Prompt Gamma-ray Spectra Emitted From Depleted Uranium Spheres Bombarded By D-T Reaction Neutrons

The D-T reaction neutron transport in the macro depleted uranium or natural uranium is one of the most important physical processes for thermonuclear weapon and fusion-fission hybrid reactor. The associated prompt gamma-rays are produced by Ⅳthe radiation capture, fission and inelastic nuclear reactions. The accuracy validation for cross section and fission energy evaluation can be conducted via the prompt gamma-rays. The prompt gamma-ray spectra emitted by macro depleted uranium spheres which bombarded by 14 MeV D-T reaction neutrons were measured.In this dissertation, the investigation object are prompt gamma-ray energy spectrum and time spectrum, the major content including measuring method & technology, data analysis and Monte-Carlo simulation.Exclude the prompt gamma-rays that produced by the three processes mentioned above, there also exist some undesired interference gamma-rays. They are decay gamma-rays caused by neutron activation, prompt gamma-rays produced by the background neutrons, prompt gamma-rays from leakage neutron bombarding the detector, and the gamma-rays emitted by the structural material and so on. In order to exclude the undesired gamma-rays, the Dual-Coincidence & Time of Flight method (DC-ToF) was developed based on gamma-rays time characteristics.In terms of computation, there are four work has been carried out. (Ⅰ) energy and intensity anisotropic distribution for D-T reaction neutrons were calculated based on TARGET code, and also the neutron average energy and energy dispersion. The calculation results were used to describe the neutron source of the MCNP5 input card. (Ⅱ) Gamma-ray response matrix and detection efficiency were simulated by MCNP5 code, the results are validated by experiment and used to unfold electron recoil spectra. (Ⅲ) The appropriate depleted uranium samples and accelerator conditions were selected according to MCNP Monte-Carlo model. (Ⅳ) For calculating the energy deposition of prompt gamma-rays induced by D-T reaction neutrons, the coupled neutron-photon Monte Carlo transport mode is needed. However, the pulse height tally does not work well with neutrons because of the nonanalog nature of neutron transport in MCNP5. Furthermore, it will cost a very long computing time if using the MCNP5 to simulate the whole macroscopic experiment model directly. As a result, a two-step calculation method is considered to avoid these problems. Firstly, the prompt γ-ray spectrum was simulated by MCNP5 code, and then simulates the ERS in liquid scintillator detector by the EGSnrc code using the prompt γ-ray spectrum that simulated by MCNP5 as input.For the measuring techniques, characterization for BC501A/BC537 liquid scintillator and CLYC scintillator detectors were investigated that can be applied in neutron gamma-ray mixed fields. The Compton edge, energy resolution, gamma-ray response matrix and neutron gamma-ray discrimination threshold were obtained. Besides the DC-ToF method, another method that based on a digitizer and ToF was also established and developed the data acquisition code, which called DG-ToF. Based on the DC-ToF and DG-ToF methods, a pulsed monoenergetic neutron beam was used in combination with BC501A and CLYC scintillator detector to measure the prompt gamma-ray spectra which produced by D-T reaction neutrons bombarding two different depleted uranium sphere models.Data analysis includes three aspects, including offline data analysis, spectrum unfolding and uncertainty analysis. For the raw data obtained with DG-ToF method, each event have three characteristic parameters as the time, charge integrating for long gate (QL) and short gate (QS). The raw data was pre-analyzed through Bad-Event-Elimination code and Neutron-Gamma-ray-Discrimination code and Data-Analysis-Spectra code based on Lab VIEW. Then the electron recoil spectrum (ERS) and time spectrum produced by prompt gamma-rays, time-energy 2D spectrum and also the spectra produced by neutrons can be obtained. Based on the ERS, the GRAVEL iterative and Tikhinov and inverse matrix unfolding methods were used for prompt gamma-ray energy spectrum. Aimed at the uncertainty sources for prompt gamma-ray spectra, the uncertainty was comprehensive analyzed and evaluated. Finally, the experimental prompt gamma-ray spectra were compared with calculations from MCNP5 and EGSnrc codes.According to this work, the experiment techniques were improved and developed for measuring prompt gamma-ray from the macroscopic samples irradiated by neutrons. The measuring method and data analysis approach can be referred in similar experiment. The prompt gamma-ray energy spectra for 0.4 MeV-3 MeV and time spectra for two depleted uranium spherical samples were obtained. Results are generally in good agreement with the calculated results based on ENDF/BII.1 library. The experiment results can be used to check the uranium nucleus parameters and to diagnoses fission energy.