Susumu Minato

Natural gamma-radiation in the Aeolian volcanic arc.

Pulse-height distributions of gamma-rays, obtained with a field NaI(Tl) scintillation spectrometer in numerous sites of the Lipari and Vulcano islands (Aeolian volcanic arc, Italy), were measured to determine the U, Th and K concentrations of the bedrock and the relative values of the air absorbed dose rate. U is spatially related to both Th and K and the Th/U ratio is on average 3.1-3.5. The magmatic evolution is reflected by the concentration of the three radioelements, as they are more abundant within the more felsic units of the volcanic series. The higher values of U (15.7-20.0 ppm) coincide with higher Th (48.3-65.9 ppm) and K (4.9-6.1%) concentrations associated with rhyolitic rocks of the third cycle (< 50 ky). The air absorbed dose rate varies from 20 to 470 nGy h(-1). The highest values (> 350 nGy h(-1)) are observed on outcrops of rhyolitic obsidian lava flows. The cosmic-ray contribution is also evaluated to estimate the total background radiation dose rate.

Bulk density estimates of buildings using cosmic rays

A simple formula is derived for propagation of cosmic rays through matter to calculate intensities inside and outside large objects of different densities. The bulk densities of the objects are estimated by comparing calculations and measurements. Evaluations for normal concrete building are made as an example of large structural material; the bulk density is shown to be around 0.5 g/cm3.

Influence of the precipitation rate on the seasonal variation in the specific radioactivity of short-lived222Rn daughters in precipitation

Data of variations in the RaB/214Pb/ and RaC/214Bi/activities in precipitation obtained from observations made for a period of almost 5 years are given together with data on changes in precipitation rate measured simultaneously. It is concluded from analysis of these data that the precipitation rate variation contributes to approximately 40% to the seasonal variation in the specific activity of precipitation.

Terrestrial gamma ray dose rates of Brunei Darussalam

GPS-indexed in-situ and car-borne survey of terrestrial gamma-ray dose rates were carried out in Brunei and adjacent areas using two portable NaI(Tl) counters. The mean and population weighted average dose rates for Brunei are 34 and 33 nGy/h, respectively. The car-borne data and the in-situ data when spectral analysed separately, were found to show fractal behaviour with D of 1.7 and 1.8, respectively. A contour map of the dose rates was also produced.

A new method of determining the total flux of environmental gamma radiation by a 2″Ø×2″ NaI(Tl) scintillation counter

Abstract A convenient and easy method for estimating the flux of environmental gamma radiation by measuring counting rate and electric current from a photomultiplier tube coupled to a 2″O×2″ NaI(Tl) scintillator has been developed.

Simple theory concerning the emission efficiency and energy deposition of electrons produced in a slab exposed to 1.25 MeV gamma rays

Abstract A simple theory concerning the photon induced electron emission and absorption is derived, based on the diffusion model proposed by Bethe, Rose and Smith. Analytical expressions are presented for emission efficiency and energy deposition of electrons produced in a slab exposed to 1.25 MeV gamma rays and compared to experimental measurements and Monte Carlo calculations. Although the agreement between them is generally good, in view of the simplified model, a considerable difference is shown for the forward emission efficiency in the case of a very thick slab compared to the electron range and for the backward emission efficiency in the case of a relatively thin slab or of very low atomic number material.