development of an active scintillating target for fission studies1 development of an active...
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Development of an Development of an active scintillating active scintillating target for fission target for fission
studiesstudiesJ. Aupiais, G. Bélier
CEA, DAM, DIF, F-91297 Arpajon France
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Motivations
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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.
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Need for a new (n,2n) reaction on 239Pu
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5 7 9 11 13 15 17 19
Neutron energy (MeV)
Cro
ss s
ectio
n (b
arns
)
J.fréhaut 1985 ENDFBVII.0
J.A.Becker 2002
Passive targetFission to be subtractedHigh uncertainties
Indirect measurement (n , xnγ)with GEANIE/WNR
Model dependent
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Count rates
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
→→ NeedNeed for a for a veryvery efficient fission vetoefficient fission veto
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target
Beam
Capture time probabilitydistribution
Counting gate50 µs
Prompt peak γ,n trigger
ΣEγ
Stockastic captures Pν
The neutron long counter CARMEN
BC521 : Gd loaded (0.5%) scintillator ~1 m3
Detection efficiency : 85% for 252Cf SF neutrons
Cap
ture
tim
e (µ
s)
Log(E)
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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• « Ease » of fabrication.
• High mass concentrations moderated volumes.
• Pulse shape discrimination.
• No specific electronic noise associated with high
masses.
• Good time resolution.
Advantages
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Fission veto
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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α detection efficiency
• Isotope dissolved in active volume high efficiencies
• Losses due to wall effects.
5 MeV α range ~ 50 µm
Simulations 0.34 %(energy loss 300 keV)
Measurement 0.320±0.058%W.J.Dowell NAS-NS-3116
Scintillator
borosilicate
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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The fission case
Two cumulative effects :• Shorter ranges• 2 Fragments geometric effet
Losses estimated to 10-6
Light fragment range ~ 30 µmHeavy fragment range ~ 20 µm
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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liquid scintillator + actinidePhoto detector
Principle
Scintillator :Toluene C7H8 7.5 mol/L (solvent).Naphthalene C10H8 1.5 mol/L.Scintillator PBBO C25H17NO 10-2 mol/L.Extractant HDEHP C16H35O4P 0.2 mol/L.
For physicists : C0.47H0.52O0.0054P0.0013N0.00007
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Minimization of quenching
Procedure:•Solution of An (up to 10 mg)0.1 M HNO3•Add hydroxylamine chlorhydrate10-2 M (for elimination of NO2)•Add 1.2 mL Alphaex™•Shaking 5 min•Centrifugation 2000 rpm 5 min•Sampling 1 mL Alphaex ™•Counting
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Commercially available : Ordela 8100AB NIM-3w
Pyrex tube
PERALS PhotoElectron-Rejecting Alpha Liquid-Scintillation
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Pulse shapre discrimination principle (PSD)
α signal
β signal
Pulse duration particule identification
Response to fission unknown
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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First test with 252Cf
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1000
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Num
ber o
f cou
nts
Channel number
α from 252Cf
β
spontaneousfission
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Bi-dimensional spectrum
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Homemade system
PM : burle 8850
Culture tube
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Optimization of PSD threshold
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
0 100 200 300 4000
20000
40000
60000
80000
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120000
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Num
ber o
f cou
nts
Channel number
β
α
spontaneousfission
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1000
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Num
ber o
f cou
nts
Channel number
α from 252Cf
β
spontaneousfission
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Bi-dimensional spectrum
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Energy non linearity
αpe
ak6,
118
MeV
TK
E=1
88 M
eV
78 MeV ~30 MeV expected !!!!
β suppressed spectra
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Light absorptionagainst actinide mass
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Natural uranium α spectra with the PERALS system
238 U
419
8 ke
v
234 U
477
4 ke
v
574 keV
Energy Resolution ~200 keV
Scintillator volume 1 cm3
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Natural uranium10 µg/cm3; 1 mg/cm3 ; 10 mg/cm3
+ 7 Bq de 252Cf
natU 10 mg/cm3
natU 1 mg/cm3
Tests with natural uranium
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Tests with thorium : representative of every actinide
232Th 10 mg/cm3
232Th 10 µg/cm3
Natural thorium (& Pu& Pu)10 µg/cm3; 1 mg/cm3 ; 10 mg/cm3
+ 7 Bq de 252Cf
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Dedicated cell + avalanche photodiode
Active target
Avalanche photodiode
Scintillator cell
Compacity
Better energy resolution -A. Reboli & J. Aupiais NIMA550(2005)593
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Open questions on the maximum attainable mass
1. Radiolyse aging for high specificactivities isotope dependent
2. Quenching from chemical specific to each isotope
3. Pile-up.
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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Perspectives
Fission studies : calorimetry, γ spectra, cross sections,
Pν1. Spontaneous fission – Bruyères le Châtel
2. Neutron induced fission -- NFS 2012…
Ultra-asymmetric fission : cluster disintegration 12C 34Si (probability about 10-11)
(n,xn) reaction CARMEN -- NFS 2012 …
CEA DAM DIF LSC 2010 Paris 06-10 Sept. 2010
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