Fission Yields and Their Impact
Independent fission yields
give the probability that a
given level is populated
following fission
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n
Y
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l
d
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Cumulative fission yields are recursively defined as:
CFY
i
=IFY
i
+
b
ki
CFY
k
where b
ki
is the probability of the level k decaying to the level i
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=
6
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o
Currently two independent fission yields library, ENDF/B and JEFF.
o
The code GEF by K.-H. Schmidt and B. Jurado has been developed in
the last few years and shows considerable capabilities.
o
Most of ENDF/B yields were released in 1992, with the exception of the
239
Pu 2 MeV data.
o
Data published in the last 25 years have not been incorporated in the
library.
o
ENDF/B-VII.1 yields are not fully compatible with modern decay data.
o
Many experiments are taking data and more will start taking data soon,
which should be incorporated in the libraries.
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.
o
ENDF-6 format doesn’t include yields as function of Z and A, as well as
nubar as function of A.
o
Covariances of fission yields have been developed, but can’t be
accommodated in the ENDF-6 format either.
o
Consultants meeting organized by the IAEA, May 23-26, 2016.
INDC-NDS-0713 report by P. Dimitriou, F.-J. Hambsch and S. Pomp.
o
Possible evaluation of
235,238
U,
239,241
Pu and
252
Cf yields as a world
effort. It will take considerable amount of funds to get it done.
Next slides
: Some of our recent work.
Fission Yield Effects in antineutrinos
It has been
known for a
while that
ENDF/B and
JEFF fission
yields were
producing
different results
We performed corrections to the ENDF/B yields to account for:
a) better decay data,
b) improved isomeric ratios,
c) anomalous yields.
Thermal
235
U electron spectrum
Corrected yields:
•
No electron excess.
•
Better agreement
with JEFF.
A.A. Sonzogni, E.A. McCutchan, T.D. Johnson, P. Dimitriou, PRL 116, 132502 (2016).
96
Y – Isomeric Ratio Effect
96
Y Isomeric Ratio
:
CFY ~ 0.05
At about 5.2 MeV,
changing IR from 0 to
100% changes the
calculated to experimental
ratio by 7%.
There is no journal
publication of IR. Estimates
vary from 18% to 70%.
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(
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=
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,
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=
0
.
5
Next slides
: some inconsistencies
2
5
2
C
f
E
N
D
F
/
B
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J
E
F
F
v
s
G
E
F
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d
s
As example, Z=44, with IFY(110Ru)=0.036 (highest in LFF)
We should expect good agreement between them
252
Cf JEFF yields are consistently lower than ENDF/B for nuclides on the
right of the maximum
Using summation method we obtain:
Delayed nubar ENDF/B=8.3E-3, Delayed nubar JEFF=6.6E-3
2
3
8
U
Y
i
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l
d
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E
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/
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t
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a
2
3
8
U
Data: F-J Hambsch, private comm.
Disagreement in
238
U Mass Yields
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A
c
t
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v
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Requiring no extra funding:
o
Participate in Isomeric Ratios experiments.
o
Explore effect on antineutrino spectra calculations.
Wish list:
o
Rebuild experimental fission yields database
o
Develop least-squares methods to obtain recommended
yields and correlations in cooperation with other national
labs.
This will require considerable funding, several FTEs for
about 5 years.
Fission yields play a crucial role in determining the probability of specific energy levels being populated after fission. This content explores independent and cumulative fission yields, the current status of fission yield libraries such as ENDF/B and JEFF, workforce shortages in fission yield evaluation, effects of fission yields in antineutrinos, and recent studies on thermal 235U electron spectra and isomeric ratios. Additionally, it highlights the efforts needed for a comprehensive worldwide evaluation of fission yields.
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Presentation Transcript
Fission Yields Independent fission yields give the probability that a given level is populated following fission Fission Yields
Cumulative fission yields are recursively defined as: CFYi=IFYi+ bki CFYk where bki is the probability of the level k decaying to the level i Z=60 Cumulative Independent Fission Yields
Fission Yields o Currently two independent fission yields library, ENDF/B and JEFF. o The code GEF by K.-H. Schmidt and B. Jurado has been developed in the last few years and shows considerable capabilities. o Most of ENDF/B yields were released in 1992, with the exception of the 239Pu 2 MeV data. o Data published in the last 25 years have not been incorporated in the library. o ENDF/B-VII.1 yields are not fully compatible with modern decay data. o Many experiments are taking data and more will start taking data soon, which should be incorporated in the libraries. Fission Yields
Fission Yields o Workforce shortage is an issue. During his plenary talk in ND2016, Tokio Fukahori considered fission yields evaluators all but extinct. o ENDF-6 format doesn t include yields as function of Z and A, as well as nubar as function of A. o Covariances of fission yields have been developed, but can t be accommodated in the ENDF-6 format either. o Consultants meeting organized by the IAEA, May 23-26, 2016. INDC-NDS-0713 report by P. Dimitriou, F.-J. Hambsch and S. Pomp. o Possible evaluation of 235,238U, 239,241Pu and 252Cf yields as a world effort. It will take considerable amount of funds to get it done. Next slides: Some of our recent work. Fission Yields
Fission Yield Effects in antineutrinos It has been known for a while that ENDF/B and JEFF fission yields were producing different results A.C. Hayes et al, PRD 92, 033015 (2015) We performed corrections to the ENDF/B yields to account for: a) better decay data, b) improved isomeric ratios, c) anomalous yields. Fission Yields
Thermal 235U electron spectrum Corrected yields: No electron excess. Better agreement with JEFF. A.A. Sonzogni, E.A. McCutchan, T.D. Johnson, P. Dimitriou, PRL 116, 132502 (2016). Fission Yields
96Y Isomeric Ratio Effect 96Y Isomeric Ratio: 96 m ( + ) IFY m Y = IR 96 96 gs ( ) ( ) IFY Y IFY Y CFY ~ 0.05 At about 5.2 MeV, changing IR from 0 to 100% changes the calculated to experimental ratio by 7%. Very recent Experiment in ILL (France), IR=0.5 Recent Penning Trap in Jyvaskyla, IR=0.5 There is no journal publication of IR. Estimates vary from 18% to 70%. Next slides: some inconsistencies Fission Yields
252Cf ENDF/B vs JEFF vs GEF yields As example, Z=44, with IFY(110Ru)=0.036 (highest in LFF) We should expect good agreement between them 252Cf JEFF yields are consistently lower than ENDF/B for nuclides on the right of the maximum Using summation method we obtain: Delayed nubar ENDF/B=8.3E-3, Delayed nubar JEFF=6.6E-3 Fission Yields
238U Yields ENDF/B vs JEFF vs GEF vs recent data Disagreement in 238U Mass Yields 238U ? Fission Yields Data: F-J Hambsch, private comm.
Future NNDC Activities Requiring no extra funding: o Participate in Isomeric Ratios experiments. o Explore effect on antineutrino spectra calculations. Wish list: o Rebuild experimental fission yields database o Develop least-squares methods to obtain recommended yields and correlations in cooperation with other national labs. This will require considerable funding, several FTEs for about 5 years. Fission Yields
