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The interlaboratory comparison that 148 laboratories participated was performed to understand the validity and variability of measurements with NaI(Tl) scintillation detectors for samples near the standard limit for radioactive cesium in general foods in Japan. Brown rice grains with certified massic activity of radioactive cesium were used as test samples. The medians of the reported massic activities of radioactive cesium, 134Cs, and 137Cs in brown rice grains agreed with the reference values. On the point of view for inspection, more than 92% of the reported values were within the acceptable range.

Main text The supplementary international comparison of activity measurement of Cs-134 and Cs-137 in brown rice (APMP.RI(II)-S3.Cs-134.Cs-137) was carried out within the framework of the Asia-Pacific Metrology Programme (APMP). The matrix of the sample was brown rice grain harvested in autumn 2011, after the accident at the Fukushima Daiichi Nuclear Power Plant. No spiking was applied to the sample. Eight institutes reported their measurement results. Averages of the reported results and their associated uncertainties were obtained using the power-moderated mean. This report describes the supplemental comparison reference value, the degree of equivalence of the results, the procedure of the comparison and the sample preparation and measurements by the participants. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database https://www.bipm.org/kcdb/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

In this study, we derived the posterior probability distribution of the total activity estimated by inverse problem solution. The posterior probability distribution was derived by applying the Monte Carlo approach of the GUM Supplement 1 to the model of evaluation. The decision threshold, the detection limit, and the limits of the coverage interval for the results, all of which are defined in ISO 11929-2 as characteristic limits, were also derived.

A test device consisting of an I-131 source, a phantom on a 3D moving table, and a NaI(Tl) scintillation detector on a fixed flat table was developed to carry out response tests of a thyroid monitor. A measurement uncertainty due to variation of configuration of the source and the detector, as well as other factors, was estimated. The estimated relative standard uncertainty of measurement at a source–detector distance of 100 mm, which was deduced to be the optimum, was 1.9%. This is sufficiently small for calibrating a thyroid monitor used for radiation protection.

Absolute measurement by the 4πβ-γ coincidence counting method was conducted by two photomultipliers facing across a plastic scintillator to be focused on β ray counting efficiency. The detector was held with a through-hole-type NaI(Tl) detector. The results include absolutely determined activity and its uncertainty especially about extrapolation. A comparison between the obtained and known activities showed agreement within their uncertainties.

A well-type HPGe detector model with the existence of a particular dead area in the HPGe crystal was developed for use in Monte Carlo simulation codes to better model gamma-ray efficiency characteristics. Dissimilarities of counting efficiencies between simulation and calibration were successfully minimized for the case of point and volume sources. Simulations using the resulting model are applicable to the activity measurement of samples both in the hole and on top of the endcap of the well-type HPGe detector.

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.

Main text A comparison of the activity concentration of an 55Fe solution was organized by the POLATOM under the auspices of the CCRI(II). The solution was sent to thirteen laboratories; ready-to-measure sources were also prepared using the same 55Fe solution in diffusive (polyethylene) vials and sent to twelve laboratories. Twelve measurement reports were received. The results, as well as relevant information on the measurement techniques, are presented and analysed in this paper. The differences in the results obtained from measurements in non-diffusive (glass) and diffusive vials are indicated. To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

In the standardization of (134)Cs by the 4πβ-γ coincidence method with a γ-window at 605keV, the satellite components of 563keV and 569keV overlapping the 605keV peak cause a steep slope and non-linearity of the efficiency extrapolation function. By shifting the lower threshold of a γ-window higher, the satellite components are eliminated, and the slope tends to horizontal. Nearly flat efficiency curves were obtained by using a CeBr3 scintillator for detecting γ-photons, as well as a NaI(Tl) scintillator.

In Japan, we conducted proficiency testing of activity measurement by using high-purity germanium detectors for 134Cs and 137Cs in brown rice grains. Among 176 reported results, 86 % (for 134Cs) and 93 % (for 137Cs) of the results satisfied |En| ≦ 1. However, 58 reports for 134Cs and 51 reports for 137Cs had some failures in their evaluations of uncertainties. The proficiency testing was effective to improve the ability of uncertainty evaluation.

The international comparison of activity measurements of 59Fe, APMP.RI(II)-K2.Fe-59, was carried out within the framework of the Asia-Pacific Metrology Programme (APMP). Nine institutes took part in the comparison, and eight institutes of them undertook absolute measurements. One ampoule prepared using the same radioactive solution as that used in the comparison was sent to the BIPM/SIR in order to link the comparison to the BIPM key comparison reference value (KCRV). Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Three new participations in the BIPM.RI(II)-K1.Fe-59 comparison have been added to the previous results and this has produced a revised value for the key comparison reference value (KCRV), calculated using the power-moderated weighted mean. A link has been made to the APMP.RI(II)-K2.Fe-59 comparison held in 2014 through the NMIJ who participated in both comparisons. Five NMIs used the K1 or K2 comparison to update their degree of equivalence. The degrees of equivalence between each equivalent activity measured in the International Reference System (SIR) and the KCRV have been calculated and the results are given in the form of a table for the remaining five NMIs in the BIPM.RI(II)-K1.Fe-59 comparison and the eight other participants in the APMP.RI(II)-K2.Fe-59 comparison. A graphical presentation is also given. Main text To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/. The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

Proceedings of the 21st International Conference on Radionuclide Metrology and its Applications (ICRM), May 15-19, 2017, Buenos Aires, Argentina. Organizer: Argentinian National Atomic Energy Commission; International audience; An international key comparison, identifier CCRI(II)-K2.Ge-68, has been performed. The National Institute of Standards and Technology (NIST) served as the pilot laboratory, distributing aliquots of a $^{68}$Ge/$^{68}$Ga solution. Results for the activity concentration, CA, of $^{68}$Ge at a reference date of 12h00 UTC 14 November 2014 were submitted by 17 laboratories, encompassing many variants of coincidence methods and liquid-scintillation counting methods. The first use of 4π(Cherenkov)β-γ coincidence and anticoincidence methods in an international comparison is reported. One participant reported results by secondary methods only. Two results, both utilizing pure liquid-scintillation methods, were identified as outliers. Evaluation using the Power-Moderated Mean method results in a proposed Comparison Reference Value (CRV) of 621.7(11) kBq g$^{−1}$, based on 14 results. The degrees of equivalence and their associated uncertainties are evaluated for each participant. Several participants submitted 3.6 mL ampoules to the BIPM to link the comparison to the International Reference System (SIR) which may lead to the evaluation of a Key Comparison Reference Value and associated degrees of equivalence.

A flexible γ detector using a liquid scintillation light guide (LSLG) was developed. The analyzed pulse height (PHA) spectrum depended on the diameter, length and scintillator concentration of the LSLG, and the distance of a γ ray irradiation point from the head of photomultiplier tube (PMT). From the analysis of PHA spectrum, it was found that the count ratio of two divided channel regions linearly decreases as the distance from the PMT head increases. It was further found that the radiation dose rate can be estimated by setting the flexible LSLG tube to a circular shape since the count rate is proportional to the dose rate measured by a conventional NaI (Tl) scintillation detector. Therefore, a flexible and long LSLG detector using a single PMT is useful for determination of the dose rate and has a potential to detect local contaminations in a certain narrow space.

We developed a new method to determine the response ratio of an ionization chamber (Ohkura ionization chamber: type I-4096 01/06) filled with dry air to that filled with P-10 gas. The response-ratio was obtained by comparing the output currents of the ionization chamber after introduction of radioactive gasses of identical activities contained in two small vessels. The obtained ratio was 0.690 ± 0.003, which agreed with the results obtained by other methods.

We aimed to develop certified reference materials that could be used for well-type HPGe detector. We chose wheat flour as a sample and evaluated the homogeneity of the sample in well-type container (5ml). Results showed that inhomogeneity was sufficiently small for validation checks of well-type HPGe detector (uhom = 0.44%).

We proposed a method to measure the radioactivity of Sr/Y-90 in the mixture of Cs-134 and Cs-137 without chemical pretreatment. It was realized by subtracting the electrons produced in Cs-134 and Cs-137 from entire electron emission rate that can be determined by the efficiency tracer technique in the 4πβ–γ coincidence counting method. The radioactivity of Cs-134 and Cs-137 can be determined by gamma ray spectrometry. The measurements were conducted using plastic and NaI(Tl) scintillation detector with a large solid angle. The validity of the measurement method was shown by agreement of the results with the known radioactivities.

We proposed a new method to determine the activity of each nuclide in a mixture of Cs-134, Cs-137 and Sr/Y-90. The point of this new measurement method is simultaneous counting between beta and gamma ray detection. We assembled a setup that employs plastic and NaI(Tl) scintillation detectors for beta- and gamma-ray detection, respectively. The obtained result shows that discrimination of Cs-134 and Cs-137 was successfully achieved. Radioactivity determined by measurement was in agreement with one prepared as a mixture. The results show that the method can be adapted to measure the radioactivity of samples contaminated by the accident at the Fukushima Daiichi Nuclear Power Plant.

After the accident at the Fukushima Daiichi nuclear power plant, we managed to carry out emergency measurements of the radioactive fallout. The included nuclides were identified via gamma-ray spectrometry using an HPGe detector. Quantifications of each radionuclide in the fallout were determined based on the efficiency calibrations and relevant corrections. The collected samples had a variety of shapes, densities, and compositions. EGS5 Monte Carlo code was used for the flexible estimation of these parameters. The measurement results show the temporal changes in the fallout quantity about a month after the accident.

We measured 4π and 2π counting efficiencies for internal conversion electrons (ICEs), gross β-particles and also β-rays alone with various source conditions regarding absorber and backing foil thickness using e-X coincidence technique. Dominant differences regarding the penetration, attenuation and backscattering properties among ICEs and β-rays were revealed. Although the abundance of internal conversion electrons of 137Cs-137Ba is only 9.35%, 60% of gross counts may be attributed to ICEs in worse source conditions. This information will be useful for radionuclide metrology and for surface contamination monitoring.

A tritium radioactivity source was measured by triple-to-double coincidence ratio (TDCR) equipment of the National Metrology Institute of Japan (NMIJ), and measured data were fitted using polynomial approximation and the Newton-Raphson method, a technique whereby equations are solved numerically by successive approximations. The method used to obtain the activity minimizes the difference between statistically calculated data and experimental data. In the fitting, since calculated statistical efficiency and TDCR values are discrete, the calculated efficiencies are approximated by quadratic functions around experimental values and the Newton-Raphson method is used for convergence at the minimal difference between experimental data and calculated data. In this way, the activity of tritium was successfully obtained.

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.

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.

A new calibration technique, referred to as e-trace, has been developed by the National Institute of Advanced Industrial Science and Technology (AIST). The e-trace technique enables rapid remote ca...

表面汚染検査装置は，放射線防護のために広く用いられている。これらの表面汚染検査装置は，荷電粒子放出率が付与された面線源により校正される。一方，産業技術総合研究所は，計量の国家標準を担っており，荷電粒子放出率については，多線式比例計数管により面線源の測定を行い，面線源を仲介標準器として，校正業務を行っている。現在まで，100mm×100mmの面線源により，校正業務を行ってきたが，今回，新しい多線式比例計数管を導入し，100mm×150mmの面線源によっても，校正業務が行えるように準備作業を進めている。この新しい多線式比例計数管についての特性評価を行うとともに，校正の不確かさ評価を行った。今後，この多線式比例計数管を，表面汚染検査装置の校正等のための面線源に，荷電粒子放出率を付与するために用いていきたい。

Technetium-99m is widely used for many diagnostic investigations in nuclear medicine, thus the standardization of this nuclide is important. In classical 4πβ−γ coincidence counting of 99mTc, the steep slope of the efficiency function and the large extrapolation range may cause a large measurement uncertainty. In order to overcome these difficulties, we apply the 4πβ+4πγ sum counting technique for the standardization. Furthermore, we adopt both the 4πβ−4πγ coincidence counting method and the 4πβ+4πγ sum counting technique for the standardization of its parent nuclide 99Mo. High efficiencies for both nuclides were easily achieved by the use of our 4πβ−4πγ counter. All the results were consistent with the reference value obtained by the conventional method obtained by NMIJ.

beta-Ray spectra after penetrating absorbing materials of various thicknesses were observed by the use of a scintillation-type beta-ray spectrometer equipped with a flat NE-102 plastic scintillator of 5mm thickness for sources of (60)Co, (90)Sr-(90)Y, (137)Cs, (147)Pm and (204)Tl. Although the spectra changed rapidly with increasing absorber thickness, the average beta-ray energy was kept nearly constant for a wider range. These results are consistent in that the beta-ray absorption curve becomes quasi-linear in a semi-logarithmic plot. Spectra including scattered beta-rays from several materials placed behind the source were also measured for (137)Cs and (204)Tl. It may be concluded that mean energy measurements by the use of beta-ray spectrometer of this kind is useful for the identification of nuclides in radiation protection purposes even in worse source-conditions.

NMIJ participated in the CCRI (II) key comparison of 55 Fe 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 55 Fe was also measured by using a 2 π 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 55 Fe. However the Si(Li) detector is also useful.

Α 4π(β+γ) integral counting technique using a 4πβ−4πγ detector configuration was adopted for the standardization of 18F. In this technique, the β-detector is composed of two thin plastic scintillators sandwiching the source, coupled with a slender photomultiplier tube. The β-detector part with the source was inserted into a large well-type NaI(Tl) scintillation detector for γ-ray detection, making a 4πβ−4πγ coincidence counting system. In this work, positron particles were detected with high efficiency in the β-channel and annihilation quanta were also detected with high efficiency in the 4πγ channel. The very small inefficiency of the 4π(β+γ) integral counter for the β-plus branch has been confirmed by EGS5 Monte Carlo simulation. The result using this technique agreed within the uncertainties with the result obtained by the conventional 4πβ−γ coincidence counting with the efficiency extrapolation technique using the same detector configuration and a conventional 4πβ−γ coincidence counter.

A simulation technique was developed for the extrapolation technique in 4πβ-γ coincidence counting method. Simultaneous emissions of β and γ rays were calculated using EGS5 code to obtain coincidence counting between both β and γ channels. The simulated extrapolation curves were compared with experimental data obtained with (134)Cs measurements using a plastic scintillator in the β channel. The variation of the extrapolation curves with γ-gate configuration was investigated by the simulation technique.

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.

We developed a compact detector that was applied to measure Sr/Y-90 radioactivity even in mixture with Cs-134 and Cs-137. A measurement for a sample of which radioactivity was known was conducted.

A positron camera, consisting of a pair of Anger-type scintillation detectors, has been developed to verify ranges by using positron emitter beams. Each detector head is equipped with a NaI(Tl) crystal (diameter: 600 mm , thickness: 30 mm ) for high detection efficiency. To get a low counting rate for this application, the electric circuit was designed for flexibility in measurement and analysis by software. The energy and position were calibrated for high measurement accuracy. A spatial resolution of 8.6 mm in FWHM within a ±50 mm region (field of view) and a linear response of a 0.3 mm standard deviation within a ±200 mm region were obtained. The camera was designed so as to measure the ranges within an accuracy of 1 mm under a dose limitation (about 100 mGyE ) to reduce the safety margin for the irradiation field, and it met the required characteristics.

An allene-doped liquid argon ionization chamber with 48 mm×48 mm×40 mm sensitive volume has been constructed for precise energy measurement of heavy ions at around 100 MeV/n. An energy resolution of 0.6%–0.7% (FWHM) was achieved for Ca and Ar ions both at 78 MeV/n.

In order to vary the counting efficiencies in the 4πβ−γ coincidence extrapolation technique, a radioactive source was coated directly with varying amounts of an electrical conducting pigment using an ink-jet printer. This method can be used to efficiently prepare the multiple sources needed to generate efficiency extrapolation curves, and was successfully applied to the standardization of a 54Mn source.

In order to clarify the γ-efficiency dependency of 4πβ-γ efficiency functions, a series of 4πβ-γ efficiency extrapolation measurements of a 134Cs source were carried out for a wide variety of γ-geometries using a 4πβ(PS)-4πγ detector configuration. As the source is situated in the plastic scintillator (PS) β-detector, the γ-efficiency of the system can be readily changed by extracting the β-detector from the well-hole in a series of stages. For data acquisition and analyses, a list-mode two-parameter data acquisition system was employed. The forms of the extrapolation curves were monitored with decreasing γ-geometry, eventually exhibiting a similar behavior to those obtained in a usual 4πβ-γ coincidence counting system. The experimental results and considerations suggested that the γ-geometry dependency of the efficiency functions were due to summing effects in the γ-channel, and some qualitative remarks on the form of the extrapolation functions are given.

For the standardization of electron capture nuclides followed by γ-transitions, the 4π(e, X)–γ coincidence counting method is mainly adopted. To examine how the spectra of the (e, X) channel change with gas nature and pressure, pulse-height spectrum measurements of signals from a 4π pressurized proportional counter were carried out under various conditions for 54 Mn and 88 Y sources together with 4π(e, X)–γ coincidence counting. The spectra were measured for each half of the counter and for the combined 4π signal. The nature of counting gas (P-10 or methane) and its pressure was reflected in the X-ray peak intensity, and the Auger electron spectra were influenced significantly by the absorption in a thin VYNS film and the source conditions. In the measurements, we employed a pill-box type 4π counter in which the anodes were very thin gold-coated tungsten wires (30 μm ∅). In this system, spectra down to 0.2 keV were clearly seen. The gas pressure can be raised up to 0.6 MPa. Counting electronics used for 4π(e, X)–γ coincidence measurements were conventional modules and a list mode two-parameter data acquisition system.

We developed a certified reference material of brown rice to measure radioactivity from the Fukushima Daiichi Nuclear Power Plant accident. The rice was planted in the spring of 2011, just after the Fukushima accident occurred, and it was harvested in the autumn of 2011. The certified value of radioactivity concentration in the rice was 33.6 Bq kg −1 of Cs-134 and 51.8 Bq kg −1 of Cs-137 on August 1, 2012. The reference material is being widely distributed by the National Metrology Institute of Japan. To determine the radioactivity and its uncertainties in the brown rice, we employed gamma-ray spectrometry with a high-purity germanium detector and Monte Carlo simulation.

The accident at the Fukushima Daiichi Nuclear Power Plant in March 2011 released radionuclides into the environment. There is concern that 90Sr will be concentrated in seafood. To measure the activities of 90Sr in a short time without chemical processes, we have designed a new detector for measuring activity that obtains count rates using 10 layers of proportional counters that are separated by walls that absorb beta particles. Monte Carlo simulations were performed to confirm that its design is appropriate.

We are encouraged to contribute to strengthen quality assurance which keeps brachytherapy safe and available. For the purpose, we aspire to determine the source strength and establish national metrological standard in Japan. It is necessary to assemble a high sensitive free air chamber for measurement of ionization current derived from the source which is very weak especially in Japan. Total uncertainty for the source strength is promising to meet required value from users of measurement instruments.

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.

An international comparison of measurement of beta particle surface emission rate from a (36)Cl large area source (APMP.RI(II)-S1.Cl-36) was carried out within the framework of the Asia-Pacific Metrology Program (APMP). Participants from APMP were NMIJ (Japan), KRISS (Korea) and INER (Chinese Taipei). Participants from the other RMOs were NIST (United States), PTB (Germany), NMISA (South Africa) and VNIIM (Russia). All the results of the participants agreed within ±1%. This was the first international comparison of measurement of surface emission rate of beta particle from a large area source.

A simple but versatile data acquisition system for software coincidence experiments is described, in which any time stamping and live time controller are not provided. Signals from β- and γ-channels are fed to separately two fast ADCs (16 bits, 25 MHz clock maximum) via variable delay circuits and pulse-height stretchers, and also to pulse-height discriminators. The discriminating level was set to just above the electronic noise. Two ADCs were controlled with a common clock signal, and triggered simultaneously by the logic OR pulses from both discriminators. Paired digital signals for each sampling were sent to buffer memories connected to main PC with a FIFO (First-In, First-Out) pipe via USB. After data acquisition in list mode, various processing including pulse-height analyses was performed using MS-Excel (version 2007 and later). The usefulness of this system was demonstrated for 4πβ(PS)–4πγ coincidence measurements of 60 Co, 134 Cs and 152 Eu. Possibilities of other extended applications will be touched upon.