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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.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).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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Related in: MedlinePlus

Linear response of the prototype to a broad range of gamma-ray dose rates. Net slopes are slopes measured with radiation source minus slope measured without radiation source. The slope measured without radiation source was determined to be 0.21 ± 0.02 V s−1 and resulted from a leakage current that was observed to be stable during these test measurements, permitting confident background subtraction.
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Figure 4: Linear response of the prototype to a broad range of gamma-ray dose rates. Net slopes are slopes measured with radiation source minus slope measured without radiation source. The slope measured without radiation source was determined to be 0.21 ± 0.02 V s−1 and resulted from a leakage current that was observed to be stable during these test measurements, permitting confident background subtraction.

Mentions: The prototype was exposed to a broad range of gamma-ray dose rates at the Stanford Linear Accelerator Center (SLAC) health physics instruments calibration facility. Both 137Cs and 60Co gamma-ray sources were used. A NIST calibrated tissue-equivalent ion chamber was used as a standard to measure dose rate at the detector position. The rate of charge increase in the charge integrator was shown to be proportional to dose rate. This is observed in Fig. 4, where the slope of the charge increase (measured in V s−1) is plotted as a function of dose rate. In this case, the net slopes are plotted; i.e., slopes measured with radiation source minus slopes measured without the radiation source. The results demonstrate (1) a linear response from ambient GCR levels to the much higher dose rates possible from a large SPE, likely less than 100 mGy h−1 during EVA (Wilson et al. 2006) and much less inside a spaceship or a shielded planetary habitat; and (2) a reproducible response as observed for measurements made on different dates using two different gamma-ray sources. It is noted that a linear response was also observed for 241AmBe neutrons tested over a similar range of slopes (from 0.0125 to 1.278 V s−1) at TAMU (data not shown). These results demonstrate system linearity and reproducibility for the measurement of charge integration, which is proportional to absorbed dose rate.


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)

Linear response of the prototype to a broad range of gamma-ray dose rates. Net slopes are slopes measured with radiation source minus slope measured without radiation source. The slope measured without radiation source was determined to be 0.21 ± 0.02 V s−1 and resulted from a leakage current that was observed to be stable during these test measurements, permitting confident background subtraction.
© Copyright Policy
Related In: Results  -  Collection

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

Figure 4: Linear response of the prototype to a broad range of gamma-ray dose rates. Net slopes are slopes measured with radiation source minus slope measured without radiation source. The slope measured without radiation source was determined to be 0.21 ± 0.02 V s−1 and resulted from a leakage current that was observed to be stable during these test measurements, permitting confident background subtraction.
Mentions: The prototype was exposed to a broad range of gamma-ray dose rates at the Stanford Linear Accelerator Center (SLAC) health physics instruments calibration facility. Both 137Cs and 60Co gamma-ray sources were used. A NIST calibrated tissue-equivalent ion chamber was used as a standard to measure dose rate at the detector position. The rate of charge increase in the charge integrator was shown to be proportional to dose rate. This is observed in Fig. 4, where the slope of the charge increase (measured in V s−1) is plotted as a function of dose rate. In this case, the net slopes are plotted; i.e., slopes measured with radiation source minus slopes measured without the radiation source. The results demonstrate (1) a linear response from ambient GCR levels to the much higher dose rates possible from a large SPE, likely less than 100 mGy h−1 during EVA (Wilson et al. 2006) and much less inside a spaceship or a shielded planetary habitat; and (2) a reproducible response as observed for measurements made on different dates using two different gamma-ray sources. It is noted that a linear response was also observed for 241AmBe neutrons tested over a similar range of slopes (from 0.0125 to 1.278 V s−1) at TAMU (data not shown). These results demonstrate system linearity and reproducibility for the measurement of charge integration, which is proportional to absorbed dose rate.

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.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).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
Related in: MedlinePlus