Post on 20-Jan-2021
Study of the (n,γf) process on 239Pu
Esther LEAL CIDONCHA, Gilles NOGUERE, Olivier BOULAND and Olivier SEROTCEA/DEN/CAD/DER/SPRC/LEPh
WONDER-2018 8-12 October 2018
CEA/Cadarache (France)
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
INTRODUCTION: REACTION CHANNELS
1/16
• The compound nucleus may decay by:
• Neutron emission (n,nʼ)
• γ-ray emission (n,γ)
• Fission (n,f)
ChannelReaction
Slow neutron-induced reactions
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
INTRODUCTION: REACTION CHANNELS
1/16
Slow neutron-induced reactions• The compound nucleus may decay by:
• Neutron emission (n,nʼ)
• γ-ray emission (n,γ)
• Fission (n,f)
• γ-ray emission + Fission (n,γf)
σn
σf
σγ
ChannelReaction
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
INTRODUCTION: FISSION CHANNELS
2/16
Slow neutron-induced reactions
J.E. Lynn, P. Talou and O. Bouland, PRC 97, 064601 (2018)
• If a γ is emitted before fission then the available excitation energy to the FF is lower and less prompt neutrons are emitted => anticorrelation between prompt neutron emission and γ multiplicities.
• Double-humped fission barrier:
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
INTRODUCTION: FISSION CHANNELS
3/16
Slow neutron-induced reactions• Double-humped fission barrier: • If a γ is emitted before fission
then the available excitation energy to the FF is lower and less prompt neutrons are emitted => anticorrelation between prompt neutron emission and γ multiplicities.
10 20 30 40 50E (eV)
0,68
0,7
0,72
0,74
0,76
0,78
! p
Gwin v1 (1984)Gwin v2 (1984)Frehaut (1973)
0,01 0,1 1 100,75
0,76
0,77
J.E. Lynn, P. Talou and O. Bouland, PRC 97, 064601 (2018)
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
NEUTRON-INDUCED FISSION IN 239PU
4/16
• The 239Pu(n,f) cross section can be described by:
σf(En) = σ(En)(n,f) + σ(En)(n,γf)
• Partial fission width:
σ γ(En) ·Γγf
Γγ
?
Γγ f (E*, J π ) = dεγ ρ(E
* − εγ , J fπ (− )Xl ) × Γγ Xl (εγ )Pf (E
* − εγ , J fπ (− )Xl )
0
E*
∫J f = J − l
J + l
∑Xl∑
multipolarity(E1,M1)
fissionprobability
nuclearlevel
density
E* = Einc + Bn π (M1)-π (E1)
Residual excitation energy
J.E. Lynn, P. Talou and O. Bouland, PRC 97, 064601 (2018)
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
NEUTRON-INDUCED FISSION IN 239PU
5/16
• Direct fission channels
• Two-step fission channels
Jπ = 0+
Jπ = 1+
Γ 1f (0+)
Γ 2f (0+)
Γ f (1+)
Jπ = 0+
Jπ = 1+
Γ γf (0+)
Γ γf (1+)
Resonances 0+
Dominate:
Resonances 1+
• The 239Pu(n,f) cross section can be described by:
σf(En) = σ(En)(n,f) + σ(En)(n,γf)
σ γ(En) ·Γγf
Γγ
?
• Partial fission widths in the R-Matrix Theory:
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
CONRAD RESONANCE ANALYSIS OF 239PU DATA
6/16
[2] J.E. Lynn, P. Talou and O. Bouland, PRC 97, 064601 (2018)
• New resonance analysis with the CONRAD* (COde for Nuclear Reaction Analysis and Dated Assimilation) R-Matrix code including:
• Two-step fission contribution from Trochon [1] vs. Bouland [2] => Γ γf
• The evaluated file of the fission cross section considers the Jπ=1+ resonances as being produced only through direct fission reactions.
• Direct reactions contribution from the evaluations => Γ γ , Γ f and Γ n
• Prompt neutron multiplicity (νp) reproduced including the two-step fission process.
[1] Trochon, Proc. 3rd Symp. Physics and Chemistry of Fission, Rochester, New York, Aug. 13-17 (1973)* Developed at CEA/Cadarache
• Multiple analysis:• Total cross section • Capture cross section • Fission cross section • Total neutron multiplicity• Prompt neutron multiplicity (Frehaut and Gwin experimental data)
• Resonance parameters:
• Free parameters:• ν nγf
• ν0 and ν1
• Normalization of experimental data
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
TWO-STEP FISSION CONTRIBUTION (Γ γf)
7/16
• Calculation of Γ γf from Trochon [1]:
• Calculation of Γ γf from Bouland [2]:
• Double-humped fission barrier.
• A low-lying M1 resonance known as the scissors mode has been also taken into account.
[2] J.E. Lynn, P. Talou and O. Bouland, PRC 97, 064601 (2018)[1] Trochon, Proc. 3rd Symp. Physics and Chemistry of Fission, Rochester, New York, Aug. 13-17 (1973)
• Single-humped fission barrier.
• Only E1 transitions are considered.
• E1 transitions are considered.
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
EXPERIMENTAL DATA (νp)
8/16
• Frehaut and Gwin experimental data:
10 20 30 40 50E (eV)
0,68
0,7
0,72
0,74
0,76
0,78
! p
Gwin v1 (1984)Gwin v2 (1984)Frehaut (1973)
0,01 0,1 1 100,75
0,76
0,77
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
EXPERIMENTAL DATA (νp)
9/16
• Problem: how to threat Frehaut data (histogram/pointwise) better description with pointwise.
0 10 20 30 40 50E (eV)
0,68
0,7
0,72
0,74
0,76
0,78
! p
Frehaut pointwise Frehaut histogram
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
CONRAD RESULTS OF νp UP TO 50 EV
10/16
• Comparison of results obtained threating Frehaut data as histogram/pointwise.
with Γ γf from Trochon
0,68
0,7
0,72
0,74
0,76
0,78
! p
0 10 20 30 40 50E (eV)
-4-2024
Res
idua
l
Frehaut histogrampointwise
0,68
0,7
0,72
0,74
0,76
0,78
! p
0 10 20 30 40 50E (eV)
-4-2024
Res
idua
l
histogrampointwise
with Γ γf from Bouland
• CONRAD results from the fit below 50 eV of Frehaut data:
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
CONRAD RESULTS OF νp UP TO 50 EV
11/16
0,68
0,7
0,72
0,74
0,76
0,78
! p
0 10 20 30 40 50E (eV)
-4-202
Res
idua
l
Frehaut with Γ γf from Boulandwith Γ γf from Trochon
< ν 0 > = 2.891 ± 0.002
< ν 1 > = 2.867 ± 0.002
< ν nγf > = 2.61 ± 0.02
< ν 0 > = 2.888 ± 0.002
< ν 1 > = 2.866 ± 0.002
< ν nγf > = 2.43 ± 0.03
N Frehaut = 0.9963 ± 0.0007
N Frehaut = 0.9965 ± 0.0007
• Output parameters:
• CONRAD results from the fit below 50 eV of Frehaut data:
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
CONRAD RESULTS OF νp UP TO 50 EV
12/16
• CONRAD results from the fit below 50 eV of Gwin data:
0,750,7520,7540,7560,7580,76
0,7620,7640,7660,7680,77
! p
10 15 20 25 30 35 40E (eV)
-4-2024
Res
idua
l
0,7580,7590,76
0,7610,7620,7630,7640,7650,7660,767
! p
0,01 0,1 1E (eV)
-4-2024
Res
idua
l
Gwin with Γ γf from Boulandwith Γ γf from Trochon
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
RESULTS OF νp UP TO 50 EV
13/16
• Final results up to 50 eV:
Frehaut (normalized)with Γ γf from Boulandwith Γ γf from Trochon
J=1
J=1J=1
J=1J=1
J=1
J=1
J=1
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
RESULTS OF νp UP TO 50 EV
14/16
• The spin contribution can reproduce the data at low energies.• The ν nγf contribution reproduces the dips of the νp up to 50 eV.
J=1
J=1 J=1
Frehaut (normalized)with Γ γf from Boulandwith Γ γf from Trochon
J=1
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
DISCUSSION ABOVE 50 EV
15/16
h_ex
pEn
tries
1
36M
ean
0
.753
6R
MS
0
.014
25
p!0.
660.
680.
70.
720.
740.
760.
780.
80.
820.
840.
86
Counts
01020304050h_
exp
Entri
es
136
Mea
n
0.7
536
RM
S
0.0
1425
const = 50.1 +/- 6.6mean = 0.7564 +/- 0.0009sigma = 0.0095 +/- 0.0009
• Large dispersion in the experimental data from Frehaut at E > 50eV.
ν nγf contribution
=> New experimental data are required.• Large error bars from Gwin experimental data => not reliable.
Large dispersion
1.2%
50 eV
• Frehaut data with high νp can not be described by the equations.
Frehaut (normalized)with Γ γf from Boulandwith Γ γf from Trochon
Esther Leal Cidoncha, WONDER-2018, 8-12 October, 2018.
CONCLUSIONS AND PERSPECTIVES
16/16
• Large dispersion (1.2%) in the experimental data from Frehaut at E > 50eV.• Frehaut data with high νp can not be described by the equations.• Large error bars from Gwin experimental data => not reliable.
• Experimental data:
• To implement this model in CONRAD.
• Model:
CONCLUSIONS
PERSPECTIVES
• Incompatibility in the normalization between Gwin and Frehaut datasets.
• Do not reproduce the data in the full energy range (above 50 eV).• The inclusion of Γ γf from Trochon/Bouland produces similar results.
• Lower < ν nγf > with Bouland data.
=> New experimental data are required.