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 × 10
4 to 2.8 × 10
4dpm/g BaSO
4. These values give a rate of deposition and an initial composition of the radionuclides in the hokutolite.
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