文摘
Passive gamma ray spectrometry and neutron capture prompt gamma activation analysis (PGAA) were used to investigate powdered cow's milk samples [termed optimal (1), optimal (2) and optimal (3)] collected from local markets in the city of Cairo, Egypt. Standard material with a total average activity of 0.830 ± 0.2 μCi and a certified reference material [IAEA (A-14)] were used to study the accuracy of a passive multi-gamma ray measurement method. Three powdered milk samples of the same geometry and volume were used in this analysis. The specific activity of 226Ra ranged from 24.5 ± 2.1 to 114 ± 1.2 Bq/kg, 232Th from 8 ± 1 to 14 ± 1.2 Bq/kg and 40K from 444 ± 28 to 1826.1 ± 3.1 Bq/kg, all of which were higher than the activities corresponding to the United Nations Scientific Committee on the Effect of Atomic Radiation (UNSCEAR) (50, 50 and 500 Bq/kg for 226Ra, 232Th and 40K, respectively). The average dose rate at 1 cm for 40K ranged from 8.21E−02 ± 0.12 to 3.3E−1 ± 0.22 mSv/h/cm. We also showed that 208Tl81, 212Pb82 and 212Bi83 should be considered products of thorium. k0-PGAA was carried out using an integrated and calibrated prompt gamma ray system with a neutron flux of 106 n/cm2 per second. The thermal to epithermal neutron flux ratio (f) and cadmium ratio were measured using a thin gold foil technique (ration = 160). Different Cl concentrations were prepared as standards for k0-PGAA. The elemental concentrations of Na, Mg, Al, Ca, Mn, Fe, Cu, Ga, Zn, As, Se, Cs, Cd, In, Th and I were measured in the three powdered milk samples. The mean ± standard deviation ranges of the elements were as follows: Na = 1069 ± 49–1583 ± 53 ppm, Mg = 347 ± 13.64–385 ± 16.71 ppm, Al = 45 ± 1.30–72 ± 2.40 ppm, Fe = 5500 ± 110–7123 ± 130 ppm, Zn = 107 ± 3–123 ± 6 ppm, Ca = 4200 ± 72–5483 ± 81 ppm, Mn = 1269 ± 69–1784 ± 72 ppm, Pr = 1.7 ± 0.02–2.6 ± 0.07 ppm, Ga = 265 ± 5–293 ± 8 ppm, Cu = 57 ± 0.5–64 ± 0.9 ppm, In = 1000± 38.64–1574 ± 41.34 ppm, Cd = 6.1 ± 2.71–12.6 ± 4.11 ppm, I = 53 ± 0.09–62 ± 1.18 ppm, Cs = 4 ± 1.56–11 ± 4.22 ppm, As = 26 ± 0.66–29 ± 0.89 ppm, Se = 126 ± 4.8–144 ± 5.7 ppm, Th = 47 ± 1.0–78 ± 6.0 ppm.
