INVESTIGATION OF PULSE SHAPE NEUTRON-GAMMA DISCRIMINATION

The role of neutron beam investigation is significant not only for fundamental science but also for various fields of applied science. This work is dedicated to the formation of neutron beams using the external 18-MeV proton beam of IBA cyclotron C18/18 with a beam current of up to 100 µA. The facility is located at the A. Alikhanyan National Science Laboratory (Yerevan Physics Institute). The possibility to obtain thermal or epithermal neutron beams using the external proton beam of the cyclotron is studied using Geant4 simulations. In this case, a quasimonoenergetic neutron source 9Be (p, n)9B reaction is chosen. As a result of the simulations, the optimal thickness of the 9Be beryllium isotope target is determined. The induced neutron beam is accompanied by a gamma ray background. To decrease the number of accompanying gamma rays, the lead absorber is considered. As a method of separating neutrons from gamma rays, the pulse shape discrimination (PSD) technique is developed. This study shows the possibility of neutron-gamma PSD and its applicability using the EJ-299-33A plastic scintillator.

Study of Atmospheric Discharges by Near Surface Electric Field Measurements

Background:In this work the disturbances of the near surface electric field are investigated, which are attributed to different types of atmospheric discharges: intracloud or cloud-to-ground.Method:The patterns of the lightning occurrences are discussed as measured by the network of the electric field mills located at the stations of Cosmic Ray Division of Yerevan Physics Institute. Discharges make changes in the near surface electric field, which can be separated into two groups. The differences of those two groups and shapes of the recovery curves are discussed using the data from electric field mills network for a stormy day on May 23, 2015.Conclusion:The results presented in this work show that magnitudes of field changes from one of the groups are larger and have shorter duration compared to another one. Recovery curves of the near surface electric field produced by lightning flashes also have a power-law or a linear dependence besides exponential shape.