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

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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 235 U

Antineutrino Spectrum: S



(E) =

S

Y i x S i (E) Y i : cumulative fission yields S i (E): individual



spectrum



- decay from Level i to level k

J i p i I k Z,N Nucleus J k p k E k 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) Anti-neutrinos #8 - Alejandro Sonzogni

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 F n s << l consider an equilibrium situation: and

(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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235 U at thermal energies

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Anti-neutrinos from reactors Flux

Principal Contributors

235 U,

238 U, 239 Pu, 241 Pu Detection through inverse  decay on proton Reaction threshold : ~1.8 MeV

NNDC calculations on the Daya signal shape

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235 U(thermal n,f) main contributors to anti neutrino spectra Nucleus

54-Xe-137 55-Cs-139 39-Y - 94 40-Zr- 99 41-Nb-100 41-Nb- 98 39-Y - 92 41-Nb-101

% at 3 MeV

3.519 3.259 3.120 3.010 2.916 2.830

2.812

2.654

Nucleus

41-Nb-100 37-Rb- 92 39-Y - 96 52-Te-135 39-Y - 94

% at 4 MeV

4.872 3.694 3.545 2.994 2.897 55-CS-140 2.780

39-Y - 95 2.646 54-Xe-139 2.606

Nucleus

37-Rb- 92 39-Y - 96 41-Nb-100 55-Cs-142 55-Cs-140 52-Te-135 39-Y - 99 38-Sr- 95

% at 5 MeV

9.171

7.475

6.592

4.585

4.153

3.636

3.460

3.435

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

92 Rb a) 2000 ENSDF

51(18) %

g.s.

92 Rb b) Update with new data

95(5) %

g.s.

Effects of Valencia TAGS data

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Anti-neutrinos for Applied Purposes

235,238 U and 239 Pu produce a different signal, in shape, maxima and multiplicity

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100 Nb,

CFY=5.89E-2, D CFY=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 Anti-neutrinos #18 - Alejandro Sonzogni

142 Cs,

CFY=2.71E-2, D CFY=2.803 % Anti-neutrinos #19 - Alejandro Sonzogni

92 Rb,

CFY=4.82E-2, D CFY=1.398 % Anti-neutrinos #20 - Alejandro Sonzogni

92 Rb,

comparison to Rudstam data Anti-neutrinos #21 - Alejandro Sonzogni

92 Rb,

comparison to Rudstam data Anti-neutrinos #22 - Alejandro Sonzogni

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 beta minus decay: Nucleus(Z,A)  Nucleus(Z+1,A) + e- + anti-neutrino In an equilibrium situation, we obtain about 6 anti neutrinos/second per fission, or ~

10 20 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 Anti-neutrinos #25 - Alejandro Sonzogni

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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239 Pu at thermal energies

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238 U at fast energies

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252 Cf spontaneous fission

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235 U



- spectra ratios The published ILL data is binned at 250 keV. Could we get the 50 keV data?

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239 Pu



- spectra ratios

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238 U



- spectra ratios

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252 Cf



- 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 Anti-neutrinos #34 - Alejandro Sonzogni High energy gamma signal

Anti-neutrino Signal

Use the anti-neutrino capture on proton: Reaction has a 1.8 MeV threshold Anti-neutrinos #35 - Alejandro Sonzogni

Daya Bay Results

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Daya Bay

Some recent experiments

Experiment in China, 6 nuclear power reactors.

Ref: F.P. An et al, Physical Rev. Lett.

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