Anti-neutrinos Spectra
from Nuclear Reactors
Alejandro Sonzogni
National Nuclear Data Center
ENDF/B VII.1 Decay Data Sub-Library
Most recent …
• Q values -- Audi 2011 mass update
• ENSDF data (when complete) else Wallet Cards (2011)
• Atomic data -- Evaluated Atomic Data Library (LLNL) –
includes X-rays and Auger electrons
• TAGS data
• Electron conversion -- BrIcc
• Theoretical calculations for neutron-rich nuclei using
beta-strength functions (Moller) and CGM (Kawano)
More details in Nuclear Data Sheets 112, 2887 (2011).
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ENDF VII.I Decay Data Sub Library
A transformation of all relevant data into computer “friendly” files
What’s in there…
3817 “materials”
g.s. and isomers
Wallet Cards
Theory (CGM)
ENSDF
New ENSDF
What’s it good for …
• Decay heat
• Antineutrino spectra
• Delayed nu-bars (reactor operation)
• Astrophysics ?
• ????
Antineutrino Experiments
Decay of fission fragments
More than 800
nuclides produced
in the fission of 235U
Antineutrino Spectrum:
S (E) =S Yi x Si(E)
Yi: cumulative fission yields
Si(E): individual  spectrum
- decay from Level i to level k
Jipi
Ik
Z,N Nucleus
Jkpk
Ek
Z+1,N-1Nucleus
a: normalization, d: shape factor, F: Fermi function. The
sum spectrum is obtained as:
b: branching ratios
All nuclear decay data from ENDF/B-VII.1 (December 2011)
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Example, 137Cs
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How to calculate anti-neutrino rates
The nuclei in the core form a
decay/processing network:
-
(n,g)
Neglect processing as Fns << l and
consider an equilibrium situation:
(n,g)
-
Then the anti-neutrino rate per fission is:
Used by Vogel et al,
1981, ENDF/B-V
We’ll repeat the calculations using the fission yields from ENDF/B-VII.1
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235U
at thermal energies
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Anti-neutrinos from reactors
Flux
Principal Contributors
235U, 238U, 239Pu, 241Pu
Detection through inverse 
decay on proton
Reaction threshold : ~1.8 MeV
NNDC calculations on the Daya signal shape
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235U(thermal
n,f) main contributors to antineutrino spectra
Nucleus
% at 3 MeV
Nucleus
54-Xe-137
3.519
55-Cs-139
Nucleus
% at 5 MeV
41-Nb-100 4.872
37-Rb- 92
9.171
3.259
37-Rb- 92
3.694
39-Y - 96
7.475
39-Y - 94
3.120
39-Y - 96
3.545
41-Nb-100 6.592
40-Zr- 99
3.010
52-Te-135
2.994
55-Cs-142
4.585
41-Nb-100 2.916
39-Y - 94
2.897
55-Cs-140
4.153
41-Nb- 98
2.830
55-CS-140 2.780
52-Te-135
3.636
39-Y - 92
2.812
39-Y - 95
2.646
39-Y - 99
3.460
54-Xe-139
2.606
38-Sr- 95
3.435
41-Nb-101 2.654
% at 4 MeV
With TAGS: 140Cs. 96Y seems is good shape. We’ll
look at some of the other nuclides and if available,
compare it to Rudstam data.
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One small nucleus, one big effect
92Rb
a) 2000 ENSDF
51(18) %
g.s.
92Rb
b) Update with
new data
95(5) %
g.s.
Effects of Valencia TAGS data
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Anti-neutrinos for Applied Purposes
235,238U
and 239Pu
produce a
different signal,
in shape,
maxima and
multiplicity
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100Nb,
CFY=5.89E-2, DCFY=16.883 %
The GS to GS transition is not well determined. It could be up
to 75%. BNL plans to submit a proposal to CARIBU. Would
include other Nb nuclides
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142Cs,
CFY=2.71E-2, DCFY=2.803 %
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92Rb,
CFY=4.82E-2, DCFY=1.398 %
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92Rb,
comparison to Rudstam data
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92Rb,
comparison to Rudstam data
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Summary
The next generation of experiments
using anti-neutrinos from nuclear
reactors have just published their first
results. More to come in the next few
years.
There is a close link between basic
nuclear structure research and the
calculation of anti-neutrino spectra.
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Why nuclear reactors?
Nearly 1,000 different fission fragments (materials)
are produced in the fission of an actinide nuclide.
Most of them are neutron rich, undergoing betaminus decay:
Nucleus(Z,A)  Nucleus(Z+1,A) + e- + anti-neutrino
In an equilibrium situation, we obtain about 6 antineutrinos/second per fission, or ~1020 anti-neutrinos
per reactor.
Anti-neutrinos interact through weak interaction, very
small cross sections, s ~ 5x10-19 barns
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Some history
In - decay, the electron energy is a continuum
distribution linking two nuclear levels (quantum).
Another particle must be involved
n  p + e- + anti-neutrino (Fermi, 1934)
First detection in 1956 by Cowan and Reines (LANL)
using neutrinos from a nuclear reactor in SRS:
anti-neutrino + p  n +e+
The positron created two 511 keV gammas and the
neutron was captured in Cd, releasing a gamma
cascade
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More history
In 1962, Leon Lederman and collaborators (BNL)
discovered the muon neutrinos:
Finally, in 1975 the Tau lepton and in 2000 the Tau
neutrino were discovered.
In the late 1960’s Ray Davies (BNL) measured the
flux of neutrinos coming from the Sun, observing a
deficit.
Neutrino oscillations were formalized to explain this
problem.
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239Pu
at thermal energies
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238U
at fast energies
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252Cf
spontaneous fission
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235U
- spectra ratios
The published ILL data is binned at 250 keV. Could we get the 50 keV
data?
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239Pu
- spectra ratios
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238U
- spectra ratios
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252Cf
- spectra ratios
More theory needed, but better agreement with
higher statistics, cleaner data
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3 near neutrino detectors and 3 far neutrino detectors
anti-neutrino + proton (water)
positron + neutron
Captured in Gd
Two 511 keV
gammas
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High energy
gamma signal
Anti-neutrino Signal
Use the anti-neutrino capture on proton:
Reaction
has a 1.8
MeV
threshold
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Daya Bay Results
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Some recent experiments
Daya Bay
Experiment in China, 6 nuclear power reactors.
Ref: F.P. An et al, Physical Rev. Lett. 108, 171803 (2012)
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