Browsing by Author "Avneet Sood, Committee Member"

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    Development of Monte Carlo Code for Coincidence Prompt Gamma-ray Neutron Activation analysis
    (2005-11-07) Han, Xiaogang; Avneet Sood, Committee Member; Robin P. Gardner, Chair, Committee Chair; Wenye Wang, Committee Member; Man-Sung Yim, Committee Member
    Prompt Gamma-Ray Neutron Activation Analysis (PGNAA) offers a non-destructive, relatively rapid on-line method for determination of elemental composition of bulk and other samples. However, PGNAA has an inherently large background. These backgrounds are primarily due to the presence of the neutron excitation source. It also includes neutron activation of the detector and the prompt gamma rays from the structure materials of PGNAA devices. These large backgrounds limit the sensitivity and accuracy of PGNAA. Since Most of the prompt gamma rays from the same element are emitted in coincidence, a possible approach for further improvement is to change the traditional PGNAA detection technique and introduce the gamma-gamma coincidence technique. It is well known that the coincidence technique can eliminate most of the interference backgrounds and improve the signal-to-noise ratio. A new Monte Carlo code CEARCPG is being developed at CEAR to predict coincidence counting in coincidence PGNAA. Compared to the other existing Monte Carlo code, a new algorithm of sampling the prompt gamma rays, which are produced from neutron capture reaction and neutron inelastic scattering reaction, is developed in this work. All the prompt gamma rays are taken into account by using this new algorithm. Before this work, the commonly used method is to interpolate the prompt gamma rays from the pre-calculated gamma-ray table. It works fine for the single spectrum. However it limits the capability to simulate the coincidence spectrum. This new algorithm is to sample the prompt gamma rays from the nucleus scheme. It makes possible to simulate the coincidence spectrum by using Monte Carlo method. The primary nuclear data library used to sample the prompt gamma rays comes from ENSDF library. Three cases are simulated and the simulated results are checked with the experiments. The first case is the prototype for ETI PGNAA application. This case is designed to check the capability of CEARCPG for single spectrum simulation. The second case and the third case are designed for coincidence simulation. CEARCPG is also applied to optimize the design of coincidence PGNAA device. A new coincidence PGNAA application is proposed in this work. The probability of extending this code is also discussed. The funding of this work is provided by the Center for Engineering Application of Radioisotopes (CEAR) at North Carolina State University (NCSU) and Nuclear Engineering Education Research.
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    Prompt Gamma-ray Imaging for Small Animals
    (2006-11-02) Xu, Libai; Avneet Sood, Committee Member; Dmitriy Y. Anistratov, Committee Member; Robin P. Gardner, Committee Chair; Wesley E. Snyder, Committee Member
    A new imaging modality called prompt gamma-ray imaging (PGI) has been identified and investigated primarily by Monte Carlo simulation. Currently it is suggested for use on small animals. This new technique could greatly enhance and extend the present capabilities of PET and SPECT imaging from ingested radioisotopes to the imaging of selected non-radioactive elements, such as Gd, Cd, Hg, and B, and has the great potential to be used in Neutron Cancer Therapy to monitor neutron distribution and neutron-capture agent distribution. This approach consists of irradiating small animals in the thermal neutron beam of a nuclear reactor to produce prompt gamma rays from the elements in the sample by the radiative capture (n, γ) reaction. These prompt gamma rays are emitted in energies that are characteristic of each element and they are also produced in characteristic coincident chains. After measuring these prompt gamma rays by surrounding spectrometry array, the distribution of each element of interest in the sample is reconstructed from the mapping of each detected signature gamma ray by either electronic collimations or mechanical collimations. In addition, the transmitted neutrons from the beam can be simultaneously used for very sensitive anatomical imaging, which provides the registration for the elemental distributions obtained from PGI. The primary approach is to use Monte Carlo simulation methods either with the specific purpose code CEARCPG, developed at NC State University or with the general purpose codes GEANT4 or MCNP5, to predict results and investigate the feasibility of this new imaging idea. Benchmark experiments have been conducted to test the capability of the code to simulate prompt gamma rays, which are produced by following the nuclear structures of each irradiated isotope, and coincidence counting techniques, which are considered the most important improvement in neutron-related gamma-ray detection applications to reduce gamma background and improve system signal-to-noise ratios. With coincidence prompt gamma rays available, two major imaging techniques, electronic collimations and mechanic collimations, are implemented in the simulation to illustrate the feasibility of imaging elemental distribution by this new technique. The expectation maximization algorithm is employed in electronic collimation to reconstruct images. The common SPECT imaging algorithms are used in mechanical collimation to get an image. Several critical topics concerning practical applications have already been discussed, such as the radiation dose to the mouse and the detection efficiency of high-energy gamma rays.