Compact Tissue-equivalent Proportional Counter for Deep Space Human Missions

Abstract

Effects on human health from the complex radiation environment in deep space have not been measured and can only be simulated here on Earth using experimental systems and beams of radiations produced by accelerators, usually one beam at a time. This makes it particularly important to develop instruments that can be used on deep-space missions to measure quantities that are known to be relatable to the biological effectiveness of space radiation. Tissue-equivalent proportional counters (TEPCs) are such instruments. Unfortunately, present TEPCs are too large and power intensive to be used beyond low Earth orbit (LEO). Here, the authors describe a prototype of a compact TEPC designed for deep space applications with the capability to detect both ambient galactic cosmic rays and intense solar particle event radiation. The device employs an approach that permits real-time determination of (and thus quality factor) using a single detector. This was accomplished by assigning sequential sampling intervals as detectors “1” and “2” and requiring the intervals to be brief compared to the change in dose rate. Tests with γ rays show that the prototype instrument maintains linear response over the wide dose-rate range expected in space with an accuracy of better than 5% for dose rates above 3 mGy h−1. Measurements of for 200 MeV n−1 carbon ions were better than 10%. Limited tests with fission spectrum neutrons show absorbed dose-rate accuracy better than 15%.

Ground-based evaluation of dosimeters for NASA high-altitude balloon flight

“…The TEPC is the de facto instrument for microdosimetry [International Commission on Radiation Units and Measurements (ICRU), 1983] and was selected for the RaD-X mission to serve as a flight standard against which the other dosimeters could be compared. TEPCs have been used for many diverse applications on Earth [e.g., Straume et al, 1991;Lindborg et al, 1999;Gersey et al, 2002;Lindborg and Nikjoo, 2011] and in space, including in the Space Shuttle [e.g., Badhwar et al, 1996] and in the International Space Station (ISS) [e.g., Perez-Nunez and Braby, 2011], and compact TEPC designs are being developed for deep-space human missions [Straume et al, 2015].…”

A practical approach for continuous in situ characterization of radiation quality factors in space

“…In practice, portable rugged microdosimeters can be used in a space flight environment to continuously measure d(y), and several such devices have already been built and tested [17][18][19][20] . In addition, a ground-based calculation www.nature.com/scientificreports/ of a time-averaged d(y) function for the relevant space environment, leading to a predicted time-averaged quality factor, will be useful for mission planning purposes.…”

“…In a space environment, d(y) can be continuously measured using a compact tissue-equivalent proportional counter 17,18,20 or a silicon microdosimeter 19,39 . Thus, given an empirical consensus biological weighting function, Q(y), the mean quality factor, Q , can be continuously assessed using Eq.…”

A Practical Approach for Continuous In Situ Characterization of Radiation Quality Factors in Space

“…In practice, portable rugged microdosimeters can be used in a space ight environment to continuously measure d(y), and several such devices have already been built and tested [17][18][19][20] . In addition, a ground-based calculation of a timeaveraged d(y) function for the relevant space environment, leading to a predicted time-averaged quality factor, will be useful for mission planning purposes.…”

“…In short, this approach generates quality factors using measured or calculated microdosimetric spectra (distributions of energy depositions within cellular-sized volumes) that are weighted with an empirically determined biological weighting function. Because microdosimetric energy distributions can be easily and continuously measured in space environments [17][18][19][20] , and assuming that an appropriate biological weighting function is available (the subject of this paper), then radiation quality factors, and thus, corresponding dose equivalents, can be continuously assessed in situ in space environments. This microdosimetric approach, originally suggested by Zaider and Brenner 21 and Bond et al 22 , and endorsed in the International Commission on Radiation Units and Measurements (ICRU) Report 40 9 , has been used extensively in other radiation exposure contexts [22][23][24][25][26][27][28][29][30][31][32][33] .…”