Measurement of neutron and gamma-ray cross-correlation functions with 4He detectors

Abstract

For the first time, the neutron and gamma-ray time-dependent cross-correlation distributions from spontaneous fission and (α, n) neutron sources are measured with the 4He fast neutron detectors. The pulse shape discrimination technique based on charge comparison is utilized to discriminate between neutrons and gamma-rays in the identification of the four possible correlated pairs: (γ, γ), (n, n), (γ, n), and (n, n). Both total and individual cross-correlation functions are obtained, and their shapes can be easily distinguished among different neutron sources. The (n, n) and (γ, n) correlations are selectively analyzed and the peak position of the (n, n) and (γ, n) pairs shows a linear correlation with source–detector distance. The measurements illustrate the feasibility of using 4He detectors to identify nuclear materials and their geometrical configurations, as well as other applications in nuclear nonproliferation and safeguards. In particular, the (n, n) correlated data can be very clearly assayed even in presence of significant gamma fields without the use of shielding.