Lung Kwang Pan

Optimization for solidification of low-level-radioactive resin using Taguchi analysis

Solidification of low-level-radioactive (LLW) resin was optimized using Taguchi analytical methodology. The ingredients in LLW mortar which caused the solidification of cement were evaluated through consecutive measurements of the effects of various concentrations of ingredients. Samples selected according to Taguchis method were separated into 18 different categories and measured at the 7th, 21st, and 28th day after fabrication on developing effects. Evaluations of the various samples focused on whether the compressive and bending strength fulfilled the special criteria of the Taiwan Power Company (TPC). Similar results indicated that both furnace slag and fly ash were the dominant material resulting from the solidification of LLW mortar. The superior combination was obtained as furnace slag 24 wt.%, fly ash 24 wt.%, and cement 8 wt.% to mix 24 wt.% of resin with 20 wt.% of water, to fulfill the contemporary requirements of TPC.

Optimizing the TLD-100 readout system for various radiotherapy beam doses using the Taguchi methodology

The TLD-100 readout system was optimized for various radiotherapy beam doses using the Taguchi method. The radiotherapy beam was produced by a Varian 21EX linear accelerator (LINAC) at 6MV. The beam doses were 50, 100 and 150cGy, and the measured data in each group were averaged from three TLD-100 chips. A total of nine combinations of four parameters were arranged, in the manner suggested by Taguchi. The four parameters were defined as initial temperature, heating rate, preheat time and maximum set temperature of the readout system during TLD reading. The loss function eta adopted herein was specifically defined to satisfy the requirements of both sharp linearity and good reproducibility of the TLD reading at various radiotherapy beam doses. The optimized values were: (1) 50( composite function)C for initial temperature, (2) 3 (degrees C)/s for heating rate, (3) 5 min for the TLD preheat time and (4) 250 degrees C for the maximum temperature for TLD reading. Additionally, the parameters that dominated the TLD readout were: (1) initial temperature, (2) heating rate and (4) maximum temperature setting for TLD reading; and the minor parameter was (3) TLD preheat time before reading. The interactions among the dominant parameters were also studied: no significant cross interaction occurred between initial temperature and heating rate or between initial temperature and maximum temperature. However, a complex cross-interaction existed between optimal heating rate and maximum temperature.

Trace elements of Taiwanese dioscorea spp. using instrumental neutron activation analysis

Abstract Twenty-two varieties categorized into six distinct species of dioscorea spp. had their concentration of trace elements evaluated by instrumental neutron activation analysis. The various dioscoreas were planted in the same plantation area to effectively suppress the diversity from different planted land, thus, the disagreement between each trace element was concluded from the nature of various species of dioscoreas themselves. Nineteen trace elements were verified and a quantified index, AT, was introduced to help classify the elements. A smaller AT indicated a close consistency of the concentration for specific trace element in various dioscorea . Thus, K, Zn, and Rb were in Group 1, which had the minimum ATs, Cl, Na, Mg, Fe, Mn, Br, and Co were in Group 2, which had the medium ATs, while the remaining of the trace elements, V, As, Sb, Cu, Se, Al, La, Sc, and Sm were all in Group 3, which had the maximum ATs. The different ATs and various species of dioscorea s were also discussed.

Bromine and iodine in Chinese medical herbs determined via epithermal neutron activation analysis

Nineteen natural herbs and two prescriptions prepared from mixed herbs were analyzed via epithermal neutron activation analysis (ENAA) to evaluate their bromine and iodine concentration. Traditional medical doctors prescribed the samples presented in this work to most Taiwanese children for strengthening their immune systems. Empirical results indicated a wide diversity of bromine in the samples. Yet, the iodine concentration was only around one to tenth or twentieth of the bromine. The maximum daily intake (MDI) for various medical herbs was also widely diversified from one to tenfold on the basis of various criteria. The minimum detectable concentration (MDC) of bromine and iodine found was 0.42±0.14 ppm and 0.067±0.016 ppm, respectively. Compared to that from conventional thermal neutron activation analysis (NAA) for a similar evaluation, the extremely low MDC obtained here was attributed to the large amount of thermal neutron absorption during sample irradiation.

Estimation of Burnup in Taiwan Research Reactor Fuel Pins by Using Nondestructive Techniques

A nondestructive measurement of spent fuel pins from the Taiwan Research Reactor has been performed at the Institute of Nuclear Energy Research. The analysis is based on a simplified balance equation for integrated flux and a series of one-group burnup-dependent microscopic cross-section libraries. A semiempirical test is used for evaluating the burnup values of two different kinds of spent fuel pins [natural uranium (0.7% [sup 235]U) and enriched uranium (7.0 % [sup 235]U)] by the [sup 134]Cs/ [sup 137]Cs activity ratio. Results are compared with radio-chemical burnup measurements. The agreement is within 3.8%, which verifies the accuracy of this method. The results are also compared with a theoretical estimation by the ORIGEN-II code. This indicates that the ORIGEN-II codes library might have an overestimated [sigma][sub a]([sup 133]Cs), which leads to a [sup 134]Cs/[sup 137]Cs ratio that would result in a burnup value [approximately]24 to 35% lower than the measured data.

Distribution of spatial photoneutrons inside a 70 kg water phantom via neutron activation analysis

This study evaluated spatial Phi(th) inside a 70kg water phantom using the NAA method. Fifty indium foils were placed inside the water phantom and exposed under 15MV LINAC for 2.5min to yield the 10Gy X-ray dose. The Phi(th) value at the isocenter of the water was 1.03x10(6)ncm(-2)/Gy-X, and the maximum quantity of Phi(th) appeared at the water surface along the z-axis, 3.99x10(6)ncm(-2)/Gy-X. The thermal neutron dose at isocenter of the water phantom occupied approximately 0.151% of the whole photo and neutron dose.

Superheated-liquid-droplet technique for measuring alpha decays in uranium solutions

Experimental and computational studies of the superheated-liquid-droplet (SLD) method for measuring alpha decays in uranium solutions have been conducted. The standard uranium solutions were mixed with the SLD emulsion. An alpha particle upon intersecting a liquid freon-12 droplet may evaporate the droplet, and form a bubble. The acoustic wave accompanying the bubble formation can be recorded by a piezoelectric sensor. The number of bubbles recorded represent a measurement of the alpha activity. The measured bubble nucleation rate was more than tenfolds of the theoretical estimation based on the model assuming that the uranium nuclides are homogeneously distributed through out the emulsion. To account for the dramatic di⁄erence between the measured result and the theoretical estimation, a revised theoretical model was proposed. The revised model assumes that uranium nuclides preferentially adhere to the surface of freon-12 droplets. Based on the revised model, the estimated eƒciencies of detecting alpha decays increase to &50% which agree well with the measured results. ( 1999 Elsevier Science B.V. All rights reserved.

Evaluation of effective dose for a patient under Ga-67 nuclear examination using TLD, water phantom and a simplified model

This study evaluated the effective dose of Ga-67 for a patient undergoing Ga-67 citrate nuclear examination by applying thermoluminescent dosimeter (TLD) technique and an indigenous water phantom. The Ga-67 radionuclide remaining in the body inevitably generated a measurable internal dose even though gamma camera scanning took only minutes to complete the clinical examination. For effective simulation of the cumulated effective dose for a patient undergoing examination, 150 TLDs were placed inside the water phantom for 6 days to monitor the gamma ray dose from the distributed Ga-67 citrate solution. The inserted TLDs represented internal organs, and the effective dose was calculated according to data in the ICRP-60 report. The water phantom was designed to model the body of a healthy human weighing 70 kg, and the water that was mixed with Ga-67 citrate solution was slowly replaced with fresh feed water to yield the required biological half life of the phantom. After continuously feeding in fresh water throughout the 6 days of TLD exposure, the TLDs were analyzed to determine the effective doses from the various biological half lives of the phantom. The derived effective dose of 185 MBq Ga-67 citrate solution for male/female (M/F) was 10.7/12.2, 10.7/12.0, 8.7/9.9 and 6.0/6.8 mSv, of biological half lives of 6.0, 4.5, 3.0 and 1.5 days, respectively. Although these experimental results correlated well with earlier empirical studies, they were lower than most calculated values. The cumulated uncertainty in the effective dose was 12.5–19.4%, which was acceptable in terms of both TLD counting statistic and reproducibility.

Use of superheated liquid dispersion technique for measuring alpha-emitting actinides in environmental samples

Abstract This paper presents a novel fast screening technique of measuring concentrations of alpha-emitting actinides in environmental samples. This novel technique is called superheated liquid dispersion (SLD), which involves dispersing fine superheated liquid (e.g. Freon-12) droplets into a mixture of glycerin and the actinide-containing chemical extractant. The interactions between alpha particles and superheated liquid droplets trigger bubbles. Therefore, one may relate the number of bubbles to the actinide concentration in the sample. The results obtained from the computer simulation and the experiment support the above claim.

A Feasibility Study of Gross Alpha Counting in Environmental Samples Using a Superheated-Liquid-Droplet Technique

AbstractA feasibility study of gross alpha counting in real environmental samples using the superheated-liquid-droplet (SLD) technique has been carried out. To find an alternative technique as a fast screening for gross alpha counting in environmental samples, various samples acquired from real groundwater and soil were mixed with the SLD emulsion. The intersections of alpha particles with the superheated liquid Freon-12 droplets trigger the vaporization of the droplet and form bubbles. The acoustic wave accompanying the bubble formation can be recorded by a piezoelectric sensor. The number of bubbles recorded represents a measurement of the gross alpha counting. These results are reasonable when compared with those obtained using the conventional methods. However, for practical application, the SLD fabrication and correlated counting process still need to be further modified.