No abstract

Field-programmable gate array (FPGA) technology has been widely used in setting up triggering systems and DAQ systems for radiation detectors, because it has several advantages such as fast digital processing, compact, programmable and high stability. Since 2010, with we have developed FPGA-based trigger systems and FPGA-based DAQ systems used for radiation detectors. Triggering systems for cosmic ray measurements, readout electronic for environmental radiation monitor in air. We also developed nuclear electronic equipment such as spectrum analyzer MCA (Flash-ADC/FPGA based), the pulse generator, counters, readout electronic for multiple radiation sensors. In this paper, we present two experiments, on the cosmic-ray induced response on the NaI(Tl) detector and environmental radiation monitoring system. For those experiments, trigger system are built by FPGA-based technology.

Full spectrum analysis, FSA, has been being widely used for the identification in environmental radioactive. In this work, firstly, FSA is developed to analyze the gamma backscattering spectrum on concrete to determine the component densities. The concrete samples are mixed of Portland cement, sand, gravel and water in the different proportions. The experiments are carried out by the radioactive source Cs137 (0.5mCi) and the detector NaI(Tl) 2 inch x 2 inch. The obtained results show that FSA would be a good approach to analyze the gamma backscattering on concrete.

The effect of the diameter of the detector collimator on the saturation thickness in gamma-scattering measurements is studied using the spectrum of singly scattering. Geometric arrangement of gamma-scattering measurement includes: a gamma-ray collimated beam with the energy of 662 keV emitted from 137Cs source is irradiated on a rectangular aluminium target with incident angle of 90o, and detector NaI(Tl) 5.1cmx5.1cm with collimator is used to record the scatterd gamma rays at scattered angle of 120°. The experimental measurements are carried out to obtain scattered spectra with various target thickness and diameter of detector collimator. The profile of the singly scattering and multiply scattering in the scattered spectra are determined by a spectrum processing technique based on the least squares fitting. The experimental results showed that the saturation thickness of the counts of singly scattering increases with increasing the window diameter of the detector collimator. These results will support for the non-destructive testing research of application of gamma-scattering method to determine the thickness or the defect of the sample.

The article describes a gamma ray spectrometer protected by a lead shield (Model 747E Canberra lead shield) and an active shield made of an 80~cm \(\times\) 80~cm \(\times\) 3~cm plastic scintillator plate in anticoincidence on top of the lead shield. The detector used as low background gamma-spectrometer is a high purity Germanium crystal of model GC2018 Canberra. The background count rate currently achieved (30-2400 keV) is 1.27 cps without anticoincidence. The level of background suppression obtained from the active protection is 0.80 overall and about 0.43 for the 511 keV gamma line. The gamma ray spectrometer is installed and operated in the Nuclear Laboratory, Department of Nuclear Physics, University of Science, HCMC-Vietnam National University.