Post on 03-Jan-2016
1
November 24 2008
Fission works in CEA DAM DIF,
E.Bauge,
Service de Physique Nucléaire
CEA DAM DIF
2
November 24 2008
capture
(Elastic), inelastic, (n,2n)
Pas fission !
neutron :0<E<10 MeV
actinide : Ex: 235U
actinide : 236U
E*=6.5MeV+En
FF1 :Z1, A1
FF2 :Z2, A2
neutrons
The fission phenomenon
3
November 24 2008
Contradictory integral and differential trends
Capture 238U Fission 238UIntegral tests
4
November 24 2008
Diagnostic : Error compensation
∑∑≠
→+ ΣΦ+ΣΦ−ΣΦ−ΣΦ=Φij
iineljj
inelii
cii
j
fjjji
ti K ν1
PNFS & Capture Inélastics
238U235U (& 238U) 235U & 238U
f 235U : very well known
0D neutronics
5
November 24 2008
PNFS measurements at WNR with FIGARO
Fission Neutron Spectrainduced by 4 - 5 MeV neutrons
1.E-02
1.E-01
1.E+00
1.E+01
1.E+02
1.E+03
1.E+04
1.E+05
0 2 4 6 8 10 12
E-fission neutron (MeV)
Yield / MeV (arb. norm)
239Pu 4-5 MeV235U 4-5 MeV
Ratio Pu/UENDF - 239Pu
ENDF - 235UENDF Ratio 239Pu/235U
235U, 238U, 239Pu, 237Np
Fission chamber
Today
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November 24 2008
LANSCE WNR
WNR facilityUnmoderated spallation neutrons source
800 MeV protons
Figaro
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November 24 2008
Experiment 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 pulse shape
discrimination
Fission neutrons measured between ~800 kev and ~ 8 MeV for bins of incident neutron energy in 1 – 200 MeV
Measurements at side angles: not sensitive to preequilibrium PFNS compatible with Watt spectra within stat.
<E> either obtained directly in the region measured or by Watt or Maxwellian fits Mean multiplicity : relative measurements, normalized to references at low energy
8
November 24 2008
Fission neutron energy spectrum
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
Region of investigation(Watt domain)
9
November 24 2008
Published results on <E> for 238U & 235U
BRC eval. are obtained independently BRC eval: ‘à la Los Alamos’ with Tudora-
Vladuca prescription and BRC partial cross sections
<E> obtained from fits of Watt parameters 1st unambiguous observation of dips at the
opening of fission chances
Phys. Lett. B 575, 221 (2003),
PRL 94, 052701 (2005)
PRL 101, 039202 (2008)
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November 24 2008
Published 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)
11
November 24 2008
237Np results
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
12
November 24 2008
Current investigation 239Pu
Data recorded in 2007 and 2008 2007:
Technical problems: signal to noise ratio degraded due to neutron scattering off fission chamber structure materials
Background noise monitored on-line 2008:
Other fission chamber with less structure materials New neutron detectors provided by CEA-BIII:
Stilbene and para-ter-phenyl crystals to lower fission neutron energy threshold
13
November 24 2008
239Pu preliminary results
2007 data (analysis by A. Chatillon at BIII) Much better data in 2008 (stat. and syst.), analysis
ongoing (AC)
Green curve: BRC 2008 eval (1-7 MeV), obtained independently
14
November 24 2008
3He counter at WNR
Grande efficacité: ≈ 30%
Goal : et P() measurements
1st measuremnt : 239Pu this fall
238U(n,f)
235U(n,f)
Very high efficiency (few corrections)
FIGARO meas.
Tomorrow morning
15
November 24 2008
PNFS measurements (n,xnf) at Geel (?) with CARMEN
+ energy and mass ratio of FF in coinc
FF1
m1 v1
FF2
m2 v2
Dét1 Dét2
Cible très mince max 100 g/cm2
Tomorrow PNFS as a function of x
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November 24 2008
NFS (neutrons for science) neutron source
40 MeV deuteron beam on C (or W) converter20 m TOF low noise room Collimated neutron beamFirst beam 2012 in GANILFuture home of the CARMEN detector for PNFS studies
Tomorrow
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November 24 2008
Fission@ELISe
Ion-electron collider at GSI-FAIR « Perfect » FF detection (A,Z) (no threshold), in coinc with neutrons
1er beam: 2015 ?
Tomorrow
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November 24 2008
Microscopic fission models
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November 24 2008
Fission microscopique
Deformation Q20 Deformation Q30
Deformation energy Neutron multiplicity (simplistic)
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November 24 2008
Microscopic fission yields : collective dyamics
0 dt(t)t
i -H(t) )t,q(*f
2
1
t
ti
=ψ∂∂ψ
∂∂
∫ h
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November 24 2008
Detailed FF decay
In TALYS code (statistical decay)Phase I : simplistic inital conditions (Done !)
Phase II : combined with inital conditionsderived from microscopic calculations
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November 24 2008
Normalizing microscopic results
With adjustement
Microscpic barriers In TALYS
Example : cross sections