Beta particle dose rates to micro-organisms in soil.

Abstract

Studies were made to estimate the beta-particle dose rates to micro-organisms of various sizes in soil. The small insects and organisms living in soil are constantly exposed to betaradiations arising from the naturally occuring radionuclides in soil as in this case no overlying tissue shields them. The technique of measuring beta-particle dose rate consisted of using of a thin plastic scintillator to measure the pulse height distribution as the beta particle traverses the scintillator. The integrated response was determined by the number and size of the photomultiplier pulses. From the data of soil analyses it was estimated that typically about 29% of the beta particles emitted per gm. of soil was contributed by the U/Ra series, 21% by the Th series and about 50% by potassium. By combining the individual spectra of these three radionuclides in the proportion found in a typical soil, a resultant spectrum was computed representing the energy distribution of the beta particles. The dose rate received by micro-organisms of different shape and size in soil was derived from the equilibrium dose rates combined with a ‘Geometrical Factor’ of the organisms. For the small organisms, the dose rates did not vary between the spherical and cylindrical types, but in case of larger organisms, the dose rates were found to be greater for the spherical of the same diameter.