Determination of Natural Radioactivity Level on Soil and Radiological Hazards in The Geotermal Area of Solok South, West Sumatera

: Solok Selatan is one of the areas in West Sumatra that has geothermal potential, contains much higher levels of radioactive substances in the soil in the form of Radium ( R 88226 a ), Thorium ( Th 90232 ), and Potassium ( K 1940 ). This study aimed to measure the concentration of R 88226 a , Th 90232 and K 1940 contained in the soil in the Solok Selatan which was then reviewed based on PERKA BAPETEN No. 9 of 2009 and UNSCEAR 2000, also evaluates the average radium equivalent activity (Ra eq ) , representative level index ( I γr ) , external hazard index ( H ex ) . Soil samples were collected from seven different locations. The radionuclide activity concentration was measured by using a gamma spectrometer in the PTKMR BATAN laboratory, with the results of the average radionuclide measurement R 88226 a being 28.58 Bq/kg, Th 90232 was 44.74 Bq/kg and K 1940 at 323.29 Bq/kg. For the average value of Ra eq is 118,051 Bq/kg, I γr is 0.853 and H ex is 0.335. Based on BAPETEN PERKA No. 9 of 2009 and UNSCEAR 2000, the radionuclide activity concentration was found still within safe limits. It does not pose a health hazard to the people living in the area.


Introduction
Geothermal energy (or geothermal energy) is a relatively environmentally friendly energy source because it comes from the heat within the earth. This geothermal potential is used as a generator of electricity, heating pumps, toiletries and so on. Solok Selatan is one of the areas in West Sumatra that has geothermal potential which has been used as a geothermal power plant.
Geothermal potential contains natural radionuclides derived from soil, rock and water below the earth's surface. Natural radioactive substances in the soil in the soil come from Radium ( 88 226 ) with a half-life (T 1/2 ) of 1602 years, Thorium ( ℎ sources. Natural radionuclides in soil can enter the human body through the process of digestion or inhalation which can cause damage and cell death due to free radicals from ionizing radiation. The existence of this threat is important to identify the place of residence of the dangers of natural radioactive substances by measuring the level of radionuclide concentration to ensure the activity of radioactive substances is still below the threshold. The maximum nuclide radiation threshold allowed by BAPETEN based on BAPETEN (BAPETEN, 2009;UNSCEAR, 2000).
Regional radiation monitoring is carried out in the work area and the environment. Monitoring is carried out with the aim of ensuring that the workplace conditions are guaranteed safe from radiation. This monitoring is also useful as a warning alarm in case of deviations from normal operating conditions so as to ensure that there is no release of radioactive substances into the environment. Monitoring can be done by taking environmental samples such as soil, grass, crops, water, air and so on, which are then processed and processed in the laboratory to obtain the level of radioactive content. Measurement of the concentration of natural radionuclide activity was carried out using a gamma spectrometer.
Research on the radioactivity level of the soil in the Dikili geothermal area, Turkey has been measured using a NaI(Tl) gamma spectrometer. Measurement of the level of radioactivity in the soil showed 92 238 values of 28.7 Bq/Kg, ℎ 90 232 of 17.6 Bq/Kg and 19 40 of 579.2 Bq/Kg. This study also evaluates health hazards associated with natural activities where the calculated radioactivity value is not too high and does not exceed a predetermined threshold value (Tabar et al., 2013).
In the area of Karimun Island, Riau Archipelago Province which has a lot of processing activities, the radioactivity level is obtained from 88 226 of (23. 63 -139.45 in some locations are relatively higher than in other areas such as Bali and East Java, so it is necessary to conduct further studies on community and environmental safety (Wahyudi et al., 2012).
Another study regarding the concentration of natural radionuclide activity in Padang, West Sumatra, was measured using the gamma spectrometer method at a soil sample depth of 0-5 cm. The measurement results showed that the activity of radionuclide 88 226 was (4.05 ± 0.29) to (53.44 ± 2.91) Bq/kg, activity ℎ 90 232 was (6.33 ± 0 .45) to (109.39 ± 5.75) Bq/kg and 19 40 activity of (38.04 ± 22.86) to (1042.08 ± 76) Bq/kg. Radionuclide activity in soil samples in Padang City is still below the safe threshold and has not caused a health hazard to the people living in the area (Despriani et al., 2020).
Research on soil samples was also carried out in the Kirkuk area, Iraq by collecting 10 soil samples. The results showed that the concentration of radionuclide activity at 88 226 was (27.4 -57.0) Bq/Kg, ℎ threshold value that was set and the value is lower than the safe threshold value. In general, there is no harmful radiation effect on the population living in this area, but there are some places that have values higher than the permissible values (Taqi et al., 2018). Measurement of radiological hazards from natural radioactivity in soil samples has been carried out in several areas in Rize Province, Turkey with the average radioactivity level obtained for 88 226 of (85.75 ± 11.77) Bq/Kg, ℎ 90 232 is (51.08 ± 9.42) Bq/Kg and 19 40 is (771.57 ± 37.65) Bq/Kg. The quantities to assess radiological hazards from natural activities include the average value of radium equivalent activity (Raeq) is 218.20 Bq/kg, representative level index (Iyr) is 1.60, external hazard index (Hex) is 0.59 where the obtained is higher than the safe limit that has been set (Dizman et al., 2016).
From several studies that have been carried out, it is known that soil samples from geothermal areas have natural radionuclide activity. Therefore, this study conducted a study on "Determining the level of natural radioactivity in soil and radiological hazards in the South Solok Geothermal Area, West Sumatra". The purpose of this study was to determine the level of natural radioactivity ( OECD (1975) which is 370 Bq/kg, the representative level index ( ) and external hazard index ( )) with a maximum value of one (UNSCEAR 1988).

Geology of Research Area
Solok Selatan is a district located in the eastern part of West Sumatra with a population of around 182,027 people. South Solok Geothermal is located in Muara Labuh. Soil sampling in the South Solok area was carried out in 7 study areas ( Figure 1).

Sampling and Sample Preparation
Sampling is in the form of soil at seven points of collection location, where the seven points are land taken in one area randomly in each sub-district in South Solok district, the soil taken is at a depth of 0-5 cm. Then, the sample is dried in the sun so that the water contained in the sample can evaporate. Conditioning the sample to be more homogeneous and smaller grain size was sieved using a 100 mesh sieve on a dry sample. The soil sample was sent to the Environmental Safety Laboratory at PTKMR BATAN for radionuclide measurements on the sample using a gamma spectrometer. Representative level index or known as radiation hazard index (Iyr) is to monitor radiation in the human body and to calculate the level of radionuclide risk in the human body when exposed to radiation from the soil, the value obtained must be less than one or equal to one to ensure the soil is hazard free. The representative level index can be formulated as follows (UNSCEAR, 1988 and 4810 from 19 40 , which gives the same gamma-ray dose rate (Beretka & Mathew, 1985). The calculated external hazard index must be less than or equal to one, it can be calculated through the following relationship (UNSCEAR, 1988):

Results and Discussion
The study was conducted in seven areas of South Solok district around geothermal, namely in the Koto Baru  in the South Solok area to ensure that the area is still safe and does not pose a health hazard to the community.  Vol. 5 No. 2 (2021) 81-91 doi: 10.20961/jphystheor-appl.v5i2.59099 Based on Table 2, the concentration of radionuclide activity 88

226
Ra in the soil sample in South Solok is the second lowest of several studies that have been carried out previously in several areas, with the lowest concentration for 88 226 found in the Padang City area with a value of The highest concentration is found in the Rize area of Turkey, which although it has a high value the area still has a radionuclide concentration value below the safe threshold allowed by BAPETEN.
For the concentration value ℎ     Table 3 shows that the value of radium equivalent activity (Raeq) varies from 73.195 Bq/kg to 220.934 Bq/kg with an average of 118.051 Bq/kg. Where the average value in this study is lower than the maximum value recommended by OECD (1975) which is 370 Bq/kg. The representative level index value (Iyr) ranges from 0.515 to 1.620, with an average value of 0.853 which has a value lower than one. However, in Tanah-1, the representative level index value has a value of 1,620 which is more than one based on the UNSCEAR (1988) determination, this indicates a high risk of radionuclides entering the human body in the Koto Baru area. While the value of the external hazard index (Hex) ranged from 0.197 to 0.596 with an average value of 0.335 for the soil sample in South Solok. The maximum value for Hex is one based on the provisions of UNSCEAR (1988), in this study the value obtained is lower than one, this indicates that the level of radiation in the human body is low.

Suggestion
Based on the research that has been done, further research is recommended to conduct more specific research by measuring the concentration of radionuclide activity 88 226 , ℎ 90 232 and 19 40 in several areas in Sungai Pagu sub-district, because the area Koto Baru is one of the areas in the sub-district that has a higher concentration value than other subdistricts, to ensure that the radionulide concentration in the sub-district is still below the threshold set by BAPETEN and UNSCEAR 2000. Furthermore, it is recommended to measure the activity of radium equivalent (Ra eq ) which is then compared with the maximum value recommended by OECD (1975), the measurement of the representative level index (I γr )and external hazard index (H ex ) in several Sungai Pagu sub-districts to ensure that the values obtained for the external hazard index are less from one.