MATERIALS AND METHODS:
1. Study area, sample collection and preparation:
A total of 10 soil samples were collected from Shrimadhopur tehshil, Sikar district of Rajasthan which are pinned
out in Fig.1. Samples were collected from an area of latitude from 27°22'42'' N to 27°38'41'' N and longitude from
75°36'49'' E to 75°59'29'' E. Table 1 presents the sampling sites along with their geographical locations.
Table 1. Coded samples based on the soil sample.
Sample code
Coordinate
Sample code
Coordinate
S1
Latitude
27°36'37"N
Longitude
75°52'33"E
S6
Latitude
27°29'29"N
Longitude
75°56'52"E
S2
27°25'1"N
75°46'36"E
S7
27°30'59"N
75°59'29"E
S3
27°38'41"N
75°56'4"E
S8
27°33'48"N
75°49'55"E
S4
27°22'42"N
75°36'29"E
S9
27°30'55"N
75°40'48"E
S5
27°28'37"N
75°44'1"E
S10
27°24'48"N
75°49'36"E
To obtain natural soil, the soil was extracted from an auger hole 0.75 meters deep. Samples of organic matter and
stones were filtered through a fine sieve. Soil samples were then dried in an oven set at 110°C for 24 hours to
eliminate any remaining moisture or weight stabilisation[13]. They were then put into an airtight, disc-shaped,
radon-impermeable petri dish with precise measurements (diameter of 90mm and thickness of 15mm) after being
weighed on an electronic balance to within 10-5 g. After that, the samples were submerged for more than four
weeks or twenty-eight days to bring 226Ra and 222Rn and their transient daughter products into equilibrium. Using
silica gel and the appropriate mass of the corresponding elements, we created standard specimens of 40K, 226Ra,
and 232Th with various degrees of activity[14-17]. Compound masses were determined using an extremely
sensitive electronic weighing device with a minimum count of 10 -5 g. Secular equilibrium was achieved by
weighing, packing, and sealing each standard in an airtight Petri dish impermeable to radon. Information regarding
the preparation of in-house standards is provided in Table 2, which displays both the calculated and actual activity.
The absolute efficiency of the curve created using point or single elemental sources of 22Na (511 keV, 1274 keV),
57
Co (122 keV, 136 keV), 60Co (1173 keV, 1332 keV), 133Ba (80.99 keV, 276.39 keV, 302.85 keV, 356.01 keV,
383.84 keV), and 137Cs (661.8 keV)[16,18,19].
Table 2. Standards of known activities are prepared using specified compounds.
Standards
Compound
Mass of the
compound
required (g)
Standard Activity
(Bq)
238
Pitchblende (U3O8)
0.35
5
Activity by
efficiency method
taking point
sources as standard
(Bq)
4.18
0.70
10
9.91
0.00283
10
9.84
0.00566
20
22.61
0.30
5
3.74
0.90
15
17.74
232
U
Th
40
K
ThO2 (99% Pure)
KCl (99.5% pure)
Radiometric analysis:
A p-type High purity Germanium (HPGe) detector with a 16.4% relative efficiency and an FWHM (Full Width at
Half Maxima) of 1.63 keV at 1332.5 keV ( 60Co) was employed in this radiometric evaluation. We used single
elemental disc sources or point sources of 137Cs (661.8 keV), 133Ba (80.99 keV, 276.39 keV, 302.85 keV, 356.01
keV, 383.84 keV), 60Co (1173 keV, 1332 keV), 57Co (122 keV, 136 keV), and 22Na (511 keV, 1274 keV) for energy
calibration[15,17,19]. The detector output was analysed using a 1000 DSA (CANBERRA) system connected to a
PC. The spectrum was then analysed with GENIE 2000 software. To prevent x-ray interference with gamma rays,
the detector was positioned in a rectangular shielding of lead that was 4 inches (10 cm) thick and had a 2 mm
inner Cu shielding[17]. The activity concentration of the Uranium series ( 226Ra) was calculated using an average
of activities of 295.22 keV (19.3%) from 214Pb, 351.93 keV (37.6%) from 214Pb, and 609.31 keV (46.1%) from
214
Bi. The photo peak corresponding to 185.7 keV energy of 235U infringes with the 186 keV energy gamma photopeak of 226Ra, so this peak was not considered for analysis[14]. The average gamma transitions of 338.32 keV
(11.27%) from 228Ac, 583.19 keV (84.5%) from 208Tl, and 911.20 keV (25.8%) from 228Ac were used to determine
the activity concentration of the thorium series (232Th). The gamma transition photo-peak of energy 1461 keV
(11%) was used to compute the activity concentration of potassium ( 40K)[15].
Table 3. List of selected gamma photopeaks (238U, 232Th, and 40K) for radiometric analysis of samples.
Parent radionuclide
Daughter radionuclide
238
232
U
Th
214Pb
214Pb
Photopeak
(keV)
295.22
351.93
Intensity
(%)
19.3
37.6
214Bi
609.31
46.1
228Ac
338.32
11.27
208Tl
583.19
84.5
228Ac
911.20
25.8
k
40Ar
1460.83
11
An HPGe detector was used for a 24-hour evaluation of the materials. The spectra were analysed to calculate the
photopeak area of 40K, the daughter products of Thorium and Uranium, and all seven photopeaks listed in Table
3. To obtain the overall area of each peak, the entire background region for each peak has been subtracted from
the corresponding photopeak. This was carried out when determining activity profiles. Three different methods
were used to compare a particular activity: the efficiency method, which used pointed sources as standards; the
efficiency method, which used home-made sources as standards; and the comparative analysis, which used homemade sources as standards. Compared to efficiency approaches, the comparator method with a recognised standard
is more accurate[16].
40