T Kurosawa

A standard for absorbed dose rate to water in a 60Co field using a graphite calorimeter at the National Metrology Institute of Japan

A primary standard for the absorbed dose rate to water in a ⁶⁰Co radiation field has been newly established at the National Metrology Institute of Japan. This primary standard combines the calorimetric measurements using a graphite calorimeter with the ionometric measurements using a thick-walled graphite cavity ionisation chamber. The calorimeter is operated in the constant temperature mode using AC Wheatstone bridges. The absorbed dose rate to water was determined to be 12 mGy s⁻¹ at a point of 1 m from the radiation source and at a water depth of 5 g cm⁻². The uncertainty on the calibration coefficient in terms of the absorbed dose to water of an ionisation chamber using this standard was estimated to be 0.39 % (k=1).

Comparison of the standards for absorbed dose to water of the NMIJ and the BIPM for60Co γ-ray beams

A comparison of the standards for absorbed dose to water of the National Metrology Institute of Japan (NMIJ) and of the Bureau International des Poids et Mesures (BIPM) was carried out in the 60Co ?-ray reference beam of the BIPM in November to December 2009 under the auspices of the key comparison BIPM.RI(I)-K4. The comparison result, based on the calibration coefficients for two transfer standards and expressed as a ratio of the NMIJ and the BIPM standards for absorbed dose to water, is 0.9960(46). The degrees of equivalence between the NMIJ and the other participants in this comparison have been calculated and the results are given in the form of a matrix for the ten national metrology institutes (NMIs) that have participated. 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 Section I, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Development of the Soft X‐ray Intensity Measurement with a Cryogenic Radiometer

A cryogenic radiometer has been revised and examined in order to improve the absolute measurement of soft X‐ray intensities. The uncertainty of the temperature rise in the cavity absorber has decreased to 0.2 % through an increase in the thermal responsivity and through the suppression of the fluctuation in the back ground temperature.

Key comparison BIPM.RI(I)-K7 of the air-kerma standards of the NIST, USA and the BIPM in mammography x-rays.

A first key comparison has been made between the air-kerma standards of the PTB and the BIPM in mammography x-ray beams. The results show the standards to be in agreement at the level of the combined standard uncertainty of 3.7 parts in 103. A comparison of the standards has also been made in simulated mammography x-ray beams. The standards agree at the level of the combined standard uncertainty of 3.5 parts in 103. The results are analysed and presented in terms of degrees of equivalence for entry in the BIPM key comparison database. 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 Section I, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

International comparison EUROMET.RI(I)-S2 of extrapolation chamber measurements of the absorbed dose rate in tissue for beta radiation (EUROMET project No 739): Final report

For quality assurance in the realization and transfer by the national standard laboratories of the unit of the absorbed dose rate at 0.07 mm tissue depth for beta radiation, comparison measurements among the primary standard facilities are needed. Although some bilateral comparisons have taken place for this quantity, the CCRI decided in May 2003 that a EUROMET supplementary comparison would be appropriate if inclusive of primary standards laboratories of other regional metrology organizations. The operation and results of such a comparison are reported here. A flat ionization chamber and measurement system was used as the transfer instrument. A comparison was made of the calibration coefficients of this transfer instrument in various beta-particle laboratory reference fields (Pm-147, Kr-85, Tl-204 and Sr-90/Y-90) measured by each of the eight participants from France, Italy, Finland, Germany, Russian Federation, USA, Canada and Japan. The PTB was the pilot laboratory and the comparison ran from January 2004 until April 2007 under EUROMET project No 739 and EUROMET.RI(I)-S2. The results for most of the participants are consistent with the stated uncertainties although an extreme deviation is apparent for Pm-147 beta radiation for one participant. 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 EUROMET, according to the provisions of the CIPM Mutual Recognition Arrangement (MRA).

Comparison of the NMIJ and the ARPANSA standards for absorbed dose to water in high-energy photon beams

The authors report the results of an indirect comparison of the standards of absorbed dose to water in high-energy photon beams from a clinical linac and (60)Co radiation beam performed between the National Metrology Institute of Japan (NMIJ) and the Australian Radiation Protection and Nuclear Safety Agency (ARPANSA). Three ionisation chambers were calibrated by the NMIJ in April and June 2013 and by the ARPANSA in May 2013. The average ratios of the calibration coefficients for the three ionisation chambers obtained by the NMIJ to those obtained by the ARPANSA were 0.9994, 1.0040 and 1.0045 for 6-, 10- and 15-MV (18 MV at the ARPANSA) high-energy photon beams, respectively. The relative standard uncertainty of the value was 7.2 × 10(-3). The ratio for (60)Co radiation was 0.9986(66), which is consistent with the results published in the key comparison of BIPM.RI(I)-K4.

Key comparison BIPM.RI(I)-K5 of the air-kerma standards of the PTB, Germany and the BIPM in 137Cs gamma radiation

A direct comparison of the standards for air kerma of the National Metrology Institute of Japan (NMIJ) and of the Bureau International des Poids et Mesures (BIPM) was carried out in the 137Cs radiation protection-level beam of the BIPM in June 2012. The comparison result, expressed as a ratio of the NMIJ and the BIPM standards for air kerma, is 0.9977 with a combined standard uncertainty of 2.6 × 10−3 Taking into account the changes made to the BIPM standard, the result of the present comparison agrees within the uncertainties with the result of the direct comparison carried out in 2001. 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).

Feasibility Study of Alanine Dosimeter for Carbon-Beam Dosimetry

Alanine dosimeters are useful tools for measuring both kilo-gray level doses and radiation therapy level doses. The National Metrology Institute of Japan is planning to develop a dose measurement service for carbon-beam therapy. The purpose of this study was to verify that the alanine dosimeter could be used for carbon-beam dosimetry. We irradiated the alanine dosimeter with 60Co-gamma rays and a carbon beam using a range of 10–30 Gy. For the gamma-ray irradiation, the alanine dosimeter was placed in a 5 g cm−2 water phantom. For the carbon-beam irradiation, the spread out Bragg peak of the 290 meV/u carbon ion was used, and the dosimeter was located at the centre of the peak region. The alanine spectra obtained under the carbon-beam irradiation were almost the same as the spectra under the gamma-ray irradiation. The alanine dosimeter irradiated with the carbon beam show a smaller signal than that obtained under the gamma-ray irradiation for the same dose. The alanine signal increased as the dose increased over the entire dosage range for both the gamma-ray and carbon-beam irradiation. This result suggests that the alanine dosimeter has potential for carbon-beam dosimetry.