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

6

November 24 2008

LANSCE WNR

WNR facilityUnmoderated spallation neutrons source

800 MeV protons

Figaro

7

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)

10

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

20

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

22

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

23

November 24 2008

Normalizing microscopic results

With adjustement

Microscpic barriers In TALYS

Example : cross sections