Development of an active scintillating target for fission studies. J. Aupiais, G. Bélier CEA, DAM, DIF, F Arpajon France

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1 Development of an active scintillating target for fission studies J. Aupiais, G. Bélier CEA, DAM, DIF, F Arpajon France 1

2 Motivations Fast neutron induced reactions are important for future nuclear plant generations, since most of the retained solutions are fast reactors. In this context fast neutron induced fission is of prime importance and one is faced to the lack of data together with incomplete understanding of the process. 2

3 Need for a new (n,2n) reaction on 239 Pu 0,8 0,7 J.fréhaut 1985 J.A.Becker 2002 ENDFBVII.0 Cross section (barns) 0,6 0,5 0,4 0,3 0,2 Passive target Fission to be subtracted High uncertainties Indirect measurement (n, xnγ) with GEANIE/WNR Model dependent 0, Neutron energy (MeV) 3

4 Count rates Need for a very efficient fission veto 4

5 The neutron long counter CARMEN BC521 : Gd loaded (0.5%) scintillator ~1 m 3 Beam Detection efficiency : 85% for 252 Cf SF neutrons target Prompt peak γ,n trigger Capture time (µs) Capture time probability distribution ΣE γ Counting gate 50 µs Stockastic captures P ν Log(E) 5

6 Advantages «Ease» of fabrication. High mass concentrations moderated volumes. Pulse shape discrimination. No specific electronic noise associated with high masses. Good time resolution. 6

7 Fission veto 7

8 α detection efficiency Isotope dissolved in active volume high efficiencies Losses due to wall effects. borosilicate 5 MeV α range ~ 50 µm Scintillator Simulations 0.34 % (energy loss 300 kev) Measurement 0.320±0.058% W.J.Dowell NAS-NS

9 The fission case Two cumulative effects : Shorter ranges 2 Fragments geometric effet Losses estimated to 10-6 Light fragment range ~ 30 µm Heavy fragment range ~ 20 µm 9

10 Principle Photo detector liquid scintillator + actinide Scintillator : Toluene C 7 H mol/l (solvent). Naphthalene C 10 H mol/l. Scintillator PBBO C 25 H 17 NO 10-2 mol/l. Extractant HDEHP C 16 H 35 O 4 P 0.2 mol/l. For physicists : C 0.47 H 0.52 O P N

11 Minimization of quenching Procedure: Solution of An (up to 10 mg) 0.1 M HNO 3 Add hydroxylamine chlorhydrate 10-2 M (for elimination of NO 2 ) Add 1.2 ml Alphaex Shaking 5 min Centrifugation 2000 rpm 5 min Sampling 1 ml Alphaex Counting 11

12 Commercially available : Ordela 8100AB NIM-3w PERALS PhotoElectron-Rejecting Alpha Liquid-Scintillation Pyrex tube 12

13 Pulse shapre discrimination principle (PSD) β signal α signal Pulse duration particule identification Response to fission unknown 13

14 First test with 252 Cf α from 252 Cf Number of counts spontaneous fission β Channel number 14

15 Bi-dimensional spectrum 15

16 Homemade system Culture tube PM : burle

17 Optimization of PSD threshold 3000 α from 252 Cf α Number of counts spontaneous fission β Number of counts β Channel number spontaneous fission Channel number 17

18 Bi-dimensional spectrum 18

19 Energy non linearity α peak 6,118 MeV TKE=188 MeV 78 MeV ~30 MeV expected!!!! β suppressed spectra 19

20 Light absorption against actinide mass 20

21 Natural uranium α spectra with the PERALS system Scintillator volume 1 cm 3 Energy Resolution ~200 kev 238 U 4198 kev 234 U 4774 kev 574 kev 21

22 Tests with natural uranium nat U1 mg/cm 3 nat U 10 mg/cm 3 Natural uranium 10 µg/cm 3 ; 1 mg/cm 3 ; 10 mg/cm Bq de 252 Cf 22

23 Tests with thorium : representative of every actinide 232 Th 10 µg/cm Th 10 mg/cm 3 Natural thorium (&& Pu) 10 µg/cm 3 ; 1 mg/cm 3 ; 10 mg/cm Bq de 252 Cf 23

24 Dedicated cell + avalanche photodiode Avalanche photodiode Scintillator cell Compacity Active target Better energy resolution -A. Reboli & J. Aupiais NIMA550(2005)593 24

25 Open questions on the maximum attainable mass 1. Radiolyse aging for high specific activities isotope dependent 2. Quenching from chemical specific to each isotope 3. Pile-up. 25

26 Perspectives Fission studies : calorimetry, γ spectra, cross sections, P ν 1. Spontaneous fission Bruyères le Châtel 2. Neutron induced fission -- NFS 2012 Ultra-asymmetric fission : cluster disintegration 12 C 34 Si (probability about ) (n,xn) reaction CARMEN -- NFS