Correlations in Prompt Neutrons and Gamma Rays from Fission

Transcription

1 Correlations in Prompt Neutrons and Gamma Rays from Fission S. A. Pozzi 1, M. J. Marcath 1, T. H. Shin 1, Angela Di Fulvio 1, S. D. Clarke 1, E. W. Larsen 1, R. Vogt 2,3, J. Randrup 4, R. C. Haight 5, P. Talou 5, T. Kawano 5, I. Stetcu 5, E. Padovani 6 1 Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI, USA 2 Lawrence Livermore National Laboratory, Livermore, CA, USA 3 University of California, Davis, CA, USA 4 Lawrence Berkeley National Laboratory, Berkeley, CA, USA 5 Los Alamos National Laboratory, Los Alamos, NM, USA 6 Department of Energy, Polytechnic of Milan, Milan, Italy

2 Motivation Nuclear nonproliferation and safeguards applications require improved models for physics of nuclear fission and detector response. Specifically, the correlated neutron and gamma ray emission properties of important nuclear isotopes such as 235 U and 239 Pu are not well known. These data are important in nuclear safeguards and nonproliferation. The present work builds on that experience and includes correlated information. There is a need for a new set of measured data to compare to fission models. Key neutron and gamma ray quantities to measure Detected multiplicity Energy spectra Relative angle of emission 2

3 3 Nuclear Fission Center of Mass Frame Lab Frame Direction of motion Neutrons emitted in the direction of motion of the fission fragment (FF) have the FF momentum added to their energy

4 4 Probability Nuclear Fission Modeling MCNPX-PoliMi The multiple variables associated with nuclear fission are sampled independently by most Monte Carlo codes. MCNPX-PoliMi spontaneous fission model samples neutrons and gamma rays from a full multiplicity distribution. Neutron multiplicity dependent energy spectra. Anisotropic neutron angular distribution Pu-240 Cf Neutrons Emitted

5 5 Nuclear Fission Modeling CGMF and FREYA Theoretical research is underway to develop CGMF and FREYA models that exhibit fissionparticle correlations. CGMF and FREYA are event-byevent Monte Carlo codes that follow the fission event from scission to de-excitation Active collaboration is underway to verify these models and PoliMi with measured data.

6 UMich and LANL ChiNu Array Cf-252 Experiments EJ-309 organic liquid scintillator 17.78Ø 5.08 cm active volume 12.7 cm Hamamatsu R H:C 0.94 g/cm3 Pulse shape discrimination capable 17.78Ø 5.08 cm EJ-309 MCNPX-PoliMi simulated 17.78Ø 5.08 cm EJ kevee threshold =~0.5 MeV deposition 6

7 7 UMich Cf-252 Experiment In the Fall of 2014, an inorganic and organic scintillator array sensitive to both gamma-ray and neutrons has been created to investigate Cf-252 spontaneous fission gamma-ray and neutron correlations. This array provides a range of correlated measureables Time cross-correlation distributions Detected neutron and detected gamma-ray multiplicities Neutron energy from photon TOF as a function of the number of detected photons

8 8 LANL ChiNu Array Cf-252 Experiment In the summer of 2015, a measurement was made of neutrons and gamma rays from a Cf-252 fission chamber with the LANL ChiNu liquid organic scintillator array Larger source-detector distance of 1 m factor 2 Stronger source factor 8 Fission chamber better timing resolution and trigger Larger solid angle coverage factor 2 ORNL designed Cf- 252 fission chamber

9 9 LANL ChiNu Array Cf-252 Experiment 3,000 cps/detector 125 MB/s 30 hours and 27 billion fissions later we have 13 TB of waveforms Post-processing time is significant Physical storage space becomes difficult with full waveforms

10 LANL ChiNu Array Cf-252 Experiment Double coincidences are analyzed, but higher order coincidences are the target measurable Constructing a detailed MCNPX model for fission model comparison Pairs of EJ-309s Results for a time cross-correlation distribution between pair of EJ-309s Count rate as a function of angle between detectors 10

11 11 Polyethylene, 60 cm UMich and LANL ChiNu Array Cf-252 Experiments Neutron Cross-Talk Characterization Scatter-based non-absorbing detectors are prone to neutron cross-talk A single neutron can scatter into one or more detectors subsequently registering multiple counts Adversely increases correlated counts Characterization of cross-talk and its effect on the total observed coincidence counts is significant when experimental systems utilize numerous detectors Need to measure isolated cross-talk neutrons from Cf-252 spontaneous fission source and validate MCNPX- PoliMi simulations Detector 1 t 1 Detector 2 t 2 1m 1m Θ Detector-sourcedetector angle Cf-252 Detector 3

12 UMich and LANL ChiNu Array Cf-252 Experiments Neutron Cross-Talk Characterization Time cross-correlation distributions were compared to MCNPX-PoliMi simulations and show good agreement. Neutron cross-talk counts within a measurement system primarily dependent on: Detector-source-detector angle Detector-detector distance Detector light output threshold Relative effects of neutron crosstalk characterized by these parameters, see poster this afternoon. Detector-Source-Detector Angle Θ Measured Integrated Count Rate [counts/sec] MCNPX-PoliMi Integrated Count Rate [counts/sec] % Difference % % % 12

13 13 Future Work Induced-Fission Measurements at WNR Facility at LANSCE WNR - fast neutron source Ultracold neutron source Lujan center moderated neutron source

14 Summary and Conclusions Measurements of correlated, prompt emissions from 252 Cf have been performed and partially analyzed There is a need for a measured correlated-data set to compare with fission model simulations Accurate models are necessary in order to effectively design such systems Advanced verification system could rely on detailed correlated emissions from fission 14

15 Acknowledgements Thanks to my mentors at LANL Robert Haight, Matthew Devlin, and Patrick Talou. This research was performed under appointment to the U.S. Department of Energy Nuclear Nonproliferation International Safeguards Graduate Fellowship Program sponsored by the National Nuclear Security Administration s Office of Nonproliferation and International Security. This work was funded in-part by the Consortium for Verification Technology under Department of Energy National Nuclear Security Administration award number DE-NA

16 Correlations in Prompt Neutrons and Gamma Rays from Fission S. A. Pozzi 1, M. J. Marcath 1, T. H. Shin 1, Angela Di Fulvio 1, S. D. Clarke 1, E. W. Larsen 1, R. Vogt 2,3, J. Randrup 4, R. C. Haight 5, P. Talou 5, T. Kawano 5, I. Stetcu 5, E. Padovani 6 1 Department of Nuclear Engineering and Radiological Sciences, University of Michigan, Ann Arbor, MI, USA 2 Lawrence Livermore National Laboratory, Livermore, CA, USA 3 University of California, Davis, CA, USA 4 Lawrence Berkeley National Laboratory, Berkeley, CA, USA 5 Los Alamos National Laboratory, Los Alamos, NM, USA 6 Department of Energy, Polytechnic of Milan, Milan, Italy