Environmental radiology assessment in Lahad Datu , Sabah

Monitoring terrestial gamma radiation is crucial to prepare a baseline data for environmental radiological protection. Radiological research was carried out in Lahad Datu, Sabah to obtain the radioactivity status and terrestrial gamma radiation level in the area. We measure the terrestrial gamma radiation dose rates and analyse the radioactivity concentration of primordial radionuclides for radiological risk assessment. We identified that the annual estimation of dose effective for public is below the public dose limit, 1 mSv per year. Public and environment safety and health are remain secure. The obtained data and results can be used as reference for environmental radiology protection.


Introduction 1.Research Background
Due to its ionising power, high terrestrial gamma radiation dose may cause a detrimental effect to the public.The dilemma faced by public, governments and international radiation protection community on radiation health effects and risk of low doses has lead to the studies in the high background natural radiation area.Since the low level exposures may bring a stochastic effects to the public, the study of background radiation is extremely vital [1].
Public exposed to the radiation that occur from natural sources.Human beings were estimated to receive about 87% natural radiation.Therefore, it is important to assess environmental radiology for health and safety purpose [2].
Since the damage of Fukushima Daiichi nuclear plant tragedy, it is reported that 80% of radionuclides has entered the Pacific Ocean [3].Therefore, this study should be conducted as in Peninsular Malaysia because the Sabah is surrounded by ocean, such as the South China Sea, Sulu Sea, the Celebes Sea and the Pacific Ocean._____________________________ *Corresponding author: sfharhana@gmail.com

Problem Statement And Research Objectives
This research is conducted to measure the terrestrial gamma radiation in Lahad Datu district.This is also to prepare baseline data of terrestrial gamma radiation.Data collection in Peninsular Malaysia has been conducted but not in Lahad Datu, Sabah [18].The accident at the Fukushima Daiichi Nuclear Power Plant in Japan in March 2011 resulted in the release of several hundred pBq of activity into the environment [5].Therefore this research will identify the concentration of primordial radioanuclide for radiological health and safety assessment.Malaysia chose nuclear energy to guarantee supply beyond 2030 [6].Baseline data is one of important aspect in assessing nuclear power plant site [7].Hence, this research will build an isodose map of ionizing radiation in Lahad Datu for further reference.

The study area
Lahad Datu district is located in southeastern Sabah, coordinated between latitudes 4° 45' N and 5° 30' N, and longitudes 117° 30' E and 119° 15' E. It covers an area of 6,501 km 2 with 195,865 population in 2010.This district is a great socio-economy contributor to Sabah State as it has the largest palm tree cultivation [8] where the world-class Palm Oil Industrial Cluster has been built here [9].The world-class tourism spot, Danum Valley Conservation Area and Tabin Wildlife Reserve are also located in this district [9].

Measurements of terrestrial gamma radiation dose rate
The sampling points were determined based on the types of soil and geology in research area as the terrestrial gamma radiation is vary depends on the radionuclides concentration in soil [10].The terrestrial gamma radiation dose rate was measured by using a survey meter (Ludlum19 micro R meter).Measurements were conducted at approximately 1 m above the surface of the land [11].

Analysis of radioactivity concentration of primordial radionuclides
The collected soil samples is prepared in Marinelli beaker for the analysis of natural concentration of radionuclide by using HPGe gamma spectrometer detector in Nuclear Laboratory, Faculty of Science, UTM.The analysis of gamma radiation spectrum is carried out by using gamma radiation counter system (GC2018-7500SL model) paired with Genie 2000 VI.3 software.The concentration of 238 U is calculated based on the energy peak of gamma ray of daughter radionuclides 214 Pb and 214 Bi in the 238 U decay series.The concentration of thorium is calculated based on the energy peak of gamma rays of daughter radionuclides 228 Ac and 208 Tl in 232 Th decay series. 40K concentration is calculated based on the gamma ray emission peak of 1460.8 keV energy [12].

Radiological risk assessment
After analysing the concentration of natural radioactivity, radiological risk assessment is carried out by calculating the Annual Estimation of Dose Effective, AEDE, the estimated probability of occurrence of cancer risk, G, the Radium Equivalent Activity, Raeq, and the Hazards Index, Hex.

Isodose mapping
Isodose map of gamma irradiation in Lahad Datu is built based on terrestrial gamma radiation survey by using spatial mapping analysis software ArcGIS 9.3.

Terrestrial gamma dose rates
A total of 86 sampling points were determined and the reading of gamma radiation dose rates was measured by using survey meter.Out of 86 sampling points, 10 soil samples labeled as S1 to S10 were taken for the analysis of the concentration of radioactivity.The soil samples were taken as representatives of different doses of dose levels; low and high doses relative to the environmental level.The highest gamma dose rate is 79.4 nGy h -1 .The lowest terrestrial gamma dose rate is 6.1 nGy h -1 .The mean terrestrial gamma dose rate is 44.7 nGy h -1 much lower than the mean terrestrial gamma dose rate proposed by UNSCEAR (2000), 57 nGy h -1 .

Radioactivity concentration of primordial radionuclides
Table 1 illustrates the radioactivity concentration of primordial radionuclides, C in soil samples.The mean value of CU-238, CTh-232 and CK-40 is 42.6 Bq kg -1 , 77.7 Bq kg -1 and 810.9 Bq kg -1 respectively.It was assumed that the high value of potassium concentration is due to the contribution of potassium content in fertilizer used in palm tree cultivation.

Radiological risk assessment
Using equation ( 1), the annual effective dose equivalent, AEDE to the public was calculated (UNSCEAR, 2000).

AEDE
= Dose rate nGy j -1 x 24 hrs x 365 days x 1 OF x 0.7 Sv Gy -1 x 10 -6 ( Annual Estimation of Dose Effective, AEDE is 0.44 mSv per year lower than public dose limit, 1 mSv per year. The probability of the risk of cancer , Gr is estimated by using equation (2).The risk factor, R is 0.05 Sv -1 and H is the AEDE value [13].
The estimated probability of the risk of cancer, Gr is 0.02 probability per year per person.The value of the probability of cancer risk is too small to be considered as radiological hazard to the public in the study area.
Radium equivalent activity, Raeq 160 Bq kg -1 which is less than the recommended limit of concentration for TENORM material which is 370 Bq kg The value of Hex must be lower than 1 which equivalent to the maximum recommended limit of radium activity, 370 Bq kg -1 [16].In this study, the Hex value is 0.58 which is lower than 1.

Isodose mapping
Figure 1 exhibits an isodose map based on the survey of gamma radiation in the field.The map contour generated in the isodose map based on the surveys are still rough where there is a large gap between the contour for the less observed area.This is because the accuracy of the interplotation data is proportional to the distance between dose rate survey points [17].By following the dose rate range of isodose maps of Peninsular Malaysia [18], Figure 1 shows a very low dose rate in research area which indicates a safe environment for public.

Conclusion
The level of gamma radiation in the environment is too small to cause an acute effect and macro stochastic effect.We identified that the annual estimation of dose effective for public is below the public dose limit, 1 mSv per year.Therefore, public and environment safety and health are remain secure.The obtained data and results from this study can be used as reference for environmental radiology protection.

Figure 1 :
Figure 1: Isodose map based on gamma radiation survey in study area.