D Kocheva

R Stegmann

G Rainovski

J Jolie

N Pietralla

C Stahl

P Petkov

A Blazhev

A Hennig

C Bauer

Th Braunroth

M P Carpenter

L Cortes

A Dewald

M Djongolov

C Fransen

K Gladnishki

R V F Janssens

V Karayonchev

M Lettmann

C J Lister

J Litzinger

Th Möller

C Müller-Gatermann

M Scheck

Ph Scholz

C Schramm

P Thöle

V Werner

D Wölk

S Zhu

P Van Isacker

Search for mixed-symmetry states of nuclei in the vicinity of the double-magic nucleus 208 Pb

Search for mixed-symmetry states of nuclei in the vicinity of the double-magic nucleus 208 Pb

Introduction

States with mixed proton-neutron symmetry (MSSs) are the lowest-lying isovector excitations in the valence shell [1] for vibrational nuclei. Even though these states are defined in the framework of an algebraic model (IBM-2) [2,[START_REF] Iachello | The Interacting Boson Model[END_REF], their properties simultaneously depend on the nuclear quadrupole collectivity, the underlying shell structure, and the proton-neutron balance of the wave function. Mixed-symmetry states are identified experimentally [START_REF] Pietralla | [END_REF] by their strong isovector M1 decay to the low-lying, fullysymmetric states (FSSs). The best examples of MSSs of stable nuclei are found in the mass A ≈ 90 region [START_REF] Pietralla | [END_REF]5]. In the last decade a large number of MSSs has been identified in the mass A ≈ 130 region [6][7][8][9][10][11]. Although experimental data for MSSs is relatively abundant, especially for properties of one-phonon 2 + 1;ms states, there are only few limited attempts to understand the mechanism that governs the formation and the evolution of these states with the number of nucleons. Apparently such mechanism should include the interplay between the single-particle structure, the quadrupole collectivity, and the isospin degrees of freedom. Heyde and Sau [12] have suggested a schematic model for formation of isovector excitations in the valence shell which, however, accounts only for the a e-mail: rig@phys.uni-sofia.bg b Present address: University of the West of Scotland, PA1 2BE Paisley, United Kingdom and Scottish Univ. Phys. Alliance, Glasgow G12 8QQ, Scotland single-particle degree of freedom. Very recently, new experimental evidence for the formation mechanism of symmetric and mixed-symmetry low-lying quadrupole collective structures was reported for the A ≈ 90 region [13]. It has been shown that the one-phonon FS and MS states result from coupling of the lowest 2-quasiparticle proton and neutron excitations to the Giant Quadrupole Resonance (GQR). Consequently, the E2 strengths of these states are dominated by the GQR contributions while M1 properties are determined by the leading valence shell configurations. Within this concept, the evolution of the M1 strengths between MS and FSSs observed in N = 80 isotones [7] and in the chain of xenon isotopes [8] can be understood; due to normalization of the wave functions, with increasing collectivity the GQR contribution will also increase at the expense of a reduction of the valence shell contribution which leads to a decrease of M1 strength. This concept also demands that the strongest M1 transitions between one-phonon MS and FSs in a given mass region occur in less collective vibrational nuclei. These nuclei are only 2 proton particles (holes) and 2 neutron particles (holes) away from double magic nuclei. Apparently, they will also have the simplest possible valence shell configurations. However, it also has been shown that the absolute B(M1; 2 + 1;ms → 2 + 1 ) strength is highly sensitive to the proton-neutron balance of the wave functions; a mechanism dubbed Configurational Isospin Polarization (CIP) [14] occurs when proton and neutron amplitudes in the wave functions of one-phonon 2 The combined effect of low collectivity and vanishing CIP has been observed in 132 Te [10] -a nucleus which is two protons and two neutron holes away from the doubly magic nucleus 132 Sn. It has been shown that the onephonon MSS of this nucleus, namely the 2 + 2 state, decays with an exceptionally strong M1 transition to the FS 2 +

1 state [10]. The opposite case of well pronounced CIP is expected for 136 Te [15] due to the expectation that the pn exchange symmetry is strongly broken as Te and Xe isotopes depart from doubly magic 132 Sn [16]. Obviously, to better understand the interplay between collectivity and the isospin degrees of freedom in forming the low-lying isovector excitations, more cases of one-phonon MSSs in the vicinity of double-magic nuclei have to be identified and quantitatively studied. However, nuclei in the vicinities of doubly magic shell closures in which the onephonon 2 + 1;ms can be studied experimentally by conventional methods are scarce. In the mass A ≈ 130 region, i.e. the mass region around the doubly magic nucleus 132 Sn, all such nuclei are radioactive, including 132 Te. A bit different is the situation around the doubly magic nucleus 208 Pb where the nuclei having valence structures build on 2 proton particles (holes) -2 neutron particles (holes) are accessible experimentally by conventional methods. 204 Hg is 2 protons holes and 2 neutron holes away from the double magic nucleus 208 Pb and is stable. It can be studied in highly-inverse Coulomb excitation reactions [6]. 212 Po, which has 2 protons and 2 neutrons more than 208 Pb, is accessible in α-transfer reactions [17]. In this contribution we present the preliminary results from two such experiments that indicate existence of one-phonon MSSs in 212 Po and 204 Hg.

Identification of the one-phonon + mixed symmetric state of 21Po

The experiment was performed at the FN Tandem facility of the University of Cologne. Excited states of 212 Po were populated using the transfer reaction 208 Pb( 12 C, 8 Be) at a beam energy of 62 MeV. The beam energy was chosen to be about 2 MeV below the Coulomb barrier. The target was a self-supporting 10 mg/cm 2 thick Pb foil enriched up to 99.14% in the isotope 208 Pb. The reaction took place in the reaction chamber of the Cologne coincidence plunger device [18] in which an array of solar cells was mounted at backward angles with respect to the beam direction in order to detect the recoiling back light reaction fragments. The solar cell array consisted of six 10 mm×10 mm cells placed at distance of about 15 mm between their centers and the target. The array covered an annular space between 116.8 • and 167.2 • . The γ-rays from the decay of the excited states of 212 Po were registered by 12 HPGe de-tectors mounted outside the plunger chamber in three rings at, on average, 12 cm from the target. Five detectors were positioned at 142.3 • with respect to the beam direction, another six formed a ring at 35 • and a single detector was placed at 0 • . Data was taken in coincidence mode of at least one solar cell and one HPGe detector (particle-γ) or when at least two HPGe detectors (γ -γ) were in coincidence.

The particle-γ coincidence data was sorted in three matrices depending on the position of the HPGe detectors. A projection of the particle-γ(@142 • ) matrix is shown in Fig. 1(a). The γ-rays in coincidence with 8 Be (or 2α's) are shown in Fig. 1(b). This spectrum is dominated by the 727 keV, the 405 keV and the 223 keV lines which are the γ transitions from the first three yrast states of 212 Po [17]. Most of the other γ lines in the spectrum in Fig. 1(b) also originated from the decay of excited states of 212 Po. A partial level scheme of the states of 212 Po populated in the present experiment was constructed on the basis of the γ -γ coincidence relationships. The level scheme is presented in Fig. 2 and is in agreement with the previously reported level schemes of 212 Po [17,[19][20][21][22]. For the spinparities of the observed states we have adopted the values reported in previous studies [17,[19][20][21][22].

The levels presented in Fig. 2 are a part of those populated in another α-transfer reaction, namely 208 Pb( 18 O, 12 C) [17]. In addition, we have populated two off-yrast 2 + states at excitation energies of 1512 keV and of 1679 keV, respectively [19]. These two states decay predominantly to the 2 + 1 state via the 785 keV and the 952 keV transitions, respectively [23]. These two transitions have well pronounced M1 character with multipole mixing ratios of +0.09(3) and +0.65(50) [19], respectively. That makes these two 2 + states potential candidates for the onephonon MSS of 212 Po. The only missing piece of experimental information that is needed to verify this hypothesis are the short lifetimes of these levels.

Both 785 keV and 952 keV lines indeed show well pronounced Doppler shapes which allows for lifetimes determination of the 2 + 2 and 2 + 3 states in 212 Po by means of the Doppler Shift Attenuation Method (DSAM) (c.f. Ref. [24] and references therein). We have performed two parallel analyses of the line shapes; in the first analysis, labelled here Analysis I, we used a Monte Carlo (MC) simulation by means of a modified [25,26] version of the program DESASTOP [27] in order to describe the slowing down of the recoiling nuclei. The electronic stopping powers used were obtained from the Northcliffe and Schilling tables [28] with corrections for the atomic structure of the medium, as discussed in Ref. [START_REF] Ziegler | Astrophysics, Chemistry, and Condensed Matter[END_REF]. An empirical reduction of f n = 0.7 was applied [START_REF] Keinonen | AIP Conf. Proc[END_REF] to downscale the nuclear stopping power predicted by the theory of Lindhard, Scharff, and Schiøtt [START_REF] Lindhard | [END_REF]. The second analysis, labelled here Analysis II, uses an integrated software named APCAD (Analysis Program for Continuous Angle DSAM) [START_REF] Stahl | New methods for the γ-ray spectroscopy with position-sensitive detector systems[END_REF]. In APCAD, the slowing down process is simulated by GEANT4 [START_REF] Agostinelli | [END_REF] with the electronic stopping process modelled in the same way as in Analysis I. On the other side, APCAD adopts a simpler approach to mod- elling the nuclear stopping process, compared with the completely discrete approach used in Analysis I; in Analysis II the angular straggling due to nuclear collisions is modelled discretely by means of MC simulation while the corresponding energy loss is considered to emerge as a result from a continuous process and the nuclear stopping powers were taken from SRIM2013 [34] and reduced by 40%. Both analyses account for the response of the HPGe detectors, for the experimental geometry, and for the restrictions on the reaction kinematics imposed by the solar cell array. The feeding histories of the levels of interest were determined from the γ -γ coincidence data. Slow feeding was introduced and fitted in the analyses only if the analysed transitions were observed in coincidence with transitions from higher-lying states. In the opposite case, only very fast feeding which can be associated with direct population of the levels of interest, was considered.

Under the above assumptions both analyses produced similar results. For example, the lifetime of the 6 -state at 2016 keV (see Fig. 2) is known to be 0.49 (16) ps [17].

The lifetime of this level derived in our analyses from the line shape of the 661.3 keV transition, with a feeding history similar to the one used in Ref. [17] (58% fast feeding and 42% slow feeding), is 0.50(4) ps in Analysis I and 0.47(3) ps in Analysis II. The lifetimes of the 2 + 2 state at 1512 keV and 2 + 3 state at 1679 keV were extracted from the line shapes of the 785 keV and the 952 keV transitions (see Fig. 2), respectively. Both of these transitions are in coincidence with 727 keV transition, only. In Fig. 3, an example of the line-shape fit for the 952 keV transition is presented. The final lifetimes together with the available spectroscopic information and the resulting transition strengths are summarized in Table 1. 3 Search for the one-phonon 2 + mixed-symmetric state of 204 Hg Low-lying states of 204 Hg were populated and studied in a Coulomb excitation reaction. The experiment was carried out at Argonne National Laboratory in inverse kinematics. The pulsed (12 MHz) 204 Hg beam, with intensity of ≈ 1.3 pnA (∼ 8 × 10 9 ions/s), was delivered by the ATLAS accelerator. It was incident on a 1 mg/cm 2thick 12 C target with an energy of 890 MeV. This energy corresponds to ≈ 82% of the Coulomb barrier for the reactions of 204 Hg ions on a 12 C target [START_REF] Pelte | Heavy Ion Collisions[END_REF]. The deexcitation γ rays, following Coulomb excitation of the projectile, were detected with the Gammasphere array [START_REF] Lee | [END_REF] which consisted of 100 HPGe detectors. Gammasphere was used in singles mode, resulting in an average counting rate of 6800 counts-per-second (cps), while the room background was about 160 cps. A total of 4.4 × 10 8 events of γ-ray fold 1 or higher was collected in about 18 hours. The contribution of the room background was eliminated in the off-line sort by correlating the γ rays with the accelerator radio-frequency (RF) signal. The final spectrum, which is a difference between the "beam-on" (with respect to the RF) spectrum and the "beam-off" spectrum, scaled to eliminate the 1461 keV room background transition following the decay of 40 K, is shown in Fig. 4. All γ rays in the spectrum originate from 204 Hg nuclei recoiling with v/c ≈ 8.4%. Most of these γ rays have already been identified in the decay scheme of 204 Hg [37,38]. About 1.4% of the data have γ-ray fold higher than 1. These events were sorted into a γ -γ coincidence matrix. This matrix was used to construct the level scheme of 204 Hg that is presented in Fig. 5.

As seen from

The spectrum in Fig. 4 is dominated by the X-rays of mercury and the 437 keV transition which decays the 2 + 1 state in 204 Hg. There are several other intensive transitions and amongst them 1511 keV is a notable one. This transition connects the 2 + 4 state at excitation energy of 1948 keV to the 2 + 1 state. Preliminary results for the angular distribution of this transition indicated almost pure dipole character. This makes the 2 + 4 level at 1948 keV a potential candidate for the one-phonon MSS. This is additionally supported by the fact that the 3 - 1 state decays quite 204 Hg @ 890 MeV

Gammasphere in-beam singles

h

Counts Energy (keV) intensively to the 2 + 4 state via a 728 keV transition (c.f. Fig. 4 and Fig. 5). The relative γ-ray yields with respect to the 2 + 1 state measure the relative Coulomb excitation (CE) cross-sections. Predictions of the Winther-De Boer theory [START_REF] Winther | Coulomb Excitation[END_REF] were fitted to the experimental yields with the multiple CE code GOSIA [START_REF] Czosnyka | [END_REF] by using the known value B(E2; 0 + 1 → 2 + 1 ) = 0.427(7)e 2 b 2 [41] for setting the absolute scale. The fitting procedure accounts for the energy loss of the beam in the target, and the size of the unknown quadrupole moments [6] and provides a set of matrix elements describing the experimentally observed relative CE cross-sections. The preliminary results indicate that the M1 strength of the decay of the 2 + 4 state to the 2 + 1 state is about 0.5μ 2 N . This unexpectedly large B(M1) value allows us to consider the 2 + 4 state of 204 Hg as a single isolated one-phonon MSS.

Conclusion

In summary, we have presented two experiments dedicated to search of MSSs of nuclei in the vicinity of the doubly magic nucleus 208 Pb. The preliminary results from these investigations indicate the existence of one-phonon MSSs of 212 Po and 204 Hg. These are the first experimentally NSRT15 identified MSSs in the mass A ≈ 208 region and they call for theoretical explanations how the states of isovector nature are formed and evolve in this mass region.

Figure 1 .

 1 Figure 1. (Color online) (a) The projection of the particle-γ(@142 • ) matrix. The vertical lines represent groups of particles found to be in coincidences with the γ rays from the indicated nuclei. (b) The γ-ray spectrum in coincidences with the group of particles indicated as " 212 Po" in panel (a).

Figure 2 .

 2 Figure 2. (Color online) Partial level scheme of 212 Po obtained in the present work.

Figure 3 .

 3 Figure 3. (Color online) An example of line-shape fit of the 952.1 keV transitions obtained with the program APCAD. The vertical dotted line shows the position of the unshifted peak.

Figure 4 .

 4 Figure 4. (Color online) Background-subtracted, Doppler-corrected γ-ray spectrum of 204 Hg observed with Gammasphere after Coulomb excitation on a carbon target. The weak transitions in 204 Hg are not indicated.

Figure 5 .

 5 Figure 5. (Color online) Partial level scheme of 204 Hg obtained in the present work. The thickness of the arrows are proportional to the γ-ray intensities. The intensity of the 437 keV transition is downscaled by a factor of 1000 for presentation purposes.

  + states are not bal-

	EPJ Web of Conferences	0 1	, 7	0 0 3	0	4	(201 ) 6
	DOI: 10.1051/ C Owned by the authors, published by EDP Sciences, 201 / 201 epjconf 0 00 7 610 3 4 anced, and either one dominates. The case of significant 6 CIP is manifested by small absolute M1 rates. The oppo-
	site case of vanishing CIP leads to a very strong M1 tran-
	sition between the one-phonon MS and FSSs. In this way
	the two lowest one-phonon, predominantly FS and MS,
	2 + states provide a tool to quantitatively study the p -n
	balance of collective nuclear states.
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Table 1 .

 1 Table 1 the 2 + 2 state of 212 Po at 1512 keV excitation energy decays with a sizeable M1 transition to the 2 + 1 state. This allows us to conclude that the 2 + 2 state of 212 Po is, at least, a fragment of the one-phonon MSS. To our knowledge this is first MSS in mass A = 208 region firmly identified on the basis of measured strong M1 decay. Properties of the 2 + 2 and the 2 + 3 states of 212 Po. E level (keV) J π τ (ps) a E γ (keV) I γ B(E2) values are given in e 2 fm 4 (1 W.u.= 75.09 e 2 fm 4 ), and the B(M1) values are given in μ 2 N . In the calculations for the transitions strengths we have assumed vanishing α-decay branches.

	NSRT15

a Preliminary results from the present experiment. b From Ref.

[23]

. c Total electron conversion coefficients. From Ref.

[23]

. d From Ref.

[20]

. e

Acknowledgements

We thank A. Astier for useful discussions regarding the utilization of the DSAM in transfer reactions. G.R. acknowledges the support from the Alexander von Humboldt foundation. This work was supported by the partnership agreement between the University of Cologne and University of Sofia, by the DAAD German-Bulgarian exchange program under grants No. PPP57082997 and No. DNTS/01/05/2014, by the DFG under grant Pi393/2-3, and by the BMBF under grants No. 05P12RDCI8 and No. 05P15RDCIA.


Raquel Bertoldo

Claire Mays

Marc Poumadère

Nina Schneider

Claus Svendsen

Susana Loureiro

Great deeds or great risks? Scientists' social representations of nanotechnology

Keywords: nanotechnology, nanomaterials, risk perception, scientists, experts, social representations

This study was made possible

Introduction: As nanotechnologies develop, do societal representations follow?

Apprehension in response to products based in groundbreaking scientific innovations is often a typical reaction of a public towards new and unfamiliar objects [START_REF] Moscovici | Why a theory of social representations? In Representations of the social[END_REF][START_REF] Marcu | Analogies, metaphors, and wondering about the future: Lay sense-making around synthetic meat[END_REF]. When doubts and debate around a given issue are observed amongst scientists themselves, they can be interpreted as part of the scientific process of knowledge production in which things are stated, contradicted and then reformulated.

Our focus in this article is to explore societal debate about nanotechnology through the lens of the representations that nanoscientists share about their own work object. How do the scientists involved in development, testing, and/or applications of nanomaterials, and in current regulatory debate, integrate the risks and benefits they perceive to be part of nanotechnology into their informed position on the matter?

Nanoscience is the study of phenomena and manipulation of materials at an atomic, molecular and macromolecular level. At this scale, material properties differ significantly from those of larger scales (Royal Society & The Royal Academy of Engineering 2004), thus opening the way for a new generation of technology-based products (Joint Economic Committee 2007). Nanotechnology and the production of engineered nanomaterials already have had a major impact on e.g. electronics, telecommunication, construction, food technology, medical technologies, drug development, consumer sanitary care products, as well as environmental technologies, new agriculture, water purification systems and (renewable) energy production [START_REF] Savolainen | Nanosafety in Europe 2015-2025: Towards safe and sustainable nanomaterials and nanotechnology innovations[END_REF]. In parallel with this development, the usage of products containing engineered nanoparticles stimulates significant concerns about possible unintended health or environmental effects (Royal Society & Royal Academy of Engineering 2004).

The excitement around this whole new area of research and economic development has provoked substantial public and private investment in R&D. Between 1993 and2003, worldwide investments in nanotechnology research grew from $430 million to about $3 billion [START_REF] Roco | Broader societal issues of nanotechnology[END_REF]-corresponding in (non-adjusted) Euro to an increase in investments from approximately €332 million to about €2,1 billion. Since then the volume of activity has continued to increase. In the first decade of the 21 st century, the United States alone invested more than $14 billion (about €11 billion) in the National Nanotechnology Initiative [START_REF] Pidgeon | Nanotechnology risk perceptions and communication: Emerging technologies, emerging challenges[END_REF]. In the Europe of Horizon 2020, nanotechnology is labeled one of the key enabling technologies that can bolster Europe"s competitiveness and its ability to provide the innovative goods and services essential for meeting global challenges; ensuring the safe and sustainable development and application of nanotechnologies in this way becomes a major European objective [START_REF] Savolainen | Nanosafety in Europe 2015-2025: Towards safe and sustainable nanomaterials and nanotechnology innovations[END_REF]) justifying a large European R&D program. Thus, H2020-NMP1 will attribute budgets of €232 million (about $300 million) in 2014 and €152 million (about $196 million) In parallel, scientists, regulators, civil society and industry seek agreement on a definition of 'nanomaterials' that will foster safety through enabling the correct application of notification, registration or authorization schemes (cf. e.g. [START_REF] Schneider | Workshop on the EU 2 nd Regulatory Review of Nanomaterials[END_REF]). The 2011 European Commission Recommendation3 defines 'nanomaterial' as 'a natural, incidental or manufactured material containing particles […] where, for 50 % or more of the particles in the number size distribution, one or more external dimensions is in the size range 1 nm-100 nm. In specific cases and where warranted by concerns for the environment, health, safety or competitiveness the number size distribution threshold of 50 % may be replaced by a threshold between 1 and 50 %.

[…]'. The Commission states that while harmonization is sought, 'sector specific solutions' may nonetheless be necessary; the definition comes under review in 2014 (European Commission 2012).

Societal perceptions have come into view during this process of scientific and economic development [START_REF] Shapira | The emergence of social science research on nanotechnology[END_REF]. In some cases interest in public perceptions reflects concern by some scientists, industrial proponents and territorial economic actors that the "fledgling industry" may spark the same polemics as have biotechnologiese.g. genetically modified organisms (GMOs) or stem cells technology [START_REF] Pidgeon | Nanotechnology risk perceptions and communication: Emerging technologies, emerging challenges[END_REF]. The assessment of how the public associates risks and benefits to a new technology is indeed a central feature of its acceptability [START_REF] Slovic | Perception of risk[END_REF]. Societal views may also be recognized as an essential component in the governance of the innovation. The "21 st century Nanotechnology R&D Act" (Law n° 108-153) enacted by the U.S. Congress in 2003 states that societal concerns must be identified through "public input and outreach to be integrated (…) by the convening of regular and ongoing public discussions, through mechanisms such as citizens" panels, consensus conferences, and educational events, as appropriate" 4 . In the UK, noting that nanoscience and technologies attracted rapidly increasing interest and investment from the public and private sector worldwide, Government tasked the Royal Society in 2003 to take stock of new challenges in the safety, regulatory or ethical domains that will require societal debate (Royal Society & Royal Academy of Engineering 2004).

Despite such resolutions, and initiatives such as the French national Public

Debate (CNDP 2010), coherent involvement of general public stakeholders in the scientific discussion and communication process is still lacking [START_REF] Savolainen | Nanosafety in Europe 2015-2025: Towards safe and sustainable nanomaterials and nanotechnology innovations[END_REF].

Moreover, nanotechnologies appear to remain largely unknown by the public [START_REF] Satterfield | Anticipating the perceived risk of nanotechnologies[END_REF]. Experts appear overall more optimistic about the potential benefits of nanotechnologies, but also more concerned about their potential long term environmental and health effects [START_REF] Scheufele | Scientists worry about some risks more than the public[END_REF]

see Siegrist 2010 for a review).

To what extent is the consumer/ taxpayer, who will eventually purchase and benefit from or be harmed by products containing nanomaterials, aware of this technology?Can we today with confidence state, which are the predominant representations? So far, very few studies have systematically explored the "qualitative associations and thinking patterns that are most likely to be evoked by the concept of nanotechnology" (Siegrist 2010, p. 843, italics added). Existing studies tend to engage readymade assumptions that nanotechnology is perceived in terms of risks and benefits.

For example, [START_REF] Cacciatore | From enabling technology to applications: The evolution of risk perceptions about nanotechnology[END_REF] identified two types of question which have most frequently framed nanotechnology risk perception research: (a) do the benefits outweigh the risks or vice-versa, and (b) what are the perceived risk and benefits associated with a series of nanotechnology applications? This polarized manner of thinking about nanotechnologies is so intuitive that evidence maps organized in the form of "pros" and "cons" were seen to have improved the reporting of hazard assessments [START_REF] Wiedemann | Evidence maps: Communicating risk assessments in societal controversies: The case of engineered nanoparticles[END_REF].

What is missing today in the literature is a demonstration of whether the positions of a well-informed population (scientists) mirror the polarized risk-benefit dimension that has dominated research framing to date. To fill this gap, we conducted two studies exploring the representations of nanotechnology by diverse scientists working with these technologies. How is the content of these representations structured? Are these different according to area of scientific specialization? Considering the transit of new ideas from the expert to the lay sphere [START_REF] Bauer | Social representations theory: A progressive research programme for social psychology[END_REF], representations by scientists might hint of what society"s perceptions may look like in the future, once the public is more aware of nanotechnologies, their associated risks and benefits. Our data then, in addition to providing insight on the present specialist situation, might outline the future evolution of representations of nanotechnology in society as a whole.

Public perceptions

In a meta-analysis of 22 studies conducted worldwide between 2004 and 2009 about the public perception of nanotechnologies, [START_REF] Satterfield | Anticipating the perceived risk of nanotechnologies[END_REF] found that more than 51% of the participants reported knowing "nothing at all" about nanotechnology. This meta finding is similar to that of 54 % found in a representative European sample (Eurobarometer 2010). This general lack of information on the matter can explain the sensitivity of nanotechnology risk perceptions to framing effects, such as the economic or governance context in which nanotechnology is presented. For instance, greater risk is attributed to this technology when its development is associated with multinational rather than small or medium-sized enterprises [START_REF] Schütz | Framing effects on risk perception of nanotechnology[END_REF]. In order to reduce this type of framing effect, some studies have provided participants with information about nanotechnology to support them while forming an attitude [START_REF] Siegrist | Laypeople"s and Experts' Perception of Nanotechnology Hazards[END_REF]. A particular study conducted in Switzerland found the lay public to be significantly more concerned about nanotechnology applications than were experts (Siegrist, Wiek, et al. 2007).

Otherwise, the public seems to endorse an overall positive image of nanotechnologies: seven out of nine studies that specifically asked the question of 'whether judged benefits exceed risks or vice-versa' found that nanotechnology"s perceived benefits outweighed its associated risks [START_REF] Satterfield | Anticipating the perceived risk of nanotechnologies[END_REF]. This positive assessment of nanotechnology may correspond to a broader and more generic orientation of our modern societies towards "scientism", or the belief that "science, especially natural science, is much the most valuable part of human learning (…) because it is the most authoritative, or serious, or beneficial" (Sorell, 2013, p. 1).

This positive assessment has been linked to persons' higher familiarity with the issue at hand (Gaskell, Eyck, Jackson, and Veltri, 2005;[START_REF] Retzbach | Public understanding of science and the perception of nanotechnology: The roles of interest in science, methodological knowledge, epistemological beliefs, and beliefs about science[END_REF] and with their consultation of scientific media [START_REF] Ho | Value predispositions, mass media, and attitudes toward nanotechnology: The interplay of public and experts[END_REF][START_REF] Scheufele | The public and nanotechnology : How citizens make sense of emerging technologies[END_REF]. In a representative US survey, [START_REF] Ho | Value predispositions, mass media, and attitudes toward nanotechnology: The interplay of public and experts[END_REF] found that the more participants claimed to consume scientific media, the more benefits they saw in nanotechnology, and the more they supported its federal funding. These results were similar to those of [START_REF] Retzbach | Public understanding of science and the perception of nanotechnology: The roles of interest in science, methodological knowledge, epistemological beliefs, and beliefs about science[END_REF], who found familiarity with nanotechnology to be positively correlated with its perceived benefits and negatively with its perceived risks. These findings encourage a look at the scientific or mass media to learn whether nanotechnologies are being presented there under a positive light.

Media coverage of nanoscience

Studies to date suggest that neither the volume nor the coverage of nanotechnology by the mass media have been sufficient to characterize it as a socially salient, or polemic, issue [START_REF] Friedman | A longitudinal study of newspaper and wire service coverage of nanotechnology risks[END_REF][START_REF] Gaskell | Imagining nanotechnology: Cultural support for technological innovation in Europe and the United States[END_REF]. Content analysis of articles about nanotechnology published in newspapers or other online news platforms, demonstrate that the technology is more often covered in terms of benefits than in terms of risk (BfR 2013;[START_REF] Kulve | Evolving repertoires: Nanotechnology in daily newspapers in the Netherlands[END_REF]. Articles reporting risk information were "overwhelmed by the much larger volume of articles about nanotechnology benefits in both United States and United Kingdom" [START_REF] Friedman | A longitudinal study of newspaper and wire service coverage of nanotechnology risks[END_REF]Egolf 2011, p. 1713, italics added). As for the smaller group of articles quoting risk information, unlike the case of controversial biotechnological risk issues (e.g. OGM) alerts about potential nanotechnology risks were frequently issued by scientistsand not by environmental or consumer groups [START_REF] Friedman | A longitudinal study of newspaper and wire service coverage of nanotechnology risks[END_REF][START_REF] Pidgeon | Nanotechnology risk perceptions and communication: Emerging technologies, emerging challenges[END_REF]. It is interesting to observe that scientists here have appeared more cautious about nanotechnology's possible risks and uncertainties than have other potentially concerned social groups.

Analyzes of how nanotechnology and its applications are being covered by the media, and how they are being received by the public, can provide important indicators of how the potential risks associated to this new technological field are either socially amplified or attenuated [START_REF] Pidgeon | The social amplification of risk[END_REF]. There are reasons to be attentive: the seemingly uncontroversial and positive view that the public and the media hold about nanotechnology does not mirror the opinion of its experts [START_REF] Besley | Expert opinion on nanotechnology: Risks, benefit, and regulation[END_REF].

Expert perceptions of nanotechnologies

In their process of socialization, experts from different fields are educated within specific scientific traditions and research programs [START_REF] Patterson | Maintaining Research Traditions on Place: Diversity of Thought and Scientific Progress[END_REF]. These scientific traditions, based in research paradigms and worldviews, can significantly influence experts" appreciations of the world. For example, [START_REF] Babbage | Philosophical Worldview and Personality Factors in Traditional and Social Scientists: Studying the World in Our Own Image[END_REF] found academics with a social science background to be more organismically-oriented, and "hard"(physical/natural) scientists to be more mechanistically-oriented. Therefore, an experts" worldview can be "at least partially determined by the scientific Zeitgeist of their field" (Babbage and Ronan 2000, p. 406).

The adoption of one paradigm or another can in some cases constitute the difference between conceiving specific realities or not [START_REF] Kuhn | Scientists and their worldviews[END_REF].

It would therefore be expected that scientists with different backgrounds would have different opinions about nanotechnology [START_REF] Besley | Expert opinion on nanotechnology: Risks, benefit, and regulation[END_REF][START_REF] Powell | New risk or old risk, high risk or no risk? How scientists" standpoints shape their nanotechnology risk frames[END_REF]. Experts from a physics or chemistry background tend to attribute less health, environmental and social risk to nanotechnology, while experts from a social sciences background acknowledge higher social and regulatory concerns [START_REF] Besley | Expert opinion on nanotechnology: Risks, benefit, and regulation[END_REF]. In a similar vein, [START_REF] Powell | New risk or old risk, high risk or no risk? How scientists" standpoints shape their nanotechnology risk frames[END_REF] found that "upstream scientists"engineers, chemists, physicists and materials scientiststend to think that nanotechnologies do not pose new or substantial risks, while most "downstream scientists"toxicologists, epidemiologists and other public health scientistsare "concerned about the potential environmental and health risks related to these materials" (p. 183).

These studies show that this technology, seemingly uncontroversial in the eyes of the media and the public, is far from being so in the eyes of experts. To study more precisely the representations which are emerging from this new technology, we propose a deeper analysis of how an involved specialist population views nanotechnology. The participating scientists are dealing with this technology on a daily basis: they are part of research groups and networks, refining methods to create, tag, and characterize nanoparticles, furthering measurement and understanding, focussing on industrial and on environmental safety questions, exchanging with their peers research results, definitions, assessments and opinions about nanotechnology. In this sense they not only produce social knowledge in the form of science, but consume it as well, taking active roles in exchanging and confronting nanotechnology's different aspects with their peers.

Social representations

The social representations approach is interested notably in how scientific ideas are integrated by society at large and become shared social knowledge [START_REF] Moscovici | La psychanalyse, son image et son public[END_REF][START_REF] Moscovici | Why a theory of social representations? In Representations of the social[END_REF]. During this process of knowledge appropriation, laypeople often resort to metaphors and images that may have little to do with the scientific corpus [START_REF] Wagner | Everyday discourse and common-sense: The theory of social representations[END_REF]. The public proceeds thus to a reconstruction of the scientific object on its own terms.

For example, a study in Austria showed that biotechnologies have been represented by the public through images of vegetables as "infected" or "monstruous"which is consistent with the strong rejection for these technologies in the country [START_REF] Wagner | Killer tomatoes! Collective symbolic coping with biotechnology[END_REF]. But when this same technology is framed or anchored in terms of its application to the medical field, it is regarded as positive and desirable [START_REF] Bauer | Controversial medical and agri-food biotechnology: A cultivation analysis[END_REF][START_REF] Castro | Genetically modified organisms in the portuguese press: Thematization and anchoring[END_REF]. This suggests that when the scientific knowledge about biotechnology reaches the public sphere (through the media, through infomal conversation, etc.)this knowledge has been understood,or anchored, either in terms of medical applicationsand thus regarded as being positiveor in terms of agricultural applicationsand thus regarded as negative.

Considering the limited public awareness of nanotechnology (Eurobarometer 2010; [START_REF] Satterfield | Anticipating the perceived risk of nanotechnologies[END_REF]) and the relatively modest attention devoted to the subject by the media, social representations theory suggests that it would be unlikely for the public to have already formed a unified or systematic representation of nanotechnology.

But scientists and experts working directly with these materials are part of another environmentone where nanotechnologies are the subject of daily encounters, casual talks, and thus of social representations.

Overview of the studies

Our goal in this paper is to analyze the representations that experts in nanotechnology from different fields share about the science in which they are actively engaged. To more systematically analyze this group"s social representations of nanotechnology, we have conducted two studies. A first exploratory study aimed to identify the main dimensions behind these experts" nanotechnology representations. The second study set out to test the validity of these dimensions with a wider international sample of nanotechnology experts.

Study 1 -Exploring scientists' representations of nanotechnology

Social representations can be considered to be a set of shared beliefs. But more than shared beliefs, social representations also contain logically organized differences, or organizing principles. Organizing principles "do not necessarily consist of shared beliefs, as they may result in different or even opposed positions taken by individuals in relation to common reference points" (Doise, Clémence and Lorenzi-Cioldi 1993, p. 4).

Considering the importance of understanding the social logic behind the nanotechnology representations, our first study sought to explore (1) the content that scientists more often associate with nanotechnologywhat is commonly shared; (2) the dimensions organizing any distinctions within this contentwhat are the differences across subjects.

Method

Participants

Thirty-nine researchers involved in a multi-disciplinary European project centred on methods development for assessing the environmental fate and effects of engineered nanoparticles 5 answered an online questionnaire between April and May 2011. This group was composed of scientists from fields such as biology, toxicology, physics, and environmental sciences, but individual replies were not identified by disciplinary background. The scientists were personally contacted by email and the results of analysis were presented to them and discussed in a project plenary meeting.

Procedure

Participants were asked "When you think of NANOTECHNOLOGY, what are the five words or notions that first come to your mind?". These free associations were then categorizedsynonyms, plural forms and short phrases were reduced to a corresponding more frequent simple form.

Secondly, these categories were submitted to a multiple correspondence analysis (MCA) [START_REF] Doise | The quantitative analysis of social representations[END_REF][START_REF] Carvalho | Análise multivariada de dados qualitativos: Utilização da análise de correspondências múltiplas com o SPSS [Multivariate analysis of qualitative data: Using the multiple correspondence analysis with SPSS[END_REF], which is a type of factor analysis suited for the analysis of categorical data. This analysis was performed with the goal of identifying, through a quali-quantitative procedure, the main oppositions [START_REF] Billig | Ideological dilemmas[END_REF]) used by scientists to convey meaning to nanotechnology. This analysis is also recommended when the goal is to find relations within categories of variables under analysis [START_REF] Carvalho | Análise multivariada de dados qualitativos: Utilização da análise de correspondências múltiplas com o SPSS [Multivariate analysis of qualitative data: Using the multiple correspondence analysis with SPSS[END_REF]

Results

Participants associated 104 different words to nanotechnology, which after the categorization were reduced to 20 different forms. The categories most frequently associated with nanotechnology were: "new products" (n = 27), "small" (26), "risk" (23),

"new" (11), "nanoparticles" ( 10) "opportunity" (9), "uncertainties" (9), "environment" (8), "new properties" (7), "revolution" (6), "medicine" (6) "legislation" (6) and "industry" (6).

These free associations show in brief that nanotechnology experts consensually think about nanotechnology in terms of nanoscale (small), rendering new products possible, which involves some unknown risks.

In order to explore the differences within this content, these free associations were arranged in a 20 (association category) X 39 (participants) contingency table that was then submitted to the multiple correspondence analysis. Of the resulting explanatory factors, the first two dimensions together explained 26.5 % of the total variance6 of the original matrix.

The first dimension explains 14.1% of the total variance (Table 1). This dimension expresses the tension between the opportunity for new products enabled by the small size of the nanoparticles vs. concerns related to the possible risk that these technologies might represent for the environment and for the human health. Thus, enthusiastic thinking typified by the categories labelled medicine and opportunity, appears to be counterposed by preoccupations typified by the categories of risk, health and environment and legislation. This dimension was therefore named "opportunityrisk" (Table 1). The second dimension explained about 12.5% of the total variance (Table 1). It expresses the tension between new opportunities opened by the technology (associated categories: opportunity, medicine, innovation) vs. new risky properties and risk potential (associated categories: new properties, toxity and reactivity) (Figure 1). This dimension demonstrates a polarity similar to that of the first dimensionwith the difference being that the 'risk' end of this second dimension focusses on the essential properties and mechanistic effects of nanomaterials, rather than on large-scale impacts.

When free association categories are projected on the plot defined by these two axes, three groups of response can be identified (Figure 1). On the first dimension we can see the differentiation between 'opportunities' on the lower righthand side and the risks that are generally associated with nanotechnology (in terms of large-scale impacts, i.e. for human health and the environment), on the lefthand side. The second dimension distinguishes between nanotechnology"s opportunities, presented in the lower part of the chart (medicine, innovation and industry) and the possible risks inherent to nanomaterial characteristics and effects, presented in the upper part of the chart (Figure 1).

Figure 1. Groupings of categorized free-associations to "nanotechnology".

Discussion

Public perceptions of nanotechnology have been mainly assessed in the past through polarized instruments, as if the technology wasand should beunderstood essentially in terms of "pros" and "cons" [START_REF] Besley | Expert opinion on nanotechnology: Risks, benefit, and regulation[END_REF][START_REF] Cacciatore | From enabling technology to applications: The evolution of risk perceptions about nanotechnology[END_REF][START_REF] Pidgeon | Deliberating the risks of nanotechnologies for energy and health applications in the United States and United Kingdom[END_REF]. Past studies surveyed participants about the degree to which they perceived either risk or opportunityin the development of nanotechnology, assuming that this technology would be represented in a bipolar manner opposing negative aspects (risk) and positive aspects (benefit, opportunity). To our knowledge, however, this representation of nanotechnology as a polarized issue had not yet been confirmed by a qualitative analysis.

We performed the qualitative analysis, without imposing the risk/benefit categories. Our results show that the experts from different scientific backgrounds participating in the NanoFATE project generally think of nanotechnology in terms of scale (small), enabling new products, which involves some unknown risks. Public thinking and meaning-making often take the shape of a debate, or a dilemma, where "socially shared images, representations and values can be seen to conflict" (Billig et al. 1988, p.14). Our results suggest that this particular group of nanoscientists also think and argue about nanotechnology in a polarized manner, limiting their enthusiasm about the technologya representation that is more widespread in the media (Friedman and Egolf 2011)with concerns about possible environmental and health risks, potentially rooted in the particular characteristics of materials at the nanoscale. In this way, our Study 1 provides a confirmation of the bipolar risk-benefit representation of nanotechnology, derived for the first time from a quali-qualitative analysis.

What we do not know from these results is whether this simultaneous understanding of nanotechnology as opportunity and as risk is shared by all scientists, irrespective of their background, or if the particular representation emerging here may mirror different perspectives by subgroups of experts over this social object [START_REF] Babbage | Philosophical Worldview and Personality Factors in Traditional and Social Scientists: Studying the World in Our Own Image[END_REF][START_REF] Doise | Droits de l'homme et force des idées [Human rights and the power of ideas[END_REF]).

If the factor dimensions revealed here are both broadly shared by individual experts, we could understand this polarization as part of an argumentative pattern constructed as yes… but [START_REF] Mouro | Local communities responding to ecological challenges: A psycho-social approach to the Natura 2000 Network[END_REF]. Yes, nanotechnology is a novelty associated with great future opportunities that will improve our lives; but it comes with some unknown qualities and potential risks for the environment and human health. The group of participants that did respond to the questionnaire includes experts with different roles in the development of nanotechnology and also with different scientific backgrounds. Our sample was mostly composed of researchers (66.4%), followed by policy actors (17.1%), administrators (15.1%) and regulators (5.9%) (participants could describe themselves with more than one response).

The main scientific background represented was environmental sciences (38.2%), followed by engineering (27.3%), toxicology (19.7%), biology (19.1%), physics (16.4%), chemistry (15.1%), social sciences (9.2%), medicine (7.2%) and pharmacy (2.6%). Some participants described themselves as having more than one type of scientific background. This distribution encompasses participants with very different standpoints from which they "frame" the characteristics and the uncertainties of this new technology [START_REF] Powell | New risk or old risk, high risk or no risk? How scientists" standpoints shape their nanotechnology risk frames[END_REF][START_REF] Althaus | A disciplinary perspective on the epistemological status of risk[END_REF].

Instrument

The nanotechnology appraisal instrument was informed by the categories identified by the first study. The individual items were grounded in more elaborated concepts emerging from one focus group conducted by the lead author with five nanotechnology researchers of different backgrounds (biologists, toxicologists and engineers) and from different departments at Universidade de Aveiro, in Portugal. The group identified its own themes and discussed various aspects related to nanomaterials, including in particular: their potential "toxicity"and "reactivity", the need to raise "public awareness"

and the need to "regulate" these technologies. After the group session, the lead author summarized the main ideas brought up by the group and submitted the summary to the five researchers for validation. The instrument was then completed by including characteristic phrases used by these specialists to refer to nanotechnology, alongside statements drawn from journals, institutional websites or research projects" dissemination websites.

Survey participants were required to judge their level of agreement with a series of 13 statements using a scale from 1 (totally disagree) to 5 (totally agree). Within this list were items considered by the authors to tap primarily the "opportunity" or the "risk" poles identified in the first study, forming two subscales. Some statements were formulated in the affirmative (e.g. 'nanotechnology is an important sector for European economic development and competitiveness') while others were 'reversed' (e.g. 'the development of nanotechnology will NOT create many jobs'). The overall order of item presentation was randomized to control response biases. Responses to the items formulated in the negative were reversed before analysis.

Results

Responses to the 13 items composing the nanotechnology appraisal instrument were submitted to a Principal Component Analysis (PCA) to explore the relation between the two proposed subscales. Varimax rotation revealed the existence of two factors clearly corresponding to the representations of nanotechnology as risk or as benefit or opportunity (KMO = .85; Bartlett"s test of sphericity: χ(78) = 596.13, p< .001). These two factors accounted together for 49.5% of the total variance (Table 2). 15. Some of our environmental problems can be addressed by good application of nanotechnological advances.

.70 -.29 11. In future years, people will think of nanotechnology as a real industrial revolution.

.66 .21

16. Human health applications of nanotechnology have great potential.

.62 -.14

12. The development of nanotechnology will NOT create many .56 -.16 jobs (reversed).

7. The development of nanomaterials should be under strict regulatory control.

-.12 .76

5.

No evidence to date suggests that nanomaterials present novel risks (reversed).

.10

.68

8. The precautionary principle should guide decisions made about nanotechnologies.

-.11 .67

1. There is reason for concern about the impact that an increasing use of nanomaterials may have on environmental health.

-.19 .65

9. The principle "no toxicological data, no market" should apply to nanomaterials.

-.23

.63

3. The potential risks associated with nanotechnology developments outweigh their future benefits.

-.22

.51

Considering the good internal consistency of both the risk (Cronbach"s α = .82) and the opportunity (α = .76) scales, each of them was averaged in a single measure of risk and opportunity. These two measures correlate negatively (r = -.37, p< .01), which means that the more one person adheres to one of these aspects of the representation, the less s/he adheres to the other.

The empirically demonstrated division of items into two main dimensions of risk and opportunity confirm that experts represent nanotechnology in a polarized way, exactly as we had found in the previous study. Moreover, the negative correlation between the aspects of risk and opportunity indicate that participants adhering to one of these representations tend to not adhereor adhere to a lesser extentto the other representation. Let us now explore how specialists with different roles and/or scientific backgrounds emphasize specific elements of the nanotechnology representationthe particular manner in which they may tend to cluster in the polarized field traversed by the risk/opportunity dimension.

Representing different perspectives

To better understand how the expert"s role influences perceptions of nanotechnology as risk or as opportunity, two one-way anovas were performed on their attribution of risks and of benefits to nanotechnology. No significant differences were observed between the way in which experts in different roles regard nanotechnologies as opportunities In order to better understand how the respondent"s scientific background (and not their role) influences perceptions of nanotechnology as either risk or benefit/opportunity, two one-way anovas were performed. Participants with different scientific backgrounds did not significantly differ in their representation of nanotechnology as opportunity (F(6,136) = .98, p = ns). This means that the surveyed experts, irrespective of their scientific background, acknowledged the opportunities or benefits presented by nanoscience (Figure 3).

The perception of risks, on the other hand, was not as consensual: experts with different scientific backgrounds agreed to a different extent with items attributing risk to nanotechnologies (F(6,136) = 5.47, p < .001). Post-hoc tests with Bonferroni pairwise comparaisons showed that scientists whose scientific background includes physics or chemistry attribute significantly less risk to nanotechnologies when compared with the group whose scientific background is in toxicology, life sciences (biology and medicine), and social sciences (all p"s < .05). Finally, the group of experts indicating a background in engineering or environmental sciences wasnot distinguished from any of the other groups regarding their risk perception (Figure 3). Overall, these results indicate that, despite a consensual view among experts that nanotechnologies represent a great opportunity, depending on scientific background they do not agree to the same extent that nanotechnology also constitutes a risk. We can identify therefore two main arguments, styles of discourse or subgroups: one that more consensually represents nanotechnology as opportunity, and another one that represents it as both an opportunity and as a risk.

Discussion

Our Study 2 validated the polarized representation of nanotechnology found in the first study: nanotechnologies are seen as great opportunities, but they also involve unknown risks. Our results also permitted the analysis of how the experts" standpoint (role and discipline) might influence their representations [START_REF] Powell | New risk or old risk, high risk or no risk? How scientists" standpoints shape their nanotechnology risk frames[END_REF]).

Nanotechnology representations were not significantly influenced by the role played by the participating specialists. We note that the roles can be performed in very different ways depending on the participants" scientific background. This could blur the differences between the perspectives adopted by participants in different roles.

On the other hand, the experts" scientific backgrounds clearly influenced, on the other hand, the way they represented nanotechnology. Despite a consensual view across experts that the development of nanotechnology provides important opportunities, they do not agree about the extent to which it constitutes a risk. "Hard science" experts see less risk in nanotechnology than do life and social scientists. Environmental scientists and engineers were not fully assimilated to nor distinguished from either of these subgroups. This finding suggests that they are a more diversified group, containing persons who attribute respectively more and less risk to nanotechnologies (Figure 3).

Our results indicate that the twofold representation found in Study 1 is actually shared by only part of the broader Study 2 samplethe subgroup of life and social scientistswho in a 'yes, but' logic regard nanotechnology as simultaneously bothopportunity and risk. As our results indicate, this dualistic view of nanotechnology as containing both opportunities and risks constitutes a paradigm adopted by only part of the researchers in our sample. By using one paradigm or another, scientists are prepared to observe different realities [START_REF] Kuhn | Scientists and their worldviews[END_REF] where different possibilities of applications are also associated with different concerns (Siegrist et al. 2007). It is therefore possible that our results mirror judgements of risks and benefits made towards different "nanotechnologies".

The group composed of "hard scientists" shares a view of nanotechnology that is mainly built on associated opportunities. These results are in line with previous results about (1) the relative lack of concern of hard science experts with nanotechnology"s possible risks and (2) the concerns of environment and human health experts regarding these new technologies [START_REF] Besley | Expert opinion on nanotechnology: Risks, benefit, and regulation[END_REF][START_REF] Powell | New risk or old risk, high risk or no risk? How scientists" standpoints shape their nanotechnology risk frames[END_REF].

General discussion

Considering that the public is still insufficiently aware of nanotechnologies (Eurobarometer 2010) to have forged by itself a stable or uniform representation of this issue, we propose in this paper a systematic assessment of how nanotechnology experts represent this object. The question here is not to investigate differences between the perceptions by the expert and by the layperson. Rather, it is to explore the way in which experts informally understand nanotechnologies. Future research could investigate if and how these experts" ideas will make their way into the social representations of larger population groups.

In a first study we have shown that nanotechnologies are generally thought of by nanoresearchers in terms of nanoscale (small), enabling new products, which involve some unknown risks. These shared beliefs can be differentiated along two dimensions that distinguish (1) opportunity vs. risk impacts for the environment, health and society associated with this new technology and (2) opportunity vs. risks specifically associated with the characteristics of nanomaterials (i.e. toxicity and increased reactivity). To our knowledge this is the first empirical demonstration, via qualitative analysis, of a polarized representation that up to now researchers have simply assumed to exist.

The polarized representation of nanotechnology as simultaneously both opportunity and risk was then confirmed in a second study with a larger sample of nanotechnology experts. The nanotechnology appraisal replies were factor-analyzed and yielded two main factors: one indicating a representation of nanotechnology as opportunity and another indicating nanotechnology as risk.

Then, these representations were analyzed first according to our participants" roles, and secondly according to their scientific backgrounds. Representations of nanotechnology as risk or opportunity were not different across the professional roles fulfilled by respondents. In contrast, scientific backgrounds do reveal differences in the way experts make sense of these new technologies. 'Upstream', physical or 'hard' scientists tend to represent nanotechnologies in terms of opportunities and not in terms of risks. Environmental, life, and social scientists tend to share a more complex or twofold representation in line with that found in the first study: nanotechnologies represent great opportunities which still are accompanied by unknown risks, described at different scales (material or environmental and societal). These results confirm a similar distinction found elsewhere between 'hard' and 'soft' or life scientists where the latter tend to be much more concerned about nanotechnologies than the former [START_REF] Besley | Expert opinion on nanotechnology: Risks, benefit, and regulation[END_REF][START_REF] Powell | New risk or old risk, high risk or no risk? How scientists" standpoints shape their nanotechnology risk frames[END_REF]. A fruitful direction for further research would be to extend our Study 2 and its nanotechnology appraisal scale to a sample of industrial actors with their various roles and backgrounds.

Our findings indicate that measuring experts" -and later on citizens"perceptions of risks and benefits related with nanotechnologies opens perspectives beyond a 'risk acceptance' paradigm [START_REF] Slovic | Perception of risk[END_REF]. We have demonstrated that the benefits or opportunities provided by nanotechnologies may be broadly acknowledged, but at the same time scientists trained in specific research programs [START_REF] Patterson | Maintaining Research Traditions on Place: Diversity of Thought and Scientific Progress[END_REF], referring to different paradigms [START_REF] Kuhn | Scientists and their worldviews[END_REF] and worldviews [START_REF] Babbage | Philosophical Worldview and Personality Factors in Traditional and Social Scientists: Studying the World in Our Own Image[END_REF], can be more or less equipped to acknowledge the risks associated with this emerging field of technologytheir scale, their impact, and indeed perhaps their significance or meaning for society. In this way, agreement on opportunity or benefit will not be a predictor of acceptance (if indeed acceptance is correlated with perceptions of risk).

Scientific backgrounds constitute the lens through which experts themselves cognitively construct these issues. This twofold perception of nanotechnology as both nanotechnology as potential risk does appear to rely on alerts voiced by scientists [START_REF] Friedman | A longitudinal study of newspaper and wire service coverage of nanotechnology risks[END_REF][START_REF] Pidgeon | Nanotechnology risk perceptions and communication: Emerging technologies, emerging challenges[END_REF]. One hypothesis could be that the media present mostly the uncontroversial view of only part of the nano community, focussed on the consensual view of the opportunities it offersthen providing less space for arguments and reflections from the other scientists who see reasons to be concerned, and who according to our findings distinguish quite finely different scales of risk and impacts. Overall, it is the subtlety of these scientists' thinking which may be artificially reduced by the media to a somewhat one-sided discussion.

Yet, as representations of nanotechnology disseminate in society, good governance will require the capacity to entertain all sides of the question as well as the meanings of eventual trade-offs between opportunity and risk.

  in 2015. The economy of products underpinned by nanotechnology is forecast to grow in Europe from a volume of 200 billion € (258 million $) in 2009 to 2 trillion € (2.58 trillion $) by 2015 2 .

  , which in our case are the different content categories spontaneously associated with nanotechnology. The multiple correspondence analysis was run in IBM SPSS (Statistical Package for Social Sciences) version 19. 5 NanoFATE (2010-2014), large-scale collaborative project n° CP-FP 247739 under EC FP7-NMPENV-2009 (Theme 4), coordinated by C. Svendsen, NERC.

  But these generally shared ideas can be divided into different sub-groups of response, distributed along two main dimensions. If on the one hand the scientists accentuate the possible benefits and opportunities enabled by this new technology, on the other hand they call attention to potential risks for the environment and society as a whole (Dimension 1), because of new or essential properties associated with the nanoscale (Dimension 2). Interestingly, these statistically meaningful dimensions of representation are indeed echoed in the very research objective of NanoFATE, which set out to determine whether the environmental safety or risk of nanomaterials ('risk' end of Dimension 1) can be assessed with classical methods, or whether the intrinsic characteristics of selected nanoparticles and their mechanisms of action on the environment ('risk' end of Dimension 2) differ so much from ionic (non-nano) forms of the same materials that specific methods would be needed (see e.g. NanoFATE 2012).

  However, the two dimensions found in this study might alternatively indicate the existence of two different representations distinguishing subgroups with a common background but different sensibilities, leading them to 'cluster' at either end of the overall risk-opportunity field. This could point to the existence of different perspectives (or anchors) for the representation of nanotechnology as a function of the group of experts[START_REF] Babbage | Philosophical Worldview and Personality Factors in Traditional and Social Scientists: Studying the World in Our Own Image[END_REF][START_REF] Doise | Droits de l'homme et force des idées [Human rights and the power of ideas[END_REF][START_REF] Doise | The quantitative analysis of social representations[END_REF]. Different scientific paradigms possibly co-exist in relation to nanotechnology (e.g.,[START_REF] Kuhn | Scientists and their worldviews[END_REF][START_REF] Patterson | Maintaining Research Traditions on Place: Diversity of Thought and Scientific Progress[END_REF] influencing some to orient their representations towards opportunities, while others might delineate their representations principally according to the risks that may be seen at the material level or broader impact levels. Previous studies have already indicated the existence of differences in the way that experts from different specialities perceive nanotechnology[START_REF] Besley | Expert opinion on nanotechnology: Risks, benefit, and regulation[END_REF][START_REF] Powell | New risk or old risk, high risk or no risk? How scientists" standpoints shape their nanotechnology risk frames[END_REF]. The NanoFATE project, whose members furnished the data of Study 1, was indeed remarkable in that it engaged a very diverse set of scientific backgrounds and skills needed to produce an integrative assessment of environmental fate and risks of engineered nanoparticles(NanoFATE 2010; 2012). However, participants' particular discipline was not surveyed in Study 1. In the next study we propose to explore, through replies from a wider group of nanoscientists, whether the polarized representation of nanotechnology (as opportunity-risk) is shared by all of them, or if one of these poles can be attributed to some groups of experts more than to others.Study 2 -Exploring the opportunity-risk dimension of the nanotechnology representationThe second study had two objectives. The first was to test the polarized risk-opportunity nature of nanotechnology"s social representations, as demonstrated by the first (dominant) dimension of the previous study. Our second objective was to identify whether experts with different backgrouds are more (or less) inclined to represent nanotechnology as risk or as opportunity.These two objectives were addressed by developing a new survey instrument based on the results of the first study, further grounded through a focus group and a review of Internet contents (details in the method section). This nanotechnology appraisal instrument consisted of a list of items reflecting different positions toward nanotechnology, in relation to which participants were requested to express their level of agreement. An enlarged sample of nanotechnology specialists was surveyed.In this part of the paper, we will present an exploratory study of the structure of this instrument. The different perceptions of nanotechnology will then be compared in relation to the different roles and scientific backgrounds of participating nanotechnology experts.MethodParticipantsOur sampling frame was composed by a mailing list of a major European nanotechnology research group, the EU NanoSafety Cluster. The EU NanoSafety Cluster is an initiative that intends to maximize the synergies between the existing European research projects addressing all aspects of nanosafety including toxicology, ecotoxicology, exposure assessment, mechanisms of interaction, risk assessment and standardization (http://www.nanosafetycluster.eu/). The sampling frame also included persons attending a workshop on the EU 2 nd Regulatory Review of Nanomaterials (cf. Schneider 2013). Our initial sample consisted therefore of 771 email addresses of scientists interested in nanotechnology, regulators and administrators. An invitation to participate in a '5-minute survey of societal perceptions of nanotechnology' was sent the total 771 email addresses between December 2012 and February 2013. Thirteen email invitations bounced, leaving us with a sample of 758 persons with professional involvement in nanotechnology who received the email containing a link to the online survey tool. One hundred and sixty-three persons responded to the online questionnaire, corresponding to a response rate of approximately 21%. Considering that we do not have data about characteristics of all participants constituting our sample, we could not control for possible sampling errors or self-selection biases.

(

  F(3,122) = 1.26, p = ns) and as risks (F(3,122) = .95, p = ns). Even if not significantly different, trends of response could however be distinguished (Figure2). Participants occupying administrative positions tend to see more opportunities in nanosciences (M = 4.14), while those in the role of regulators tend to see fewer (M = 3.73). Concerning the perception of risk, policy actors tend to attribute more risk to nanotechnology (M = 3.68), while researchers tend to attribute less (M = 3.4) (Figure2).

Figure 2 .

 2 Figure 2. Means of opportunity and risk attributed to nanotechnology per role.

Figure 3 .

 3 Figure 3. Means of opportunity and risk attributed to nanotechnology per scientific background.

  opportunity and risk may be meaningful also in other other risk fields: people only engage in conversation (which generates social representations) because of the ambivalence that arises from the duality between an issue's positive (good products and medical advancements) and negative (risk) aspects. If only positive or only negative aspects were present, societal debate on a given issue would be far less pronounced in comparison with e.g.what is observed today in relation to the climate change debate, where skepticism has quickly gained momentum over the last years[START_REF] Jaspal | Contesting science by appealing to its norms: Readers discuss climate science in the Daily Mail[END_REF][START_REF] Smith | The rise of global warming skepticism: Exploring affective image associations in the United States over time[END_REF].Our results show finally that a seemingly consensual view by scientists regarding nanotechnology as conveyed by the media[START_REF] Friedman | A longitudinal study of newspaper and wire service coverage of nanotechnology risks[END_REF] and subsequently adopted by the public (Ho, Scheufele, and Corley 2010; Scheufele and Lewenstein 2005)is in fact open to discussion. The restricted media attention to

Table 1 .

 1 Dimensions explaining the response categories of nanotechnologies.

	Dimension	Cronbach's α	Inertia	% of Variance
	1. Benefit-risk	.68	.14	14.1%
	2. Opportunity-	.63	.12	12.5%
	toxicity

Table 2 .

 2 Nanotechnology appraisal items and their loadings on each of the factors.

	Opport.	Risks
	(34.05%)	(15.45%)

H2020-NMP-2014-2015, "H2020 Calls", European Comission, http://ec.europa.eu/research/participants/portal/desktop/en/opportunities/h2020/master_calls.html# h2020-nmp-2014-2015 (accessed May 19,

2014) 2 "Ireland"s Nanotechnology Commercialisation Framework 2010 -2014", Forfás, http://www.forfas.ie/media/forfas310810-nanotech_commercialisation_framework_2010-2014.pdf, cited in European Commission (2012).

Commission Recommandation 2011/696/EU, OJ L 275, 20.10.2011, http://eurlex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2011:275:0038:0040:EN:PDF

4 US Public Law n° 108-153, Section 2 (10), par. D, http://www.gpo.gov/fdsys/pkg/PLAW-108publ153/html/PLAW-108publ153.htm

This analysis took into account only those categories contributing to the dimension more than the dimension"s inertia, as indicated in Table1.

thanks to the participation of scientists from the multidisciplinary EC project NanoFATE (Nanoparticle Fate Assessment and Toxicity in the Environment, www.nanofate.eu) coordinated by C. Svendsen (NERC). Thanks are due as well to members of the project's broader