Search

Activity of 225Ac was measured by the digital anti-coincidence spectroscopy technique using a 4πα–γ detector configuration, composed of a sandwich type 4π plastic scintillator and Ge detectors. Ultrathin plastic scintillators were used for selective detection of α-particles emitted from 225Ac and its progenies, and the α-counting efficiencies of a 4π plastic scintillation detector for individual nuclides in the decay chain were determined as well. A list-mode multichannel analyzer was employed to record coincidence/anti-coincidence events for off-line analyses. The time difference distribution spectra revealed α-particle emission following 213Po decay without β-particle interference from 213Bi. • Selective α-particle detection using ultrathin plastic scintillators for 225Ac. • Individual α-efficiencies determined by 4πα(PS)–γ(Ge) anti-coincidence spectroscopy. • α-particles from short-lived 213Po(T 1/2 = 3.7 μs) detected without interference. • Effect of β-particle from 213Bi confirmed from γ–α/β time difference distribution. • Results were consistent with those obtained using the CN method with LSC. [ABSTRACT FROM AUTHOR]

Possible extended utilization of a 68 Ge/ 68 Ga source as a surrogate 18 F reference source was studied. Some effects and uncertainties might arise from the difference of constructions between chambers that were used in the source calibration and those practically in use. To extend utilization of the surrogate source, response ratio of real 18 F to 68 Ge/ 68 Ga sources were determined for three models of chambers. Monte-Carlo simulation using EGS5 code was also carried out to evaluate uncertainties expected. The present result shows that such a surrogate source would adapt to calibration even for chambers have with different construction from the reference chamber used as the determination of 18 F equivalent activity of the 68 Ge/ 68 Ga surrogate source. [ABSTRACT FROM AUTHOR]

A food inspection service system for home grown products or wild plants collected by individual consumers for self-consumption was implemented in Fukushima in Nov. 2012. About 500 NaI(Tl) scintillation spectrometers were distributed to 300 or more temporary testing laboratories which were set up in public halls or meeting places of the municipalities. The screening method for radiocaesium was adapted to the present inspection service system. The performance of the equipment under field conditions was evaluated using sampled data obtained by temporary testing laboratories. From the present results of evaluation the confidence of these inspections was confirmed. Totally about 550,000 food samples have been tested with a pass rate of 90% or more. [ABSTRACT FROM AUTHOR]

This study aimed to evaluate the applicability of non-destructive radioactivity measurement equipments for screening radio-cesium in whole foods without sample preparation procedures. Wild mushrooms and bamboo shoots were collected and studied using five different non-destructive radioactivity devices, and activity concentration was determined by conventional gamma-ray spectrometry using a Ge-detector. Linear regression analyses of activity concentrations were conducted and prediction intervals determined as uncertainties. Overall, non-destructive radioactivity measurement devices found to be suitable for screening radioactive cesium contamination in foods with an effective screening level. • Radioactive contamination in food was checked via non-destructive measurement. • Wild mushroom and bamboo shoot varieties were collected as specimens. • Results were compared with activity concentration from gamma-ray spectrometry. • Applicability of the non-destructive devices in radioactivity screening was tested. • Results indicated the devices to be befitting for the screening purpose. [ABSTRACT FROM AUTHOR]

Abstract: If high-energy beta particles are required for the efficiency determination of surface contamination monitors, wide area filtered 90Sr/90Y sources are commonly used instead of short-lived pure 90Y sources. In this work we show how the instrument efficiencies are dependent on filtering. Significant difference in the instrument efficiencies between filtered 90Sr/90Y and pure 90Y source was obtained due to spectral degradation of the beta emission spectrum. Changes in the β-particle spectra were investigated by the use of a plastic scintillation spectrometer and the anisotropy of β-particle fluences was examined to clarify the possible reason of such discrepancy. [Copyright &y& Elsevier]

Abstract: For diagnostic nuclear medicine, radiopharmaceuticals are labeled with γ-ray emitting nuclides. Routine activity measurements for these drugs are mainly performed with re-entrant ionization chambers. For radiotherapeutic applications, β-ray emitting nuclides are also used. Since very few gamma transitions are involved in these nuclides, an ionization chamber responds only to weak bremsstrahlung. In order to apply the re-entrant chamber method to routine activity assay for these β-ray emitting nuclides, detailed studies were carried out. It was determined that the response was strongly affected by the choice of thickness of the inner wall of the well in the measurement of high energy beta particle emitting nuclides. The geometrical dependences were successfully reduced. Accordingly, routine assay of radioactivity of 90Y therapeutic pharmaceuticals can be performed within an acceptable uncertainty with ordinary re-entrant dose calibrators that are commercially available and equipped in most hospitals. [Copyright &y& Elsevier]

Abstract: Quantitative performance tests and evaluations were carried out for large area reference sources fabricated by the ink-jet printing technique developed by NMIJ/AIST. The present tests were performed quantitatively with emphasis on uniformity, surface emission rate and long-term stability. Some techniques to minimize the self-absorption and to control the amount of radioactivity were established. The prototype source fabricated in this study safely satisfies the requirements specified in ISO 8769. [Copyright &y& Elsevier]

Abstract: Calibrations of instrument efficiency of surface contamination meters are usually made with extended reference sources which are standardized in terms of 2π surface β-particle emission rates from the source surface including backscattered particles. Extended sources supplied from various metrology institutes or calibration laboratories, but the source-types such as structure, preparation method, backing and covering materials vary between manufacturers. In this work first we show how the calibration results are dependent on the source type. Second, in order to clarify the possible reason of such discrepancy, we examined the isotropy of β-particle fluences by the use of a proportional counter and also observed the angular dependence of β-particle spectra by the use of small plastic scintillation spectrometer, where the source mount can rotate relative to the detector window at various obliquities. The discrepancy in the instrument-calibration of surface contamination meters, which are mainly used under the conditions of large source-to-detector geometry, can be explained. [Copyright &y& Elsevier]

Abstract: The National Metrology Institute of Japan (NMIJ) participated in the CCRI(II) Key-comparison of 85Kr activity measurement. The absolute internal gas-counting method was used, with a set of proportional counters of different length. The original 85Kr gas was diluted by a factor of 2×105 in order to achieve the suitable activity concentration for the proportional counters. A new dilution method was introduced, based on a large-volume balloon and gravimetric determination of the dilution volume with small uncertainties. [Copyright &y& Elsevier]

Abstract: NMIJ participated in the CCRI (II) key comparison of 55Fe activity measurement. A planar-type Si(Li) detector and a liquid-scintillation counter were used to calibrate the activity. The calibration result obtained by the Si(Li) detector agreed with that obtained by the liquid-scintillation counter using the CIEMAT/NIST method within uncertainty. The result was reported to the BIPM in 2006. The activity of 55Fe was also measured by using a 2π pressurized proportional counter. The result obtained by the 2π pressurized proportional counter agreed with the above results within uncertainty. The measurement by the Si(Li) detector was very simple and its procedure was a combination of conventional methods. The measurement by the liquid-scintillation counter is most popular to calibrate the activity of 55Fe. However the Si(Li) detector is also useful. [Copyright &y& Elsevier]

Abstract: The 4πβ−4πγ coincidence counting and 4π(β+γ) integral counting techniques were applied for the standardization of 152Eu and 154Eu. In these techniques, the β-detector is composed of two thin plastic scintillators sandwiching the source coupled with a slender photomultiplier tube. This β-detector was inserted into a large well-type NaI(Tl) scintillation detector for γ-ray detection, making a 4πβ−4πγ detector configuration. The results obtained by the above two techniques were in good agreement and consistent with the results of international comparisons. [Copyright &y& Elsevier]

Abstract: A method has been studied for the analysis of the pulse-height spectrum of a mixed 134Cs and 137Cs source obtained with a NaI(Tl) scintillation spectrometer. A peak fitting technique using maximum likelihood estimation was used with a specially developed deconvolution computer program. The activities obtained by this program were compared with the reference value in order to validate the analysis algorithm. Peak-area determination for NaI(Tl) scintillation spectrometry was successfully carried out even for spectra that included peak doublet and were recorded with low statistics. The results obtained by the maximum likelihood estimation agreed with each reference value within their statistical uncertainties. [Copyright &y& Elsevier]

We found that problems of α/β pulse-height overlapping can be solved by use of ultra-thin plastic scintillator sheets. In order to determine individual α-counting efficiencies for nuclides in the 223Ra decay-chain, the 4πα−γ anti-coincidence spectrometry technique was employed with a 4πα-γ detector configuration composed of a source sandwiched between ultra-thin plastic scintillator sheets and a Ge detector. This technique was applied to the activity measurements of 223Ra. This type of sandwich source is useful to prevent possible leakage of 219Rn gas. • Selective α-rays detection can be performed with very thin plastic scintillator. • Individual α-efficiencies can be determined by anti-coincidence spectrometry. • α-efficiency does not depend on energies when ultra thin scintillator was used. • The leakage of 219Rn can be avoided by source sandwiched with scintillators. [ABSTRACT FROM AUTHOR]

Alpha-particle discrimination using ultra-thin plastic scintillator sheets for measuring the activity of α-emitters under the existence of α- and β-emitters was investigated. 241Am, 32P and 223Ra were also used to evaluate the applicability of the present technique to α-emitters for medicine, and the self-absorption effect due to additives was investigated for validation. The results demonstrated that ≥95% of detection efficiency for α-particles emitted from 241Am with ≤1% β-contribution of 32P for the low carrier salt concentration solution. Regarding using 223Ra, ≥90% of α-efficiency was achievable with ≤1% β-contribution through sufficient dilution and selection of scintillator sheets of appropriate thicknesses. • α- and β-counting efficiencies of ultra-thin plastic scintillators were determined. • β-particle contributions can be reduced by pulse height discrimination. • Loss of α-efficiencies due to insufficient dilution of solution were found. • A selective α-efficiency of ≥95% was achieved with ≤1% of β-contribution. [ABSTRACT FROM AUTHOR]

Using the TAC technique, the timing properties of a 4πβ–γ coincidence counting system were experimentally studied with an emphasis on saturated pulses. Experiments were performed for several discriminators (integral mode of TSCA) each with different kinds of timing techniques. Timing spectra were measured at various applied voltage to the 4π proportional detector covering the entire region of the plateau. Most of timing discriminators show good timing property when the pulses remain the linear region, but suddenly deteriorate after the pulses was saturated, and the timing spectra expands seriously up to a few μs in some types of timing discriminator. To overcome this problem, two techniques were proposed. [ABSTRACT FROM AUTHOR]

When conducting uniformity measurements of a wide area reference source with a detector having a window of a size similar to that of a gridded individual portion area on the source, it is important to carefully consider neighbor effects on measuring emission rates of the individual target portion resulting from the gap between the source and detector window. Optimization of the uniformity measurement conditions was studied for beta-emitting wide area reference sources in this study. A measurement system consisting of a PR-gas (Ar: 90%+CH 4 : 10%) flow type windowed proportional counter and a motorized XY stage was installed. This system is adapted to the uniformity measurement of two different types of 36 Cl sources made by different manufacturers. Uniformity measurement of a 100 mm×100 mm source divided into 16 portions of 6.25 cm 2 (25 mm squared) each could be conducted using our system under the present conditions with a neighbor effect of around 15% or less. The measurement results by use of this system were also compared with those using the imaging plate technique. [ABSTRACT FROM AUTHOR]

We developed a new fabrication method for standard surface sources by using an inkjet printer with inks in which a radioactive material is mixed to print on a sheet of paper. Three printed test patterns have been prepared: (1) 100 mm×100 mm uniformity-test patterns, (2) positional-resolution test patterns with different widths and intervals of straight lines, and (3) logarithmic intensity test patterns with different radioactive intensities. The results revealed that the fabricated standard surface sources had high uniformity, high positional resolution, arbitrary shapes and a broad intensity range. [Copyright &y& Elsevier]

Abstract: In the APMP radioactivity group (TCRI), a series of intercomparisons were conducted between member laboratories, with the aim to improve the calibration of ionization chambers used as secondary standards for radioactivity measurement. Several sources were sent to the participating institutes and the measurement results of calibration factors have been compared. Good agreement between laboratories was found for radioisotopes where the major contribution to the ionization current stems from high-energy gamma rays. It was expected in this energy region that these ratios would become unity for any type of chamber by normalizing with the same type of reference sources. However, where the dominating contribution to the measured ionization current is due to the presence of low-energy gamma rays, there were some serious discrepancies between participating institutes. In order to understand these differences, Monte Carlo simulation has been utilized by studying the effects of changing the wall thickness of the re-entrant well, the materials of the sample holder and the composition of the ionizing gas. [Copyright &y& Elsevier]

Abstract: The angular distribution of photon energy spectra emitted from an I-125 brachytherapy source was measured using a specially designed jig in the range of ±70° in the plane of the long axis of the source. It is important to investigate the angular dependence of photon emissions from these sources for the calibration of the air kerma rate. The results show that the influence of the distributions between 0° and ±8° is small enough to allow a calibration using current primary instruments which have a large entrance window. [Copyright &y& Elsevier]