ABSTRACT

The concentrations of radium isotopes (²²⁶Ra and ²²⁸Ra) and thorium isotopes (²³²Th, ²³⁰Th and ²²⁸Th) in a calcium carbonate sinter cone and hokutolites were determined. These nuclides were analyzed either by non-destructive γ-ray spectrometry or by α-ray sepctrometry after radiochemical separation. The concentrations of ²³²Th, ²²⁸Ra and ²²⁸Th (thorium series nuclides) in a sinter cone were 2.4 × 10^-2, 4.3 × 10^-1 and 7.1 × 10^-1 dpm/g, respectively. It was confirmed that thorium series nuclides in this sample were not in radioactive equilibrium with their parent, ²³²Th. Hokutolite samples collected recently showed higher radioactivities of ²²⁸Ra, ranging from 9.6 × 10⁴ to 2.8 × 10⁴dpm/g BaSO₄. These values give a rate of deposition and an initial composition of the radionuclides in the hokutolite.