Neutron-neutron angular correlations in spontaneous fission of Cf252 and Pu240

Verbeke, J. M.; Nakae, L. F.; Vogt, R.

doi:10.1103/PhysRevC.97.044601

Title: Neutron-neutron angular correlations in spontaneous fission of ${}^{252}{Cf}$ and ${}^{240}{Pu}$

Journal Article · Sun Apr 01 00:00:00 EDT 2018 · Physical Review C

DOI:https://doi.org/10.1103/PhysRevC.97.044601· OSTI ID:1488798

Verbeke, J. M. ^[1]; Nakae, L. F. ^[1]; Vogt, R. ^[2]

Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Nuclear and Chemical Sciences Division
Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States). Nuclear and Chemical Sciences Division; Univ. of California, Davis, CA (United States). Dept. of Physics

Background: Angular anisotropy has been observed between prompt neutrons emitted during the fission process. Such an anisotropy arises because the emitted neutrons are boosted along the direction of the parent fragment. Purpose: To measure the neutron-neutron angular correlations from the spontaneous fission of ²⁵²Cf and ²⁴⁰Pu oxide samples using a liquid scintillator array capable of pulse-shape discrimination. To compare these correlations to simulations combining the Monte Carlo radiation transport code MCNPX with the fission event generator FREYA. Method: Two different analysis methods were used to study the neutron-neutron correlations with varying energy thresholds. The first is based on setting a light output threshold while the second imposes a time-of-flight cutoff. The second method has the advantage of being truly detector independent. Results: The neutron-neutron correlation modeled by FREYA depends strongly on the sharing of the excitation energy between the two fragments. The measured asymmetry enabled us to adjust the FREYA parameter x in ²⁴⁰Pu , which controls the energy partition between the fragments and is so far inaccessible in other measurements. The ²⁴⁰Pu data in this analysis was the first available to quantify the energy partition for this isotope. The agreement between data and simulation is overall very good for ²⁵²Cf ( sf ) and ²⁴⁰Pu ( sf ). Conclusions: The asymmetry in the measured neutron-neutron angular distributions can be predicted by FREYA. The shape of the correlation function depends on how the excitation energy is partitioned between the two fission fragments. Lastly, experimental data suggest that the lighter fragment is disproportionately excited.

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Research Organization:: Lawrence Livermore National Lab. (LLNL), Livermore, CA (United States)

Sponsoring Organization:: USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation

Grant/Contract Number:: AC52-07NA27344

OSTI ID:: 1488798

Alternate ID(s):: OSTI ID: 1430782

Report Number(s):: LLNL-JRNL-731534; PRVCAN; 878683

Journal Information:: Physical Review C, Vol. 97, Issue 4; ISSN 2469-9985

Publisher:: American Physical Society (APS)Copyright Statement

Country of Publication:: United States

Language:: English

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Cited by: 15 works

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