Decontamination Factors (DFs) of HEPA filter were measured against 239Pu oxide aerosols. Collection performance of HEPA filter media was investigated using monodisperse NaCl aerosols at various air flow face velocities. From the penetration curves the most penetrating particle size, MPPS, and the maximum penetration, Pmax, were obtained in each face velocity. The MPPSs at 0.8-11cm s-1 flow were not found in 0.3μm size range but in 0.1-0.15μm size range. The reciprocal of Pmax, which means the minimum of decontamination factor, DFmin, linearly increased with decreasing face velocity in a logarithmic paper. Experimental DFs against Pu aerosols in the MPPS range were nearly equal to the DFmin, and the others were always larger than the DFmin. This means that there are no differences between Pu and NaCl aerosols in terms of filtration. The DFmin estimated from the nonradioactive test aerosols is important for evaluating the performance of HEPA filters in the radiation protection field.
A new alternative method to calculate the migration rate of excess 210Pb from undisturbed soil profiles was developed on the basis of the same advection equation used in the previous work. In this method, no assumptions are made to evaluate migration rate and travel time. The authors have already described two different methods with some assumptions. The method can numerically calculate the migration rate of excess 210Pb at every horizon of interest, and estimate their changes through the ground. The numerical approximation method was considered to be the most appropriate one of the three, which were outlined and illustrated. Undisturbed soil samples were collected from three sites in Kyoto City, Japan and the contents of 210Pb and 226Ra were analyzed with a γ-ray spectrometry to obtain excess 210Pb profiles in the ground surface. Each method was applied to these observed profiles and the results were compared. Irrespective of the estimating methods, the average migration rates were almost the same for each site, and were found to be within a range of about 1-2mm/y. The average deposition rate of 210Pb for three sites was also estimated to about 140MBq/km2·y.
A new version of the dose calculation program, JEUNESSE-2 code, was developed which copes with external neutrons as well as photons. The code is capable of calculating the effective dose E for six different age groups: 0-, 1-, 5-, 10- and 15-year, and adult. The continuous function of the radiation weighting factor and the new tissue weighting factors, specified in ICRP Publication 60, were employed in the calculation of E. The Monte Carlo code MORSE-CG was incorporated in the JEUNESSE-2 code to calculate the transport of neutrons and produced γ-rays from a source to organs or tissues of the phantoms. A sample calculation for isotropic neutron incidence showed a significant age dependence of E. A comparison of the resultant E for adult males with other results gave good agreement.
Cosmic-ray count rates in the energy range above 3 MeV have been continuously observed with a 3″φ×3″ NaI (T1) scintillation detector at environmental radiation monitoring stations in Maizuru. Variations of cosmic-ray intensities were analyzed in relation to atmospheric pressure and temperature. The results indicated that an increase of 1hPa in atmospheric pressure decreased the count rate by 0.2%, and an increase of 1°C in atmospheric temperature at 500hPa level decreased the rate by 0.1%.
The recent development of instruments for radiation measurement has made measurement of low-level environmental gamma ray dose rates simpler and easier. Many of these instruments are commercially available. However, it is still indispensable to separate unnecessary component from the measured data, or to make appropriate corrections considering the physical meanings of the measured quantity when one trys to measure environmental gamma ray dose rate with high accuracy. In this report, a procedure of data treatment for measurement of environmental gamma ray dose rates with high accuracy using a NaI (T1) scintillation detector and spectrometric techniques is mentioned. It includes separation of unnecessary component involved in the measured pulse height spectra, correction of the angular response of the detector, calibration of the relation between pulse height and gamma ray energy, and the process of data treatment.