Measurement of (n, xn γ) reaction cross sections in W ...186W (28.4 %) Greg Henning (IPHC) – June...

1Greg Henning (IPHC) – June 19th, 2015 @ VARENNA 2015

Measurement of (n, xn γ) reaction cross sections in W isotopes

Greg HenningIPHC/CNRS

▼▼

◄

2

Context: Nuclear data evaluations for applications

▼

▲4th generation nuclear reactors and new fuel cycles, currently understudy, will met safety, sustainability, environment and economic challenges.

Development and risk analysis are done with numerical simulations that use evaluated nuclear data bases.

Generation IV International Forum, www.gen-4.org

Greg Henning (IPHC) – June 19th, 2015 @ VARENNA 2015

Evaluations are built from experimental data and theoretical predictions. These databases still present large uncertainties, because of a lack of data and limits of models.

This leads to uncertainty on calculations of control parameters in nuclear applications( k

eff, power, ...)

Uncertainty on keff

in GFR σ

keff = 1.88 % (NEA/WPEC-26)

% of total

50

20

60

40

30

10

0

238 U239 Pu239 Pu

238U(n,n')

Fundamental interest:

The mechanism probes different reaction regimes● Direct nucleon-nucleon interaction,● Compound nucleus,● Pre-equilibrium.

3

(n, xn) : reactions of interest for evaluations

▼

▲

Experimental study:

● Detection of scattered neutrons,● Activation, ● (n, xn γ) reactions ► strong constrains on models

Impact on reactors:

Change the number and energy of neutrons, create new isotopes.

Reaction time

Eout

σ

Compound nucleus Pre-equilibrium Direct

Nucleus

Neutron

Residu

Emitted neutrons


Reaction mechanism, Nuclear de-excitation, Nucleus level structure.

4

Why study Tungsten ?

▼

▲Practical interests:● Present in many alloys in reactors (fission and fusion).● High melting point, strong mechanical resistance, low thermal expansion, resist to oxidation, acids, alkalines.

Easier experiment to setup (compared to actinides):● No radioactivity, chemical toxicity,● 3 times less expensive than natU (raw material price).

Theoretical interests:● Deformation similar to uraniums.● No fission channel (B

fLD ~ 20 MeV) → simpler description by models.

0,2

0,22

0,24

0,26

Def

omat

ion

(bet

a_2)

● Applications use natural tungsten.● Need to study

● 182W (26.5 %),● 183W (14.3 %),● 184W (30.6 %),● 186W (28.4 %)


5

Why study Tungsten ?

▼

▲● Only a few measurements available today, the majority of points comes from one experiment only.● Most on (n,2n), some (n,3n)

– ENDF/B-VII.1– JEFF-3.2– JENDL-4.0– FENDL/E-2.1■ Available data(J. Frehaut et al., 1980)

(n,n') (n,2n) (n,3n)

182W

184W

186W

● Level production cross sections exist for (n,n')


6

Experimental study of (n, xn γ) reactions

▼

▲

GELINA

Neutron beam at GELINA (IRMM, Geel, BE):● Electrons accelerated on Uranium target,● Neutron production by fission,● Pulsed beam (800 Hz),● E

n between keV and 20 MeV,

● Our experiment set up at 30 m.

γ

γ

γ

fission chamber

pulsed neutron beam

HPGe detectors

sample110°

110°149°

149°

Neu

tron

bea

m

● Fission chamber to measure neutron flux,● Large sample (diameter > 55 mm),● Detection of γ rays emitted in (n, xn) reactions

using 4 planar Ge detectors,● Connected to a digital acquisition recording

time and energy in list mode.


7

Analysis principle: Eγ vs. ToF

▼

▲

232Th(n,n’ )232Th

232Th(n,2n )231Th

Radioactivity

Temps de vol [arb.un.]

Eγ

[arb

.un .

]

Time of Flight [arb.un.]

232Th(n,3n )230Th

Target : 232Th

FlashGreg Henning (IPHC) – June 19th, 2015 @ VARENNA 2015

En (ToF )=[√1

1−( DoF /ToFc )

2−1]mnc

2

8

Analysis principle: (n, xnγ) cross section extraction

▼

▲

0+

2+

4+

122 keV

186W

395 keV

d σdΩ

(En ,γ ;θ)=N γ(En , γ ;θ)

ε(Eγ)

1N target

σ 235U (n , f )(En)εCF

N CF(En)

● The intensity of the gamma line is determined for different time intervals.

● No correction for electronic conversion « true (n, xn γ) »,

● The ratio to the flux gives the production cross section.

2 1518 Neutron energy [MeV]

500 1000500 1500500 2000 25002000 3000

Num

ber

of h

it s

Nγ @ 110 deg


Time Of Flight [ns]

9

Structure of Tungsten

▼

▲● Focus on even-even isotopes: 182, 184, 186● Studied at the same time in natW sample● Rotational band ● 2+ (γ), 0+ (β) bands

182W 184W 186W


10

Ground state rotational band

▼

▲184W 186W

Cro

ss s

ect

ion

[ba

rn]

Incident neutron energy [keV]

2+→g.s.

4+→2+

Eγ=111 keV E

γ=122 keV

Eγ=273 keVE

γ=253 keV

PRELIMINARYPRELIMINARY

– Experiment– TALYS-1.2 (P. Romain, 2011)


Correction for 183W(n,2n)

182W

Eγ=100 keV

Eγ=229 keV

TALYS over estimates gsb contribution at high En

11

Interband transitions

▼

▲

Cro

ss s

ectio

n [b

arn

]

182W

2+2→2+

2+2→g.s.


PRELIMINARY

PRELIMINARY

Mixedmultipolarity

M1+E2

Incident neutron energy [keV]

184W 186WE

γ=615 keVE

γ=792 keV

Eγ=903 keV E

γ=738 keV

TALYS under estimates inter band transitions


– Experiment– TALYS-1.2 (P. Romain, 2011) E

γ=1121 keV

Eγ=1221 keV

12

Effect of reaction mechanism ?

▼

▲Decomposition of 186W(n,n') cross section into contribution of individual levels reproduces well (2011) experimental values (w/ +15 % scaling) up to ~ 4 MeV.

Contribution of scattering off individual states

Contribution of scattering off continuum

Experimental 2+ cross section

Incident neutron energy [MeV]

Cro

ss s

ecti

o n [

mba

rn]

P. Romain (CEA Bruyères-le-châtel)

TALYS 2+ level cross section2+ level, CN inelastic

2+ level, direct inelastic



186W

D.Lister et al., 1967P.T.Guenther et al., 1977

13

Effect of reaction mechanism ?

▼

▲PRELIMINARYPRELIMINARY

● Bad reproduction above ~5 MeV.? Decay channels competition,? Effect of spin distribution in pre-equilibrium,? Separation and coupling between continuum and discrete level scheme.


Cro

ss s

ecti

o n [

mba

rn]


Cro

ss s

ecti

o n [

mba

rn]


P. R

omai

n ( C

EA

Bru

yère

s-le

-châ

tel)

186W 186W

14

Conclusion and perspectives

▼

▲First results from preliminary analysis on 182,184,186W in natW:● TALYS over estimates population of high spin states in the gsb and under estimates

inter‑band transitions.

● Also, bad reproduction of cross section shape in 2+→g.s. at high En.

● Possible effects of structure and/or pre-equilibrium model.● Extraction of level cross section would help to distinguish BR effect (and comparison with

existing data), but only an upper limit is possible.

Perspectives:● 5 consistent data sets (nat,182,183,184,186W) to analyze → cross check and normalization,● 10-15 transitions to study per isotope,● Covariant analysis to reflect correlations between the measurements,● … will produce a very rich and constraining set of experimental values to compare with the

models.

Part of larger (n, xn γ) study program on isotopes from 7Li to 238U in collaboration with IRMM, IFIN‑HH, CEA/DAM, CEA/DEN.


15

Collaborators

▼

▲Greg Henning, A. Bacquias, Ph. Dessagne, M. Kerveno, G. Rudolf, P. Scholtes,

IPHC/CNRS & Université de Strasbourg, France

A.J.M. Plompen, F. Belloni, M. Nyman, E. Pirovano,J.C. Drohé, R. Wynants, W. Motta,

G. Sibbens, A. Moens, S. Melis, EC/ JRC-IRMM, Geel, Belgique

C. Borcea, A. Negret, A. Olacel G. SulimanNat. Inst. Of Phys. And Nucl. Eng., Bucharest, Roumanie

P. Romain, M. Dupuis, S. Hilaire, B. MorillonCEA Bruyères-le-châtel

D. Bernard, P. Lecomte, C. de Saint JeanCEA Cadarache

NUDATRAEUFRATNUDAME

ERINDAANDESCHANDA

GEDEPEONNEEDS


Measurement of (n, xn γ) reaction cross sections in W ...186W (28.4 %) Greg Henning (IPHC) – June...

Documents

Transcript of Measurement of (n, xn γ) reaction cross sections in W ...186W (28.4 %) Greg Henning (IPHC) – June...