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Eight ancient bronze swords possessed at archaeological research laboratory of Hiroshima University were investigated non-destructively. Gamma-ray radiography using 137Cs and 60Co were developed to obtain transmission images of swords. X-ray fluorescence analysis were applied for the characteristic and qualitative elemental analysis of the swords. Magnetic response were also utilized to know the distribution of iron cores. It has been identified that all bronze swords has iron cores inside of the grip part of the sword. Up to now, existence of iron cores were assumed as a ritual symbol or functional meaning, but, it has revealed that these swords had originally iron blade, which were replaced to present bronze blade just to raise the commercial value. The connecting part was soldered and painted in bronze color. These findings are deeply related to the process of the production of bimetal swords in ancient Iran. Further researches on the ancient bimetal swords are needed.

We estimated external and internal effective doses for 15 residents who lived approximately 37 km northwest of the Fukushima Dai-ichi Nuclear Power Plant. The average cumulative effective dose was 8.4 mSv for adults and 5.1 mSv for children. The average committed effective dose from 134Cs and 137Cs was 0.055 mSv for adults and 0.029 mSv for children. The committed effective doses for thyroid gland was 27-66 mSv at maximum.

広島原爆が投下されたあとの1945年（昭和20年）10月から12月に原爆災害の岩石学的調査が行われ，岩石資料の収集が行われた。広島大学ではこれらの被爆資料がそのまま保管されていたので，40年後の昭和63年以降，原爆中性子線量評価と広島市内にのこる原爆のフォールアウトの調査に使用された。被爆資料中に生成された中性子誘導放射能，152Euおよび60Coを測定することにより，現在では資料の収集が不可能な爆心地周辺原爆中性子線量を決定する貴重なデータを提供した。また，戦後の核実験によるグローバルフォールアウトの影響を受けていないので広島市内における原爆フォールアウトの被爆者に及ぼす被曝線量を推定することができた。これらの資料は平成24年3月に広島大学総合博物館に寄託された。, In September 1945 after detonation of the atomic bombs at Hiroshima and Nagasaki, a special investigation committee was organized by the National Research Council of Japan. The purpose of the committee was to study scientific, engineering and medical aspects of the atomic bomb catastrophe. In the geological and geographical field, in situ observation and sampling were performed from October to December in 1945. Many stones, bricks, roof tiles and ceramic products near the hypocenter were collected, which provided information on the effects of heat on various substances. Since then these samples have been preserved without disturbance at Hiroshima University, and have played an important role in the evaluation of atomic-bomb radiation studies through the measurement of residual radioactivities of 152Eu and 60Co, and fallout of 137Cs. These samples were consigned to the Hiroshima University Museum in 2014 for peace education and to serve peace education.

Absorbed doses from main charged-particle beams and charged-particle fragments have been measured with high accuracy for particle therapy, but there are few reports for doses from neutron components produced as fragments. This study describes the measurements on neutron doses produced by carbon beams; microdosimetric distributions of secondary neutrons produced by 290 MeV/nucleon carbon beams have been measured by using a tissue equivalent proportional counter at the Heavy Ion Medical Accelerator in Chiba, Japan at the National Institute of Radiological Sciences. The microdosimetric distributions of the secondary neutron were measured on the distal and lateral faces of a body-simulated acrylic phantom (300 mm heightx300 mm width x253 mm thickness). To confirm the dose measurements, the neutron energy spectra produced by incident carbon beams in the acrylic phantom were simulated by the particle and heavy ion transport code system. The absorbed doses obtained by multiplying the simulated neutron energy spectra with the kerma factor calculated by MCNPX agree with the corresponding experimental data fairly well. Downstream of the Bragg peak, the ratio of the neutron dose to the carbon dose at the Bragg peak was found to be a maximum of 1.4x10−4 and the ratio of neutron dose was a maximum of 3.0x10−7 at a lateral face of the acrylic phantom. The ratios of neutrons to charged particle fragments were 11% to 89% in the absorbed doses at the lateral and the distal faces of the acrylic phantom. We can conclude that the treatment dose will not induce serious secondary neutron effects at distances greater than 90 mm from the Bragg peak in carbon particle therapy.

Residual ^Co activity in five steel samples induced by neutrons from the Nagasaki atomic bomb has been measured within about 1000 m from the hypocenter. The chemical separation of cobalt and nickel from steel samples was performed, and cobalt-enriched samples were prepared for all samples. Gamma-ray measurements were carried out with a low-background well-type germanium detector. The gamma-ray spectra for five samples were compared with the spectrum of a control sample to ensure that the observed ^Co was actually induced by A-bomb neutrons. The activation of cobalt by environmental neutrons was also investigated. It has been shown that the present ^Co data are consistent with earlier Hashizume's data., Journal of radiation research. 2002, 43(4), p.387-396

The depth profile of 152Eu activity induced in a large granite stone pillar by Hiroshima atomic bomb neutrons was calculated by a Monte Carlo N-Particle Transport Code (MCNP). The pillar was on the Motoyasu Bridge, located at a distance of 132 m (WSW) from the hypocenter. It was a square column with a horizontal sectional size of 82.5 cm x 82.5 cm and height of 179 cm. Twenty-one cells from the north to south surface at the central height of the column were specified for the calculation and Eu activities for each cell were calculated. The incident neutron spectrum was assumed to be the angular fluence data of the Dosimetry System 1986 (DS86). The angular dependence of the spectrum was taken into account by dividmg the whole solid angle into twenty-six directions. The calculated depth profile of specific activity did not agree with the measured profile. A discrepancy was found in the absolute values at each depth with a mean multiplication factor of 0.58 and also in the shape of the relative profile. The results indicated that a reassessment of the neutron energy spectrum in DS86 is required for co汀ect dose estimation.

There is a systematic discrepancy between the measured radionuclide activation yieldsin materials exposed to neutrons from the Hiroshima atomic bomb (A-bomb) and the calculated activation based on the Dosimetry System 1986 (DS86). The data at lkm are 2-10-times greater than the calculation and this implies that the actual level of exposure from the A-bomb must be higher than previously thought. In this paper, these activity data, including 152Eu, 60Co, 36C1 and 32P, were analyzed using a computer code (the Monte Carlo neutron and photon (MCNP) transport code system) to investigate the cause of the discrepancy. We present a possible mechanism of the neutron emission in Hiroshima which can reproduce the activity yields of 152Eu, 60Co, 36C1 and 32P assuming a small amount of leakage in the lateral direction (leakage except that in the direction to the hypocenter area). The DS86 calculation did not take such leakage into account. In addition to this leakage, we assume increase of the burst height about 90 m to adjust the activity yields at relatively short ground distances. Taking these two assumptions into account and using a simple bomb model and leakage, it is shown that our calculation reproduces reasonably both the slopes and the absolute yield data of 152Eu, 32P, 60Co and 36C1 within about 1 km ground range. Over the ground range of about 1 km, it seems that further consideration is necessary concerning not only the calculation but also the data themselves to explain the DS86 discrepancy.

For the early entrance survivors in Hiroshima and Nagasaki atomic bomb (A-bomb), radiation doses from activated materials induced by the A-bomb neutrons are dominant. For estimation of such doses, element compositions of surrounded materials such as soil and nibbles are necessary. Especially Sc density in soil is important for estimating radiation doses at the time of a few 10 days after explosion. Because 46Sc which has the half-life of 84 days, is induced the A-bomb neutrons. However, few data of Sc density in soil are available in both of Hiroshima and Nagasaki cities. Purpose of this study is evaluation of Sc density in soil and the uncertainty using activation analysis. Soil samples were taken from 11 locations within 4 km from A-bomb hypocenter at Hiroshima city. The soil samples and reference rock sample of JA-11) were activated in Kyoto University Reactor (KUR). Element compositions are relatively obtained from each identified radionuclide counting rates in soil and reference rock by Ge-detectors. Twenty three element compositions including Al, Mn, Na and Sc are obtained by the activation analysis. The obtained element compositions are compared with values in Dosimetric System 1986 (DS86) and those are roughly the same as the reported values in DS86. Sc density in Hiroshima soil was estimated to be 5.12±0.59 (ppm). It was found the unevenness of Sc density in soils for 11 location of Hiroshima city is about 12%. Using element compositions by the activation analysis, time variation of the exposure rate by activated soil are estimated. It was found that exposure rate in the few minute time range is dominated by 28A1, in the several days by 24Na, and in the a few 10 days by 46Sc. This estimated result is compared with measured dose rate measured after a few months after explosion. It was found that the estimated dose rate is quite similar to the measured one.

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A new low-background shielding was installed for a Ge detector. Background gamma-ray spectrum was measured and compared with that of old shielding to investigate how improved the background counting rate. Additional improvements for the new shielding was installed to reduce background counting rate. It has been shown that shielding of the neck part of Ge detector cryostat and concrete floor are effective to reduce background contribution. The reduction factor of ^K 1461 keV gamma-ray was much improved from 51 of old shield to 4290 of new shield.

13th SYmposium on Microdosimetry