Estimation of 'dose-depth' profile in the surface layers of a quartz-containing tile from the former Hiroshima University building indicates the possible presence of beta-irradiation from residual radioactivity after A-bombing.

The problem of differentiating between primary irradiation and exposure due to residual radioactivity following A-bombing (including beta-exposure), is the subject of special attention and discussions in order to understand the health effects following the Hiroshima and Nagasaki A-bombings, especially among newcomers to cities soon after the detonations. In this work, the method of single quartz grain luminescence retrospective dosimetry was applied for a retrospective estimation of the 'dose-depth' profile in a quartz-containing tile extracted from the building of former Hiroshima University (HU), which was a 'witness' of the Hiroshima atomic bombing on the 6 August 1945. It has been shown that results of retrospective estimates of the 'dose-depth' profile using the method of optically stimulated luminescence (OSL) from inclusions of quartz grains in very thin layers of the sample, in combination with the calculations of the 'dose-depth' profile using the Monte Carlo method, indicates the possible presence of beta irradiation of thin layers of the sample located near the surface of the tile facing the air, where there is no electronic equilibrium from gamma radiation.

Internal exposure to neutron-activated 56Mn dioxide powder in Wistar rats: part 1: dosimetry.

There were two sources of ionizing irradiation after the atomic bombings of Hiroshima and Nagasaki: (1) initial gamma-neutron irradiation at the moment of detonation and (2) residual radioactivity. Residual radioactivity consisted of two components: radioactive fallout containing fission products, including radioactive fissile materials from nuclear device, and neutron-activated radioisotopes from materials on the ground. The dosimetry systems DS86 and DS02 were mainly devoted to the assessment of initial radiation exposure to neutrons and gamma rays, while only brief considerations were given for the estimation of doses caused by residual radiation exposure. Currently, estimation of internal exposure of atomic bomb survivors due to dispersed radioactivity and neutron-activated radioisotopes from materials on the ground is a matter of some interest, in Japan. The main neutron-activated radionuclides in soil dust were 24Na, 28Al, 31Si, 32P, 38Cl, 42K, 45Ca, 46Sc, 56Mn, 59Fe, 60Co, and 134Cs. The radionuclide 56Mn (T 1/2 = 2.58 h) is known as one of the dominant beta- and gamma emitters during the first few hours after neutron irradiation of soil and other materials on ground, dispersed in the form of dust after a nuclear explosion in the atmosphere. To investigate the peculiarities of biological effects of internal exposure to 56Mn in comparison with external gamma irradiation, a dedicated experiment with Wistar rats exposed to neutron-activated 56Mn dioxide powder was performed recently by Shichijo and coworkers. The dosimetry required for this experiment is described here. Assessment of internal radiation doses was performed on the basis of measured 56Mn activity in the organs and tissues of the rats and of absorbed fractions of internal exposure to photons and electrons calculated with the MCNP-4C Monte Carlo using a mathematical rat phantom. The first results of this international multicenter study show that the internal irradiation due to incorporated 56Mn powder is highly inhomogeneous, and that the most irradiated organs of the experimental animals are: large intestine, small intestine, stomach, and lungs. Accumulated absorbed organ doses were 1.65, 1.33, 0.24, 0.10 Gy for large intestine, small intestine, stomach, and lungs, respectively. Other organs were irradiated at lower dose levels. These results will be useful for interpretation of the biological effects of internal exposure of experimental rats to powdered 56Mn as observed by Shichijo and coworkers.

Determination of the Average Native Background and the Light-Induced EPR Signals and their Variation in the Teeth Enamel Based on Large-Scale Survey of the Population.

The aim of the study is to determine the average intensity and variation of the native background signal amplitude (NSA) and of the solar light-induced signal amplitude (LSA) in electron paramagnetic resonance (EPR) spectra of tooth enamel for different kinds of teeth and different groups of people. These values are necessary for determination of the intensity of the radiation-induced signal amplitude (RSA) by subtraction of the expected NSA and LSA from the total signal amplitude measured in L-band for in vivo EPR dosimetry. Variation of these signals should be taken into account when estimating the uncertainty of the estimated RSA. A new analysis of several hundred EPR spectra that were measured earlier at X-band in a large-scale examination of the population of the Central Russia was performed. Based on this analysis, the average values and the variation (standard deviation, SD) of the amplitude of the NSA for the teeth from different positions, as well as LSA in outer enamel of the front teeth for different population groups, were determined. To convert data acquired at X-band to values corresponding to the conditions of measurement at L-band, the experimental dependencies of the intensities of the RSA, LSA and NSA on the m.w. power, measured at both X and L-band, were analysed. For the two central upper incisors, which are mainly used in in vivo dosimetry, the mean LSA annual rate induced only in the outer side enamel and its variation were obtained as 10 ± 2 (SD = 8) mGy y-1, the same for X- and L-bands (results are presented as the mean ± error of mean). Mean NSA in enamel and its variation for the upper incisors was calculated at 2.0 ± 0.2 (SD = 0.5) Gy, relative to the calibrated RSA dose-response to gamma radiation measured under non-power saturation conditions at X-band. Assuming the same value for L-band under non-power saturating conditions, then for in vivo measurements at L-band at 25 mW (power saturation conditions), a mean NSA and its variation correspond to 4.0 ± 0.4 (SD = 1.0) Gy.