Dose Measurement, Its Distribution and Individual External Dose Assessments of Inhabitants in the High Background Radiation Areas in China

Abstract

As a part of the China-Japan cooperative research on natural radiation epidemiology, we have carried out a dose-assessment study to evaluate the external exposure to natural radiation in the high background radiation areas (HBRA) of Yangjiang in Guangdong province and in the control areas (CA) of Enping prefecture since 1991. Because of the difficulties in measuring the individual doses of all inhabitants directly by personal dosimeters, an indirect method was applied in which the exposed individual doses were estimated from the environmental radiation doses measured by survey meters and the occupancy factors of each hamlet. We analyzed the dose in the hamlets and the variation in the occupancy factors to obtain the parameters of dose estimation on the inhabitants in selected hamlets; Madi and several hamlets of different dose levels in HBRA and Hampizai hamlet in CA. With these parameters, we estimated individual dose rates and compared them with those obtained from direct measurement using dosimeters carried by selected individuals. The results obtained are as follows. 1) The environmental radiation doses are influenced by the natural radioactive nuclide concentrations in building materials, the age of the building and the arrangement of the houses in a hamlet. There existed a fairly large and heterogeneous distribution of indoor and outdoor environmental radiations. The indoor radiation doses were due to exposure from the natural radioactive nuclides in the building materials and were about two times as large as the outdoor radiation doses. The difference between indoor and outdoor doses was not observed in CA. 2) The occupancy factor was influenced by the age of individuals and by the season of the year. The occupancy factor was higher for infants and aged individuals than for other age groups. This lead to higher dose rates of exposure to those age groups. 3) A good correlation was observed between the dose assessed indirectly and that measured directly and the correlation factor was 0.97.

Radiation survey on Fukushima Medical University premises about four years after the Fukushima nuclear disaster

“…As mentioned previously, the airkerma rates were 0.04 -0.52 μGy h -1 on the FMU premises. These values are comparable to those in the high -background -radiation areas such as Kerala, India (0.04 -2.1 μGy h -1 , outdoors) 45) and Yangjiang, China (0.26 -0.60 μGy h -1 , indoors) 46) . The high air -kerma rates in these areas are attributed to the presence of naturally occurring thorium -rich soil, which is distributed in along the coast in Kerala 45) and is used as in building materials in Yangjiang 46) .…”

“…These values are comparable to those in the high -background -radiation areas such as Kerala, India (0.04 -2.1 μGy h -1 , outdoors) 45) and Yangjiang, China (0.26 -0.60 μGy h -1 , indoors) 46) . The high air -kerma rates in these areas are attributed to the presence of naturally occurring thorium -rich soil, which is distributed in along the coast in Kerala 45) and is used as in building materials in Yangjiang 46) . Epidemiological surveys on the health effects due to external exposure in these areas indicated no statistically significant increase in mortality due to cancer or non -cancer diseases 47,48) .…”

Life under Conditions of Ionizing Radiation

“…However, there are certain areas with higher background radiation levels around the world. For an area in China dose rates of about 3-4 mGy/year have been reported [17] and on the Southwest coast of India the doses from external radiation by monazite deposits is 5-6 mGy/year with maximal doses up to 32.6 mGy/year [18]. Along certain beaches in Brazil where monazite sand deposits are found external radiation levels range up to 400 mGy/year [19].…”

A pilot study for dose evaluation in high-level natural radiation areas of Yangjiang, China

“…In the HBRA, indoor ambient gamma dose rate is higher than the outdoor dose rate, and it distributes widely between 260 and 600 nGy h -1 [2]. Different from the HBRAs such as Kerala, India, where external exposure is dominant [3], Yangjiang is characterized by dominant internal exposure.…”

“…A China-Japan cooperative study was organized and radiological and epidemiological studies were carried out [2,[5][6][7][8][9][10]. These studies did not find any statistically significant excess mortality due to cancer or non-cancer diseases [8,9].…”