J.P.Y. Ho

Effects of stirring on the bulk etch rate of CR-39 detector

Abstract It is well established that the bulk etch rates for solid state nuclear track detectors are affected by the concentration and the temperature of the etchant. Recently, we found that the bulk etch rate for the LR 115 detector to be affected by stirring during etching. In the present work, the effects of stirring on the bulk etch rate of the CR-39 detector is investigated. One set of sample was etched under continuous stirring by a magnetic stirrer at 70°C in a 6.25 N NaOH solution, while the other set of samples was etched without the magnetic stirrer. After etching, the bulk etch thickness was measured using Form Talysurf PGI (Taylor Hobson, Leicester, England). It was found that magnetic stirring did not affect the bulk etch of the CR-39 detector, which was in contrast to the results for the LR 115 detector.

A fast method to measure the thickness of removed layer from etching of SSNTD based on EDXRF

Abstract Solid state nuclear track detectors are commonly used for measurements of concentrations of radon gas and/or radon progeny. All these measurements depend critically on the thickness of the removed 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 for the LR 115 detector. We propose here to measure the thickness of the removed layer by using energy-dispersive X-ray fluorescence spectrometry. In the present work, a reference silver nitrate pellet is placed beneath the LR 115 detector, and the fluorescence X-ray intensity for silver is then measured. We have found a linear relationship between the X-ray intensity and the thickness of the removed layer for LR 115 detector. This provides a fast method to measure the thickness of removed layer from etching of LR 115 detector. However, this method was found to be inapplicable for the CR-39 detector. Therefore, alternative methods have yet to be explored for the CR-39 detector.

Comparison among alpha-particle energy losses in air obtained from data of SRIM. ICRU and experiments

Abstract In the present work, we compare the alpha-particle energy losses in air obtained from experiments and from stopping powers given in Report 49 of the International Commission of Radiation Units and Measurements (ICRU49) and Stopping and Range of Ions in Matter-2000 (SRIM-2000). The alpha energy losses have been experimentally determined for both 241Am and 230Th sources using alpha spectroscopy; such losses are observed to deviate significantly from the calculated ones. The deviations suggested that the stopping powers given by SRIM-2000 might be too high and those given by ICRU might be even higher.

Deposition fractions of 218Po in diffusion chambers

After radon gas diffuses into a diffusion chamber, 218Po will be formed. Due to its short half-life, a fraction f of 218Po decays before deposition onto available inner surfaces of the chamber, and the deposition fraction (1-f) represents the part which decays after deposition. In the present work, f has been experimentally determined for six diffusion chambers with different materials and dimensions using the radial distribution of track density on the LR115 detectors inside the diffusion chambers. For all the six studied diffusion chambers, f was found to be approximately 0.4. Therefore, the deposition fraction does not depend on the shape and dimensions of the diffusion chambers, the surface to volume ratios or the internal surface materials of the diffusion chambers.

Feasibility and limitation of track studies using atomic force microscopy

Atomic force microscopy (AFM) has been employed to investigate characteristics of tracks of heavy charged particles in solid state nuclear track detectors (SSNTDs). In the present work, we have performed simulations of the track structures revealed by AFM based only on geometrical considerations of the tracks and two types of probes (the ultralever and the ultrahigh aspect ration probe). The purpose of this work is to determine the limitations and constraints of the AFM technique when it is applied to track investigations. The ultralever has comparable dimensions as the tracks in SSNTDs etched for a short time. In some cases, the ultralever is too large or its geometry does not match those of the tracks, so these tracks cannot be scanned properly. In most cases, the ultralever can measure the diameter of the tracks with a rather high precision, but measurements of the depths can be misleading if the track depths are larger than the length of the ultralever. The ultrahigh aspect ratio probe, with an aspect ratio better than 10:1, can record tracks with rather high accuracy if the track depths are not larger than probe length. The technique involving the mounting of nanotubes on AFM tips, which has become available in recent years, should be able to record almost perfect track profiles.

Study of inhomogeneity in thickness of LR 115 detector with SEM and Form Talysurf

Abstract Long-term measurements of radon progeny concentrations using Solid-State nuclear tract detector are being actively explored. These measurements depend critically on the thickness of the removed layer during etching. Scanning electron microscope (SEM) observations have identified irregularities in etched LR 115 detectors, such as detachment of the active layer from the substrate and formation of air gaps in the substrate. After discarding these irregularities, by using “Form Talysurf” surface profile measurements, the thickness of the active layers for the LR 115 detector are found to be 11.8±0.2 and 5.0±0.4 μm before and after 2 h of etching, respectively. The coefficient of variation has thus risen from 1.7% to 8.0% on etching. The increased inhomogeneity is explained by the formation of track-like damages, which have been observed using Form Talysurf, SEM, optical microscope and atomic force microscope. With this relative large coefficient of variation, the thickness of the active layer in the LR 115 detector cannot be assumed to be homogeneous in general, and the associated uncertainties should be considered carefully when the detector is used for alpha spectroscopy.

Sensitivity of LR115 detector in diffusion chamber to 222Rn in the presence of 220Rn

Determination has been made of the sensitivity of LR115 type 2-track detectors (in units of m) to 222Rn, measured in the presence of 220Rn. Measurements have been made by means of a widely used diffusion chamber while Monte Carlo simulations have also been conducted. The experimentally derived sensitivities for 222Rn and 220Rn were found to be 0.470+/-0.022 and 0.486+/-0.042 m, respectively. For Monte Carlo simulations, the sensitivities to 222Rn gas were found to range from 0.618 x 10(-2) m (assuming that all 218Po progeny decay before deposition onto the internal walls of the diffusion chamber) to 0.405 x 10(-2) m (assuming that all 215Po progeny are deposited on the internal walls of the same containment vessel before decaying). The sensitivity to 220Rn gas of 0.465 x 10(-2) m found from Monte Carlo simulations agrees to within uncertainty with experimental findings. The experimentally derived sensitivity value for 222Rn indicates that 30% of the 218Po progeny decay before deposition onto the internal walls of the diffusion chamber.

Enhancement of hrp binding on plasmatreated ultra-high molecular weight polyethylene

Summary form only given. Immunoassay technique is one of the actively researched areas since reliable, low cost and sensitive diagnostic immunoassay systems are required for public health care. The enzyme-linked immunosorbent assay (ELISA) is common technique to detect diseases such as HIV or hepatitis virus. The aim of the present work is to modify the surface of ultra-high molecular weight polyethylene (UHMWPE) by plasma immersion ion implantation to increase the number of the specific active enzyme binding sites on the polymer surface. The specimens are incubated in horseradish peroxidase (HRP) overnight and washed by 10 mM PO4 buffer six times. The quantity of HRP can be changed by adding TMB (HRPs substrate) on the polyethylene surface. The optical densities of the treated and untreated samples are monitored and compared. Our results show more active HRP on the plasma-treated PE. In addition, our tests show highly stable and reproductive results and demonstrate that plasma immersion ion implantation is a viable technique

Deposition of Iron-Containing Single-And Multi-Layered Amorphous Carbon Films using Dual-Target Filtered Pulsed Cathodic Vacuum Arc (FCVA)

Summary form only given. The filtered pulsed cathodic vacuum arc (FCVA) technique is designed to produce plasmas from solid targets. Single element target is traditionally employed, but it cannot satisfy the needs when two or more elements are needed for plasma implantation or deposition. Introducing gases into the chamber and using alloys or composite targets are some of the solutions. These methods, however, have some problems such as difficulty to produce films with precise composition and it is not easy to prepare composite targets. In this paper, filtered pulsed cathodic vacuum arc deposition utilizing dual targets is presented. The approach is attractive because we are able to control the firing sequence of the targets to produce various combinations of plasmas. Using this unique technique, we have synthesized iron-containing single- and multi-layered amorphous carbon films. The films that are characterized by scanning electron microscopy (SEM), energy-dispersive X-ray spectrometry (EDS) and transmission electron microscopy (TEM) exhibit excellent properties

Suppression of Nickel Out-Diffusion from Porous Nickel-Titanium Shape Memory Alloy by Plasma Immersion Ion Implantation

Summary form only given. Porous nickel titanium is a promising material for medical application not only because of its super elasticity and shape memory effect but also the porous structure which may enhance bone growth due to the increased surface area. It is thus especially suitable for bone tissue in-growth and fixation of biomedical implants. However, like its dense counterpart, Ni leaching from the materials causes health concern. Thus, in order to suppress Ni diffusion from the materials to body fluids and tissues in humans, a diffusion barrier or similar structure must be introduced. In this work, we produced this diffusion barrier layer by oxygen or nitrogen plasma immersion ion implantation (PIII). In vitro tests were conducted by immersing the plasma-treated NiTi into simulated body fluid (SBF) at 37plusmn0.5degC for 5 weeks and the resulting SBF was analyzed for Ni and Ti using inductively-coupled plasma mass spectrometry (ICMPS). Our results show that Ni leaching is significantly mitigated by both nitrogen and oxygen PIII.