Development of an active scintillating target for fission studies J. Aupiais, G. Bélier CEA, DAM, DIF, F-91297 Arpajon France 1
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
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 0,1 0 5 7 9 11 13 15 17 19 Neutron energy (MeV) 3
Count rates Need for a very efficient fission veto 4
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
Advantages «Ease» of fabrication. High mass concentrations moderated volumes. Pulse shape discrimination. No specific electronic noise associated with high masses. Good time resolution. 6
Fission veto 7
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-3116 8
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
Principle Photo detector liquid scintillator + actinide Scintillator : Toluene C 7 H 8 7.5 mol/l (solvent). Naphthalene C 10 H 8 1.5 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 0.0054 P 0.0013 N 0.00007 10
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
Commercially available : Ordela 8100AB NIM-3w PERALS PhotoElectron-Rejecting Alpha Liquid-Scintillation Pyrex tube 12
Pulse shapre discrimination principle (PSD) β signal α signal Pulse duration particule identification Response to fission unknown 13
First test with 252 Cf 3000 2500 α from 252 Cf Number of counts 2000 1500 1000 500 spontaneous fission β 0 0 200 400 600 800 1000 1200 Channel number 14
Bi-dimensional spectrum 15
Homemade system Culture tube PM : burle 8850 16
Optimization of PSD threshold 3000 α from 252 Cf 2500 180000 160000 140000 α Number of counts 2000 1500 1000 500 spontaneous fission β Number of counts 120000 100000 80000 60000 β 0 0 200 400 600 800 1000 1200 Channel number 40000 20000 spontaneous fission 0 0 100 200 300 400 Channel number 17
Bi-dimensional spectrum 18
Energy non linearity α peak 6,118 MeV TKE=188 MeV 78 MeV ~30 MeV expected!!!! β suppressed spectra 19
Light absorption against actinide mass 20
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
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 3 + 7 Bq de 252 Cf 22
Tests with thorium : representative of every actinide 232 Th 10 µg/cm 3 232 Th 10 mg/cm 3 Natural thorium (&& Pu) 10 µg/cm 3 ; 1 mg/cm 3 ; 10 mg/cm 3 + 7 Bq de 252 Cf 23
Dedicated cell + avalanche photodiode Avalanche photodiode Scintillator cell Compacity Active target Better energy resolution -A. Reboli & J. Aupiais NIMA550(2005)593 24
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
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 10-11 ) (n,xn) reaction CARMEN -- NFS 2012 26