Title: Experimental determination of parameters of tracks on solid state nuclear track detectors from alpha particles with different incident energies and angles
The use of solid state nuclear track detectors (SSNTDs) has already become a well-known technique which has been widely applied in monitoring concentrations of radon gas by recording their emitted alpha particles. The development of methods for long-term integration measurements of radon progeny concentrations in air based on alpha spectrometry employing SSNTDs, however, are still being explored. To develop the method, determining the dependencies of track parameters on incident energies and angles of alpha particles would be an essential procedure. In the present study, the main task is to determine the major axes and minor axes for the tracks of alpha particles with different incident energies and angles for SSNTDs (CR-39 and LR 115 detectors) experimentally. For this purpose, the first step is the experimental determination of alpha particle energy losses in air. Measurements of the track parameters critically depend on the thickness of the removed layer of the SSNTDs during etching. However, based on observations using scanning electron microscope (SEM) and surface profilometry (using Form Talysurf), inhomogeneities in the thickness of the unetched and etched LR 115 detectors have been identified. These features are studied and the results show that LR 115 detectors cannot be assumed to be homogeneous in general. In order to obtain a large set of precise data for the major axes and minor axes of the alpha tracks, fast and precise measurements of the thickness of the active layers of the SSNTDs are needed. It is found that the thickness of the removed layer of an etched LR 115 detector can be measured accurately and rapidly using Energy Dispersive X-Ray Fluorescence (EDXRF). It is also found that stirring during the etching process can increase the bulk etch rate of the LR115 detector. The latter can help shorten the etching time and obtain the major axes and minor axes of the alpha tracks more efficiently. For the main task, the major axes and minor axes for the tracks of alpha particles with different incident energies and angles on the CR-39 and LR 115 detectors have been determined. The tracks on the CR-39 detectors were systematically irradiated by alpha particles with energies from 1 to.5 MeV and incident angles from 40° up to 90° and with specific thickness of removed layers. A set of new coefficients for a chosen V function (which is the ratio between the track etch rate Vt to the bulk etch rate Vb) by fitting the experimental data with the data generated with a track growth model incorporating the chosen V function. For the tracks on the LR 115 detectors, the experimental procedures were similar to those for the CR-39 detectors (i.e., incident energies from 1 to 5 MeV and incident angles from 30° up to 90°, and with specific thickness of removed layers). The functional form of the Durrani-Green’s V function (Durrani et al., 1999) with a set of new coefficients was used to fit the parameters. The experimental data were found to fit the respective models of V function satisfactorily…
Contents
Chapter 1 Introduction
Chapter 2 Literature review
2.1 Radon and alpha particles
2.2 Track Formation Mechanism in SSNTDs
2.3 Track parameters measurements
2.4 Stopping power
Chapter 3 Methodology
3.1 Experimental determination of energy losses of alpha particles in air
3.2 Study of inhomogeneities in thickness of LR 115 detector with SEM and Form Talysurf
3.3 Effects of stirring on the bulk etch rate of the LR 115 detector
3.4 Using EDXRF to measure the thickness of removed layer from etching of the LR 115 detector and the CR 39 detector
3.4.1 Active layer thickness measurements for LR 115 detectors
3.4.2 Etched layer thickness measurements for CR-39 detectors
3.4.3 Measurements using Energy Dispersive X-Ray Fluorescence (EDXRF)
3.5 Experimental determination of major axes and minor axes for
the tracks from alpha particles with different incident energies
and angles 213.5.1 Experimental measurements for the LR 115 detector
3.5.2 Experimental measurements for the CR-39 detector
Chapter 4 Results and Discussion
4.1 Experimental determination of alpha particle energy losses in air
4.2 Study of inhomogeneity in thickness of LR115 detector with SEM and Form Talysurf
4.3 Effects of stirring on the bulk etch rate of LR115 detector
4.4 Using EDXRF to measure the thickness of removed layer from etching of LR115 detector and CR39 detector
4.4.1 LR115 detector
4.4.2 CR39 detector
4.5 Experimental determination of major axes and minor axes for the tracks of alpha particles with different incident energies and angles for LR 115 detector
4.5.1 Experimental results and the modified V function
4.5.2 Corrections for the residual active layer thicknesses
4.5.3 Generation of databanks for various thickness of the removed layer
4.6 Experimental determination of major axes and minor axes for the tracks of alpha particles with different incident energies and angles for CR-39 detector
4.6.1 Experimental data and fitting using a track growth model
4.6.2 Corrections for different bulk etch rates
4.6.3 Generation of databanks for various thickness of the removed layer
4.7 Interpolation program for experimental data from the databanks
Chapter 5 Conclusions
References
Appendix A: Interpolation program
Appendix B: Experimental data of major & minor axes for SSNTDs
Appendix C: Images of the real tracks in CR-39 and LR 115 detectors under the optical microscope
Author: Yip, Wai Yi
Source: City University of Hong Kong
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