Hiroshige Morishima

Residual 152eu and 60co Activities Induced by Neutrons from the Hiroshima Atomic Bomb

Specific activities of 152Eu:Eu in stone samples exposed to the Hiroshima atomic bomb were determined for 70 samples up to a 1,500-m slant range from the epicenter. The specific activities of 60Co:Co were also determined for six samples near the Hiroshima hypocenter. First, the 152Eu data were investigated to find out the directional dependence of neutron activation. Directional anisotropy was not definite; however, there was an indication that the activation in the west-southwest was lower than in other directions. Second, measured 152Eu and 60Co radioactivity data were compared with activation calculations based on DS86 neutrons. It is clearly shown that the measured data are lower than the calculation near the hypocenter and vice versa at long distances beyond 1,000 m. The calculated-to-measured ratios of 152Eu are 1.6 at the hypocenter, 1.0 at approximately 900 m, and 0.05 at a 1,500-m slant range. Present results indicate that systematic errors exist in the DS86 neutrons concerning the source-term spectrum, neutron transport calculations in air, and/or activation measurements.

Decaying Patterns of Optically Stimulated Luminescence from Al2O3:C for Different Quality Radiations

Decaying Patterns of Optically Stimulated Luminescence from Al2O3:C for Different Quality Radiations Hiroshi YASUDA a , Ikuo KOBAYASHI b & Hiroshige MORISHIMA c a National Institute of Radiological Sciences , 4-9-1, Anagawa, Inage-ku, Chiba , 263-8555 b Nagase Landauer, Ltd. , Hisamatsu-cho, Nihonbashi, Chuo-ku , Tokyo , 103-8487 c Atomic Energy Research Institute, Kinki University , Kowakae 3-4-1, Higashi-Osaka-shi, Osaka , 577-8502 Published online: 07 Feb 2012.

Mortality and Cancer Incidence in Misasa, Japan, a Spa Area with Elevated Radon Levels

A historical cohort study was conducted in Misasa town, Tottori prefecture, Japan, where radon spas have been operating for a long time. Misasa town was divided into an elevated radon level area and a control area, with mean indoor radon levels of about 60 and 20 Bq/m3, respectively. In total, 3,083 subjects in the elevated radon level area and 1,248 in the control area, all aged 40 or older on January 1, 1976, were followed up until December 31, 1993, for a mean period of 14 years. The mortality rates from all causes exhibited no difference between the elevated radon level area and the control area for both sexes. No difference was observed in the incidence of all‐site cancers (age, period‐adjusted rate ratios by Poisson regression, RR=1.06, 95% confidence interval (CI) 0.79–1.42 for males, RR=0.90, 95% CI 0.65–1.24 for females), while stomach cancer incidence seemed to decrease for both sexes (RR=0.70, 95% CI 0.44–1.11 for male, RR=0.58, 95% CI 0.34–1.00 for female) and lung cancer incidence for males only seemed to increase (RR=1.65, 95% CI 0.83–3.30 for male, RR=1.07, 95% CI 0.28–4.14 for female) in the elevated radon level area. Caution is needed in the interpretation of these findings, however, since the individual exposure level was not measured and major confounding factors, such as smoking and diet, could not be controlled in this study.

Europium-152 depth profile of a stone bridge pillar exposed to the Hiroshima atomic bomb: 152Eu activities for analysis of the neutron spectrum

The 152Eu activity depth profile of a granite pillar of the Motoyasu bridge located 132 m from the Hiroshima atomic bomb hypocenter was assessed. The pillars each measured 82 cm in depth, 82 cm in width and 193 cm in height. One of the pillars was bored and 6.8-cm-diameter core samples were removed and cut into 2-cm-thick disks. Two gamma rays of 152Eu, 122 keV and 344 keV, in each disk were measured using a low background, gamma-ray spectrometer, and the activity distribution was determined as a function of depth in the granite. A concentration of stable Eu in the granite was determined by activation analysis. The specific radioactivity of 152Eu and 154Eu at the pillar surface was determined to have been 117 and 24 Bq per mg Eu, respectively, at the time of detonation. The value of 152Eu agrees within 20% of that calculated by Loewe. The depth profile of 152Eu in granite demonstrates a distinct difference from the estimates made only by thermal neutrons. Present data provide valuable information for the analysis of the neutron spectrum of the Hiroshima atomic bomb and its intensity.

Neutron imaging using an optical stimulated luminescent material: /spl alpha/-Al/sub 2/O/sub 3/:C+Gd/sub 2/O/sub 3//sup */

An optical stimulated luminescent (OSL) material /spl alpha/-Al/sub 2/O/sub 3/:C is sensitized for neutrons. Basic performances of neutron sensitivity, linearity, and fading characteristics are studied for three types of neutron sensitive OSL sheets using a prompt OSL reader. Neutron imaging is also studied using an imaging OSL reader. Preliminary results of neutron image will be shown in this paper.

Chromosome translocation in residents of high background radiation area in China

Abstract Utilizing our improved cytogenetic methods specifically developed for the study of the low dose effect, we analyzed chromosome translocations in the lymphocytes in 5 children and 11 old men in the naturally high background radiation area (HBRA) and in 6 children and 10 old men in the control area. Children had less number of translocations having less variation compared with the old men. The frequency of translocations among elder individuals is widely varied. Effect of the high background radiation on the frequency of translocation was not detected. The present study demonstrates that the contribution of radiation to the induction of stable chromosome type aberrations which accumulate in the body and therefore have statistically potential risk of causing malignant and/or congenital diseases is not significant compared with those of chemical mutagens and/or metabolic factors.

A mysterious spot on the outdoor concentration of radon isotopes

Abstract Temporal and spatial distribution of 222 Rn and 220 Rn and their progeny concentrations in the open atmosphere, 222 Rn and 220 Rn exhalation rates, radioactivities in soil and underground water, including some meteorological factors, were measured at a spot of high 222 Rn and 220 Rn concentrations to investigate the source and occurrence mechanism. Hourly mean concentrations of 222 Rn and 220 Rn during August 1993 were about 230 Bq m −3 and 130 Bq m −3 at 1 m above ground surface. Diurnal variations were high at daytime and low at nighttime, which gives an inverse variation compared with the typical variation in the normal environment. 222 Rn concentrations varied quickly in a few minutes and reached a maximum of about 14 kBq m −3 . The maximum daily mean 222 Rn concentration at 5 cm above ground surface was 11 kBq m −3 . Concentrations of 218 Po, 214 Pb, 214 Bi, and 220 Rn progeny were 8∼61 Bqm −3 , 1∼7 Bqm −3 , 0.5∼5 Bq m −3 , and 0.02∼0.14 Bq m −3 , respectively. The equilibrium factor for 222 Rn was estimated to be 0.01∼0.2. The main source of the mysterious spot of high 222 Rn and 220 Rn concentrations was a small but deep channel between the basement of the building and the surrounding soil, and the extremely localized weather condition.

Effect of spring water on the radon concentration in the air at Masutomi spa in Yamanashi Prefecture, Japan

The concentrations of 222Rn existing in air have been studied by using a convenient and highly sensitive Pico-rad detector system at Masutomi spa in Yamanashi Prefecture, Japan. The measurements in air were carried out indoors and outdoors during the winter of 2000 and the summers of 1999 and 2005. The concentrations of 222Rn in spring water in this region were measured by the liquid scintillation method. The concentrations of natural radionuclides contained in soils surrounding spa areas were also examined by means of the γ-ray energy spectrometry technique using a Ge diode detector to investigate the correlation between the radionuclides contents and 222Rn concentrations in air at each point of interest. The atmospheric 222Rn concentrations in these areas were high, ranging from 5 Bq/m3 to 2676 Bq/m3. The radon concentration at each hotel was high in the order of the bath room, the dressing room, the lobby, and the outdoor area near the hotel, with averages and standard deviations of the concentration of 441 ± 79 Bq/m3, 351 ± 283 Bq/m3, 121 ± 5 Bq/m3, and 23 ± 1 Bq/m3, respectively. The source of 222Rn in the air in the bath room is more likely to be the spring water than the soil. The spring water plays carries the radon to the atmosphere. Our measurements indicated that the 222Rn concentration in the air was affected by the 222Rn concentration in spring water rather than that in soil.

Characteristics of neutron radiography facility constructed at Kinki University reactor.

A neutron radiography facility was constructed at the Research Reactor of Kinki University (Advanced Argonaut Type, 1Wt). The facility has a Bi filter, divergent collimators (L/D=22.2 or 10.2) and drawers which can be loaded with samples, converters and films. Neutron fluence rate on one of the drawers is 1×104cm-2·s-1, which deposits grade 2 in density to a Fuji FG film contacted with an NE-426 converter during 40min irradiation. Neutron radiograph of ASTM beam purity and sensitivity indicator shows that themal neutron content is 60, scattered neutron contribution 4.1, γ contribution 1.8, pair production contribution 0.5, the number of detectable holes 3 and the number of detectable gaps 7. The characteristics have been proved that the facility will be fully useful for the research of neutron radiography.

STUDIES ON THE RELEASE OF RADIOACTIVITIES FROM THE ION EXCHANGE RESINS INTO THE SEA WATER

Abstract For the purpose of estimating the release of radioactivities from ion exchange resins disposed into sea water, we have conducted a series of experiments in a water bath containing natural sea water, using such radioactive nuclides as 51Cr, 55Fe, 60Co, 89Sr and fission products by changing the weight ratio of ion exchange resin to the sea water and the amount of nuclide initially adsorbed on the ion exchange resin under static and turbulent conditions. The results are summarized as follows: 1 The radioactivities were rapidly released from the ion exchange resin particles (Dowex 50 and Dowex 1, 50–100 mesh) on contact with the sea water. However, some differences were observed in the degree of release depending on the different nuclides. Such nuclides as 60Co and 89Sr were easily released, while 51Cr and 55Fe not so easily. 2 The released activity was observed to increase with the decreasing weight ratio of the ion exchange resin to the sea water, but with the weight ratio below 10–4 of the ion exchange resin to the sea water no remarkable difference was observed. 3 The results of fractionation of suspended matter in sea water containing 55Fe, 60Co and 89Sr will be discussed also.