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 , S.M. Mosby 1 , J.M. O’Donnell 1 , N. Fotiadis 1 , D. Neudecker 1 , P . Talou 1 , M.E. Rising 1 , M.C. White 1 , C.J. Solomon 1 , C.Y. Wu 2 , B. Bucher 2 , M.Q. Buckner 2 , R.A. Henderson 2 1 Los Alamos National Laboratory 2 Lawrence Livermore National Laboratory LA-UR-17-22656 Slide 1 of 10 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
Chi-Nu Goals, Method, and Challenges Method Challenges Goals Double TOF Measure the E inc � 0.7 MeV n PPAC † for fission neutron χ -matrix 20 MeV E out < 2 MeV E out 252 Cf, 235 U, 239 Pu n � 0.01 MeV n 22 6 Li-glass 10 MeV PFNS for ranges E out > 800 keV of E inc Detailed n n 54 Liquid Scint. Uncertainties % -Matrix !′ !′ Neutron Detection (- 7 ) Pulsed, White ! Source (- 1 ) &'( !′ ! " Fission Event (- . ) Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA LANSCE / Flux LSDS (Fission) WNR Lujan Center "# $ % &' % ( (Chi-Nu, LENZ, …) (DANCE, …) 21 m Flight Path ! #"$ ! " Operated by Los Alamos National Security, LLC for the U.S. Department of Energ † C.Y. Wu et al. , NIM A, 794 (2015) 76 +*, (&') ) * Slide 2 of 10 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
Characterizing the 6 Li-glass Detector Response E = Initial n Energy 6 Li-glass Fission Neutron Spectrum E 0 = n Energy upon Detection Data 1200 3.5 6 E t = Measured n Energy via TOF Li( n , ) t Cross Section α 3 1000 Cross Section (barns) 2.5 800 Counts C ( p ( E ) , E t ) = Counts measured at E t 2 600 Z 1 1.5 = p ( E ) R ( E , E t ) dE 400 1 E t 200 0.5 Z 1 0 S ( E , E 0 , E t ) ✏ ( E 0 ) dE 0 − 1 w/ R ( E , E t ) = 10 1 Outgoing Neutron Energy from Time of Flight (MeV) 0 235 U: 1.0 MeV E inc 1.5 MeV n S ( E , E 0 , E t ) = Scattering Matrix Large peak in data p ( E ) = PFNS 240-keV 6 Li( n , α ) t resonance ✏ ( E 0 ) = Detector Efficiency at E 0 Background subtracted † R ( E , E t ) = Response Matrix † J.M. O’Donnell, Nucl. Instrum. and Methods A, 805 (2016) 87 Slide 3 of 10 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
� 6 Li-glass Detector Response Matrix, R ( E , E t ) MCNP R Detector Response Changes with Experimental Environment 10 Initial Outgoing Neutron Energy (MeV) 3 10 1 2 10 1 − 10 10 2 − 10 1 1 − 10 1 10 Outgoing Neutron Energy from Time of Flight (MeV) Slide 4 of 10 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
� Spectra Calculation of New MCNP R Without Running New Simulations † PFNS (1/MeV) 0.1 0.5 0.4 0.3 0.2 0.4 0.3 0.2 0.1 10 Initial Outgoing Neutron Energy (MeV) 1. Choose any PFNS 3 Scale with p (E) 10 1 2. Scale R ( E , E t ) 1 1 with p ( E ) 2 10 3. Project out new 10 -1 1 10 10 spectrum 2 1 − − 2 1 10 10 1 10 Project onto E t axis Z 1 20000 Maxwellian kT = 1.1 MeV Maxwellian kT = 1.2 MeV 18000 C ( p ( E ) , E t ) = p ( E ) R ( E , E t ) dE Maxwellian kT = 1.3 MeV 16000 Maxwellian kT = 1.4 MeV E t 14000 12000 Counts 10000 Takes < 1 s, as opposed to hours or days 8000 for a single simulation 6000 4000 Must be careful with uncertainties! 2000 − 1 10 1 Outgoing Neutron Energy from Time of Flight (MeV) † K.J. Kelly et al. , Nucl. Instrum. and Methods A, submitted Slide 5 of 10 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
Method of PFNS Extraction: Ratio-of-Ratios Method † Based on the approximate equality of D α = Double Ratio C ( p α ( E ) , E t ) ⇡ C ( p β ( E ) , E t ) C ( p α ( E ) , E t ) / p α ( E t ) = p α ( E t ) p β ( E t ) C ( p maxw ( E ) , E t ) / p maxw ( E t ) True within ⇠ 5–10% for a typical PFNS Average over reasonable 1.12 PFNS range and set equal 235 U Watt (T=0.988 MeV; E =0.549 MeV) f 239 1.1 to the experimental ratio Pu Watt (T=0.966 MeV; E =0.663 MeV) f 252 Cf Watt (T=1.025 MeV; E =0.769 MeV) f κ 239 inc C ( p α , E t ) = C ( p exp , E t ) 1 Pu ENDF/BVII.1 (E =1.0 MeV) 1.08 n X 252 Cf Mannhart (1989) Double Ratio p α ( E t ) p exp ( E t ) Double Ratio Average 1.06 α = 1 C ( p exp , E t ) 1.04 ) p exp ( E ) = C ( p α , E t ) P κ 1 1.02 α = 1 κ p α ( E t ) 1 Quickly extracts PFNS without 0.98 assuming anything about the 1 − 10 1 Outgoing Neutron Energy from Time of Flight (MeV) PFNS shape † T.N. Taddeucci et al. , Nucl. Data Sheets, 1232 (2015) 135 Slide 6 of 10 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
Results for 235 U Low-Energy PFNS 2 − 10 − 3 10 1 Neutron Energy from T.O.F. (MeV) 0.5 4 − 10 0.4 PFNS (1/MeV) − 5 10 0.3 inc E = 2.0-3.0 MeV n 6 − − 1 10 10 Chi-Nu 0.2 − 7 inc 10 ENDF/B-VII.1: E =2.0 MeV n 0.1 8 − 10 9 − 2 − 10 10 2 1 − − − 2 − 1 10 10 1 10 10 1 Neutron Energy from T.O.F. (MeV) Initial Outgoing Neutron Energy (MeV) PFNS Calculated for ⇠ 1 MeV E inc ranges from 0.7-20 MeV n 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 Slide 7 of 10 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
Future Work Forward Analysis Iteratively vary parameters of a Model; Successful tests with p maxw ( E ) Makes use of R ( E , E t ) 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 , E t ) 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 239 Pu Low-Energy Results Data acquisition completed in December 2016 (2.5 Months) Data analysis is underway Liquid Scintillator Results on 235 U and 239 Pu Data on 235 U have been collected; Data analysis is underway Preliminary test 239 Pu data set collected; Further acquisition this summer Slide 8 of 10 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
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 Slide 9 of 10 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
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 Slide 10 of 10 Operated by Los Alamos National Security, LLC for the U.S. Department of Energy’s NNSA
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