Presentation On the Use of Superheated Bubble Detectors on Space Missions

Benton, Eric  ,  Machrafi, Rachid  ,  Tomi, Leena  ,  Kitamura, Hisashi  ,  Kodaira, Satoshi

Superheated bubble detectors (SBD) have been used aboard spacecraft for over two detectors, including aboard the Russian Mir Space Station, the International Space Station, and on Russian BioSatellites. Interpretation of bubble detector readings made in space has been problematic due to the fact the space radiation environment is dominated by charged particles and especially protons, while the characterization of SBD has largely been confined to neutrons. By means of experiments carried out using heavy ion and proton beams of known LET at particle accelerators, we demonstrate that SBDs are high- LET threshold detectors. Heavy charged particles with LET greater than a certain LET threshold will produce bubbles through direct ionization (i.e.electromagnetic rather than nuclear processes). High energy (relativistic) protons, α-particles and light ions of LET below the LET threshold can only produce bubbles via nuclear target fragmentation reactions that yield secondary charged particles of LET above the threshold within the semsitive vilume of the detector. Neutrons are detected by SBD by undergoing nuclear interactions and producing secondary charged particles of LET above the threshold within the sensitive volume of the detector. For the SBD sprcifically designed for use aboard spacecraft, we determined the threshold for bubble formation to be LET∞H2O110±10keV/μm. We plan to determine a conversion coefficient to convert bubble detector readings, in different space missions, to an operational dosimetric quantity.
The 20th Workshop on Radiation Monitoring for the International Space Station

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