Impact of x-ray dose on track formation and data analysis for CR-39-based proton diagnostics

Abstract

The nuclear track detector CR-39 is used extensively for charged particle diagnosis, in particular proton spectroscopy, at inertial confinement fusion facilities. These detectors can absorb x-ray doses from the experiments in the order of 1-100 Gy, the effects of which are not accounted for in the previous detector calibrations. X-ray dose absorbed in the CR-39 has previously been shown to affect the track size of alpha particles in the detector, primarily due to a measured reduction in the material bulk etch rate [Rojas-Herrera et al., Rev. Sci. Instrum. 86, 033501 (2015)]. Similar to the previous findings for alpha particles, protons with energies in the range 0.5-9.1 MeV are shown to produce tracks that are systematically smaller as a function of the absorbed x-ray dose in the CR-39. The reduction of track size due to x-ray dose is found to diminish with time between exposure and etching if the CR-39 is stored at ambient temperature, and complete recovery is observed after two weeks. The impact of this effect on the analysis of data from existing CR-39-based proton diagnostics on OMEGA and the National Ignition Facility is evaluated and best practices are proposed for cases in which the effect of x rays is significant.

Spatial distribution of ion emission in gas-puff z-pinches and dense plasma foci

“…On shot no.1771, the CR-39 detector behind a 50 μm Al absorber recorded only a small spot which was created by protons or deuterons with energies above 2.3 MeV or 3.0 MeV, respectively (see figure 9(c)). The etching and the visibility of tracks could be influenced by high dose x-ray and electron irradiation [43][44][45]. Nevertheless, it was clear that the total number of >2MeV hydrogen ions emitted towards the anode was at least three orders of magnitude lower than towards the cathode.…”