I NTERDISCIPLINARY RESEARCH

In document RAPPORT D ACTIVITÉ (Page 32-44)

Nuclear waste management

O

ver the past two years, in the framework of the GUINEVERE experiment and FREYA program we have pursued the experiments carried out at the subcritical, lead moderated VENUS-F fast core. Pulsed Neutron Source measurements (PNS) and short continuous beam interruptions were performed and analysed in order to estimate the reactivity of various configurations of the reactor.

The second part of our activities was devoted to the development of an original experimental device in the framework of the FALSTAFF project whose objective is the study of fission using the neutron source facility (NFS) at SPIRAL2.

G. Ban, T. Chevret*, F-R. Lecolley, J-L. Lecouey, G. Lehaut, N. Marie-Nourry

Collaboration : LPSC Grenoble, IPHC Strasbourg, SCK.GEN Mol (Belgique), CEA Cadarache, CEA/IRFU Saclay, GANIL Caen

*PHD student

The GUINEVERE Experiment

Brief description

T

he GUINEVERE (Generator of Uninterrupted Intense NEutrons at the lead Venus REactor) experiment [GUI] is dedicated to feasibility studies for Accelerator Driven Systems (ADS) which are envisaged in partitioning and transmutation strategies. It aims at providing a zero power experimental facility to investigate sub-criticality on-line monitoring procedures and to validate simulation tools. These issues are of major importance in view of the achievement of a future powerful ADS such as the MYRRHA project [MYR]. The GUINEVERE facility is hosted at the SCKCEN site in Mol (Belgium) and consists in the coupling of the fast VENUS-F reactor to a neutron source provided by the GENEPI-3C accelerator.

The fast VENUS-F reactor consists of square fuel assemblies (FA) composed of a 5×5 pattern mixture of fuel and solid lead rodlets, the latter acting as a fast system coolant. Radially and axially the fissile zone is surrounded by lead reflectors. The outer side length of a FA is 80 mm. The fuel is 30%235U enriched metallic uranium provided by CEA. The FA are arranged in a cylindrical geometry (~800 mm in diameter, 600 mm in height). The VENUS-F core is equipped with six safety rods, two control rods (CR) and an absorbent rod (PEAR rod).

The GENEPI-3C accelerator [GUI] provides neutrons via T(d,n)4He fusion reactions. It accelerates deuteron ions up to the energy of 220 keV and guides them onto a tritiated target located at the VENUS-F core centre. This provides a quasi-isotropic field of about 14 MeV neutrons. It can be operated in continuous mode or in pulsed mode with adjustable frequency.

In a first step, a critical configuration called CR0 was loaded and experimentally characterized [CR0]. In a second step, a sub-critical configuration called SC1 (keff~0.96) was obtained by replacing the four central FA by the device devoted to the accelerator pipe hosting.

Estimate of the reactivity of SC1 configuration using the MSM method

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he MSM method has been used to estimate the reactivity of the so-called SC1 configuration of the VENUS-F core for different heights of the two control rods (see table 1). This reference measurement of SC1 subcritical level configurations by MSM method was used to estimate the reliability of the other methods of reactivity determination which could be applied in industrial ADS facilities. These methods (PNS, Source Jerk, Beam Interruption and others) have been investigated in the GENEPI-3C-driven subcritical VENUS-F core in the framework of the FREYA Project [FREYA] during the past two years.

Pulsed Neutron Source measurements – Area method

T

he “current-to-flux” technique was proposed to be combined to absolute reactivity measurements in order to establish a complete on-line reactivity measurement procedure for ADS [MUSE]. The absolute reactivity values are foreseen to be deduced from dynamical measurements requiring source variations. The study of the techniques used to analyse such measurements is one of the purposes of the GUINEVERE program. To evaluate their accuracy, they have to be applied in Pulsed Neutron Source (PNS) conditions for a given reactivity and their results have to be compared to the reference value given by the MSM method.

One of the first methods investigated was the Area method [AREA] also referred as the Sjostrand method. It is based on the analysis of the time dependent response of detectors placed in the reactor to a pulsed neutron excitation and it allows determining in a straightforward way the reactivity of a subcritical nuclear reactor with no input from theoretical calculations as long as the assumptions of the neutron point kinetics holds in the reactor. Indeed within the one-delayed group approximation the equation of the time decrease of the neutron population (Eq. 1) after a pulse exhibits two components: a fast one due to prompt neutrons and a slow one due to delayed neutrons leading by simple integration over time respectively to the prompt surfaceApand the delayed surfaceAd.

Then, the ratio of these two surfaces gives directly the value of the antireactivity in dollars (Eq 1).

(1) Configuration CR height

(mm)

MSM ρ ρρ ρ$

AREA ρ ρρ ρ$

BIM ρ ρρ ρ$

SC1/CR@600 mm 600 -5.08±0.13 -5.09±0.03 -5.06±0.02

SC1 479.3 -5.28±0.13 -5.26±0.03 -5.29±0.02

SC1/CR@200 mm 200 --- -5.90±0.15 -5.89±0.02

SC1/CR@0 mm 0 -6.33±0.13 -6.31±0.05 -6.30±0.03

Table 1: Average reactivity value given by the Area method (AREA) and the Beam Interruption method (BIM) compared with the MSM reference value, for the different reactor configurations.

− ρ

$

= A

p

A

d

= − ρ β

eff

Experimentally, for a set of pulses repeated with a fixed frequency, a single PNS histogram (an example is shown in Fig. 1) is constructed by summing all the detector time responses as a function of the time elapsed after the neutron pulse. After integrating the time spectrum to get the surfaces Apand Ad, the antireactivity can be calculated using Eq. 1.

Fig. 1: Time-dependent PNS histograms obtained with four different fission chambers.

If the dispersion of the reactivity values given by the Area method is due to spatial effects, it should be possible to use Monte Carlo simulations of neutron pulses to correct for these effects since Monte Carlo simulations transport neutrons without approximations. MCNP [MCNP] correction factors were then calculated for each configuration and each detector location with a simplified version of the VENUS-F reactor. Corrected values are symbolized by open squares on Fig. 2. Except for the fission chambers installed in the outer lead reflector, the corrected values are all compatible with the value given by the MSM method.

Finally, discarding the results obtained for the fission chambers located in the outer part of the reflector, the average corrected value of reactivity was calculated for the three configurations studied. To calculate the uncertainty, it was assumed conservatively that the correlations are at maximum between the values given by the detectors. As can be seen in Table 1, the agreement between the MSM reactivity and the Area Method is remarkable.

Continuous Beam measurement - Beam Interruption Method

T

hanks to the presence of an external source in an ADS, one can extract the reactivity of the sub-critical reactor using interruptions of the source in a continuous mode within the neutron point kinetic model (Equation 4).

(2)

With ρ$(t)the reactivity in dollar, n(t) the neutron population, n(t) the constant neutron population level before the beam interruption, Λeff the mean generation time, β eff the effective delayed-neutron fraction, β ieff the effective delayed-neutron fraction of the delayed-neutron groupi, λithe decay constant of the delayed-neutron groupi, andGthe number of delayed-neutron groups.

If one assumes that point kinetic holds in the reactor, all the detector count rates evolve the same way as the neutron population andn(t)can be replaced in Eq. 2 by count rates from any detector and the reactivity is then readily extracted, once the kinetic parameters have been calculated using the deterministic code ERANOS [ERA].

During the experiment, beam interruptions were performed with a period of 25 ms (40 Hz) and the source was switched off for 2 ms. Fission event coming from fission chambers (FCs) were time stamped over a time range including each beam trip plus and minus 300 ms. For each FC, the histogram is obtained by summing all the time responses as a function of the time elapsed after each source jerk. Figure 3 shows histograms normalized to the same maximum for different detector location: in the core (CFUF34), in the inner part of the reflector (RS-10071) and in the outer part of the reflector (RS-10075).

Fig. 2: Uncorrected (solid dots) and corrected (open squares) reactivity values extracted from detector counts for the reactor configuration SC1. The MSM reference value is the dashed line and its uncertainty range is given by the

solid lines.

The area method was applied to reaction rates measured by ten fission chambers during the PNS experiments for the three different subcritical configurations obtained by moving the control rods. The beam frequency was tuned at 220 Hz.

Fig. 2 shows the results for the SC1 configuration. Similar results were obtained for the other configurations derived from SC1. Reactivity values extracted according to Eq. 1 are represented by solid dots. The error bars were calculated by taking into account the statistical as well as the systematic errors. The horizontal dashed line represents the reactivity of the subcritical configuration as measured using the MSM method, while the solid horizontal lines show the uncertainty range on the MSM value.

One notices a dispersion of the results, which seem to depend on the detector location in the reactor. Three groups can be identified. The first one contains only the CFUF34 detector, which is the only one located in the reactor core. It is also the only one from which the reactivity value obtained with the Area method is in very good agreement with that of the MSM method.

The second group gathers six detectors, which are located either at the core-reflector interface or in the corners of the grid, in the inner part of the reflector. The last detectors (RS10075, CFUL653 and CFUL659) form the third group and are located rather far away from the core, in the outer part of the reflector. Clearly the Area Method fails at providing the correct value of the reactivity when the detectors are not in the core. The effect seems to be stronger when the detector is farther from the core.

( ) ( ) ( )

 

 

 ∑

G

= i

t

= t'

λi λi

eff ieff G

= i

λi eff ieff 0

eff eff

$

t' dt'

e t' t n β e

+ β e t β n β dt + dn β Λ t + n

= ρ t

1 0

1

1 1

Fig. 3: MCNP simulations (red with concrete walls, black without) compared to experimental data (blue) for three detectors at three different locations: CFUF34 in the core (left), RS-10071 in the inner reflector (centre) and RS-10075 in

the outer reflector (right).

At first, the neutron population decreases right after the source jerk, which corresponds to the prompt neutron population decrease. Then, more or less rapidly depending on the position of the detector, the neutron population tends to reach its delayed neutron level. As can be observed, the shape of the neutron population histogram over time strongly depends on the position of the detector in the reactor, as in the case of the PNS experiments. The CFUF34 detector seems to be the only one in agreement with Point Kinetics. Moreover, the farther the detector from the centre of the reactor, the more different the experimental shapes are from that predicted by Point Kinetics, and the later the neutron population reaches its delayed neutron level. This clearly indicates the presence of spatial effects that are not considered in Point Kinetics.

In Fig. 4, the reactivity values (denoted “raw reactivity”) given by the analysis of ten time dependent FC count rate histograms using equation 2 and taking into account several corrections (dead time, duty cycle, etc…) are shown as solid black circles and compared to the reference values given by the MSM method.

Fig. 4: Raw reactivity values (solid dots) and corrected reactivity values (open squares) for each detector and for the four configurations studied: SC1/CR@0 mm at the upper left corner of

the figure, SC1/CR@240 mm at the upper right corner, SC1 at the bottom left corner and SC1/CR@600 mm at the bottom right corner. The MSM reference value is symbolized by the

dashed line (red), and the solid lines (red) are its uncertainty range.

As expected, the reactivity extracted depends strongly on the detector position. The CFUF34 detector, which is located inside the core and which exhibits a neutron population shape closer to that given by Point Kinetics, is the only one giving an anti-reactivity in agreement with the MSM reference values. The anti-reactivity values obtained using the six detectors located in the inner reflector are significantly underestimated and gathered around the same value. As for the detectors located in the outer reflector, they give reactivity values even farther off. This is not surprising since they exhibit the time responses which are the least similar to those given by Point Kinetics.

In order to investigate the origin of these strong spatial effects that are not considered in Point Kinetics and lead to such scatter of the results, Monte Carlo simulations were carried out using MCNP and a simplified reactor geometry. At first, simulations were done without the concrete walls surrounding the reactor vessel and fail to reproduce the diversity of the experimental FC time histograms, all the simulated count rate evolution shapes being similar. However, when simulations include the concrete walls around the reactor, experimental shapes are well reproduced (see Fig. 3). Neutrons leaving the reactor can collide with the concrete wall elements, and thus may have their energy greatly reduced by collisions on light elements in the walls. Since the FC deposits are made of235U whose cross-section is the largest for low-energy neutrons, the influence of a small amount of slowed-down neutrons on the detector count rates can become quite significant. It appears that the concrete walls must be considered as a part of the reactor reflector.

The fact that taking into account the concrete walls in the geometry allows reproducing the experimental data with a very good agreement opens up a way to correct the raw reactivity values obtained experimentally. The corrected results are shown as open squares in Fig. 4. An impressive consistency between the MSM reference values and the corrected ones derived from beam interruption analyses is observed. As expected given the comparison between experimental data and Point Kinetics, the reactivity obtained from the CFUF34 detector located in the core is almost left unchanged by the correction. Except for CFUL01-658, we observe that all detectors provide final reactivity values in agreement with the MSM method for all the configurations studied. It is important to note that, in industrial ADS, it might be difficult to install detectors in the reactor core due to the high flux that would prevail in it. Being able to correct the spatial effects that occur in the inner and the outer reflector is therefore an important result.

To conclude with the extraction of the reactivity by studying the evolution of the neutron population during a beam interruption, Table 1 gathers the reactivity value obtained for each configuration by averaging the results from all detectors, and the MSM reference values. The uncertainties were computed assuming maximum correlations between the values given by the detectors. The agreement between the MSM technique and the beam interruption analysis method is very good.

Conclusion

T

aking advantage of the different operating mode of the GENEPI3-C accelerator, two different methods to estimate the reactivity of a sub-critical reactor based on the analysis of the evolution of the neutron population have been tested on data collected at the GUINEVERE facility within the FREYA project: the Area method with a Pulsed Neutron Source and the Beam Interruption method with a Continuous Beam. The data analysis, using point kinetics theory, has been applied to count rates obtained with ten fission chambers located in the VENUS-F reactor. First, various shapes for the time dependent FC count rates were observed depending on the FC position. That indicated the presence of spatial effects, that appear to get stronger as the location of the detector is farther away from the core centre. MCNP simulations have then been used to compute correction factors in order to correct the raw reactivities obtained from the point kinetics analysis.

Finally, corrected reactivity values are compatible with the MSM reference ones.

Brief description of the project

T

he FALSTAFF project [FALS] aims at providing highly constraining data to significantly improve the description of the fission process. More specifically, the goal is to measure the neutron multiplicity as a function of the fragment characteristics (mass, nuclear charge and kinetic energy) in neutron-induced fission of specific actinides in the MeV range.

New developments on microscopic calculations and the future generation of nuclear reactors are two of the main motivations for new experimental programs devoted to the study of fission.

The FALSTAFF Project

Ionization chamber with scintillating gas

I

n order to minimize energy straggling of fission fragments, one possibility is to use ionization chamber (IC) not only to identify and measure the energy of the fission fragments but also to measure their velocity via the well-known time-of-flight technique. However the time response of an IC does not reach the resolutions required for a good determination of the fission fragment velocity. That is the reason why we have developed an IC filled with scintillating gas and coupled to a pair of photomultipliers (PMT) through transparent windows (Fig. 5). The light emitted by the gas provides the stop signal for the time-of-flight measurement.

During the past two years, this scintillating IC has been qualify using several gas (N2, CF4) at different pressure, ranging from atmospheric pressure down to 200 mbar, with alpha particle and fission fragment emitted by a252Cf source.

The energy resolution (table 2) has been determined using a tri-alpha source at atmospheric pressure.

Fig. 5: Sketch of the ionization chamber with scintillating gas

Ealpha(MeV) σσσσ(keV) – N2 σσσσ(keV) – CF4

5.14 143 87

5.44 115 85

5.80 106 80

Table 2: σ(keV) of each alpha peaks for the different gas

Fig. 6: Left: correlation plot of the PMT, right: time distribution of correlated events in both PMT. Top: CF4, bottom: N2.

Fig. 6, left part, shows the correlation distribution between the number of photo-electron detected in each PMT for CF4 and N2 gas respectively, at atmospheric pressure and with an alpha source. The coincidence time resolutions extracted from the gaussian fits (Fig. 6, right part) areσ=0.34 ns in CF4and 1.4 ns in N2. Fig. 7 shows the correlation distribution between the number of photo-electron detected in each PMT for the CF4gas at different pressure and with a californium 252 source. By selecting events upper the red line, we have then measured the coincidence time resolution associated to fission fragment. At the lowest pressure (250 mbar) a coincidence time resolution of σ=210 ps was found, leading to a time resolution ofσ=150 ps for each PMT.

Conclusion

D

espite a good time resolution when using the CF4gas, the performance of our scintillating ionization chamber does not meet the FALSTAFF requirement if one wants to measure fission fragment masses after neutron evaporation with an accuracy of 1 mass unit. However, this kind of detector can be envisaged in other applications, e.g. cross-section measurement of alpha particle production in neutron induced reaction on oxygen below 20 MeV with the use of a gas mixture (CF4+ CO2). This latter reaction is of interest for the community and is one of the request of the High Priority Request List of the NEA/OCDE [HPRL]

References

[AREA] – N.G. Sjostrand, Arkiv för Fysik Band 11 nr 13, 233 (1956) [CR0] – W. Uyttenhoveet al., “Experimental Results from the VENUS-F Critical Reference State for the GUINEVERE Accelerator Driven System Project”, Proceeding of the Int. Conf. on

Advancements in Nuclear Instrumentation, Measurement Methods and their Application, ANIMMA, Ghent, Belgium (June 6-9 2011).

[ERA] – M. Carta, private communication

[FALS] – F.R. Lecolleyet al., AccApp 2013, Bruges (Belgium) [FREYA] – FREYA collaboration, FP7-269665

[GUI] – A. Billebaudet al., “The GUINEVERE Project for Accelerator Driven System Physics”, Proceedings of Global 2009, Paris, France (September 6-11, 2009).

[HPRL] – http://www.oecd-nea.org/dbdata/hprl/

[MCNP] – MCNP - A General Monte Carlo N-Particle Code, Version 5, LA-ORNL, RSICC LA-UR-03-1987, Los Alamos National Laboratory (2003)

[MUSE] – MUSE collaboration, 5th EURATOM FP-Contract#FIKW-CT-2000-00063. Deliverable #8: Final Report (2005)

[MYR] – H.A. Abderrahimet al.,“MYRRHA Technical Description”, Technical Report for the OECD MYRRHA Review Team, SCKCEN, Belgium (2008).

Publication

Experimental Results From the VENUS-F Critical Reference State for the GUINEVERE Accelerator Driven System Project Uyttenhove W., Baeten P., Ban G., Billebaud A., Chabod S. et al.

IEEE Transactions on Nuclear Science 59 (2012) 3194-3200

A. Billebaud, A. Kochetkov, S. Chabod, X. Doligez, G. Lehaut, F.-R. Lecolley, J.-L. Lecouey, N. Marie, F. Mellier, V. Bécares, D. Villamarin, G. Vittiglio, H.-E. Thyébault, W. Uyttenhove, J.Wagemans

FREYA project, 7th EURATOM FP-Contract #269665. Deliverable 1.1: Current subcritical core results, 2013.

S.Di Maria, A. Kochetkov, G.Mila, S.Argiro, M.Carta, F. Gabrielli, G. Vittiglio, S. Chabod, P. Gajda, N. Marie, W. Uyttenhove, G. Lehaut, A. Billebaud, X. Doligez, F.-R. Lecolley, J.-L. Lecouey, V. Bécares, D. Villamarin, Y.Romanets

FREYA project, 7th EURATOM FP-Contract #269665. Deliverable 1.2: Deep subcritical experiments, 2013.

Publication

Experimental Results From the VENUS-F Critical Reference State for the GUINEVERE Accelerator Driven System Project Uyttenhove W., Baeten P., Ban G., Billebaud A., Chabod S. et al.

IEEE Transactions on Nuclear Science 59 (2012) 3194-3200

A. Billebaud, A. Kochetkov, S. Chabod, X. Doligez, G. Lehaut, F.-R. Lecolley, J.-L. Lecouey, N. Marie, F. Mellier, V. Bécares, D. Villamarin, G. Vittiglio, H.-E. Thyébault, W. Uyttenhove, J.Wagemans

FREYA project, 7th EURATOM FP-Contract #269665. Deliverable 1.1: Current subcritical core results, 2013.

S.Di Maria, A. Kochetkov, G.Mila, S.Argiro, M.Carta, F. Gabrielli, G. Vittiglio, S. Chabod, P. Gajda, N. Marie, W. Uyttenhove, G. Lehaut, A. Billebaud, X. Doligez, F.-R. Lecolley, J.-L. Lecouey, V. Bécares, D. Villamarin, Y.Romanets

FREYA project, 7th EURATOM FP-Contract #269665. Deliverable 1.2: Deep subcritical experiments, 2013.

Fig. 7: Correlation plot of the PMT at different pressure in CF4.

Medical and industrial applications

T

he "Medical and Industrial Applications" team is involved in dosimetry measurements for medical and industrial purposes since its creation. For eight years the group is strongly involved into the development of beam monitors and carbon fragmentation studies for hadrontherapy.

Hadrontherapy consists in irradiating cancerous tumours with light nuclei such as proton or carbon ions. Proton therapy is now widely spread worldwide. Carbon therapy is growing in importance. To be as efficient as possible in irradiating the tumour, all physics and biological processes which may occur during the treatments must be kept under control. A specific software, the Treatment Planning System or TPS, is used to define the machine parameters for a given patient, pathology and accelerator. Once these parameters are determined, different set-ups are necessary to control the irradiation process. Nuclear physicists can contribute to hadrontherapy in two ways: by optimizing the dose calculation module of TPS by studying the physical processes involved in the irradiation process ; by designing and building devices which can help to monitor the beam and which may allow controlling the dose deposition in the patient.

The "Medical and Industrial Applications" team is also strongly involved in the ARCHADE project. This centre will be dedicated to the medical, biological and physical research in carbon-therapy and will be located at Caen. The group contributes to FRANCE-HADRON which gathers all the scientific terms in medicine, biology and physics which contribute to the development of hadrontherapy in France.

G. Boissonnat*, J. Colin, D. Cussol, J. Dudouet*, J.M. Fontbonne, M. Labalme, S. Salvador

*PHD students

Beam monitors

T

he "Medical and Industrial Applications" team is developing beam monitors for the radio-biology experiments and for treatment centres.

The use of swept pencil beams is more and more common in proton-therapy. It consists in delivering the dose by scanning the tumour with several beam spots. Each spot corresponds to a given beam location, energy and fluency. The main advantage compared to a passive beam dose delivery which uses beam range shifters and boluses to conform the dose to the tumour geometry is that less matter is set in the beam and hence less secondary particles (mainly neutrons) are produced. The price to pay is that the beam delivery is more complex. The correlations between the beam fluency, its energy and location have to be accurately controlled all along the irradiation. The beam monitor has to be as transparent as possible in order to minimize its disturbance on the beam (angular spreading, intensity attenuation, energy diminution).

In order to minimize the irradiation time during proton-therapy treatments, the trend is to increase proton beam intensities.

The former IC2/3 beam monitor is not well suited anymore. In collaboration with the Ion Beam Applications (IBA) Company, new studies have been initiated to design and build a proton beam monitor for high intensities up to 109ions per second.

This is the subject of the PhD thesis of G. Boissonnat.

A beam monitor for radio-biology experiments at GANIL has also been developed and tested at GANIL in September 2013 in the framework of the FRANCE-HADRON collaboration. This beam monitor called DOSION III is an adaption of the IC2/3 beam monitor for GANIL beams.

T

he "Medical and Industrial Applications" team is also studying the fragmentation processes of carbon ions which contribute to spread the dose deposition beyond the Bragg peak.

Although hadrontherapy has an obvious ballistic advantage compared to conventional radiation therapies, fragmentation processes may reduce this advantage. They occur when a projectile hits a nucleus present in the tissues. Secondary fragments produced by this interaction are much lighter and have a velocity close to the velocity of the projectile. As a result, the secondary particles have a longer range and deposit some dose in and beyond the Bragg peak of the initial projectile.

The effect of the nuclear fragmentation process is twofold. The number of projectiles which do not experience a nucleus-nucleus collision decreases strongly with respect to the penetration depth. Only one half of the initial carbon projectiles at 290 MeV/u reaches the maximum range. As a consequence, the dose deposition at the Bragg peak is strongly influenced by the nuclear reaction cross section. The other effect of the fragmentation process is the appearance of a tail beyond the Bragg peak. This so called "fragmentation tail" is mainly due to protons and alpha particles having a longer range. In addition, the secondary fragments may have different biological effects (cell death, mutation rates and metabolic changes) according to their nature.

In order to compute accurately the dose deposition and the resulting biological effects, it is necessary to have an accurate knowledge of the fragmentation process of the projectile in human tissues. The ideal situation would be to have a valuable model which could predict the production rates of secondary particles and their angular and energy distributions.

Uncertainties on the dose calculations are dominated by the uncertainties on fragmentation cross sections and on nuclear reaction models.

Two experiments have been performed in May 2008 and in May 2011 with the ECLAN reaction chamber at the GANIL G22 beam line. These experiments have been performed in the framework of the GDR MI2B and in collaboration with the IPHC Strasbourg, IPN Lyon and SPhN Saclay. The carbon energy was 95 MeV/u for both experiments. A schematic view of the May 2011 experimental set-up is shown on Fig. 1. It included five three-layer ∆E/∆E/E telescopes for charged particles detection. The telescopes were fixed on rotating stages of the ECLAN chamber. This allowed covering angles ranging from 4°to 70°. For the may 2008 experiment, six PMMA targets (C5H8O2; d=1.19 g/cm3) of different thicknesses: 5, 10, 15, 20, 25 and 40 mm were used.

For the May 2011 experiment, the experimental set-up was very similar and thin C, CH2, Al, Al2O3and Ti target were used.

The nuclear reaction cross sections and the fragments production rates for H, C, O and Ca (close to Ti) nuclei have been extracted from this experiment. These nuclei are the most abundant nuclei in human tissues (more than 90%). This experiment used the FASTER acquisition system. The measurements for a thin PMMA target have also been performed for cross-checking. In September 2013 at GANIL, a complementary experiment has been performed in the framework of the FRANCE-HADRON collaboration to measure the secondary fragments production cross sections at 0°for carbon ions at 95 MeV/u colliding thin C, CH2, Al and Ti targets. The particle identification was done by using the standard ∆E/E technique.

Fragmentation studies

Fig. 1: Schematic view of the experimental set-up of the May 2011 experiment at GANIL.

In document RAPPORT D ACTIVITÉ (Page 32-44)