction of gamma-rays with matter from a descriptive viewpoint in the previous chapter and we saw that the Compton and Photoelectric Effects were the major mechanisms. We will consider the subject again here but this time from an analytical perspective. This will allow us to develop a more general understanding of the phenomenon.

Note that the treatment here also refers to the attenuation of X-rays since, as we noted before gamma-rays and X-rays are essentially the same physical entities.

Our treatment begins with a description of a simple radiation experiment which can be performed easily in the laboratory and which many of the early pioneers in this field did. We will then build on the information obtained from such an experiment to develop a simple equation and some simple concepts which will allow us generalise the situation to any attenuation situation.

Attenuation Experiment
The experiment is quite simple. It involves firing a narrow beam of gamma-rays at a material and measuring how much of the radiation gets through. We can vary the energy of the gamma-rays we use and the type of absorbing material as well as its thickness and density.

The experimental set-up is illustrated in the figure below. We refer to the intensity of the radiation which strikes the absorber as the incident intensity, I0, and the intensity of the radiation which gets through the absorber as the transmitted intensity, Ix. Notice also that the thickness of the absorber is denoted by x.

From what we covered in the previous chapter we can appreciate that some of the gamma-rays will be subjected to interactions such as the Photoelectric Effect and the Compton Effect as they pass through the absorber. The transmitted gamma-rays will in the main be those which pass through without any interactions at all.

We can therefore expect to find that the transmitted intensity will be less than the incident intensity, that is

$$I_x < I_0\,\!$$

But by how much you might ask. Before we consider this let us denote the difference between Ix and I0 as ∆I, that is

$$\Delta I = I_0 - I_x\,\!$$

Effect of Atomic Number

 * Let us start exploring the magnitude of ∆I by placing different absorbers in turn in the radiation beam. What we would find is that the magnitude of ∆I is highly dependent on the atomic number of the absorbing material.  For example we would find that ∆I would be quite low in the case of an absorber made from carbon (Z=6) and very large in the case of lead (Z=82).

 * We can gain an appreciation of why this is so from the following figure:

 * The figure illustrates a high atomic number absorber by the large circles which represent individual atoms and a low atomic number material by smaller circles. The incident radiation beam is represented by the arrows entering each absorber from the left.  Notice that the atoms of the high atomic number absorber present larger targets for the radiation to strike and hence the chances for interactions via the Photoelectric and Compton Effects is relatively high.  The attenuation should therefore be relatively large.

 * In the case of the low atomic number absorber however the individual atoms are smaller and hence the chances of interactions are reduced. In other words the radiation has a greater probability of being transmitted through the absorber and the attenuation is consequently lower than in the high atomic number case.

 * With respect to our spaceship analogy used in the previous chapter the atomic number can be thought of as the size of individual meteors in the meteor cloud.

 * If we were to precisely control our experimental set-up and carefully analyse our results we would find that:

$$\Delta I \propto Z^3\,\!$$

 * Therefore if we were to double the atomic number of our absorber we would increase the attenuation by a factor of two cubed, that is 8, if we were to triple the atomic number we would increase the attenuation by a factor of 27, that is three cubed, and so on.

 * It is for this reason that high atomic number materials (e.g. Pb) are used for radiation protection.

Effect of Density

 * A second approach to exploring the magnitude of ∆I is to see what happens when we change the density of the absorber. We can see from the following figure that a low density absorber will give rise to less attenuation than a high density absorber since the chances of an interaction between the radiation and the atoms of the absorber are relatively lower. In addition, the density determines the transmission coefficient as it relates to the sample, since the lower the density, the higher the transmission coefficient due to the porous nature of the material.

 * So in our analogy of the spaceship entering a meteor cloud think of meteor clouds of different density and the chances of the spaceship colliding with a meteor.

Effect of Thickness

 * A third factor which we could vary is the thickness of the absorber. As you should be able to predict at this stage the thicker the absorber the greater the attenuation.

Effect of Gamma-Ray Energy

 * Finally in our experiment we could vary the energy of the gamma-ray beam. We would find without going into it in any great detail that the greater the energy of the gamma-rays the less the attenuation.  You might like to think of it in terms of the energy with which the spaceship approaches the meteor cloud and the likelihood of a slow spaceship getting through as opposed to a spaceship travelling with a higher energy.

Mathematical Model
We will consider a mathematical model here which will help us to express our experimental observations in more general terms. You will find that the mathematical approach adopted and the result obtained is quite similar to what we encountered earlier with Radioactive Decay. So you will not have to plod your way through any new maths below, just a different application of the same form of mathematical analysis!

Let us start quite simply and assume that we vary only the thickness of the absorber. In other words we use an absorber of the same material (i.e. same atomic number) and the same density and use gamma-rays of the same energy for the experiment. Only the thickness of the absorber is changed.

From our reasoning above it is easy to appreciate that the magnitude of ∆I should be dependent on the radiation intensity as well as the thickness of the absorber, that is for an infinitesimally small change in absorber thickness:

$$-d I \propto I \cdot dx\,\!$$

the minus sign indicating that the intensity is reduced by the absorber.

Turning the proportionality in this equation into an equality, we can write:

$$-d I = \mu I \cdot dx\,\!$$

where the constant of proportionality, μ, is called the Linear Attenuation Coefficient.

Dividing across by I we can rewrite this equation as:

$$-\frac{d I}{I} = \mu \cdot dx$$

So this equation describes the situation for any tiny change in absorber thickness, dx. To find out what happens for the complete thickness of an absorber we simply add up what happens in each small thickness. In other words we integrate the above equation. Expressing this more formally we can say that for thicknesses from x = 0 to any other thickness x, the radiation intensity will decrease from I0 to Ix, so that:

$$- \int_{I_0}^{I_x} \frac{dI}{I} = \mu \int_{0}^x dx$$

$$\therefore \ln \left ( \frac{I_x}{I_0} \right ) = -\mu x$$

$$\therefore \frac{I_x}{I_0} = \text{exp}\ (-\mu x)$$

$$\therefore I_x = I_0\ \text{exp}\ (-\mu x)\,\!$$

This final expression tells us that the radiation intensity will decrease in an exponential fashion with the thickness of the absorber with the rate of decrease being controlled by the Linear Attenuation Coefficient. The expression is shown in graphical form below. The graph plots the intensity against thickness, x. We can see that the intensity decreases from I0, that is the number at x = 0, in a rapid fashion initially and then more slowly in the classic exponential manner.

The influence of the Linear Attenuation Coefficient can be seen in the next figure. All three curves here are exponential in nature, only the Linear Attenuation Coefficient is different. Notice that when the Linear Attenuation Coefficient has a low value the curve decreases relatively slowly and when the Linear Attenuation Coefficient is large the curve decreases very quickly.

The Linear Attenuation Coefficient is characteristic of individual absorbing materials. Some like carbon have a small value and are easily penetrated by gamma-rays. Other materials such as lead have a relatively large Linear Attenuation Coefficient and are relatively good absorbers of radiation:

The materials listed in the table above are air, water and a range of elements from carbon (Z=6) through to lead (Z=82) and their Linear Attenuation Coefficients are given for three gamma-ray energies. The first point to note is that the Linear Attenuation Coefficient increases as the atomic number of the absorber increases. For example it increases from a very small value of 0.000195 cm-1 for air at 100 keV to almost 60 cm-1 for lead. The second point to note is that the Linear Attenuation Coefficient for all materials decreases with the energy of the gamma-rays. For example the value for copper decreases from about 3.8 cm-1 at 100 keV to 0.73 cm-1 at 500 keV. The third point to note is that the trends in the table are consistent with the analysis presented earlier.

Finally it is important to appreciate that our analysis above is only strictly true when we are dealing with narrow radiation beams. Other factors need to be taken into account when broad radiation beams are involved.

Half Value Layer
As with using the Half Life to describe the Radioactive Decay Law an indicator is usually derived from the exponential attenuation equation above which helps us think more clearly about what is going on. This indicator is called the Half Value Layer and it expresses the thickness of absorbing material which is needed to reduce the incident radiation intensity by a factor of two. From a graphical point of view we can say that when:

$$I_x = \frac{I_0}{2}$$

the thickness of absorber is the Half Value Layer:

The Half Value Layer for a range of absorbers is listed in the following table for three gamma-ray energies:

The first point to note is that the Half Value Layer decreases as the atomic number increases. For example the value for air at 100 keV is about 35 meters and it decreases to just 0.12 mm for lead at this energy. In other words 35 m of air is needed to reduce the intensity of a 100 keV gamma-ray beam by a factor of two whereas just 0.12 mm of lead can do the same thing. The second thing to note is that the Half Value Layer increases with increasing gamma-ray energy. For example from 0.18 cm for copper at 100 keV to about 1 cm at 500 keV. Thirdly note that relative to the data in the previous table there is a reciprocal relationship between the Half Value Layer and the Linear Attenuation Coefficient, which we will now investigate.

Relationship between μ and the HVL
As was the case with the Radioactive Decay Law, where we explored the relationship between the Half Life and the Decay Constant, a relationship can be derived between the Half Value Layer and the Linear Attenuation Coefficient. We can do this by using the definition of the Half Value Layer:

$$I = \frac{I_0}{2}$$

when

$$x = x_{\frac{1}{2}}$$

and inserting it in the exponential attenuation equation, that is:

$$I = I_0\ \text{exp}\ (-\mu x)\,\!$$

to give

$$\frac{I_0}{2} = I_0\ \text{exp}\ (-\mu x_{\frac{1}{2}})$$

Therefore

$$\frac{1}{2} = \text{exp}\ (-\mu x_{\frac{1}{2}})$$

$$\therefore 2^{-1} = \text{exp}\ (-\mu x_{\frac{1}{2}})$$

$$\therefore \ln 2^{-1} = -\mu x_{\frac{1}{2}}$$

$$\therefore \ln 2 = \mu x_{\frac{1}{2}}$$

$$\therefore 0.693 = \mu x_{\frac{1}{2}}$$

$$\mu = \frac{0.693}{x_{\frac{1}{2}}}$$

and

$$x_{\frac{1}{2}} = \frac{0.693}{\mu}$$

These last two equations express the relationship between the Linear Attenuation Coefficient and the Half Value Layer. They are very useful as you will see when solving numerical questions relating to attenuation and frequently form the first step in solving a numerical problem.

Mass Attenuation Coefficient
We implied above that the Linear Attenuation Coefficient was useful when we were considering an absorbing material of the same density but of different thicknesses. A related coefficient can be of value when we wish to include the density, ρ, of the absorber in our analysis. This is the Mass Attenuation Coefficient which is defined as the:

$$\frac{\text{Linear Attenuation Coefficient}}{\text{Density}} = \frac{\mu}{\rho}$$

The measurement unit used for the Linear Attenuation Coefficient in the table above is cm-1, and a common unit of density is the g cm-3. You might like to derive for yourself on this basis that the cm2 g-1 is the equivalent unit of the Mass Attenuation Coefficient.

Questions
Two questions are given below to help you develop your understanding of the material presented in this chapter. The first one is relatively straight-forward and will exercise your application of the exponential attenuation equation. The second question is a lot more challenging and will help you relate exponential attenuation to radioactivity and radiation exposure.

Question 1

How much aluminium is required to reduce the intensity of a 200 keV gamma-ray beam to 10% of its incident intensity? Assume that the Half Value Layer for 200 keV gamma-rays in Al is 2.14 cm.

Answer

 * The question phrased in terms of the symbols used above is:

$$I = \frac{I_0}{10},\ \text{when}\ x = \text{?}$$

 * We are told that the Half Value Layer is 2.14 cm. Therefore the Linear Attenuation Coefficient is

$$\mu = \frac{0.693}{x_{\frac{1}{2}}} = \frac{0.693}{2.14} = 0.324\ \text{cm}^{-1}$$

 * Now combining all this with the exponential attenuation equation:

$$I = I_0\ \text{exp}\ (-\mu x)\,\!$$

 * we can write:

$$\frac{I_0}{10} = I_0\ \text{exp}\ (-0.324x)$$

 * Therefore

$$\frac{1}{10} = \text{exp}\ (-0.324x)$$

$$\therefore -\ln 10 = -0.324x$$

$$\therefore x = \frac{\ln 10}{0.324} = \frac{2.3}{0.324} = 7.1\ \text{cm}$$

$$\therefore x \approx 7\ \text{cm}$$

 * So the thickness of aluminium required to reduce these gamma-rays by a factor of ten is about 7 cm. This relatively large thickness is the reason why aluminium is not generally used in radiation protection - its atomic number is not high enough for efficient and significant attenuation of gamma-rays.

 * You might like to try this question for the case when Pb is the absorber - but you will need to find out the Half Value Layer for the 200 keV gamma-rays yourself!

 * Here's a hint though: have a look at one of the tables above.

 * And here's the answer for you to check when you've finished: 2.2 mm.

 * In other words a relatively thin thickness of Pb is required to do the same job as 7 cm of aluminium.

Question 2

A 105 MBq source of 137Cs is to be contained in a Pb box so that the exposure rate 1 m away from the source is less than 0.5 mR/hour. If the Half Value Layer for 137Cs gamma-rays in Pb is 0.6 cm, what thickness of Pb is required? The Specific Gamma Ray Constant for 137Cs is 3.3 R hr-1 mCi-1 at 1 cm.

Answer

 * This is a fairly typical question which arises when someone is using radioactive materials. We wish to use a certain quantity of the material and we wish to store it in a lead container so that the exposure rate when we are working a certain distance away is below some level for safety reasons.  We know the radioactivity of the material we will be using.  But its quoted in SI units.  We look up a reference book to find out the exposure rate for this radioisotope and find that the Specific Gamma Ray Constant is quoted in traditional units.  Just as in our question!

 * So let us start by getting our units right. The Specific Gamma Ray Constant is given as:

3.3 R hr-1 mCi-1 at 1 cm from the source.

 * This is equal to:

3300 mR hr-1 mCi-1 at 1 cm from the source,

 * which is equal to:

$$\frac{3300}{(100)^2}\ \text{mR hr}^{-1}\ \text{mCi}^{-1}\ \text{at 1 m from the source}$$

 * on the basis of the Inverse Square Law. This result expressed per becquerel is

$$\frac{3300}{10^4 (3.7 \cdot 10^7)}\ \text{mR hr}^{-1}\ \text{Bq}^{-1}\ \text{at 1 m from the source}$$

 * since 1 mCi = 3.7 x 107 Bq. And therefore for 105 MBq, the exposure rate is:

$$\frac{3300 \cdot 10^5 \cdot 10^6}{10^4 (3.7 \cdot 10^7)}\ \text{mR hr}^{-1}\ (10^5\ \text{MBq})^{-1}\ \text{at 1 m from the source}$$

 * That is the exposure rate 1 meter from our source is 891.9 mR hr-1.

 * We wish to reduce this exposure rate according to the question to less than 0.5 mR hr-1 using Pb.

 * You should be able at this stage to use the exponential attenuation equation along with the Half Value Layer for these gamma-rays in Pb to calculate that the thickness of Pb required is about 6.5 cm.


text:
User:TaoPhoenix

I live on Cape Cod, Massachusetts.

I will be contributing to the Wiki projects more in the medium future.

title: User:TaoPhoenix