rendements de fission
DESCRIPTION
Rendements de fission. Experimental program on PFNS measurements at the CEA in Bruyères le Ch â tel. T. Granier, B. Laurent, A. Chatillon. Historical. Bertin et al. Historical measurements PFNS measurements for fission of 238 U and 235 U induced by fast neutrons 0.6 MeV and 7 MeV - PowerPoint PPT PresentationTRANSCRIPT
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Rendements de fissionExperimental program
on PFNS measurements
at the CEA in Bruyères le Châtel
T. Granier, B. Laurent, A. Chatillon
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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
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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>
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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
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5PFNS measurements at Figaro239Pu(n,f) PFNS Preliminary(analysis by A. Chatillon)
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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
)
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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
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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
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9PFNS measurement test in Bruyères
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10PFNS measurement test in Bruyères
TDC channel
Num
ber
of c
ount
s
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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
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12
Additional material
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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
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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)
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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)
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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