Evaluating Gamma and Neutron Spectra and Multiplicities of 242Pu Spontaneous Fission

The measurement of gammas and neutrons produced from spontaneous fission (sf) is useful for non-destructive assay of actinides. Using Los Alamos National Laboratory’s Chi-Nu array with 54 EJ-309 plastic scintillators surrounding a fission chamber containing 242Pu, the observed prompt fission neutron spectrum (PFNS) and prompt fission gamma spectrum (PFGS) for 242Pu(sf) and multiplicities can be measured. These measurements can be converted to the emitted spectra by determining the calibrated light response of the scintillator using MCNPX-PoliMi models of the Chi-Nu detector array and generating response matrix kernels that fit the observed spectral data. Additionally, the sf neutron and gamma number distribution, or multiplicities, can be determined via timing correlations in the detector system and pulse shape discrimination techniques.