High energy neutron flux detection with dielectric plastics

Abstract

Dielectric plastics were irradiated with high energy neutrons to investigate their usefulness as flux detectors. Shields thick to heavy particles and of varying composition were placed in front of the plastics to test their effectiveness as radiators. Track producing particles resulted from (n, ⁴He) reactions and from recoils of light nuclei. Elements possessing high (n, ⁴He) cross sections were chosen as shields along with other heavy elements chosen to screen the surface of the plastic from all external track-producing particles. Carbon and aluminum satisfied the first condition while gold and lead satisfied the second. After etching, the track densities in cellulose nitrate were counted. The sensitivity under graphite varied from about 2.7 × 10⁻⁵ to 3.4 × 10⁻⁵ tracks/neutron for neutrons between 13.1 and 17.1 MeV. Useful track densities are produced by fluxes in the range of about 2 × 10⁸ to 5 × 10¹⁰ n ₀/cm². The ¹²C (n, n'3 ⁴He) reaction also took place in the carbon nuclei within the plastic itself. This allowed the triple-⁴He particle tracks to be counted. The sensitivity of this method varied from about 2.7 × 10⁻⁸ to 5.7 × 10⁻⁸ tracks/neutron. The useful flux range in the best case (under gold) was from 5 × 10¹⁰ to 5 × 10¹¹ n ₀/cm².