Jiunn-Hsing Chao

Determination of 135Cs by neutron activation analysis

Determination of 135Cs and 137Cs/135Cs ratio by neutron activation method is introduced in this study. Cesium isotopes in various radioactive and radwaste samples were chemically purified before neutron irradiation. 135Cs and the corresponding 137Cs/135Cs ratio were determined by measuring the characteristic gamma rays emitted from the activated nuclide 136Cs. Experimental results show that the neutron activation is a practical analytical method for determination of 135Cs and is convenient for researchers in a nuclear-based facility. The isotopic ratio can be used to explain the possible origins as well as age of a radioactive or radwaste sample.

Low-level determination of 129I in environmental samples by neutron activation

Low-level determination of 129I and 129I/127I ratio in environmental samples by neutron activation is described. The iodine was chemically separated from kombu (Laminaria japonica) samples by solvent extraction and subsequent reduction to an inorganic form prior to neutron irradiation, the activated 126I and 130I were measured by a germanium gamma-ray spectrometer after irradiation with a cooling time of 16 h. The lowest detection amount is estimated to be 10−3 Bq or a corresponding 129I/127I ratio of 10−11. The average 129I/127I ratio for kombu samples, collected from local markets, was found to be 10−10, lower than those of terrestrial samples reported elsewhere.

A CsI(Tl) scintillating crystal detector for the studies of low-energy neutrino interactions

Abstract Scintillating crystal detector may offer some potential advantages in the low-energy, low-background experiments. A 500 kg CsI(Tl) detector to be placed near the core of Kuo-sheng Nuclear Power Station in Taiwan is being constructed for the studies of electron–neutrino scatterings and other keV–MeV range neutrino interactions. The motivations of this detector approach, the physics to be addressed, the basic experimental design, and the characteristic performance of prototype modules are described. The expected background channels and their experimental handles are discussed.Scintillating crystal detector may offer some potential advantages in the low-energy, low-background experiments. A 500 kg CsI(Tl) detector to be placed near the core of Nuclear Power Station II in Taiwan is being constructed for the studies of electron-neutrino scatterings and other keV−MeV range neutrino interactions. The motivations of this detector approach, the physics to be addressed, the basic experimental design, and the characteristic performance of prototype modules are described. The expected background channels and their experimental handles are discussed. PACS Codes: 14.60.Pq; 29.40.Mc

Using medical accelerators and photon activation to determine Sr/Ca concentration ratios in teeth.

This paper describes a photon activation method, studied by using two medical accelerators (energies: 15 and 18 MeV) as photon sources, for determining Sr and Ca levels and Sr/Ca ratios in tooth samples. The radionuclides formed by various photonuclear reactions were measured and identified using a gamma-spectrometry with HPGe detection system. The yields of the corresponding photonuclear reactions and the detection sensitivities for the alkaline earth metals (e.g., Ca, Sr) were surveyed and estimated in relation to the radiation dose. The minimum detectable amount of Sr was estimated to be less than 1 microg g(-1), allowing the Sr/Ca ratios in teeth to be determined conveniently. The Sr/Ca ratios in deciduous and permanent tooth samples obtained from local dental clinics were 0.390 and 0.565 mg g(-1), respectively. This photon activation method of determining Sr/Ca ratio in bones and teeth using medical accelerators for cancer treatment is thought to be useful also in biological and archaeological studies.

Preconcentration of Trace Elements from Natural Water for Analysis by Neutron Activation

The coprecipitation of trace elements from natural water samples by Pb and Bi salts of pyrrolidine dithiocarbamate or Bi salts with oxine and thionalide was studied with radiotracers. The concentration of the trace elements in samples of sea water was studied by coprecipitation followed by neutron activation analysis.

Sequential extraction separation for determination of technetium-99 in radwastes by ICP-MS

An approach based on sequential extraction separation and the subsequent ICP-MS measurement was introduced to determine 99Tc in radioactive wastes. The radwastes were firstly alkaline-fused and the 99Tc was separated by a sequential solvent extraction prior to ICP-MS measurement. NaDDC was selected as a chelation reagent in the solvent extraction processes. The influence of HCl and matrix concentration on the recovery yield and the effectiveness of removing isobar and unwanted radionuclides, such as 137Cs, 54Mn, 60Co and 110mAg, were evaluated. The designed sequential extraction procedure was optimized by an extraction experiment. The proposed technique is proven to be a simple and practical alternative for 99Tc determination in low-level radioactive wastes; chemical separation of 99Tc can be simplified and preconcentration such as precipitation and/or ion exchange, before the solvent extraction, can be excluded.

Optimization of in situ prompt gamma-ray analysis of lake water using a HPGe-252Cf probe

Abstract A self-designed HPGe-252Cf probe based on neutron-induced prompt gamma-ray techniques is described in this work to identify the optimum conditions of various-intensity 252Cf neutron sources employed in the in situ measurement of elemental concentrations in water. 252Cf neutron sources weighing 1.3, 8.0, 44 and 260 μg, respectively, were available for the laboratory test which simulated the field operation. The optimized operating depth for each neutron source was determined according to the minimum detectable concentration of chlorine measured by the 6111 keV prompt gamma ray, resulting in optimum neutron-source depths below the water line of 20, 35, 70 and 105 cm, respectively. The detecting efficiencies and detection limits for other elements were evaluated and calculated at optimized conditions to judge potential application of the probe in a rapid field survey.

Analysis of I-129 in radwastes by neutron activation

Abstract Determination of 129I activity of low-level waste has become important from the standpoint of radiation safety and environmental concern. The 129I generated from power plants could be released into the environment through the subsequent fuel reprocessing and waste disposal. In order to minimize this impact, the concentrations of 129I and some affiliated radionuclides in the wastes to be disposed of should be determined and put in compliance with the stipulated regulations. In this work, neutron activation analysis is proposed to determine 129I/127I and 129I in radwastes. The long-lived 126I, activated from 127I, is selected to replace 128I as an indicator of stable iodine. Long-term neutron irradiation and γ-ray counting are permitted and the related detection limit can be improved. In addition, the proposed method has related advantages of low-counting interferences and convenience for chemical operation over traditional methods; these make it a practical alternative for analyzing 129I in radwastes in a facility near a research reactor.

Neutron-induced gamma-rays in germanium detectors

Abstract A 10% HPGe detector was irradiated with thermal neutrons with a fluence of 4 × 10 6 n/cm 2 to observe neutron-induced gamma-rays in the detector itself; these rays are considered to be the main source of spectral background in neutron in-beam experiments. The significances of the observed peaks in the spectrum were described in terms of both their intensities and detectabilities relative to the 596 keV peak. The contributions of prompt and delayed gamma-rays to the spectral background and the activities remaining in the detector after irradiation are discussed.

Relationship between radioactivity of radium and concentrations of barium and lead in hokutolite

Hokutolite consists of barite (BaSO(4)) and anglesite (PbSO(4)), and contains significant amounts of radium isotopes as a radioactive mineral. Photon activation and gamma-ray spectrometry were employed to determine Ba, Pb and (226)Ra contents in hokutolite samples and to investigate the correlation between (226)Ra activity and both Ba and Pb content. (226)Ra activity in 30 hokutolite samples were estimated in the range of 40-65Bq/g and was positively related to Ba content (r=0.859, p<0.001), but independent of Pb content (r=-0.236, p=0.217). Experimental results implied that (226)Ra preferably precipitated with Ba over Pb. The (226)Ra activity in hokutolite from the Peitou Hot Spring was experimentally estimated based on the Ba/Pb ratio and expressed as (226)Ra (Bq/g)=14.67 (Ba/Pb)(molar)+14.13.