perspectives on measurements of prompt fission neutron ... · m. coppola and h.h. knitter, z....

Operated by Los Alamos National Security, LLC for NNSA

Perspectives on Measurements of Prompt Fission Neutron Spectra

for Fission Induced by Fast Neutrons

Robert C. Haight

Los Alamos National Laboratory

Second International Workshop on Perspectives on Nuclear Data for the Next Decade

CEA Bruyères-le-Chȃtel, France

October 14-17, 2014 LA-UR-14-27963 and LA-UR-14-23021


•  Spontaneous fission (252Cf) •  Neutron-induced fission

•  Thermal neutron-induced fission •  Fast neutron-induced fission

Perspectives on measurements of prompt fission neutron spectra


Components for neutron-induced PFNS measurements

•  Experiments –  Neutron source – intense, low background neededs

–  Detectors – good neutron identification (psd or ?), good efficiency, “modelable” in MCNP, GEANT, …

–  Data acquisition – implementation of new hardware, firmware, software – good resolution, good timing, programmable, capable of handling high counting rates

•  Modeling neutron transport as corrections to literature data, and design and analysis of new experiments

3


Predictions for PFNS measurement technologies

•  Experiments –  Neutron source – intense, low background needed -- no new

facilities for this type of measurement (?) :- (

–  Detectors – good neutron identification (psd or ?), good efficiency, “modelable” in MCNP, GEANT … -- nothing for greatly advanced capabilities :- ( , :- )

–  Data acquisition – implementation of new hardware, firmware, software – good resolution, good timing, programmable, capable of handling high counting rates -- In progress :- )

•  Modeling neutron transport as corrections to literature data, and design and analysis of new experiments-- NOW and continuing :- )

4


Predictions for PFNS measurements – work to be done

•  239Pu(n,f) – for incident neutron energies > 0.5 MeV and to requested accuracy –  Resolve discrepancies for PFNS > 0.5 MeV – probable in 2-3

years –  Produce new data for PFNS in range 0.05 to 0.50 MeV -- maybe in

3-4 years

•  235U(n,f) – for incident neutron energies > 0.5 MeV –  Data for PFNS > 0.5 MeV – probable in 3-4 years –  Produce new data for PFNS in range 0.05 to 0.50 MeV -- maybe in

4-5 years

5


Data in the literature: PFNS for 239Pu(n,f) – incident monoenergetic sources

15.4112.8410.708.927.436.195.164.303.582.992.492.071.731.441.201.000.8330.6940.5790.4820.4020.3350.2790.2330.1940.1620.1350.1120.0930.0780.0650.0540.0450.0380.0310.0260.0220.018

0.010483 ThermalThermalThermalThermalThermalThermal 40 keV 0.215 MeV 0.5 1.5 2.5 3.5 10

Belov Werle AbramsonStarostovBoytsovLaitai Conde Knitter Staples 1 Staples 2 Staples 3 Staples 3Nefedov

EXFOR# 40137 20616 20997 40930 40873 30704

year 1968

1971

1977

1983

1983

1985

1965

1975

1995

1995

1995

1995

0.04 0.21 0.50 - 3.5 E-incident (MeV)

10. thermal

15.

5.

1.

0.3

0.1

0.03

Staples Knitter Condé

Out

goin

g en

ergy

(MeV

)

Smith


Discrepancy in monoenergetic data for high-energy end of PFNS

7


Literature data, discrepancies and target accuracies

8

239Pu


9

38.34 31.95 26.62 22.19 LiG Proton StilbeneMany LiG LiG NE224 BC501 BC501 BC501 BC50118.49 NE102ARecoil NE10215.41 15.4112.84 12.8410.70 10.708.92 8.927.43 7.436.19 6.195.16 5.164.30 4.303.58 3.582.99 2.992.49 2.492.07 2.071.73 1.731.44 1.441.20 1.201.00 1.000.83 0.8330.69 0.6940.58 0.5790.48 0.4820.40 0.4020.33 0.3350.28 0.2790.23 0.2330.19 0.1940.16 0.1620.13 0.1350.11 0.1120.09 0.0930.08 0.0780.06 0.0650.05 0.0540.05 0.0450.04 0.0380.03 0.0310.03 0.0260.02 0.0220.02 0.0180.02 0.01 0.01 0.010483 ThermalThermalThermalThermalThermalThermal 40 keV 0.215 MeV 0.5 1.5 2.5 3.5 10

Belov Werle AbramsonStarostovBoytsovLaitai Conde Knitter Staples 1 Staples 2 Staples 3 Staples 3Nefedov

EXFOR# 40137 20616 20997 40930 40873 30704

year 1968

1971

1977

1983

1983

1985

1965

1975

1995

1995

1995

1995

0.04 0.21 0.50 - 3.5 E-incident (MeV)

10. thermal

15.

5.

1.

0.3

0.1

0.03 Out

goin

g en

ergy

(MeV

) Data in the literature: PFNS for 239Pu(n,f) – incident continuous sources

Previous LANSCE (2) Noda + Chatillon


Measurements made with “white” neutron source at LANSCE for 239Pu(n,f): CEA-LANL collaboration

S. Noda et al., Phys. Rev. C 83, 034604 (2011)

A. Chatillon et al., Phys. Rev. C 89, 014611 (2014)

Data > ENDF for Eout > 7 MeV Data < ENDF for Eout > 7 MeV

Note: Data for both also for Einc = 1.0 to > 20 MeV 10


•  Correction will reduce data points above 7 MeV but not so much as Noda data because of better time resolution by Chatillon fission chamber

•  Major difference with

Noda is in calibration of neutron detector efficiency, which explains why Chatillon < Noda above 7 MeV.

A. Chatillon et al.,Phys. Rev. C89, 014611 (2014)

Chatillon data will also be reduced due to time resolution. Detector calibration difference needs to be included also.


Los Alamos Neutron Science Center

WNR/LANSCE provides neutrons from 100 keV to 200 MeV for PFNS Studies

Neutron spectrum

30 MeV

Double time-of-flight experiment


Fission sample and fission counter (LLNL) to contain ~ 100 mg of 239Pu •  Parallel-Plate Avalanche Counter (PPAC)

Source – PPAC à Time of flight (1) à Energy of incident neutron


•  22 6Li-glass scintillation detectors - - or

•  54 liquid scintillation neutron detectors

Chi-Nu array of fast neutron detectors measures prompt neutron spectra emitted in fission

x

Double time-of-flight experiment

21.5 m from WNR source

Fission chamber (PPAC)

Neutron beam

6Li-glass detector array


Neutron detectors – two types

54 Liquid scintillators – 1.0 m flight path

22 6Li-glass scintillators – 0.4 m flight path

15 PPAC – neutron detector à Time of flight (2) à Energy of outgoing neutron


Modeling Neutron Transport in PFNS Experiments

Terry Taddeucci

16

Operated by the Los Alamos National Security, LLC for the DOE/NNSA

MCNP simulations have been used to investigatesome previous measurements of the PFNS

Two standard papers for 239Pu:

P. Staples et al., Nucl. Phys. A591, 41 (1995)

H.H. Knitter, Atomkernenergie 26, 76 (1975)

Some possible sources of systematic error:

multiple scattering in the target

multiple scattering in the collimation

detector efficiency

background subtraction

Calibrations (TOF, PH, flight path, etc)

these are not necessarily decoupled

previous1.plt: 22 Apr 2014 11:57:02


Experimental layout for the measurements by Staples et al.

drawing not to scale

staples-expt.plt: 22 Apr 2014 12:41:23


Experimental layout for the measurements by Knitter

typical for this facility (CBNM, Geel)

M. Coppola and H.H. Knitter, Z. Physik 232, 286 (1970)

knitter-expt.plt: 22 Apr 2014 12:53:17


How did Knitter and Staples handle target corrections?

Staples:

"Multiple scattering corrections and neutron attenuation corrections

have not been performed because the samples are so small that these

effects can be neglected."

Knitter:

"The result of the fit gave an average fission neutron energy of

= 3/2T = 2.12 ± 0.01 MeV

This result contains a small calculable systematic error, since the

fission neutrons produced in the sample can make secondary interactions

with the sample material. Correction calculations were done in the

manner described in a previous paper [1]."

[1] Kiefhaber,E., D. Thiem: Panel Proceedings Series, p127, IAEA Vienna (1972)

cf. Islam and Knitter, Nucl. Sci. Eng. 50, 108 (1973)

corrections.plt: 22 Apr 2014 16:05:16

U N C L A S S I F I E D

U N C L A S S I F I E D


Multiple scattering plays a significant role in the 239Pumeasurements of Knitter

0.01 0.1 1 2 5 10 20

MCNP flux at the detector position

neutron energy (MeV)

dN

/dE

(n

/Me

V)

target + shields

target only

Watt

two effects:

n-multiplication

in-scattering

calculations for

239Pu target

knitter-Pu-mcnp.plt: 23 Apr 2013 21:57:26


Comparison of MCNP calculations to the 239Pumeasurements of Knitter

0.1 1 2 5 10 20

MCNP flux at the detector position


dN

/dE

(n

/Me

V)

target + shields

target only

data (0.215 MeV)

Watt

two effects:

n-multiplication

in-scattering

calculations for

239Pu target

knitter-Pu-mcnp-data2.plt: 23 Apr 2014 14:36:40


Target and collimator effects in the 239Pu dataof Staples et al.

0.1 0.5 1 2 5 10 200.9

1.0

1.1

1.2

1.3

1.4

1.5

MCNP output / input


ratio

data range

t

c

p

calculation:

target (t)

collimator (c)

product (p = t × c)

staples-Pu-ratio.plt: 22 Apr 2014 12:42:57


Target and collimator effects in the 239Pu dataof Knitter

0.1 0.5 1 2 5 10 200.9

1.0

1.1

1.2

1.3

1.4

1.5

MCNP output / input


ratio

data range

t

c

p

calculation:

target (t)

collimator (c)

product (p = t × c)

knitter-Pu-ratio.plt: 22 Apr 2014 12:53:40


Modeling of Our Present Experiments

Terry Taddeucci

17


The low-energy part of the PFNS is being measuredwith an array of 6Li-glass detectors

active thin target (~100 mg)

many detectors (22)

open geometry

(no shielding)

beam

array-top.plt: 22 Apr 2014 13:00:58


The Chi-Nu MCNP model accounts for neutron scatteringfrom all nearby objects

top view front view

model space (∆x,∆y,∆z) = 7.5 × 7.6 × 6.9 m3 = 393.3 m3

room2.plt: 22 Apr 2014 13:36:15


Multiple scattering is a significant problemfor energies < 1 MeV

0.01 0.1 1 10 200.0

0.1

0.2

0.3

0.4

0.5

0.6


dN

/dE

(n

/Me

V)

energy spectra derived from TOF (det#03)

1

2

3

41 = Watt

2 = PPAC

3 = + det-frame

4 = + 21 dets

dnde-diff2.plt: 21 Apr 2014 14:22:19


Multiple scattering effects are more accuratelyrepresented by including the detector response

0.01 0.1 1 10 20


co

un

ts/M

eV

det #03

σ × Watt

full model

no dets

no frame

no PPAC

1 calculation =

46 cpu-h

(MCNP-PoliMi)

dnde2.plt: 24 Apr 2014 11:01:35


A preliminary comparison of simulation and datashows good agreement

0.01 0.1 1 10 20


co

un

ts/M

eV

252Cf spectrum

σ × Watt

MCNP

data

239 cpu-h

dnde-det2.plt: 23 Apr 2014 10:00:16


19

PFNS for 239Pu(nth,f) –

Is it a good guide for PFNS in fast-neutron-induced fission?


20

•  Prompt fission neutron spectra have been measured at thermal

for 235U and 235Pu. Reactions at thermal can be dominated by one or only a few resonances

•  Do the data at thermal have any relevance to

PFNS for fission induced by higher energy neutrons?

•  Zero order analysis – look at average number of neutrons emitted

in fission. If they vary with incident neutron energy, then there could well be a change in the spectra of emitted neutrons

PFNS for 239Pu(nth,f) – is it a good guide for PFNS in fast-neutron-induced fission?


Are PFNS measured at thermal relevant for higher incident neutrons?

•  Nu-bar for 235U(n,f) has no structure structure

Note also the scale:


Correlate structure in nu-bar for 239Pu(n,f) with fission cross section

•  Fission cross section from Weston [NSE 115,164 (1993)] •  Subtract a constant (2.82) from nu-bar for clarity of display •  Add spins and parities (all positive) from Mughabghab

–  0+ resonance shows no effect in nu-bar –  1+ resonances show varying effects

Nu-bar – 2.82

1+ 1+ 1+ 1+

1+ 1+ 1+ 0+

Probably (n,γ f) process


Now the good news (maybe)

•  Nu-bar at thermal for 239Pu(n,f) is almost the same as for 1-10 keV. Maybe the thermal neutron PFNS is relevant to higher energies

•  Q: Is nu-bar at thermal dominated by the 1+ resonance at 0.3 eV ?

0.025 eV (thermal)


Prospects for PFNS measurements with fission induced by epithermal neutrons

•  239Pu(n,f) – for incident neutron energies in resonance region – not planned but would be interesting physics! –  Note: gamma production from fission in resonance region has been

studied. Yes, spectra do depend on incident neutron energy and correlate with variations in nu-bar!

Ref: S. Mosby et al., DANCE collaborations

24


25

Fission total γ-ray energy vs. incident neutron energy for 239Pu(n,f)

25

•  Fluctuations in prompt fission gamma energy anti-correlated with neutron emission

•  More detailed information on 239Pu(n,γf) process (Lynn, 1965) •  Qualitative behavior reported by Shackleton in 1972

Mea

n to

tal g

-ene

rgy

(MeV

) bef

ore

corr

ectio

n fo

r det

ecto

r res

pons

e Prom

pt Neutron Yield


Advanced PFNS measurements

•  Correlate PFNS with fission products (Z,A) – difficult – could improve models of fission physics

26


Acknowledgments

•  This work is performed under the auspices of the U.S. Department of Energy by

Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344

and the Los Alamos National Laboratory under Contract DE-AC52-06NA25396.

27


•  LANL: H. Y. Lee, T. N. Taddeucci, J. M. O’Donnell, N. Fotiades, M. Devlin, J. L. Ullmann, T. Bredeweg, M.

Jandel, R. O. Nelson, S. A. Wender, D. Neudecker, M. Rising, S. Mosby, S. Sjue, M. White; R. C. Haight

•  LLNL: C.-Y. Wu, B. Bucher, R. Henderson

•  CEA: T. Ethvignot, T. Granier, A. Chatillon, J. Taieb, B. Laurent, Alix Sardet

Colleagues in PFNS experiments at LANSCE

perspectives on measurements of prompt fission neutron ... · m. coppola and h.h. knitter, z....

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