Experimental measurement of effective atomic numbers and albedo factors for some alloys using the backscattering technique

Abstract

Alloys of the type Pb60Sn20ZnxCd(20-x) where x = 0, 5, 10, 15 or 20 were prepared by a conventional melt quench technique. The intensity distribution of backscattered photons from the radioactive isotopes 22Na and 137Cs (with photon energies of 511 keV and 662 keV, respectively) were recorded for different thicknesses of alloy samples and some metallic samples (Al, Zn, Sn and Pb) with use of a GAMMA-RAD5 spectrometer (76 mm × 76 mm NaI(Tl) scintillation detector). Backscattered photon intensities were plotted as a function of both the atomic number and the target thickness. A best fit curve was drawn between backscattered photon counts and the atomic number of the metallic samples, from which the effective atomic numbers (Zeff) of the alloys were obtained at a particular photon energy as well as thickness. The experimentally obtained Zeff values are in good agreement with the theoretical ones (based on mass attenuation coefficients from the WinXCom database). The plot of intensity versus thickness shows that the intensity of backscattered photons increases with sample thickness. The albedo factors (energy albedo, number albedo and dose albedo) were also determined experimentally at these photon energies for the alloys and metallic samples. In the Compton scattering dominant region, the albedo factors decrease with an increase in atomic number as well as with an increase in photon energy.