Vertical profiles and enrichment pattern of natural radionuclides in monazite areas of coastal Kerala

Detailed studies on radionuclides concentration in different environmental matrices of high background areas were undertaken in the coastal areas of Karunagapalli, Chavara, Neendakara and Kollam to study the distribution and enrichment of the radionuclides in the region. The sand samples collected at different distances from sea waterline and at different depths, were analysed for primordial radionuclides by gamma spectrometry. The activity of primordial radionuclides was determined for the different size fractions of sand to study the enrichment pattern. The highest activity was found confined in 125-63 μm particle size fraction in sand. The minimum ²³²Th activity was 9.4 Bq kg^-1, found in Kollam at a depth of 10-20 cm, 40 m away from waterline in 500-250 μm particle size fraction and maximum activity of 136,811.2 Bq kg^-1 was observed in Chavara in grains of size 125-63 μm at a depth of 0-10 cm for a sample collected 20 m away from waterline. The lowest ²²⁶Ra activity observed was 29.6 Bq kg^-1 at Kollam beach for a sample 40 m away from waterline in grains of size 1000-500 μm and at a depth of 20-30 cm and the highest activity observed was 10,309 Bq kg^-1 in grains of size 125-63 μm for a sample collected at a distance 20 m away from waterline and at a depth of 0-10 cm. The activity of ⁴⁰K was below detectable level in most of the samples collected from the high background monazite area. The ²³²Th, ²²⁶Ra activities decrease with depth for the samples collected 20 m away from the waterline and increase with depth for the samples collected 40 m away from the waterline at Chavara and Kollam beaches. No definite correlation was found between variation of the concentrations of ²³²Th and ²²⁶Ra with depth at Karunagapalli and Neendakara beach sands. There exists a strong correlation between ²²⁶Ra and ²³²Th activities in the region. The results of these investigations are presented and discussed in this paper.