The use of lichen (Canoparmelia texana) asbiomonitor of atmospheric deposition of naturalradionuclides from U-238 and Th-232 series

摘要

Lichens have been used in studies of environmental pollution monitoring of various airpollutants, especially heavy metals. This paper aims to study the possibility of using this specimenfor the assessment of radionuclides deposition in the vicinity of a nuclear research institute,Instituto de Pesquisas Energeticas e Nucleares (IPEN) located in Sao Paulo, Brazil. This Institutehas as major activity to perform research in the field of the nuclear fuel cycle, and therefore dealswith considerable amounts of natural radionuclides of the U and Th series. The activity of thenaturally occurring radionuclides U-238, Ra-226, Ra-226 and Pb-210 was determined in samplesof lichen (Canopannelia texana) and soil collected at IPEN campus. The concentrations of Ra-228, Ra-226 and Pb-210 were determined by measuring alpha and beta gross counting in a gasflow proportional detector; U and Th were determined by neutron activation analysis. The valuesobtained varied from 164 Bq/kg to 864 Bq/kg, 13 Bq/kg to 50 Bq/kg, and from 287 Bq/kg to 730Bq/kg for Ra-228, Ra-226 and Pb-210 respectively. For natural U and Th the values obtainedvaried from 1.2 Bq/kg to 162 Bq/kg and 1.84 Bq/kg to 5.17 Bq/kg respectively. The resultsobtained so far suggest that the Canoparmelia texana can be used as radionuclide monitor in thevicinity of nuclear installations.