Characteristics of beta reference radiation fields at the Facility of Radiation Standards (FRS), JAEA for their practical applications in beta dosimetry

Yoshitomi, Hiroshi; Kowatari, Munehiko; Suzuki, Takashi

Proceedings of 4th Asian and Oceanic Congress on Radiation Protection (AOCRP-4) (CD-ROM), 4 Pages, 2015/07

The Facility of Radiation Standards (FRS) in the Japan Atomic Energy Agency (JAEA) provides beta-ray calibration fields for the customers to calibrate dosemeters. Two different types of beta-ray irradiation systems, so called BSS2 and JBS, have been installed and operated in the FRS. They have quite different types of the beta-ray radiation sources, which might be attributed to variations in dosimetric quantities. Variations in these quantities would affect the calibration factor of a dosemeter. A comparison of dosimetric quantities for beta reference radiation fields of both beta-ray irradiation systems was made, in order to investigate how these quantities differ between them and how much differences affect calibration results. With regard to the depth dose curve which is one of the key dosimetric quantities, it was found that they showed different profiles between both systems reflecting their characteristics. This implies that the difference between two systems might affect the calibration of dosemeters, especially one with more than 400 mg/cm thickness or one made of high-Z materials for Sr/Y field.

Study on migration behaviour of Np and Am in near-surface environments

Tanaka, Tadao; Ya-Anant, N.*

Radiation Protection Dosimetry, 146(1-3), p.303 - 306, 2011/07

https://doi.org/10.1093/rpd/ncr176

Laboratory scale experiments were performed to investigate migration behavior of Np and Am, which were deposited onto the ground surface from spent fuel reprocessing facilities, in near-surface environment. Column migration experiments were conducted by varying the volume of eluting solution, for a sandy soil and a reddish soil. There seemed to be two chemical species of Np in the sandy soil column; one is cationic and the other is particulate form. The particulates moved without significant interaction with the sandy soil. The sorption of cationic Np was controlled by both a reversible ion-exchange reaction and irreversible reactions. Most of Am formed rather large particulates and trapped in the sandy soil column. The Np and Am loaded into the reddish soil column moved deeper with increasing eluting volume. The sorption was mainly controlled by ion-exchange reaction. The migration behavior could be significantly evaluated by the distribution coefficient.

WAZA-ARI; Computational dosimetry system for X-ray CT examinations, 2; Development of web-based system

Ban, Nobuhiko*; Takahashi, Fumiaki; Ono, Koji*; Hasegawa, Takayuki*; Yoshitake, Takayasu*; Katsunuma, Yasushi*; Sato, Kaoru; Endo, Akira; Kai, Michiaki*

Radiation Protection Dosimetry, 146(1-3), p.244 - 247, 2011/07

https://doi.org/10.1093/rpd/ncr161

We are developing a web-based system, WAZA-ARI, for the dose calculation of patients undergoing X-ray CT examinations. Tissue doses were calculated in a Japanese adult male phantom (JM phantom) using a Monte Carlo code, PHITS, and the normalized dose coefficient data are stored as XML files. The system is implemented in Java on a Linux server running Apache Tomcat, which is accessed via a web browser over a network. Users are requested to choose scanning options and to input parameters in the data entry screen. The corresponding dose data are called upon input, and they are summed over the scan range specified by the user to estimate unit tissue doses. Tissue doses are computed based on the radiographic exposure (mAs), the beam pitch and air kerma at the beam center on the axis of rotation. Users can also use their own air kerma, CTDI vol and DLP values for the dose computation instead of the default setting. Although the dose coefficients are prepared for only limited CT scanner models currently, our system has achieved high usability and easy maintenance without commercial software. Possibility of further expansion for the practical application is also discussed.

Verification analysis of thermoluminescent albedo neutron dosimetry at MOX fuel facilities

Nakagawa, Takahiro; Takada, Chie; Tsujimura, Norio

Radiation Protection Dosimetry, 146(1-3), p.140 - 143, 2011/07

https://doi.org/10.1093/rpd/ncr138

Radiation workers engaging in the fabrication of MOX fuels are exposed to neutrons, and hence thermoluminescent albedo dosemeters (TLAD) need to be used at JAEA-NCL. Because estimating the doses using TLADs are susceptible to the neutron energy spectrum, the authors have issued TLADs incorporating Solid-State Nuclear Tracks Detectors (SSNTDs) to selected workers who are routinely exposed to neutrons and been analyzing the relationship between the SSNTD and the TLAD (T/Rf) over the past 6 years. Consequently, the / in each year was 10-20 (3.363 mm)/(mSv Cs eq.), which is smaller than the data during 1991-1993, although the neutron spectra had not changed compared with that of the early 1990s. This decrease of the / implies that the ratio of work carried out nearby the gloveboxes to total work decreased.

Development of a microcalorimeter with transition edge sensor for detection of LX rays emitted by transuranium elements

Nakamura, Keisuke; Maeda, Makoto*; Yasumune, Takashi*; Maehata, Keisuke*; Ishibashi, Kenji*; Tanaka, Keiichi*; Umeno, Takahiro*; Takasaki, Koji; Momose, Takumaro

Radiation Protection Dosimetry, 146(1-3), p.88 - 91, 2011/07

https://doi.org/10.1093/rpd/ncr118

A Transition Edge Sensor (TES) microcalorimeter has been developed for use as an energy dispersive X-ray spectrometer. A TES microcalorimeter is a thermal detector used to measure the energy of an incident photon with increase in temperature. In this work, a TES microcalorimeter with a 5m Au absorber was developed for use in measuring LX rays emitted from transuranium elements. Furthermore, as a cooling system a dilution refrigerator utilizing a Gifford-McMahon refrigerator was used, which needs no liquid helium. The performance of the TES microcalorimeter was evaluated by measuring the LX rays emitted by an Am source. This system proved effective in the measurement of the LX rays because the full width at half maximum of the LX ray was about 80 eV.

Dose evaluation from multiple detector outputs using convex optimisation

Hashimoto, Makoto; Iimoto, Takeshi*; Kosako, Toshiso*

Radiation Protection Dosimetry, 146(1-3), p.65 - 68, 2011/07

https://doi.org/10.1093/rpd/ncr113

A dose evaluation using multiple radiation detector outputs can be improved by the convex optimisation. It enables flexible dose evaluation corresponding to the radiation field. The neutron ambient dose equivalent is evaluated using a mixed-gas proportional counter. The reliability of evaluated dose values are comparable with current dosimeter. An application to neutron individual dose equivalent measurement is also investigated. The combination of dosimeters with high orthogonality of response characteristics tends to show good suitability for dose evaluation.

Radiation protection at nuclear fuel cycle facilities

Endo, Kuniaki; Momose, Takumaro; Furuta, Sadaaki

Radiation Protection Dosimetry, 146(1-3), p.119 - 122, 2011/07

https://doi.org/10.1093/rpd/ncr132

Monitoring network of atmospheric Radon-222 concentration in East Asia and backward trajectory analysis of Radon-222 concentration trend at a small solitary island on Pacific Ocean

Okura, Takehisa; Yamazawa, Hiromi*; Moriizumi, Jun*; Hirao, Shigekazu*; Guo, Q.*; Tojima, Yasunori*; Iida, Takao*

Proceedings of 3rd Asian and Oceanic Congress on Radiation Protection (AOCRP-3) (CD-ROM), 3 Pages, 2010/05

Monitoring network of Rn concentration in air which was measured in Beijing, Nagoya, Hegura-jima, Hachijo-jima and Hateruma-jima, as a tracer for long-range transport in East Asia was established. At inland sites, Beijing and Nagoya, high concentrations Rn were measured, at marine sites, Hachijo-jima and Hateruma-jima, Rn concentrations level was very low. Seasonal variations of the Rn concentration show that Rn concentration was the lowest in the summer and the highest in the winter. Diurnal variations were measured at inland sites. At marine sites several-day-cycle variations were measured. It was pointed out by this study that the several-day-cycle variations at Hachijo-jima were dependent on synoptic-scale atmospheric disturbance. Backward trajectory analysis of the relationship between atmospheric Rn concentrations at Hachijo-jima and transport pathway of air mass indicates that atmospheric Rn at Hachijo-jima has much to do with transport pathway of air.

Prediction analysis of dose equivalent responses of neutron dosemeters used at a MOX fuel facility

Tsujimura, Norio; Yoshida, Tadayoshi; Takada, Chie

Proceedings of 3rd Asian and Oceanic Congress on Radiation Protection (AOCRP-3) (CD-ROM), 3 Pages, 2010/05

To predict how accurately the neutron dosemeters can measure the neutron dose equivalent (rate) in MOX fuel fabrication facility work environments, the calculations of the dose equivalent responses of neutron dosemeters were performed by the spectral folding method. The dosemeters selected included two types of personal dosemeters (a thermoluminescent albedo neutron dosemeter and an electronic neutron dosemeter), three moderator-based neutron survey meters and one special instrument called an (10) monitor. The calculations revealed the energy dependences of the responses expected within the entire range of neutron spectral variation observed in neutron fields at workplaces.

Equations for estimating chest wall thickness in lung counting at JAEA-NCL

Kanai, Katsuta; Kurihara, Osamu

Proceedings of 3rd Asian and Oceanic Congress on Radiation Protection (AOCRP-3) (CD-ROM), 3 Pages, 2010/05

Chest wall thickness (CWT) of the subject is an important modifier to determine the lung burden of inhaled actinides such as Pu isotopes or Am through lung counting. CWT prediction equations as a function of biometric indexes have been proposed by many authors based on chest wall measurements made with an ultrasound device. In the present study we derived such equations from CWT data of our subjects and then evaluated their applicability to monitoring with our currently used lung counter, mainly examining the accuracy of determinations of Am, useful as a unique indicator that can be detected in most cases of internal contamination with Pu compounds. The error of the equations obtained was found to be within the range of - 8 mm to + 6 mm against actual CWT values of our subjects, complying with the bias performance criteria for direct measurements. However, further studies might be needed to clarify the effect of the difference in posture on the CWT caused by the modification of the counting geometry made for our lung counter.