An image reconstruction method for transmission computed tomography with the constraint of the linear attenuation coefficients.

For the reconstructed image of transmission computed tomography, the linear attenuation coefficients of the diagnosed object may improve the image quality by adding additional constraint besides the projection data. In the present work, an image reconstruction method with the constraint of the linear attenuation coefficients is developed and two models including a classical numerical Shepp-Logan model and a Monte Carlo model are used to show the corresponding benefits. The results indicate that the number of the projection angles is potentially decreased to 1/3 of itself while the quality of the reconstructed image is not deteriorated.

Enhancing the sensitivity for weak radioactive source detection.

Considering the difficulties of the low signal-to-noise ratio in weak radioactive source detections, this study proposes an abandon Gaussian tails method based on the analysis of the characteristic information denoted by the full-energy peak of the gamma spectrum of a gamma-emitting radioactive source. Based on the study of the signal-to-background ratio and the statistical fluctuations in the signal of the weak radioactive source, a factor ζ, incorporating the statistical fluctuations of signal and background and the signal-to-background ratio, is suggested to characterize the sensitivity of a radioactive source detection. When ζ reaches its maximum value, the optimal counting window around the centroid of the full-energy peak can be obtained. To evaluate the effectiveness of the proposed approach, comparisons between the proposed abandon Gaussian tails, the conventional full-energy counting, and other experiential methods were performed. The results show that the sensitivity can be significantly improved. Further, experiments with different intensity of radiation sources and duplicated experiments were conducted to examine the stability of the proposed method.

A method to calibrate the n-γ discrimination property of scintillators in low energy region.

Scintillators with n-γ discrimination property are widely used in the measurement of neutrons. In sub MeV region, the n-γ discrimination property will be greatly deteriorated so that the neutron and γ-ray events can't be accurately discriminated. As a result, the determination of the proportions of neutron and γ-ray events beyond the discrimination threshold is important if scintillators are applied to measure the low energy neutrons. In the present work, a method based on the time-of-flight technique is proposed to calibrate the proportions of neutron and γ-ray events beyond the discrimination threshold. After the calibration, the numbers of the measured neutron and γ-ray events can be separately determined even if the neutron and γ-ray events can't be perfectly discriminated.

Determination of the number of 238U target nuclei and simulation of the neutron induced fission fragment energy spectrum.

A Monte Carlo simulation of the energy spectrum of the α particles emitted from a 238U3O8 sample is performed. Through comparing the simulated and measured energy spectra of the α particles, the non-uniformity of the 238U3O8 sample is obtained, and then the number of 238U target nuclei is determined. Using the obtained non-uniformity, a Monte Carlo simulation is developed to simulate the energy spectrum of neutron induced fission fragments. The simulated and measured energy spectra of neutron induced fission fragments agree well with each other.

Study of the wall effect of the sample position well of the Frisch-grid ionization chamber.

When measuring the charged particles using a Frisch-grid ionization chamber, the sample is usually placed at the bottom of a sample position well on the common cathode. Thus, there will be the wall effect of the sample position well and this will change the measured energy spectrum of the charged particles. The wall effect of the sample position well is proved to be noticeable by the present work using experiments and simulations.