Characteristics of neutrons and proton beams arising from two different Beam Nozzles

Abstract

Tandem or Van de Graaff accelerator with an energy of 3-MeV is typically used for PIXE analysis. In this study, the beam line design used in PIXE analysis was used to increase the production of isotopes instead of the typical low-energy accelerator from a 13-MeV cyclotron. For PIXE analysis, the proton beam should be focused at the target through the use of a nozzle after degrading the proton beam energy from 13-MeV to 3-MeV using an energy degrader. Previous studies have been conducted to determine the most appropriate material and thickness of the energy degrader. Based on the energy distribution of the degraded proton beam and the neutron occurrence rate at the degrader an aluminum nozzle of X thickness was determined to be the most appropriate nozzle construction. Neutrons are created by the collision of 3-MeV protons into the nozzle after passage through energy degrader. In addition, a sufficient intensity of proton beam is required for non-destructive analysis of PIXE. Therefore, in order to optimize nozzle design, it is necessary to consider the number of neutrons which arise from the collision of protons inside the nozzle, as well as the track direction of the generated secondary neutrons, with the primary aim of ensuring a sufficient number of protons passing through the nozzle as a direct beam. A number of laboratories are currently conducting research related to the design of nozzles used in accelerator fields, mostly relating to medical fields. In this paper, a comparative analysis was carried out for two typical nozzle shapes in order to minimize losses of protons and generation of secondary neutrons. The neutron occurrence rate and the number of protons after passing through the nozzle were analyzed using a Particle and Heavy Ion Transport code System (PHITS) program, in order to identify the nozzle which generated the strongest proton beam.