Task Lunar EVA Dosimetry: Design of a Radiation Dosimeter for Astronauts During Lunar Extravehicular Activities (Completed)
Last Published:  11/23/20 11:55:12 AM (Central)
Short Title: SR Dosimeter-Borak
Responsible HRP Element: Space Radiation
Collaborating Org(s):
National Space Biomedical Research Institute (NSBRI)
Funding Status: Completed - Task completed and produced a deliverable
Procurement Mechanism(s):
Task 1: Design, Fabrication and Testing Mod1 prototype detector
The purpose of this task was to design, build and assemble a prototype Tissue Equivalent Proportional Counter (TEPC) that would satisfy the basic specifications outlined by NASA for a dosimeter for astronauts during lunar EVAs.

The spherical TEPC is based on a single-wire anode with recessed guard ring insulators to shape the electric field near the poles. The diameter of the gas cavity is 18mm and the wall thickness is 3mm for a total diameter of 24mm (~ 1 inch). A stainless steel vacuum chamber designed to accommodate the TEPC and pre amplifier has been fabricated and leak tested. The hemispherical dome surrounding the TEPC has a wall thickness of 1 mm. This is welded to a cylindrical sleeve with a vacuum tight flange that can be easily removed whenever modifications to the components are necessary.

Task 2: Modeling Detector Response

The objective of this task is to determine the response of the TEPC under ambient conditions and during SPE events on the lunar surface.Computations using the Monte Carlo Code PHITS have been made to determine the energy deposition in the TEPC using protons with an energy spectrum from a SPE in October 2003. These data were compared with the dose that would be delivered to the skin beneath a space suit with an areal density of 0.4 g/cm2. It is clear that a stainless steel vacuum chamber in Mod 1 needs to be replaced with lighter and thinner materials. These results will be important in determining what additional modifications will be necessary to achieve the design goal for real time measurements to the skin and BFO.

Task 3: Modeling the Variance-Covariance Method

We are developing a method based on using one detector in a variance-covariance scheme. The concepts are based on collecting the charge, zi, in a single TEPC for n successive time intervals. The method proposed by Borak at CSU separates the data set into two groups of n/2 entries of values for zi based on odd and even indices. The n/2 pairs of data (odd and even) are used to obtain the covariance and each of the two sets of n/2 values (odd or even) to estimate a variance. Monte Carlo codes have been written to test the algorithms and determine if there are any limitations to this process.
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