Non-destructive measurement of active-layer thickness of LR 115 SSNTD

LR 115 is a solid-state nuclear track detector (SSNTD) based on cellulose nitrate and has been commonly used for measurements of concentrations of radon gas and/or radon progeny. These measurements depend critically on the removed thickness of the active layer during etching. However, the thickness of removed layer calculated using the etching period does not necessarily provide a sufficiently accurate measure of the thickness. For example, the bulk etch rate depends on the strength of stirring during etching. We propose here to measure the thickness of the active layer by using Fourier Transform Infrared (FTIR) spectroscopy, with the wave number at 1598 cm^-1 corresponding to the O-NO₂ bond. We have found an exponential decay relationship between the infrared transmittance at the wave number at 1598 cm^-1 and the thickness of the active layer for LR 115 detector. This provides a fast and non-destructive method to measure the thickness of removed layer from etching of LR 115 detector. © 2003 Elsevier Ltd. All rights reserved.