E . Srinivasa et al .: Radioprotection 2024 , 59 ( 4 ), 317 – 326 319 corrections were applied , background counts are subtracted , and counting was made for 60,000 s . The activity of radionuclides ( Bq kg �1 ) was calculated using the following formula ( IAEA / RCA , 1989 ).
ActivityðBq : kg �1 Þ¼ ðS ± sÞ 100 1000 100 EWA ð1Þ
where s is the net counts per second under the photo peak of intensity , s is the standard deviation of s , E is the counting (%), and A is the gamma abundance (%) of the radionuclides and W is the mass of the sample in grams .
3 Results and discussion
3.1 Distribution of radionuclides in soil samples
The average activity concentrations of the primordial radionuclides , such as 238 U , 226 Ra , 232 Th , and 40 K , present in the soil samples collected from the study region have been calculated using equation ( 1 ), and the results are given in Table 1 . The activity concentrations of 238 U , 226 Ra , 232 Th , and 40 K in the soil samples under investigation vary from 16 ± 1 to 72 ± 2 , 13 ± 1 to 64 ± 2 , 19 ± 1 to 185 ± 2 , and 197 ± 9 to 1214 ± 22 Bq kg �1 , with an average value of 42 ± 2 , 39 ± 1 , 58 ± 2 , and 592 ± 15 Bq kg �1 , respectively . It is observed that the activity concentration of 238 U and 226 Ra are same in almost all samples , which confirms the radioactive equilibrium between them .
The average 238 U , 226 Ra , 232 Th , and 40 K activity concentrations and gamma absorbed dose rates in soil samples are found to be higher in some locations ; Arsikere , Bageshpura , Javgal , Malnad Engineering College , MMIL ( Katihally ), Gorur , Holenarsipura , Arehally , Padavalahippe , and Devanur . The activity concentrations of 238 U , 226 Ra , 232 Th , and 40 K in the soil samples largely depend on the types
of rock from which , the soil is originating and the types of formation and transfer processes that are involved ( Srinivasa et al ., 2019 ; Ahmed , 2005 ; Srilatha et al ., 2015 ). The types of rocks in these locations are granite , pegmatite , titaniferous magnetite , and other associated rocks , which have higher concentrations of 238 U , 226 Ra , 232 Th , and 40 K than other rock types , and hence higher activity in soil samples was also observed ( Srilatha et al ., 2015 ; Rangaswamy et al ., 2016 ). A slightly higher activity concentration of 238 U , 226 Ra , 232 Th , and 40 K and a gamma absorbed dose rate from these radionuclides
were observed in rock and soil samples collected from the locations Ramanathapura , Magge , Byrapura , Halebeedu , Yagachi , Thagadur , Nuggehally , Gorur , the Master Control Facility ( MCF ), Nonavinakere , Chiknayakanahally , Kadur , and Devanur . This is due to the fact that these regions were attributed to gneiss , altered grey granites , titaniferous magnetite , and pegmatite rocks ( Srinivasa et al ., 2015, 2019 ). In Nuggehally , Thagadur , Byrapura , and Channarayapatna , which contain slightly less concentration of 238 U , 226 Ra , 232 Th , and 40 K compared to pink and grey granites ( Srilatha et al ., 2015 ).
The lower average activity concentrations of 238 U , 226 Ra , 232 Th , 40 K , and gamma absorbed dose rates in soil samples are
found at some locations in Palya , Kundur , Konanur ,
Doddamagge , Vijay nagar , Sakaleshpura , Anemahal , Konanuru , Belur , Hagare and Hethur . The lower activity concentration in these locations is due to fact that the rock samples mainly consist of ultramafic schist , gneiss , dolerite ( green colour ) rocks , and sedimentary rocks , which contain lower concentrations of 238 U , 226 Ra , 232 Th , and 40 K in these regions ( Megumi et al ., 1988 ; Rafique et al ., 2014 ). The results show that the average activity concentration of 40 K in soil samples in the study area has a higher activity concentration than the global average value of 400 Bq kg �1 . In some locations , the activity concentration of 232 Th is higher than 238 U and 226 Ra due to intrusion of pegmatite rocks into the granitic rocks ( Ningappa et al ., 2008 ).
The activity concentration values of 238 U , 226 Ra , 232 Th , and 40 K obtained from the study area were higher than the values reported for Indian soils and for normal background areas , respectively ( UNSCEAR , 2008 ). According to the UNSCEAR 2008 report , the Indian average activity concentrations of 238 U , 226 Ra , 232 Th , and 40 K in soil samples are 31 , 29 , 64 and 400 Bq kg �1 , respectively ( UNSCEAR , 2000 , 2008 ). It is clear from this study that , except for 232 Th , the average activities of 238 U , 226 Ra , and 40 K values are slightly higher than the Indian average . The world average activity concentration values of 238 U , 226 Ra , 232 Th , and 40 K for soil are 35 , 32 , 45 , and 420 Bq kg �1 , respectively ( UNSCEAR , 2000 ). The data shows that the average activity concentration values of 238 U , 226 Ra , 232 Th , and 40 K in soil samples from the study area were found to be slightly higher than the global average values ( UNSCEAR , 2000 ). The average activity concentration values of 238 U , 226 Ra , 232 Th , and 40 K as obtained in the study area were compared with the values reported in different parts of Karnataka shown in Table 2 ( UNSCEAR , 2000 ; Srinivasa et al ., 2022 ; Ningappa et al ., 2008 ; Narayana et al ., 2001 ; Prasad et al ., 2008 ; Shivakumara et al ., 2014 ; Sannappa et al ., 2010 ; Karunakara et al ., 2001 ; Yashodhara et al ., 2011 ; Suresh et al ., 2022 ; Kerur et al ., 2011 ; Srilatha et al ., 2015 ; Umesh Reddy et al ., 2017 ).
3.2 Frequency distribution graphs for radionuclides in soil
Figures 2a – 2c represent the frequency distribution graphs of 226 Ra , 232 Th , and 40 K measured by using HPGe in soil samples of the study area , respectively . The frequency distribution graph of 226 Ra in the study area is shown in Figure 2a . The results reveal that about 57.5 % of the soil samples were below 40 Bq kg �1 , and the remaining 42.5 % of the samples showed concentrations above 40 Bq kg �1 . The frequency distribution of activity of 232 Th in the study area is shown in Figure 2b . The results reveal that about 37.5 % of the soil samples were below the 40 Bq kg �1 , and the remaining 62.5 % of the samples showed concentrations above 40 Bq kg �1 . The frequency distribution of activity of 40 K in the study area is shown in Figure 2 ( c ). The results reveal that , only 22.5 % of the soil samples were lower than 400 Bq kg �1 , and the remaining 77.5 % of the samples showed concentrations above 400 Bq kg �1 .