No abstract

NaI(Tl) scintillation detectors have been widely applied for gamma-ray spectrum measurements owing to advantages such as high detection efficiency and low price. However, the mitigation of the limited energy resolution of these detectors, which detracts from an accurate analysis of the instrument spectra obtained, remains a crucial need. Based on the physical properties and spectrum formation processes of NaI(Tl) scintillation detectors, the detector response to gamma photons with different energies is represented by photopeaks that are approximately Gaussian in shape with unique full-width-at-half-maximum (FWHM) values. The FWHM is established as a detector parameter based on resolution calibrations and is used in the construction of a general Gaussian response matrix, which is employed for the inverse decomposition of gamma spectra obtained from the detector. The Gold and Boosted Gold iterative algorithms are employed to accelerate the decomposition of the measured spectrum. Tests of the inverse decomposition method on multiple simulated overlapping peaks and on experimentally obtained U and Th radionuclide series spectra verify the practicability of the method, particularly in the low-energy region of the spectrum, providing for the accurate qualitative and quantitative analysis of radionuclides.

A GaN-based pin neutron detector with a 6LiF conversion layer was fabricated, and can be used to detect thermal neutrons. Measurement of the electrical characteristic of the GaN-based pin neutron detector showed that the reverse leakage current of the neutron detector was reduced significantly after deposition of a 6LiF conversion layer on the detector surface. The thermal neutrons used in this experiment were obtained from an 241Am–Be fast neutron source after being moderated by 100-mm-thick high-density polyethylene. The experimental results show that the detector with 16.9-μm thick 6LiF achieved a maximum neutron detection efficiency of 1.9% at a reverse bias of 0 V, which is less than the theoretical detection efficiency of 4.1% calculated for our GaN neutron detectors.

In order to solve the problem of searching a radioactive source in a wide area, we developed a mobile CsI detector. This paper presented the performance of the detector during the spectra collection investigation. The 1 s spectrum collected by the detector was low-count spectrum and it is hard to distinguish whether it contains radioactive source signals. A rapid detection method of radioactive source based on low-count gamma spectra was proposed. Principal component analysis (PCA) was the key technology of the method. According to the PCA, the source information was efficiently extracted. With the method, the detect sensitivity and accuracy of the detector were optimized.

In this study, hexagonal boron nitride (h-BN) films were synthesized by dual temperature zone low-pressure chemical vapor deposition (LPCVD) using a single ammonia borane precursor on a non-catalytic c-plane Al2O3 substrate. The grown films were confirmed by various characterization methods for h-BN. Meanwhile, the growth rate and crystal quality of h-BN films at different positions in the dual temperature zone were studied. This study found that the growth rate and crystal quality of the h-BN films at different positions on the substrate were significantly different. The growth rate of the h-BN thin films showed a decreasing trend with the rearward position, while the crystal quality improved. This work provides an experimental basis for the preparation of large area wafer thick h-BN films by LPCVD.