Nuclear Technology / Volume 165 / Number 1 / January 2009 / Pages 111-123
Technical Paper / Accelerators
Accelerator-based target design and optimization are presented in this paper as an approach for the analysis of neutron generation and characteristics. Electron-based targets and proton-based targets driven by high-energy accelerator beams are investigated. The target plays an important role in the external neutron sources in which the target was driven by high-energy accelerator beams to generate neutrons. The optimization of target design in this work is to obtain the maximum generation of neutrons out of targets considering target material and geometry, accelerator beam energy, and beam size. A three-dimensional particle detection methodology and a surface matrix arithmetic technique were used to determine the spatial distribution of the source particles (electron and proton) and the total neutron generation from the target outer surfaces. Neutron generation and characteristics were analyzed based on the optimized targets regarding neutron spectrum, average energy, and average flux. Monte Carlo calculations were performed by using MCNPX to estimate the particle interaction inside the target and to calculate the neutrons escaping out of the target surfaces.
Results in this work indicated that a high-energy (1-GeV) electron accelerator beam is capable of producing high-intensity neutron flux at the range of 1.60 × 1013 n/cm2s of 1-mA electron. Compared to an electron accelerator beam, a proton beam (1 GeV) generates higher-intensity neutron flux at the level of 4.83 × 1013 n/cm2s of 1-mA proton. The neutron generation ratio (neutron per incident particle escaping from the target) was computed as 0.76 neutrons per electron and 38.8 neutrons per proton for the selected targets. In the electron accelerator-based target, neutron generation was mostly through photonuclear reactions (88%), followed by prompt fission (12%). Neutron production in the target of the proton accelerator-based target was mainly due to spallation reactions (40%) and prompt fissions (48%). The optimized size of the target for the electron accelerator-based target, in terms of the volume, was about 16 times smaller than that for the proton accelerator-based target. The estimated neutron energy distribution was much narrower, with the electron accelerator target ranging from 1.0 × 10-3 to 30 MeV. In the proton accelerator target, the neutron energies ranged between 1.0 × 10-5 MeV and 1 GeV.