Investigation of the bubble detector response to high LET space radiation

Abstract

The radiation environment aboard spacecraft is a complex mixture of neutrons, photons, protons, heavy ions and other particles. A special type of superheated droplet detectors referred to as space bubble detectors (SBD) have been used to evaluate the equivalent dose due to neutrons in various space missions aboard the International Space Station. Protons and other heavy charged particles are a significant component of the high LET radiation field and also contribute to the SBD measurements. The calibration of the bubble detectors is established using a known Americium Beryllium(AmBe) neutron field. However, the space neutron field is considerably different from the AmBe field. Current models assume that bubbles are formed as a result of radiation interactions above a certain minimum LET threshold and experiments have shown that the LET threshold may be different for different ions.In order to interpret the bubble detector measurements in space radiation fields, a systematic investigation of the response of bubble detectors to high LET radiation encountered inspace has been performed. A series of experiments have been conducted with different high LET radiation including protons and energetic heavy ions using different facilities at the National Institute of Radiological Science in Chiba, Japan, and the ProCure Proton Therapy Center in Oklahoma, USA. High energy neutron experiments were conducted at the Los Alamos Neutron Science Center. A correction factor of 1.8 ± 0.2 has been determined to correlate the AmBe calibrated sensitivity to neutron equivalent dose measurements aboard the ISS. The LET threshold required to form a bubble in SBD was found to depend on the charge Z of the ion. An analytical model to evaluate the SBD response to high LET radiation aboard the ISS has been developed and compared to measurements.