Evaluation of the sensitivity function V for registration of α-particles in PADC CR-39 solid state nuclear track detector material

Distribution of alpha particle tracks on CR-39 detector in radon diffusion chamber

V-function to investigate tracks of the alpha particle irradiated CR-39 detector

A computer program was developed to calculate the light scattered from an assembly of alpha particle tracks in a PADC film. The tracks were randomly seeded on the film to simulate the irradiation by alpha particles emitted by the naturally occurring radon gas and its short-lived progeny. The ray-tracing method was applied to simulate light propagation through the tracks. The angular distribution of scattered light showed a strong maximum between 10° and 20°. The distribution of the scattered light was found to be independent of the equilibrium factor between radon and its progeny. The total amount of scattering increased linearly with the track density and quadratically with the removed layer during chemical etching of the irradiated PADC film.

Light scattering from an assembly of tracks in a PADC film

The computer programs TRACK_TEST and TRACK_VISION were previously developed to model profiles and optical appearances of tracks developed in solid-state nuclear track detectors. The programs were based on a track development model that involved the bulk etch rate Vb and the track etch rate Vt or the V function (i.e., Vt/Vb). The present work reported our work to update and modify these two programs. In the revised TRACK_TEST, two new V functions were added and enabled. Sample results for the CR-39 detector obtained using the three original and the two new V functions were compared. Discrepancies were within ~10% and 1 MeV, respectively. Another major revision of TRACK_TEST was to enable calculations for the Makrofol detector. In the revised TRACK_VISION, the two new V functions, as well as the option for the Makrofol detector, were also added. The experimental results on the Makrofol detectors were obtained (irradiated with 3.6-MeV alpha particles under normal incidence and then etched to achieve a removed detector thickness of 30 μm) for comparisons with the modeled results using the revised TRACK_VISION. The track diameters obtained from the experiment and model were 24.7 and 23.2 μm, respectively. Moreover, a bright area in the central parts, together with an outer dark ring, were present in both the simulated and experimental tracks. The track-opening diameters and the general optical appearances of the tracks were in good agreement.

https://www.mdpi.com/2073-4360/13/4/560/pdf

Updates to TRACK_TEST and TRACK_VISION Computer Programs

In the present work, the V function (=  V t /V b , ratio between the track etch rate and the bulk etch rate) of alpha particles in the CR-39 detector was determined. CR-39 detectors were irradiated with alpha particles with different energies in the range 0.5 to 5.1 MeV. After irradiation, the detectors were etched in a 6.25 N aqueous solution of NaOH maintained at 70 °C by a water bath for 15 min, which was much shorter than the normally employed etching time. Atomic Force Microscopy (AFM) was used to measure the track lengths in order to calculate V. The corresponding alpha energies were converted into ranges in the CR-39 detector using the SRIM software. Our V values were based on very short etching time and direct measurements, so the determined V function should be more accurate.

J.P.Y. Ho

Papers

Determination of the V Function for CR-39 by Atomic Force Microscope