Time Resolution of Nuclear Material Time Cross-correlation Measurement System Based on EJ299-33A Detector

The neutron and gamma time cross-correlation measurement could extract mass and multiplication coefficient of nuclear material, in which time resolution is an important parameter to characterize the correlation precision. Based on the means of digital data acquisition and processing, the time resolution was assessed for nuclear material time cross-correlation measurement system, which consisted of two novel plastic scintillator EJ299-33A detectors with particle discrimination capability, and the effect of the source was analyzed by comparing the ⁶⁰Co and ²²Na measurements. Furthermore, the equivalent electron energy threshold dependence of time resolution was given by off-line inversion, and the influences on different coincidence events were discussed by decoupling of the timecorrelated spectrum of ²⁵²Cf. The results show that the time resolution of system decreases with the increase of equivalent threshold, and the time resolution of 560 ps was obtained at the threshold of 230 keVee by ⁶⁰Co measurement, which could meet the accuracy requirement of the nuclear material time cross-correlation measurements. Nevertheless, the result acquired by ²²Na measurement is widened to about 816 ps at the same threshold due to the uncertainty of positron annihilation position and the delayed coincidence. In the fission events correlated measurement, the relative influence of time resolution on n-n coincidences is smaller than that on γ-γ coincidences.