Kajian fizik kesihatan negeri Selangor, Wilayah Persekutuan Kuala Lumpur dan Putrajaya

Abstract

Terrestrial gamma radiation is one of the main constituents of background radiation and the irradiation is due to the terrestrial radioactivity. Health physics study were carried out to obtain the baseline data of radioactivity and terrestrial gama radiation (TGR) level in State of Selangor, Federal Territories of Kuala Lumpur and Putrajaya. The study provide a methodology of sampling for TGR dose rate survey and a statistical regression model for predicting the TGR dose rate based on linear relationship between total dose rate with geological background, Dg and soil types, Ds. The TGR dose rate survey, Dm has been conducted using scintillation detector Ludlum 19 micro R meter NaI (Tl). Based on airborne survey map, geological background map and soil survey map, the sampling method was used to determine survey point Dm. For quality control of the sensitive TGR dose rates, Dm at environmental level, a statistical interpolation of gradient between calculated dose rate, Dc and Dm have been carried out to obtain the correction factor, Cf using radioactivity data of ? - rays emitters 238U, 232Th and 40K in soil samples. The analysis of radioactivity concentration of radionuclides 238U, 232Th and 40K in soil samples were carried out using coaxial hyper-purity germanium (HPGe) gamma spectrometer. Based on baseline information of TGR dose rate data from previous research (1995 - 2013), 9884 data were analysed using Shapiro - Wilk, Kolgomorov - Smirnov and Levene statistical test for the normality distribution test. For verification of relationships of geological background and soil types on TGR dose rate, statistical hypothesis analysis of Welch’s ANOVA and Tamhane T2 were carried out. Based on baseline information, statistical regression model was built to predict TGR dose rates, Dp. The study has found that the average value of TGR, Dm dose rate was (182 ± 81) nGy h-1 which is three times higher than global average value and two times higher than average value for Malaysia with measurements range within 17.4 nGy h-1 - 500.0 nGy h-1. The derived equation for statistical regression model for predicting the TGR dose rate was given as Dp = [0.664 Dg + 0.414 Ds - 12.134]. The p value of ANOVA regression model analysis was p < 0.001 with F - ratio (f(2, 983) = 2341.053) and Pearson’s correlation value R is 0.903. At significant level of 0.05, null hypothesis was rejected and it is concluded that the dose rates of Dg and Ds influenced Dp value and there is a strong correlation between geological background and soil types. For statistical verification of the model validity, Dm and Dp data were analysed using ANOVA test and the F - ratio obtained (0.004) is smaller than F - critical (4.08) and H0: µx = µ0 were accepted at (fcal f1, 40, 0.05 = 4.08). Based on obtained regression model and the TGR dose rate survey, the baseline data are presented as an isodose map.