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.
