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


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

0

0,1

0,2

0,3

0,4

0,5

0,6

0,7

0,8

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


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Count rates


→→ 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)


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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


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Fission veto


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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


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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


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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


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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


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Pulse shapre discrimination principle (PSD)

α signal

β signal

Pulse duration particule identification

Response to fission unknown


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First test with 252Cf

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500

1000

1500

2000

2500

3000

Num

ber o

f cou

nts

Channel number

α from 252Cf

β

spontaneousfission

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Bi-dimensional spectrum


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Homemade system

PM : burle 8850

Culture tube


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Optimization of PSD threshold


0 100 200 300 4000

20000

40000

60000

80000

100000

120000

140000

160000

180000

Num

ber o

f cou

nts

Channel number

β

α

spontaneousfission

0 200 400 600 800 1000 12000

500

1000

1500

2000

2500

3000

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


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Light absorptionagainst actinide mass


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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


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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


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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


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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


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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.


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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 …


development of an active scintillating target for fission studies1 development of an active...

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