Impact of x-ray dose on the response of CR-39 nuclear track detector to 1-5.5 MeV alphas and 0.5-9.1 MeV protons for spectroscopy at the OMEGA Laser Facility and the National Ignition Facility

Abstract

The CR-39 nuclear track detector is used in many nuclear diagnostics fielded at inertial confinement fusion (ICF) facilities. Large x-ray fluences generated by ICF experiments may impact the CR-39 response to incident charged particles. To determine the impact of x-ray exposure on the CR-39 response to protons and alpha particles, a thick-target bremsstrahlung x-ray generator was used to expose CR-39 to various doses of 30 and 8keV Cu-K[alpha] and K[beta] x-rays. The CR-39 detectors were then exposed to 1-5.5 MeV alphas or 0.5- 9.1 MeV protons. The regions of the CR-39 exposed to x-rays showed a smaller track diameter than those not exposed to x-rays: for example, a dose of 3.0±0.1 Gy causes a decrease of (19±2)% in the track diameter of a 5.5 MeV alpha, while a dose of 6.0±0.1 Gy results in a decrease of (29±1)% in the track diameter of a 3.0 MeV proton. The reduced track diameters were found to be predominantly caused by a comparable reduction in the bulk etch rate of the CR-39 with x-ray dose. A residual effect, due to changes in track etch rate and dependent on incident particle energy, was characterized by an empirical formula.