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

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1 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 M. Devlin, J.A. Gomez, R.C. Haight, H.Y. Lee, T.N. Taddeucci, S.M. Mosby, J.M. O Donnell, N. Fotiadis, D. Neudecker, P. Talou, M.E. Rising, M.C. White, C.J. Solomon, C.Y. Wu 2, B. Bucher 2, M.Q. Buckner 2, R.A. Henderson 2 Los Alamos National Laboratory 2 Lawrence Livermore National Laboratory LA-UR Slide of 0

2 Chi-Nu Goals, Method, and Challenges Goals Measure the neutron -matrix 252 Cf, 235 U, 239 Pu PFNS for ranges of E inc n Method Double TOF PPAC for fission En out < 2 MeV 22 6 Li-glass E out n > 800 kev 54 Liquid Scint. Challenges E inc n E out n 0.7 MeV apple20 MeV 0.0 MeV apple0 MeV Detailed Uncertainties %-Matrix (- ) Pulsed, White! Source!! Neutron Detection (- 7 )! " &'( Fission Event (-. ) Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA! LANSCE / Flux LSDS (Fission)! " #"$! "# $ % &' % ( Lujan Center (DANCE, ) WNR (Chi-Nu, LENZ, ) 2 m Flight Path Operated by Los Alamos National Security, LLC for the U.S. Department of Ener C.Y. Wu et al., NIM A, 794 (205) 76 ) * +*, (&') Operated by Los Alamos National Security, LLC for the U.S. Department of Energy's NNSA Slide 2 of 0

3 Characterizing the 6 Li-glass Detector Response Counts 6 Li-glass Fission Neutron Spectrum Data 6 Li(n,α)t Cross Section Outgoing Neutron Energy from Time of Flight (MeV) 235 U:.0 MeV apple E inc n apple.5 MeV Large peak in data 240-keV 6 Li(n, )t resonance Background subtracted Cross Section (barns) E = Initial n Energy E 0 = n Energy upon Detection E t = Measured n Energy via TOF C(p(E), E t )=Counts measured at E t = Z E t p(e) R(E, E t ) de w/ R(E, E t )= Z 0 S(E, E 0, E t ) (E 0 ) de 0 S(E, E 0, E t )=Scattering Matrix p(e) =PFNS (E 0 )=Detector Efficiency at E 0 R(E, E t )=Response Matrix J.M. O Donnell, Nucl. Instrum. and Methods A, 805 (206) 87 Slide 3 of 0

4 MCNP R 6 Li-glass Detector Response Matrix, R(E, E t ) Initial Outgoing Neutron Energy (MeV) Detector Response Changes with Experimental Environment Outgoing Neutron Energy from Time of Flight (MeV) Slide 4 of 0

5 Calculation of New MCNP R Spectra Without Running New Simulations 0.5 PFNS (/MeV) Choose any PFNS 2. Scale R(E, E t ) with p(e) 3. Project out new spectrum Initial Outgoing Neutron Energy (MeV) Initial Outgoing Neutron Energy (MeV) 0 - Scale with p(e) Project onto E t axis C(p(E), E t )= Z E t p(e) R(E, E t ) de Takes < s, as opposed to hours or days for a single simulation Must be careful with uncertainties! Counts Maxwellian kt =. MeV Maxwellian kt =.2 MeV Maxwellian kt =.3 MeV Maxwellian kt =.4 MeV Outgoing Neutron Energy from Time of Flight (MeV) K.J. Kelly et al., Nucl. Instrum. and Methods A, submitted Slide 5 of 0

6 Method of PFNS Extraction: Ratio-of-Ratios Method Double Ratio Based on the approximate equality of C(p (E), E t ) p (E t ) C(p (E), E t) p (E t ) True within 5 0% for a typical PFNS 235 U Watt (T=0.988 MeV; E =0.549 MeV) f 239 Pu Watt (T=0.966 MeV; E =0.663 MeV) f 252 Cf Watt (T=.025 MeV; E =0.769 MeV) f 239 inc Pu ENDF/BVII. (E =.0 MeV) 252 Cf Mannhart (989) Double Ratio Average n D = Double Ratio C(p (E), E t )/p (E t ) = C(p maxw (E), E t )/p maxw (E t ) Average over reasonable PFNS range and set equal to the experimental ratio apple applex = C(p, E t ) p (E t ) = C(p exp, E t ) p exp (E t ) ) p exp (E) = C(p exp, E t ) apple P apple = C(p,E t ) p (E t ) 0.98 Outgoing Neutron Energy from Time of Flight (MeV) Quickly extracts PFNS without assuming anything about the PFNS shape T.N. Taddeucci et al., Nucl. Data Sheets, 232 (205) 35 Slide 6 of 0

7 Results for 235 U Low-Energy PFNS Full Covariance Matrix in Normalized PFNS Units 0 PFNS (/MeV) inc E n Chi-Nu = MeV inc ENDF/B-VII.: E n =2.0 MeV Neutron Energy from T.O.F. (MeV) Initial Outgoing Neutron Energy (MeV) 0 0 Neutron Energy from T.O.F. (MeV) 9 0 PFNS Calculated for MeV En inc ranges from 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 Slide 7 of 0

8 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 206 (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 0

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 Slide 9 of 0

10 References C.Y. Wu, R.A Henderson, R.C. Haight, H.Y. Lee, T.N. Taddeucci, et al., Nucl. Instrum. Methods A, 794 (205) 76 J.M. O Donnell, Nucl. Instrum. Methods A, 805 (206) 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 232 (205) 35 S.A. Pozzi, S.D. Clarke, W.J. Walsh, E.C. Miller, J.L. Dolan, et al., Nucl. Instrum. and Methods A 694 (202) 9 R.C. Haight, C.Y. Wu, H.Y. Lee, T.N. Taddeucci, B.A. Perdue, et al., Nucl. Data Sheets 23 (205) 30. C.Y. Wu, R.A. Henderson, R.C. Haight, H.Y. Lee, T.N. Taddeucci, et al., Nucl. Instrum. and Methods A 794 (205) 76. H.Y. Lee, T.N. Taddeucci, R.C. Haight, T.A. Bredeweg, A. Chyzh, et al., Nucl. Instrum. and Methods A 703 (203) 23. D. Neudecker, P. Talou, T. Kawano, A.C. Kahler, M.E. Rising, et al., EPJ Web of Conferences (206) Slide 0 of 0