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Journal Articles

Attempt to estimate the background pulse height spectrum of the CeBr$$_{3}$$ scintillation spectrometer due to terrestrial gamma ray components; Application in environmental radiation monitoring

Kowatari, Munehiko; Tanimura, Yoshihiko; Kessler, P.*; R$"o$ttger, A.*

Radiation Measurements, 138, p.106431_1 - 106431_6, 2020/11

 Times Cited Count:0 Percentile:0.01(Nuclear Science & Technology)

Journal Articles

Experimental determination of anisotropic emission of neutrons from $$^{252}$$Cf neutron source with the spherical protection case

Kowatari, Munehiko; Nishino, Sho; Romallosa, K. M. D.*; Yoshitomi, Hiroshi; Tanimura, Yoshihiko; Oishi, Tetsuya

Radiation Protection Dosimetry, 189(4), p.436 - 443, 2020/05

 Times Cited Count:0 Percentile:0.01(Environmental Sciences)

The anisotropic emission of neutrons from a cylindrical X1 $$^{252}$$Cf source with the spherical external casing was experimentally determined. The influence of metal materials and shapes of the external casing to the anisotropy factor, $$F_{I}$$($$theta$$) was assessed by the Monte Carlo calculation, before performing the measurement. The results of the calculation result implied that light and spherical-shaped external casing decreases the anisotropic emission of neutrons from a cylindrical source and the nature of the material does not affect the anisotropic emission to a large extent. The experimental results obtained when a spherical-shaped aluminum protection case was employed also revealed that the anisotropy factor was close to 1.0 with a wide zenith angle range.

Journal Articles

Exposure inhomogeneity from $$^{241}$$Am and $$^{90}$$Sr/$$^{90}$$Y sources in terms of the eye lens monitoring in the nuclear facilities

Yoshitomi, Hiroshi; Kowatari, Munehiko

Radiation Protection Dosimetry, 188(2), p.191 - 198, 2020/02

 Times Cited Count:0 Percentile:0.01(Environmental Sciences)

Journal Articles

Establishment of a low dose rate gamma ray calibration field for environmental radiation monitoring devices

Kowatari, Munehiko; Yoshitomi, Hiroshi; Nishino, Sho; Tanimura, Yoshihiko; Oishi, Tetsuya; Kessler, P.*; Neumaier, S.*; R$"o$ttger, A.*

Radiation Protection Dosimetry, 187(1), p.61 - 68, 2019/12

 Times Cited Count:1 Percentile:23.13(Environmental Sciences)

Journal Articles

Corrigendum; Establishment of a low dose rate gamma ray calibration field for environmental radiation monitoring devices

Kowatari, Munehiko; Yoshitomi, Hiroshi; Nishino, Sho; Tanimura, Yoshihiko; Oishi, Tetsuya; Kessler, P.*; Neumaier, S.*; R$"o$ttger, A.*

Radiation Protection Dosimetry, 186(4), P. 538, 2019/12

 Times Cited Count:0 Percentile:1.45(Environmental Sciences)

In the original version of this article an error occurred in Table 5. In section (b), the unit $$mu$$Sv h$$^{-1}$$ has been amended to nSv h$$^{-1}$$. The corrected table appears below. The author apologises for this error.

Journal Articles

Quantitative estimation of exposure inhomogeneity in terms of eye lens and extremity monitoring for radiation workers in the nuclear industry

Yoshitomi, Hiroshi; Kowatari, Munehiko; Hagiwara, Masayuki*; Nagaguro, Seiji*; Nakamura, Hajime*

Radiation Protection Dosimetry, 184(2), p.179 - 188, 2019/08

 Times Cited Count:1 Percentile:23.13(Environmental Sciences)

Journal Articles

Characteristics of commercially available CdZnTe detector as gamma-ray spectrometer under severe nuclear accident

Tanimura, Yoshihiko; Nishino, Sho; Yoshitomi, Hiroshi; Kowatari, Munehiko; Oishi, Tetsuya

Progress in Nuclear Science and Technology (Internet), 6, p.134 - 138, 2019/01

At the severe nuclear accidents like the Fukushima Daiichi Nuclear Power Plant, various radionuclides will be dispersed into the environment and raise the dose rate. The $$in$$-$$situ$$ measurements of $$gamma$$ ray spectra and identifying radionuclides using the results are important for the radiological protection from both external and internal exposure. For this application a commercially available CdZnTe spectrometer (Kromek GR-1) was characterized at the calibration fields of FRS/JAEA. The angular dependence of the detection efficiency was studied and the efficiency was kept within 15 % degradation in $$pm$$135 degree incident angle, which covers 85 % of all. The usable dose range was evaluated and the spectrometer could correctly measure the $$gamma$$ ray spectra below 200 $$mu$$Gy/h.

Journal Articles

Correction factors for attenuation and scattering of the wall of a cylindrical ionization chamber in the 6-7 MeV high-energy photon reference field

Kowatari, Munehiko; Zutz, H.*; Hupe, O.*

Radiation Protection Dosimetry, 178(1), p.48 - 56, 2018/01

 Times Cited Count:0 Percentile:0.01(Environmental Sciences)

In high energy photon reference fields the value of the air kerma rate is determined by using ionization chambers. From the charge collected inside the ionization chamber the dose can be calculated using a set of calibration and correction factors according to ISO 4037-2. A crucial parameter is the correction for the attenuation and scattering of the primary radiation due to the chamber wall. This parameter can be determined using Monte Carlo calculations. The evaluation of the factor was performed for a commercially available ionization chamber of the type Victoreen 550-3 under different build-up conditions. The results were verified by measurements in the R-F high energy photon fields according to ISO 4037-1 at the Physikalisch-Technische Bundesanstalt (PTB) and the Japan Atomic Energy Agency (JAEA).

Journal Articles

Comprehensive study on the response of neutron dosimeters in various simulated workplace neutron calibration fields

Nishino, Sho; Hoshi, Katsuya; Tsujimura, Norio; Kowatari, Munehiko; Yoshida, Tadayoshi

Proceedings of 14th International Congress of the International Radiation Protection Association (IRPA-14), Vol.3 (Internet), p.1258 - 1263, 2017/11

In order to investigate how neutron dosimeters respond in the continuous neutron fields in workplaces, we performed performance tests of four widely-used neutron survey meters in various simulated workplace neutron calibration fields established in two calibration facilities (FRS and ICF) in JAEA. As a result, we found that survey meters significantly over or underestimate neutron dose in the fields which have spectral components only in the energy range below 1 MeV, while those show good performance in the fields which have spectral components in the energy range above 1 MeV.

Journal Articles

Assessment of equivalent dose of the lens of the eyes and the extremities to workers under nonhomogeneous exposure situation in nuclear and accelerator facilities by means of measurements using a phantom coupled with Monte Carlo simulation

Yoshitomi, Hiroshi; Hagiwara, Masayuki*; Kowatari, Munehiko; Nishino, Sho; Sanami, Toshiya*; Iwase, Hiroshi*

Proceedings of 14th International Congress of the International Radiation Protection Association (IRPA-14), Vol.3 (Internet), p.1188 - 1195, 2017/11

The equivalent doses to the lens of the eye and extremities for radiation workers should be assessed properly to ensure that the dose limits are not exceeded. Recently, the following two issues has pressed demand on more appropriate evaluation of the equivalent doses of the lens of the eye and extremity. One is the new occupational dose limit for the lens of the eye the ICRP recommended. The other is growing demand on handling of highly activated materials in the maintenance works of an accelerator and contaminated materials during the decommissioning works of nuclear facility, which increases the potential exposure risk to the extremities to a wider variety of radio-nuclides. Since the points to be assessed for the exposures to the lens of the eye and the extremities are apart from the trunk, the homogeneity of the radiation fields would be significantly impact on the assessment of these equivalent doses. However, there has been no sufficient and available method to identify the nonhomogeneous situations systematically in terms of the eye lens or extremity monitoring. The goal of this study is to provide the framework to identify the nonhomogeneous exposure situations. In order to fulfil this purpose, newly proposed indices to represent the homogeneity were calculated by Monte Carlo simulation incorporated with mathematical phantom, verifying the benchmark measurements. Important parameters that significantly impact on these indices were also shown from the various trials of calculations of homogeneity indices.

Journal Articles

A Radioisotope neutron source and its application for dosimetry

Kowatari, Munehiko

Hamon, 27(3), p.109 - 112, 2017/08

A various kinds of radioactive neutron sources have been developed since neutron had been first discovered. The reactions which are mainly taken advantage for generating neutrons as radioactive neutron source are ($$alpha$$,n) reaction, ($$gamma$$,n) reaction and nuclear fission reaction. Only $$^{241}$$Am-Be and $$^{252}$$Cf neutron sources are now available due to reliable reproducibility of neutron emission, long half-lives and less disturbing $$gamma$$ ray emission. Both are designated as a "reference neutron source" by ISO 8529 series describing principle of establishment of neutron calibration field. Total neutron emission rate from neutron source must be well defined in terms of sophisticated method by national metrological laboratory. Correction factor for anisotropic emission from cylindrical-shaped neutron source must be experimentally determined for neutron fluence rate at a point of test in the calibration laboratory.

Journal Articles

Influence of different types of phantoms on the calibration of dosemeters for eye lens dosimetry

Yoshitomi, Hiroshi; Kowatari, Munehiko

Radiation Protection Dosimetry, 170(1-4), p.199 - 203, 2016/09

 Times Cited Count:4 Percentile:45.9(Environmental Sciences)

Both cylinder and slab phantoms have been recommended for the calibration phantoms for eye lens dosimetry in the |IAEA TECDOC. This study aims to investigate the influence of these phantoms on the calibration of dosemeters for eye lens dosimetry. In order to fulfill the purpose, the backscatters of photons and electrons from practically used water-filled phantoms were evaluated by calculations and experiments. Calculations showed cylinder phantom and slab phantom were found to well-simulate the effect of backscattered photons within 10% and 5%, respectively. It was also found that a cylinder phantom had 10% lower backscattered effect over the range of 50-100 keV. Due to this, the measured calibration factors of cylinder phantom for non-filtered Optically Stimulated Luminescence (OSL) and Radio-Photo Luminescence (RPL) dosemeters increased by 20% and 10%, respectively when compared to the slab phantom. For electrons, no difference was found between cylinder and slab phantoms.

Journal Articles

Investigation on the energy dependence of various types of survey meter in gamma and X-ray field

Kamwang, N.*; Kowatari, Munehiko; Yoshitomi, Hiroshi

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

Journal Articles

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$$^2$$ thickness or one made of high-Z materials for $$^{90}$$Sr/$$^{90}$$Y field.

Journal Articles

Series studies on inter-comparison of radiation calibration fields and calibration techniques between KAERI and JAEA

Yoshitomi, Hiroshi; Tanimura, Yoshihiko*; Tatebe, Yosuke; Tsutsumi, Masahiro; Kawasaki, Katsuya; Kowatari, Munehiko; Yoshizawa, Michio; Shimizu, Shigeru*; Kim, J.-S.*; Lee, J.-G.*; et al.

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

Journal Articles

Measurement of air kerma rates for 6- to 7-MeV high-energy $$gamma$$-ray field by ionisation chamber and build-up plate

Kowatari, Munehiko; Tanimura, Yoshihiko; Tsutsumi, Masahiro

Radiation Protection Dosimetry, 162(4), p.446 - 458, 2014/12

 Times Cited Count:3 Percentile:28.59(Environmental Sciences)

no abstracts in English

Journal Articles

An Attempt to decrease anisotropic emissions of neutrons from a cylindrical $$^{241}$$Am-Be-encapsulation source

Kowatari, Munehiko; Tanimura, Yoshihiko; Yoshizawa, Michio

Radiation Protection Dosimetry, 161(1-4), p.166 - 170, 2014/10

 Times Cited Count:2 Percentile:19.81(Environmental Sciences)

An attempt to decrease the anisotropic emissions of neutrons from a cylindrical $$^{241}$$Am-Be encapsulated X3 source was conducted out by Monte Carlo calculations and experiments. Influence of metal materials and shapes of the external casing to the anisotropy factor were focused on. Results obtained by calculations using MCNP4C implied that a light and spherical-shaped casing decreases the anisotropic emission of neutrons. Experimental results using the spherical-shaped aluminum protection case also revealed that the anisotropy factor was close to 1.0 with wide zenith angle ranges.

Journal Articles

Mono-energetic neutron fields using 4 MV pelletron accelerator at FRS/JAEA

Tanimura, Yoshihiko; Kowatari, Munehiko; Yoshitomi, Hiroshi; Nishino, Sho; Yoshizawa, Michio

IAEA-TECDOC-1743, Annex (CD-ROM), p.133 - 138, 2014/07

Mono-energetic neutron calibration fields have been developed in the energy range of 8 keV to 19 MeV using a 4 MV Pelletron accelerator at the FRS in the JAEA. Protons or deuterons are accelerated and transported to bombard various targets for neutron production. The targets are prepared by depositing Sc, LiF or TiT on the backing disks for $$^{45}$$Sc(p,n)$$^{45}$$Ti, $$^{7}$$Li(p,n)$$^{7}$$Be and, $$^{3}$$H(p,n)$$^{3}$$He and $$^{3}$$H(d,n)$$^{4}$$He reactions, respectively. For $$^{2}$$H(d,n)$$^{3}$$He reaction, a gas target is prepared by filling a target cell with D$$_{2}$$ gas. A pulsed beam with a minimum width of 2 ns can be derived with the pulsing system. Neutron fluence rates were measured with a Bonner sphere, a Li glass detector, a Si-SSD with a polyethylene radiator and a BC501A detector. Though the maximum fluence rates should not be high enough to obtain the nuclear data using an activation method, they can be available to obtain the nuclear data by using the prompt $$gamma$$ ray analysis.

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