Fast Neutron Dosimeter for the Space Environment

The space environment is inherently complicated with multiple sources of radiation. Within a space craft, these radiation fields are further complicated by the production of secondary particles. When assessing the radiation risk for humans, the impact of the absorbed energy within the body is quantified using a quality factor. Because neutrons can deliver a dose, they are a major contributor to the human equivalent dose and need to be accounted for. It is typically difficult to isolate interactions from various types of neutral particles, such as gamma rays, neutrons, and neutral ions, where each particle may yield vastly different quality factors.

RMD has demonstrated the capabilities with DPA scintillation material for fast neutron detection. Using this material, neutrons and gamma ray events can be discriminated using an appropriate algorithm based on the differences in pulse shapes. The other key component to the compact neutron spectrometer is solid-state photomultipers that can be used to read out the scintillation light from the DPA material. When used with a set of detector elements, a system can be devised to isolate neutral particles from charged particles and discriminate neutrons from other neutral particles, such as gamma rays. Using a modular design, the system can easily be scaled to improve sensitivity. The system will have the capability to provide dose information from each detector component.

To be a useful dosimeter for space radiation environments, the device must be sensitive to the expected radiation fields (rejecting backgrounds from primary particle and gamma-rays), while providing a workable, deployable device with the hardware restrictions of space flight. RMD’s device will measure flux, fluence, dose rate, cumulative dose, and energy deposition spectra, as well as provide information on dose equivalent rate and cumulative dose equivalent. The prototype is being designed to meet the following requirements:

  • Sensitive to neutrons with energies from 0.5 to 150 MeV,
  • Proton/ion rejection approaching 100%,
  • Sensitive to ambient dose equivalent of 0.02 mSv over a 1 hour measurement,
  • Store all scientific data on an event-by-event basis for off-line analysis,
  • Mass limit: 5 kg,
  • Volume limit: 6000 cm3.