Active Solid State Dosimetry for Lunar EVA. J.D. Wrbanek,1 G.F. Fralick,1 S.Y. Wrbanek1 and L.Y. Chen2 1NASA Glenn Research Center, Instrumentation & Controls Division, Cleveland, Ohio. 2Ohio Aerospace Institute, Brook Park, Ohio.

Introduction: The primary threat to astronauts

from space radiation is high-energy charged particles, such as electrons, protons, alpha and heavier particles, originating from galactic cosmic radiation (GCR), so-lar particle events (SPEs) and trapped radiation belts in Earth orbit. There is also the added threat of secon-dary neutrons generated as the space radiation interacts with atmosphere, soil and structural materials.[1]

For Lunar exploration missions, the habitats and transfer vehicles are expected to provide shielding from standard background radiation. Unfortunately, the Lunar Extravehicular Activity (EVA) suit is not expected to afford such shielding. Astronauts need to be aware of potentially hazardous conditions in their immediate area on EVA before a health and hardware risk arises. These conditions would include fluctua-tions of the local radiation field due to changes in the space radiation field and unknown variations in the local surface composition. Should undue exposure occur, knowledge of the dynamic intensity conditions during the exposure will allow more precise diagnostic assessment of the potential health risk to the exposed individual.[2]

Technology Need: An active personal dosimeter for Low Earth Orbit (LEO) EVA use is specifically recommended by NASA JSC’s Radiation Dosimetry Working Group, and the National Council on Radia-tion Protection and Measurements (NCRP) recom-mends personal radiation monitoring for real-time dose rate and integrated dose in LEO.[3] Compared to the current LEO missions, the expeditions to the Moon will place crews at a significantly increased risk of hazardous radiation exposure.

Current radiation measurement and warning sys-tems may be not adequate for the future Lunar mis-sions, and currently instruments do not exist that can make these measurements and be incorporated into the Lunar EVA suit. However, MEMS devices fabricated from silicon carbide (SiC) to conduct low-noise neu-tron and alpha particle spectrometry have recently been reported outside of the context of personal do-simetry.[4]

Development Effort: NASA GRC has been lead-ing the world in the development of SiC semiconduc-tor technology, producing SiC semiconductor surfaces of much higher quality than commercially available, as shown in figure 1. These surfaces have demonstrated advantages over standard materials for other sensor applications.[5] In other activities, NASA GRC is attempting to verify claims of nuclear energy in sono-

luminescence using thin film coated scintillation detec-tors fabricated at NASA GRC as part of the Vehicle Systems Program, shown in figure 2.[6]

NASA GRC is leveraging these efforts to investi-gate small and large area MEMS devices for sensitivity to radiation and to compare with commercial devices. If these initial results look promising as a path for the design and fabrication of a prototype solid state do-simeter, further testing would be required in conjunc-tion with other researchers in the space radiation field over the next few years. The long term objective of this effort is to provide a compact, low power active electronic dosimetry system that would not be ad-versely affected by radiation, with improved sensitivity and detection capability for real-time monitoring of Lunar EVA conditions.

Figure 1: Examples of NASA GRC SiC Fabrica-

tion: Defect free (far left) & typical (center left) SiC surfaces, and a SiC circuit (right).

Figure 2: Radiation Detector Development: NASA

GRC is attempting to verify claims of nuclear energy in sonoluminescence (left) using thin film coated scin-tillation detectors fabricated at NASA GRC (right).

References: [1] Johnson A.S., Badhwar G.D., Golightly M.J., Hardy A.C., Konradi A. and Yang T.C. (1993) NASA TM-104782. [2] R. Turner (2000) LWS Community Workshop. [3] Vetter R.J., et al. (2002) NCRP Report No. 142, 47-49. [4] Ruddy F.H., Dulloo A.R., Seidel J.G., Palmour J.W. and Singh R. (2003) Nucl. Instr. and Meth. A 505, 159–162. [5] Hunter G.W., Neudeck P.G., Xu J., Lucko D., Trunek A., Artale M., Lampard P., Androjna D., Makel D., Ward B. and Liu C.C. (2004) Mat. Res. Soc. Symp. Proc. 815, 287-297. [6] Wrbanek J.D., Fralick G.C., Wrbanek S.Y. and Weiland K.E. (2005) NASA TM-2005-213419, 46-7.

https://ntrs.nasa.gov/search.jsp?R=20060013413 2018-06-26T09:28:56+00:00Z

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once

pt