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Title: Experimental determination of alpha-particle track depths in CR-39 detectors
Other Titles: Zai CR-39 tan ce qi zhong alpha li zi jing ji chang du zhi ce liang fang fa
Zai CR-39 tan ce qi zhong α li zi jing ji chang du zhi ce liang fang fa
在 CR-39 探測器中 alpha 粒子徑跡長度之測量方法
在 CR-39 探測器中 α 粒子徑跡長度之測量方法
Authors: Ng, Man Fong (吳文鳳)
Department: Dept. of Physics and Materials Science
Degree: Master of Philosophy
Issue Date: 2006
Publisher: City University of Hong Kong
Subjects: Alpha rays -- Measurement
Particle tracks (Nuclear physics) -- Measurement
Notes: CityU Call Number: QC793.3.T67 N45 2006
Includes bibliographical references (leaves 82-86)
Thesis (M.Phil.)--City University of Hong Kong, 2006
vi, 86 leaves : ill. (some col.) ; 30 cm.
Type: Thesis
Abstract: Methods for long-term monitoring of the 222Rn gas itself are well established, such as through the use of solid-state nuclear track detectors (SSNTDs) (see e.g., Nikolaev and Ilic (1999) for a survey). However, methods for long-term monitoring of the concentrations of radon progeny are still being explored. One approach is based on alpha spectrometry employing SSNTDs. To develop the method, determining the dependence of the alpha-particle track parameters on incident energies would be a critical step. In the present study, the main task is to experimentally determine the heights of alpha-particle tracks in SSNTDs formed with different alpha-particle energies. The three methods proposed and studied in the present project to determine the track heights are the surface profilometry method, cross section method and replica method. Before track height measurements, the detectors were irradiated with different alpha energies and then etched in a 6.25 N aqueous solution of NaOH at 70 oC for different etching durations. The surface profilometry method involved directly scanning the alpha-particle tracks using the Form Talysurf PGI Profilometer with a 90o conisphere shaped stylus. By considering the geometry of the stylus, 4-MeV alpha-particle tracks with etching duration of 15 h and 18 h were used to demonstrate the feasibility of this method in the track height measurement. The results showed that the track height can be truly reflected if the ratio S between the recorded track diameter and the recorded track depth is larger than 2. The second method, namely, the cross section method, is actually an optical method that reveals the track length from the cross section of the tracks observed under the optical microscope. Clear images of the cross sections of the tracks can be obtained after polishing the side of the detector. With the help of an image analyzing software, the track heights can be determined. Although the cross-section method is a direct and relatively straightforward method, it has limitations for very short tracks due to the limited resolution of the general optical microscope. The third method is based on surface profilometry to determine the track lengths in CR-39 detectors through measurements of their replicas. Replicas from different phases of track development (sub-micron scale tracks, sharp-phase and spherical-phase tracks) were produced first, and the Atomic Force Microscope (AFM) and Form Talysurf PGI Profilometor were then used to measure the replica heights. Good agreement was achieved between the replica method and cross section method for spherical-phase tracks but not for sharp-phase tracks. It was found that replicas for sharp phase tracks are easier to collapse or deform, so the surface profilometry method may not give correct results. As an example of application of the studies on the track heights, the heights of the sub-micron scale tracks have been used to derive a V function for the CR-39 detectors used in the present study.
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