322 E . Srinivasa et al .: Radioprotection 2024 , 59 ( 4 ), 317 – 326 Table 3 . Various radiological hazard indices calculating formulae . Parameter Formula Reference Radium equivalent Activity ( Ra eq )
� Ra eq Bqkg �1
¼ CRa þ 1:43 C Th þ 0:07 C K 370
( ICRP , 1993 , IAEA / RCA , 1989 )
Gamma absorbed dose rate ( D )
Internal hazard indices ( H in )
� D nGyh �1 ( UNSCEAR , 2000 , ¼ 0 : 462 CRa þ 0:604 C Th þ 0:0417 C K
Suresh et al ., 2022 )
H in ¼
C Ra 185 þ C Th
259 þ C
K
4810
1
( Beretka and Mathew , 1985 , UNSCEAR , 1993 ) External hazard indices ( H ex )
Gamma index
H ex ¼
I g ¼
C Ra 370 þ C Th
259 þ C
K
4810
1
C Ra 300 þ C Th
200 þ C
K
1 3000
( Beretka and Mathew , 1985 , UNSCEAR , 1993 )
( European Commission , 1999 )
Indoor Annual effective dose equivalent ( AEDE )
Outdoor Annual effective dose equivalent ( AEDE )
� E in mSvy �1
¼ Din 8760hy �1 0:8 0:7SvGy �1 10 �6 ( UNSCEAR , 2000 , Suresh et al ., 2022 )
� E out mSvy �1
¼ Dout 8760hy �1 0:2 0:7SvGy �1 10 �6 ( UNSCEAR , 2000 , Suresh et al ., 2022 )
3.3 Radiological characterization
Radium-equivalent activity ( Ra eq ) can be used to calculate the radiological effect of radionuclides because of internal and external exposure . Gamma absorbed dose rate ( GADR ) ( D ), AEDE , internal and external hazard indices ( H in and H ext ), and gamma index ( Ig ), in all these calculations , C Ra , C Th , and C K are the activity concentrations of 226 Ra , 232 Th , and 40 Kin Bq kg �1 respectively . Various radiological hazard indices were calculated using the standard formulas and are listed in Table 3 . The average values of radium equivalent activity , gamma absorbed dose rate ( GADR ) ( D ), AEDE , internal and external hazard indices ( H in and H ext ), and gamma index ( Ig ) are summarised in Table 4 .
The Ra eq values in the soil samples range from 68 to 395 Bq kg �1 , with a mean value of 168 Bq kg �1 . The mean Ra eq value of the present study is less than the criterion limit of 370 Bq . kg �1 ( Beretka and Mathew , 1985 ), and as such , this soil does not pose any radiological hazard when used for construction purposes .
The estimated gamma absorbed dose rate due to the primordial radionuclides in soil samples varies from 31 to 176 nGy h �1 , with an average value of 78 nGyh �1 , which is higher than the average value of global primordial radiation of 44 nGy h �1 for soil and the all-India average value of 69 nGy h �1 ( Srinivasa et al ., 2015 ). The annual equivalent effective dose rate in soil is found to vary from 0.19 to 1.08 mSv y �1 , with an average of 0.49 mSv y �1 . The average annual effective dose is higher than the average value for India of 0.0843 mSv y �1 ( Nambi et al ., 1986 ) and the world average value of 0.0725 mSv y �1 ( Srinivasa et al ., 2015 ).
External gamma dose rates in air were measured at the same locations where soil samples were taken using a portable GM tube-based environmental radiation dosimeter ( ER-709 , manufactured by Nucleonix Systems Pvt . Ltd .) in Hyderabad , India . Table 4 also displays the results of these measurements .
The measured values of indoor gamma absorbed dose rates were found in the range of 80 ± 5 to 391 ± 6 nGy h �1 , with an average value of 200 ± 7 nGy h �1 . This value is nearly two times higher than the world average of 84 nGy h �1 ( Srinivasa et al ., 2015 ). Similarly , outdoor gamma absorbed dose rates were found in the range of 63 ± 4 to 356 ± 11 nGy h �1 , with an average value of 166 ± 6 nGy h �1 . This value is nearly three times higher than the global average of 59 nGy h �1 . The total annual effective dose for adults living in the study area ranges from 0.47 to 2.35 mSv y �1 , with a mean of 1.18 mSv y �1 , Nambi et al . found dose levels in India to be ( 0.44 mSv y �1 ) ( Nambi et al ., 1986 ).
The correlation between the annual effective dose measured by the dosimeter and the activity of the soil sample is shown in Figure 3 . It is clear from Figure 3 that there is a good positive correlation between the radiation dose measured by the portable radiation survey meter and the estimated dose from the HPGe detector , with a correlation coefficient of 0.73 . A comparison between the measured and estimated doses showed very good agreement between the two . This good correlation confirms the meter ’ s accuracy and assists the researcher in quickly determining the dose at any location . There is little difference between the estimated and measured values of the absorbed dose because it is only the estimated dose in the soil , and this measurement does not include the dose due to rocks , building materials and the cosmic ray component . The ratio of indoor to outdoor gamma absorbed dose rates varies from 0.98 to 2.23 , with a median value of 1.21 . The ratio of indoor to outdoor absorbed doses of gamma radiation has been found to be approximately 1.2 in areas with normal background radiation in India ( Nambi et al ., 1986 ).