Study of soil-fern transfer of naturally occurring alpha emitting radionuclides in the Southern Region of Cameroon

Abstract

This study was carried out in the localities Melondo and Ngombas located in the Southern Region of Cameroon where there are known to be uranium-bearing and high background radiation areas. Activity concentrations of naturally occurring radionuclides 210Po, 238U, 235U, 234U, 232Th, 230Th, 228Th and 226Ra were determined in soil and fern (filicophyta) samples collected at 10 points in both localities. In soil, the average values of these activity concentrations (in Bq.kg−1 d.w.) were 210Po(130 ± 10), 238U(126 ± 11.6), 235U(5 ± 1), 234U(131 ± 10), 232Th(400 ± 22), 230Th(145 ± 11), 228Th(381 ± 21) and 226Ra(154 ± 28) at Melondo; and 210Po(228 ± 1), 238U(170 ± 11), 235U(9 ± 2), 234U(179 ± 12), 232Th(200 ± 18), 230Th(184 ± 18), 228Th(228 ± 22) and 226Ra(416 ± 7) at Ngomba. In fern the average activity concentrations were: 210Po(35 ± 3), 238U(0.68 ± 0.05), 235U(0.042 ± 0.01), 234U(0.90 ± 0.05), 232Th(1.2 ± 0.2), 230Th(0.7 ± 0.1), 228Th(39 ± 3) and 226Ra(14 ± 3) at Melondo and 210Po(24 ± 2), 238U(0.82 ± 0.06), 235U(0.046 ± 0.01), 234U(0.92 ± 0.06), 232Th(0.8 ± 0.2), 230Th(0.9 ± 0.2), 228Th(15 ± 5) and 226Ra(14 ± 3) at Ngomba. The soil-fern transfer factors (TF) (in kg.kg−1) were respectively 210Po(1.64 × 10−1), 238U (5 × 10−3), 235U(7 × 10−3), 234U(6 × 10−3), 232Th(3 × 10−3), 230Th(5 × 10−3), 228Th(7.9 × 10−2), and 226Ra(5.1 × 10−2). The highest TF for fern was for 210Po, probably because of atmospheric deposition. The TFs of uranium and thorium were comparable to those given in the IAEA handbook for grass.