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Compact Tissue-equivalent Proportional Counter for Deep Space Human Missions.

Straume T, Braby LA, Borak TB, Lusby T, Warner DW, Perez-Nunez D - Health Phys (2015)

Bottom Line: 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.Measurements of yD 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%.

View Article: PubMed Central - PubMed

Affiliation: *NASA Ames Research Center, Moffett Field, CA 94035; †Texas A&M University, College Station, TX 77843; ‡Colorado State University, Ft. Collins, CO 80523.

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 yD (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 g 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 yD 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%.

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MCA spectra compared for 226‐MeV protons and 200‐MeV n−1 carbon ions. Background (source off) is plotted for comparison. The x-axis was converted from channel number to pulse height in volts.
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Figure 3: MCA spectra compared for 226‐MeV protons and 200‐MeV n−1 carbon ions. Background (source off) is plotted for comparison. The x-axis was converted from channel number to pulse height in volts.

Mentions: Observed in Fig. 3 are the MCA spectra measured for protons and carbon ions. These are compared with a background measurement when the beam was turned off. For these measurements, the authors used identical high-voltage and exposure durations. One can see that these low-LET protons were detected above background, which was one of the considerations in performing the initial prototype test measurements. Another consideration was evaluating the angular dependence of the sensor. The carbon-ion results were used to characterize the response as a function of incident angle as described below.


Compact Tissue-equivalent Proportional Counter for Deep Space Human Missions.

Straume T, Braby LA, Borak TB, Lusby T, Warner DW, Perez-Nunez D - Health Phys (2015)

MCA spectra compared for 226‐MeV protons and 200‐MeV n−1 carbon ions. Background (source off) is plotted for comparison. The x-axis was converted from channel number to pulse height in volts.
© Copyright Policy
Related In: Results  -  Collection

Show All Figures
getmorefigures.php?uid=PMC4554228&req=5

Figure 3: MCA spectra compared for 226‐MeV protons and 200‐MeV n−1 carbon ions. Background (source off) is plotted for comparison. The x-axis was converted from channel number to pulse height in volts.
Mentions: Observed in Fig. 3 are the MCA spectra measured for protons and carbon ions. These are compared with a background measurement when the beam was turned off. For these measurements, the authors used identical high-voltage and exposure durations. One can see that these low-LET protons were detected above background, which was one of the considerations in performing the initial prototype test measurements. Another consideration was evaluating the angular dependence of the sensor. The carbon-ion results were used to characterize the response as a function of incident angle as described below.

Bottom Line: 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.Measurements of yD 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%.

View Article: PubMed Central - PubMed

Affiliation: *NASA Ames Research Center, Moffett Field, CA 94035; †Texas A&M University, College Station, TX 77843; ‡Colorado State University, Ft. Collins, CO 80523.

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 yD (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 g 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 yD 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%.

Show MeSH