Etched track dosimeters (ETDs) based on CR-39 foils are the most frequently used passive detectors for neutron personal dosimetry at various nuclear facilities. That applying a pre-treatment in carbon dioxide (hereafter, CO₂ pre-treatment) can improve the CR-39 detection sensitivity and enlarge the tracks is extremely valuable and warrants further investigation.

This study aims to investigate the effect of CO₂ pre-treatment on the sensitivity and the track size distributions of CR-39 detectors, and to obtain an optimal CO₂ pre-treatment condition.

A parametric study was conducted to evaluate the effect of CO₂ pre-treatments at different pressures and durations on CR-39 detectors. The detectors were firstly irradiated by a standard ²⁵²Cf neutron source, delivering a personal dose equivalent H_p(10) of 2 mSv. Then, the detectors were subjected to carbon dioxide treatment prior to undergoing chemical etching for durations ranging from 6 h to 168 h at partial pressures varying between 0.1 MPa to 1.6 MPa. Finally, the correlation between detector sensitivity and pre-treatment condition was obtained by analyzing the number of registered tracks and track size distribution under each pre-treatment condition.

The obtained results indicate that the CO₂ pre-treatment significantly improves sensitivity and maximum track size, with the sensitivity increasing by up to 870% and the maximum track size expanding from 20 μm to 40 μm. The sensitivity increases linearly with pre-treatment pressures, and the saturation point of the maximum track size appears around 40 μm. As the time and pressure continue to increase, the neutron spectrometry information contained in the track size distributions will be erased, the optimal sensitivity for CR-39 to retain the spectral information in the track size distributions is 6.25 tracks·mm^-2·mSv^-1.

This study is of significance for improving the sensitivity of CR-39 detectors in neutron dosimetry and selecting CO₂ pre-treatment conditions, providing a processing method to enhance the track readability whilst preserving the spectral information in the track distributions for practical applications of CR-39 detectors in neutron dosimetry and spectrometry.