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Measurements of the Prompt Fission Neutron Spectrum at LANSCE: The Chi-Nu Experiment 6 th Workshop on Nuclear Fission and Spectroscopy of Neutron-Rich Nuclei K.J. Kelly 1 M. Devlin 1 , J.A. Gomez 1 , R.C. Haight 1 , H.Y. Lee 1 , T.N. Taddeucci 1

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Measurements of the Prompt Fission Neutron Spectrum at LANSCE: The Chi-Nu Experiment

6th Workshop on Nuclear Fission and Spectroscopy of Neutron-Rich Nuclei K.J. Kelly1

  • M. Devlin1, J.A. Gomez1, R.C. Haight1, H.Y. Lee1, T.N. Taddeucci1,

S.M. Mosby1, J.M. O’Donnell1, N. Fotiadis1, D. Neudecker1, P . Talou1, M.E. Rising1, M.C. White1, C.J. Solomon1, C.Y. Wu2, B. Bucher2, M.Q. Buckner2, R.A. Henderson2

1Los Alamos National Laboratory 2Lawrence Livermore National Laboratory

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Slide 1 of 10

LA-UR-17-22656

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SLIDE 2

Chi-Nu Goals, Method, and Challenges

Goals

Measure the neutron χ-matrix

252Cf, 235U, 239Pu

PFNS for ranges

  • f Einc

n

Method

Double TOF PPAC† for fission Eout

n

< 2 MeV

22 6Li-glass

Eout

n

> 800 keV

54 Liquid Scint.

Challenges

Einc

n

0.7 MeV 20 MeV Eout

n

0.01 MeV 10 MeV Detailed Uncertainties

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#"$

%-Matrix

!"

&'(

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Pulsed, White ! Source Fission Event (-.) !′ !′ !′ (-1) Neutron Detection (-7)

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA

! "#$ % &' % (

)*

+*,(&')

LANSCE / Flux

WNR (Chi-Nu, LENZ, …) 21 m Flight Path LSDS (Fission) Lujan Center (DANCE, …)

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Slide 2 of 10

†C.Y. Wu et al., NIM A, 794 (2015) 76

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SLIDE 3

Characterizing the 6Li-glass Detector Response

6Li-glass Fission Neutron Spectrum

Outgoing Neutron Energy from Time of Flight (MeV)

1 −

10 1

Counts

200 400 600 800 1000 1200

Cross Section (barns) 0.5 1 1.5 2 2.5 3 3.5

Data Cross Section t ) α , n Li(

6

235U: 1.0 MeV  Einc n

 1.5 MeV Large peak in data

240-keV 6Li(n,α)t resonance

Background subtracted† E = Initial n Energy E0 = n Energy upon Detection Et = Measured n Energy via TOF C(p(E) , Et) = Counts measured at Et = Z 1

Et

p(E) R(E, Et) dE w/ R(E, Et) = Z 1 S(E, E0, Et) ✏(E0) dE0 S(E, E0, Et) = Scattering Matrix p(E) = PFNS ✏(E0) = Detector Efficiency at E0 R(E, Et) = Response Matrix

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Slide 3 of 10

†J.M. O’Donnell, Nucl. Instrum. and Methods A, 805 (2016) 87

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SLIDE 4

MCNP

R

6Li-glass Detector Response Matrix, R(E, Et)

Detector Response Changes with Experimental Environment

Outgoing Neutron Energy from Time of Flight (MeV)

1 −

10 1 10

Initial Outgoing Neutron Energy (MeV)

2 −

10

1 −

10 1 10 1 10

2

10

3

10

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Slide 4 of 10

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SLIDE 5

Calculation of New MCNP R

Spectra

Without Running New Simulations†

  • 1. Choose any PFNS
  • 2. Scale R(E, Et)

with p(E)

  • 3. Project out new

spectrum

2 −

10

1 −

10 1 10

2 1

1 10 1 10

2

10

3

10

Outgoing Neutron Energy from Time of Flight (MeV)

1 −

10 1

Counts

2000 4000 6000 8000 10000 12000 14000 16000 18000 20000 Maxwellian kT = 1.1 MeV Maxwellian kT = 1.2 MeV Maxwellian kT = 1.3 MeV Maxwellian kT = 1.4 MeV

10 1 0.1 0.2 0.3 0.4 0.5

PFNS (1/MeV) Initial Outgoing Neutron Energy (MeV)

1 10-1 0.1 0.2 0.3 0.4

Scale with p(E) Project onto Et axis

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Slide 5 of 10

C(p(E), Et) = Z 1

Et

p(E) R(E, Et) dE Takes < 1 s, as opposed to hours or days for a single simulation Must be careful with uncertainties!

†K.J. Kelly et al., Nucl. Instrum. and Methods A, submitted

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SLIDE 6

Method of PFNS Extraction: Ratio-of-Ratios Method†

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Slide 6 of 10

Based on the approximate equality of C(pα(E), Et) pα(Et) ⇡ C(pβ(E), Et) pβ(Et) True within ⇠5–10% for a typical PFNS Dα = Double Ratio = C(pα(E), Et)/pα(Et) C(pmaxw(E), Et)/pmaxw(Et) Average over reasonable PFNS range and set equal to the experimental ratio 1 

κ

X

α=1

C(pα, Et) pα(Et) = C(pexp, Et) pexp(Et) ) pexp(E) = C(pexp, Et)

1 κ

Pκ

α=1 C(pα,Et) pα(Et)

Quickly extracts PFNS without assuming anything about the PFNS shape

Outgoing Neutron Energy from Time of Flight (MeV)

1 −

10 1

Double Ratio

0.98 1 1.02 1.04 1.06 1.08 1.1 1.12

=0.549 MeV)

f

U Watt (T=0.988 MeV; E

235

=0.663 MeV)

f

Pu Watt (T=0.966 MeV; E

239

=0.769 MeV)

f

Cf Watt (T=1.025 MeV; E

252

=1.0 MeV)

inc n

Pu ENDF/BVII.1 (E

239

Cf Mannhart (1989)

252

Double Ratio Average

†T.N. Taddeucci et al., Nucl. Data Sheets, 1232 (2015) 135

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SLIDE 7

Results for 235U Low-Energy PFNS

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Slide 7 of 10

Initial Outgoing Neutron Energy (MeV)

2 −

10

1 −

10 1

PFNS (1/MeV)

0.1 0.2 0.3 0.4 0.5

Chi-Nu =2.0 MeV

inc n

ENDF/B-VII.1: E

= 2.0-3.0 MeV

inc n

E

9 −

10

8 −

10

7 −

10

6 −

10

5 −

10

4 −

10

3 −

10

2 −

10 Neutron Energy from T.O.F. (MeV)

2 −

10

1 −

10 1 Neutron Energy from T.O.F. (MeV)

2 −

10

1 −

10 1

PFNS Calculated for ⇠1 MeV Einc

n

ranges from 0.7-20 MeV Full covariance matrix calculated with:

Statistical Uncertainty: Data, Background, and MCNP Systematic Uncertainty: Background Measurement Need to calculate MCNP systematics

†J.A. Gomez et al., Nucl. Data Sheets, to appear

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SLIDE 8

Future Work

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Slide 8 of 10

Forward Analysis

Iteratively vary parameters of a Model; Successful tests with pmaxw(E) Makes use of R(E, Et) to create new simulation spectra for each iteration Disadvantage: Have to assume a functional form for the PFNS Disadvantage: Difficult to describe multi-chance fission transition regions without a sophisticated model (Los Alamos Model, etc.)

Unfolding

Also makes use of R(E, Et) to remove effects of detector response Advantage: No assumption about the shape of the PFNS Advantage: Can accurately describe transition regions Disadvantage: any amount of noise in the data is strongly amplified

239Pu Low-Energy Results

Data acquisition completed in December 2016 (2.5 Months) Data analysis is underway

Liquid Scintillator Results on 235U and 239Pu

Data on 235U have been collected; Data analysis is underway Preliminary test 239Pu data set collected; Further acquisition this summer

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SLIDE 9

Acknowledgments

Los Alamos National Laboratory

  • M. Devlin, J.A. Gomez, R.C. Haight, H.Y. Lee, T.N. Taddeucci,

S.M. Mosby, J.M. O’Donnell, N. Fotiades, D. Neudecker, P . Talou, M.E. Rising, M.C. White, and C.J. Solomon

Lawrence Livermore National Laboratory

C.Y. Wu, B. Bucher, M.Q. Buckner, and R.A. Henderson This work was performed under the auspices of the U.S. Department of Energy by Los Alamos National Laboratory under Contract DE-AC52-06NA25396 and by Lawrence Livermore National Security, LLC under contract DE-AC52-07NA27344

Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA

Slide 9 of 10

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SLIDE 10

References

C.Y. Wu, R.A Henderson, R.C. Haight, H.Y. Lee, T.N. Taddeucci, et al.,

  • Nucl. Instrum. Methods A, 794 (2015) 76

J.M. O’Donnell, Nucl. Instrum. Methods A, 805 (2016) 87 K.J. Kelly, J.M. O’Donnell, J.A. Gomez, T.N. Taddeucci, M. Devlin, et al.,

  • Nucl. Instrum. and Methods A, submitted

T.N. Taddeucci, R.C. Haight, H.Y. Lee, D. Neudecker, J.M. O’Donnell, et al.,

  • Nucl. Data Sheets 1232 (2015) 135

S.A. Pozzi, S.D. Clarke, W.J. Walsh, E.C. Miller, J.L. Dolan, et al.,

  • Nucl. Instrum. and Methods A 694 (2012) 119

R.C. Haight, C.Y. Wu, H.Y. Lee, T.N. Taddeucci, B.A. Perdue, et al., Nucl. Data Sheets 123 (2015) 130. C.Y. Wu, R.A. Henderson, R.C. Haight, H.Y. Lee, T.N. Taddeucci, et al.,

  • Nucl. Instrum. and Methods A 794 (2015) 76.

H.Y. Lee, T.N. Taddeucci, R.C. Haight, T.A. Bredeweg, A. Chyzh, et al.,

  • Nucl. Instrum. and Methods A 703 (2013) 213.
  • D. Neudecker, P

. Talou, T. Kawano, A.C. Kahler, M.E. Rising, et al., EPJ Web of Conferences 111 (2016) 05004

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