Specific activities and radioactive contour maps of natural and anthropogenic radionuclides in beach sand samples (Patong, Kamala, Kata, Karon and Nai Yang) after tsunami disaster in Phuket province, Thailand

摘要

Specific activities of natural (~(40)K, ~(226)Ra and ~(232)Th) and anthropogenic (~(137)Cs) radionuclides in 155 beach sand samples collected from Patong, Kamala, Kata, Karon and Nai Yang beaches, which were affected by the 2004 tsunami disaster, in Phuket province, Thailand, have been studied and measured. Experimental results were obtained by using a high-purity germanium detector and gamma spectrometry analysis system. Gamma ray from radioactive standard sources Cesium-137 (~(137)Cs), Cobalt-60 (~(60)Co) and Barium-133 (~(133)Ba) were used to calibrate the measurement system. KCl, two well-known (IAEA/RGU-1 and IAEA/RGTh-1) and IAEA/SL-2 reference materials obtained from the International Atomic Energy Agency were used to analyze and compute the ~(40)K, ~(226)Ra,~(232)Th and ~(137)Cs specific activities in samples from five beaches. The measuring time of each sample is 10,800 s. It was found that the average specific activity of ~(40)K in these areas (2459.14 ± 171.71 Bq/kg) was rather high. Furthermore, the results were also used to evaluate the absorbed dose rates in air (D), the radium equivalent (Ra_(eq)), the external hazard index (H_(ex)) and the annual effective dose rate (AED_(out)) in all beach areas. Moreover, experimental results were compared with the Office of Atoms for Peace research data, Thailand as well as with global radioactivity measurements and evaluations. All of the calculated values (~(40)K, ~(226)Ra, ~(232)Th and ~(137)Cs) were also compared with the recommended values which were proposed by the Organization for Economic Cooperation and Development (Exposure to radiation from natural radioactivity in building materials, 1979) and United Nations Scientific Committee on the Effects of Atomic Radiation (Sources, effects and risk of ionizing radiation, 1988; Exposure from natural sources of radiation, 1993; Sources, effects and risk of ionizing radiation, 2000). The data can be also used to create the radioactive contour maps of the investigated area.