In this work, a gamma scattering technique using 137Cs (5mCi) source with the NaI(Tl) detector is arranged to record the scattered photon beam at scattering angle of 1200 for investigating the liquid density. We used standard liquid such as water, H2SO4, HCl, glycerol, HNO3, ethanol and A92 petrol to fit the single scattering peak, multiple scattering, and total counts versus standard liquid densities. The interpolating of the single scattering peak, multiple scattering, and total counts of the testing sample at scattering angle of 1200 is 0.702 g.cm-3, 0.783 g.cm-3, and 0.747 g.cm-3, respectively. The discrepancy of the experiment and true testing density is about 8 %, 3 %, and 2 %, respectively. The result shows that multiple scattering or total counts can be used to propose the density measurement.

In the environmental radioactivity analyzing methods using gamma-ray spectrometry, the natural activities of radionuclides were required to be higher than the minimum detectable activity (MDA). To reduce MDA, one of the popular methods is to improve the ability of reducing the background radiation of the gamma-ray spectrometry. In this work, we designed the shielding configuration with 5 cm lead and 2 mm copper (thickness of walls and top). The MDAs of gamma-ray spectrometer were 2.6–4.24 times times for 40K (1460.8 keV), 232Th (208Tl- 2614.5 keV) and 238U (214Pb- 352 keV; 214Bi- 609.3 keV, 214Bi- 1764.5 keV). In the other hand, MDA for 238U with this shielding configuration is smaller than the activity of 238U inside surface soils in Vietnam. These results showed that the gamma spectrometer with NaI(Tl) detector and this shielding configuration was suitable for measurements activity of 238U in the environmental samples.

In this paper, we present an analytical calculation model of full energy peak efficiency for cylindrical detectors without collimator based on efficiency transfer method. A calculation program by Mathematica language is developed to apply to this model. The validity of the calculation model was checked by comparison with MCNP5 simulated efficiency values for measurements of point source in the waste drum containing matrix of rubber or concrete. The discrepancy between MCNP5 simulated and calculated efficiencies is smaller 11 %. This shows that the calculation model is reliable and can be applied to calculate the full energy peak efficiency for assays of radioactive waste drums. Besides, the calculated time by the this program is much faster than the simulation using MCNP5 program.

In this study, we used Monte Carlo method to simulate each separate component of the gamma scattering spectrum. The gamma rays emitted from a 137Cs source, scatter on aluminum targets and recorded by a NaI(Tl) detector. Based on the distribution characteristics of each scattering component, we propose a new method to analyze scattered gamma spectra. This method was applied for simulated spectra to estimate the material thickness gives good results.

In this study, we deploy and compare spectrum processing methods based on gamma scattering technique to determine the interface between insoluble fluids stored in the container. The gamma scattering measurement system included: a 5 mCi radioactive source of 137Cs, a cylindrical glass vase with a diameter of 6.5 cm containing the fluids, and a NaI(Tl) detector with a 7.62 × 7.62 cm scintillation crystal. The detector was arranged to obtain the scattered photon beam at the angle of 120o. Two of the three processing methods showed good results with the biggest difference of 5 mm. In addition, the results also show the feasibility of using SCA in gamma scattering measurement system to determine the interface between insoluble environments.