1

Rendements de fissionExperimental program

on PFNS measurements

at the CEA in Bruyères le Châtel

T. Granier, B. Laurent, A. Chatillon

2Historical

Bertin et al. Historical measurements

PFNS measurements for fission of 238U and 235U induced by fast neutrons 0.6 MeV and 7 MeV

Fission chamber method

3Recent history and present

• Experiments at Los Alamos with FIGARO (CEA-NNSA collaboration)

– Comprehensive measurements in the 1-200 MeV region (white neutron source)– First experimental evidence of the dip in <E> at opening of 2nd chance– Results on <E> and nu bar vs En in 1-200 MeV published for 238, 235,

presented to conf for 237Np– Preliminary results for 239Pu: spectra and <E>

4The FIGARO instrument in the fission configuration

Collimated Neutron beam

45°

135°

20 neutron detectors

CEA multifoilFission ChamberUp to 180 deposits,~400 mg of actinide

5PFNS measurements at Figaro239Pu(n,f) PFNS Preliminary(analysis by A. Chatillon)

6PFNS measurements at Figaro

239Pu(n,f) <E> for E in 0.6-7 MeV - Preliminary(analysis by A. Chatillon)Model: BRC09 B. Morillon

Neutron Energy (MeV)

<E

> (

MeV

)

7New measurement program at Bruyères• PFNS ~0.2 – 6 MeV using fission chambers

– 4 MV Van de Graaff in Bruyères le Chatel• (quasi) Mono energetic neutrons (p+Li, p+T, d+D, d+T) 0.5, 2.5, 4, 6, 14 MeV

– Fission chambers containing from 100 to 4000 mg of actinides– Neutron detectors: Paraterphenyl, NE213– Neutron time of flight measurement, flight path ~50 cm– Detection efficiency: 252Cf measurements, simulations

Paraterphenyldetector

n shielding(Li paraffin)

Fission chamberTiT or TiD target

~0.5 m flight path

N-γ shadow bar

p or d beam

Lead shielding

8New measurement program at Bruyères

NE213detector

n shielding(Li paraffin)

Actinide sampleLi target

~2 m flight path

N-γ shadow bar

p beam

Lead shielding

• PFNS 0.5 – 10 MeV using passive targets– 4 MV Van de Graaff in Bruyères le Châtel

• Mono energetic 500 keV neutrons from p+Li reaction

– Passive sample – Neutron detector: NE213 calibrated at PTB– Neutron time of flight measurement, flight path ~200 cm– Detection efficiency: 252Cf measurements, simulations

9PFNS measurement test in Bruyères

10PFNS measurement test in Bruyères

TDC channel

Num

ber

of c

ount

s

11PFNS measurements

• Actinides for which we have fission chambers– 238U, 235U, 237Np, 239Pu, 232Th

• Statistics expected below 800 keV: 1000 fission neutrons (1 week)

• Measurement plan- Year 1

Start with non fissile actinides: 238U or 237Np- Year 2

Measurements on 235U and 239Pu- Year 3

Measurements on 235U and 239Pu

12

Additional material

13Experiment Principle

TOF 2 / ~1 m

Neutron detectors

FissionChamber

TOF 1 / ~22 m

Pulsed neutronBeam(1-~200 MeV)

• Double time of flight– Incident n energy (22 m)– Fission n energy (~1 m)

• Typical resolution:– Incident: 1% at 2 MeV

15% at 200 MeV

– Fission: 15% at 800 keV

50% at 8 MeV

• Detection efficiency obtained by measuring known PFNS (252Cf spont. Fiss.)

• Total efficiency ~ 1 %

• Neutron/gamma discrimination on pulse shape

14

Neutron energy (MeV)

Neu

tron

yie

ld p

er M

eV

BRIC calculation (H. Duarte, BIII)239Pu(n,F), En=50 MeV

Pre-equilibrium

Fragment evap.

Prefission evap.

Normalized Total Neutron spectrum

PFNS measurements at Figaro

Region of investigation(Watt domain)

15Published results on <E> for 238U & 235U

• BRIC (BRIEF): MC Intra-Nuc. Cascade code (H. Duarte, PRC 75, 024611), includes evaporation and fission models

• Red curve: experimental angular cuts + Watt fit over 0.7-7 MeV (same as experimental analysis)

16Results on 237Np

• Data analysis: J. Taieb• Presented by J. Taieb at ND-2007, Nice• Results to be published

237Np(n,f)

1,7

1,8

1,9

2

2,1

2,2

2,3

0 5 10 15 20

Incident neutron energy (MeV)

Lovchikova et al, (1996)Boykov et al, (1993)MaslovThis work

<E

> (

MeV

)

• <E> obtained from fits of Watt parameters• Red curve: eval. by V. Maslov