Deconvolution of Mono-Energetic and Multi-Lines Gamma-Ray Spectra Obtained with NaI(Tl) Scintillation Detectors Using Direct Matrix Inversion Method

Performance of a NaI(Tl) scintillation detector based on the gamma-ray spectroscopy system is not satisfactory in retaining its original peak (which is delta like function) of various gamma ray spectrum. The method of achieving precise peak for the various gamma ray was conducted by converting the observed pulse-height distribution of the NaI(Tl) detector to a true photon spectrum. This method is obtained experimentally with the help of an inverse matrix deconvolution method. The method is based on response matrix generated by the Monte Carlo simulation based on Geant4 package of mono-energy gamma-ray photon ranging from 0.050 to 2.04 MeV in the interval of 10 keV. The comparison of the measured and simulated response function was also performed in order to authenticate the simulation response function. Good agreement was observed around the photo-peak region of the spectrum, but slight deviation was observed at low energy region especially below 0.2 MeV. The Compton backscattering and Compton continuum counts was significantly transferred into the corresponding photo-peak and consequently the peak to total(P/T) ratio was improved. The P/T ratio results obtained after application of the deconvolution method taken with three calibration sources with gamma-ray’s energies of 81 keV, 303 keV and 356 keV (for 133Ba), 662 keV (for 137Cs), 1173 keV and 1333keV (for 60Co), were improved from(to) 0.50(0.90), 0.40(0.83), 0.57(0.93), 0.31(0.92), 0.18(0.84) and 0.15(0.83), respectively.

Measurement of the angular distribution of neutrons scattered from deuterium below 3 MeV

The differential cross section of neutron scattering on deuterium was investigated in the energy range from 400 keV to 2.5 MeV using the recoil detection method, irradiating with monoenergetic neutrons a proportional counter filled with deuterated gases. Comparing simulations of the transport of neutrons and recoil nuclei in the detector to the experimental pulse-height distribution, it was possible to establish a procedure for the determination of the coefficients of the Legendre expansion of the n-d angular distribution.

CAR-BORNE SURVEY OF NATURAL BACKGROUND GAMMA RADIATION IN WESTERN, EASTERN AND SOUTHERN THAILAND

Natural background gamma radiation was measured along the main roads in the eastern, western and southern regions of Thailand using a car-borne survey system with a 3-in × 3-in NaI (Tl) scintillation spectrometer. The system was able to quickly survey a large area and obtain outdoor absorbed dose rate in air from a gamma ray pulse height distribution. A total of 19 219 data of the outdoor absorbed dose rate in air were collected. The average outdoor absorbed dose rate in air in the eastern, western and southern regions were found to be 8–127, 16–119 and 16–141 nGy h -1 , respectively. The highest outdoor absorbed dose rate in air was detected in the southern region of Thailand. The corresponding average outdoor annual effective dose to the public ranged from 11.7 to 80.8 μSv.

Energy-dependent dead-time correction in digital pulse processors applied to silicon drift detector's X-ray spectra

Dead-time effects in X-ray spectra taken with a digital pulse processor and a silicon drift detector were investigated when the number of events at the low-energy end of the spectrum was more than half of the total, at counting rates up to 56 kHz. It was found that dead-time losses in the spectra are energy dependent and an analytical correction for this effect, which takes into account pulse pile-up, is proposed. This and the usual models have been applied to experimental measurements, evaluating the dead-time fraction either from the calculations or using the value given by the detector acquisition system. The energy-dependent dead-time model proposed fits accurately the experimental energy spectra in the range of counting rates explored in this work. A selection chart of the simplest mathematical model able to correct the pulse-height distribution according to counting rate and energy spectrum characteristics is included.