Evaluation of the Response of a Neutron Detector of the Long-Counter Type Using Monte Carlo Transport Simulation

The Instituto de Estudos Avan ados (IEAv) is developing activities to study the dose levels of ionizing radiation from cosmic rays (CR) received by aircraft crews, sensitive equipment (on-board computers, for example) and embedded electronics in Brazilian airspace. Neutrons generated by the interaction of CR with the atmosphere are the dominant particles in the dose accumulation in electronic circuits and aircraft crews at flight altitude. Their production by spallation reactions and intranuclear cascade processes has a high-energy spectrum and the atmosphere interactions of these neutrons moderate them as well, producing secondary neutrons and resulting in a wide energy spectrum. The final neutron spectrum ranges from thermal neutrons to neutrons of several hundreds of MeV, making their flux determination a difficult process. To observe the temporal variation in neutron flux during the measurements, a detector of the Long Counter (LC) type is being used. This detector is designed to measure the directional flow of neutrons with near constant response over a wide energy range (thermal to 20 MeV). However, to measure cosmic rays, the dependence of the response on the angle of incidence, as well as energy, should be properly investigated.