3.1. Collections of Sample
Twenty of types of grains samples (wheat, barley, corn, millet, mungbean, and rice), these samples were collected from different sites of Kerbala Governorate. The grains samples were labeled with special codes. The information complete about samples was written, as shown in Table 1.
TABLE 1. Grains samples from deferent sites in kerbala
No.
|
Type of grain
|
Sample code
|
Original
|
1
|
Wheat
|
G1
|
Iraq (Eayn Al-Tamr)
|
2
|
G2
|
Iraq (Al-Jadwal Al-Gharbiu)
|
3
|
Barley
|
G3
|
Iraq (Eayn Al-Tamr)
|
4
|
G4
|
Iraq (Al-Jadwal Al-Gharbiu)
|
5
|
Corn
|
G5
|
Iraq (Eayn Al-Tamr)
|
6
|
G6
|
Iraq (Al-Jadwal Al-Gharbiu)
|
7
|
Millet
|
G7
|
Iraq (Eayn Al-Tamr)
|
8
|
G8
|
Iraq (Al-Jadwal Al-Gharbiu)
|
9
|
Mung bean
|
G9
|
Iraq (Eayn Al-Tamr)
|
10
|
G10
|
Iraq (Al-Jadwal Al-Gharbiu)
|
11
|
G11
|
Iraq (Aoun)
|
12
|
Rice
|
G12
|
India (Gold)
|
13
|
G13
|
USA (Camolino)
|
14
|
G14
|
Iraq (Eayn Al-Tamr)
|
15
|
G15
|
Iraq (Al-Jadwal Al-Gharbiu)
|
16
|
G16
|
Iraq (Al-Jadwal Al-Gharbiu)
|
17
|
G17
|
India (Abu Araba)
|
18
|
G18
|
India (Royal)
|
19
|
G19
|
Iraq (Aoun)
|
20
|
G20
|
USA (Jasmine)
|
3.2. Preparations of Sample
After collecting the grains samples were transferred in nuclear laboratory in Kerbala university for preparation to measure gamma and alpha emitters. The preparation method of samples was done by several processing such as cleaned the samples, dried in an oven at 100 oC for 4 hours, crushed the samples, sieved by sieve for 2 mm mesh, weighted by digital balance, and put samples in marinelli beakers (I L) and plastic container (radius 5 cm, higher 7 cm) for measuring gamma and alpha emitters, respectably. Next, all samples were stored at least for1 month for getting secular equilibrium between radium-226 and radon-222 [11, 12].
3.3. Experimental Methods
In the present study, it was measured gamma emitters (Uranium-238, Thorium-232, and Potsium-40) using NaI(Tl) detection system and alpha emitters (Radon-222, Radium-226, and Uraium-238) using CR-39 detectors. The NaI(Tl) detector was a 3"×3" crystal dimension which it is calibrated using 137Cs, 22Na, 60Co, and 152Eu. There are three energies of spectrum used to find specific activity of gamma emitters according to secular equilibrium propriety which it is 1764.5 KeV for 214Bi (238U or 226Ra), 2614 KeV for 208Tl (232Th), and 1460 KeV for 40Ar (40K) [13]. A CR-39 detector has density 1.32 gm/m3, thickness 1mm and dimension 2.5×2.5cm2, which it is made by TASTRAK Analysis System, Ltd., UK. Also, it has special code that suited the TASL image system. The chemical etching procedure was carried out by NaOH with a 6.25 N at temperature 85oC [14]. CR-39 in the present study was calibrated factor using standard source 226Ra for different time exposure such as 0.5, 1, 1.5, 2, 2.5, and 3 days which it is equal (0.28±0.043) Track.cm2 /Bqm-3.day. The background radiation for two detection system (NaI(Tl) and CR-39) was measured at same container and time for sample measurements that used in the present study.
3.4. Theoretical Equations
3.4.1. Gamma emitters
The specific activity (A) for gamma emitters that depend on many parameters as shown in Equation (1) was found by following [15,16]:
where, N is area of under photopeak, B is the areas under photopeak background. t is counting time which it is equal 18000 secs, ε is the efficiency of the detector, Iγ is the probability of gamma emission, and m is the mass of sample.
Radium Equivalent Activity (Raeq) and Internal hazard index (Hin) due to gamma emitters that calculated using equations (2) and (3), respectively [17, 18]:
While, the annual effective dose (AED) in grain samples of the present study was calculated using equation (4), as following [19]:
where, I mean consumption rate of grains samples in unit (Kg/y) which taken from previous studies [20-26], Ai is the specific activity for gamma emitters, and CFi is conversion factor in unit Sv/Bq that equal 2.80×10-7 for 238U (226Ra), 2.30×10-7 for 232Th, and 6.20×10-9 for 40K [27].
Also, it was calculated threshold consumption rate (DIthresh) in grains samples using equation (5), as following [28]:
where, Eave is equal 0.320 that means an acceptable limit of annual effective dose [5].
Finally, for gamma emitters theoretical equations, can be calculated Excess lifetime cancer risk (ELCR) using equation (6) [15, 28]:
where, DL is life expectancy (70 y) while RF is fatal risk factor in (Sievert) and it is pegged at 0.05 per Sievert.
3.4.1. Alpha emitters
222Rn Concentrations that measured in the airspace of container (C) and within samples (CRn), were determined by equations (7) and (8), respectively, as following [29, 12]:
where ρ is the track density which determined by TASL device, T is time irradiation for sample with CR-39 detector in container which was equal 90 days, K is calibration factor, λRn is rador-222 of the decay constant which equal 0.1814 1/day, h is distance of samples to CR-39 detector, and l is higher of samples in container.
While, equation (9) was used to find the effective radium content in sample (CRa) as following [5]:
The uranium concentration (CU) in samples of the present study in unit (ppm) was calculated using equation (10), which depend on secular equilibrium propriety between uranium-238 and radon-222, as following [30]:
The equation (11) was used to determine AED due to alpha emitters in food samples which depend on many parameters such as specific activity of radon-222, radium-226 and uranium-238 in sample (CAlpha) in unit (Bq/kg), consumption rate of samples (I) in unit (Kg/y), and conversion dose factor (CF) in unit (Sv/Bq), as following [30]
Where, the values of conversion dose factor are 3.5 nSv/Bq [27] for radon-222, 280 nSv/Bq [31] for radium-226 and 45 nSv/Bq for uranium-238 [31]. Finally, can be determined ELCR using equation (6).