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Human Research Program

Lunar EVA Dosimetry: Small Active Dosimetry System for Lunar Extravehicular Activity Missions: Spacesuit and Tool-Box Applications

Completed Technology Project

Project Introduction

During year 4 (final year for this grant) we developed and fabricated final components, assembled, and tested. The tissue-equivalent sensor was redesigned to improve mechanical reliability. The original design used a single crimp fastener to tension the anode wire and make the electrical connection between the anode and the charge integrator input. This crimp connector could slip in the high molecular weight anode insulator when it was being connected or disconnected from the integrator, resulting in a loose or broken anode wire. This problem was eliminated by replacing the aluminum flange with one machined from stainless steel. The completed detector and charge integrator assembly was tested using both gamma-ray and neutron sources, with data acquisition accomplished using a commercial data logger and later with the miniaturized electronics package. The relative variance minus the relative covariance (v-c) was then calculated. The slope of the change in output voltage was determined and the calibration factor for the detector/charge integrator was determined. The calibration factor was then used to convert v-c, which is calculated in volts, to dose mean single event specific energy in Gy, and the geometry and mass of gas in the detector was used to convert single event specific energy to lineal energy in keV/µm. This approach produced results consistent with published values of the dose mean lineal energy for the radiation sources measured. The final electronic schematics and board fabrication files were developed and prototype fabricated for testing with radiation sources. The design consisted of a main board, daughter board, and sensor interface board. These boards fit into a compact aluminum enclosure. The prototype can be programmed in ANSI C, operate from battery power, communicate through USB through a simple terminal, and connect to a standard evaluation board to measure apparent diffusion coefficient (ADC) performance. Each unit has auxiliary user pins for connection of additional inputs or outputs. C-programming was developed for control and for processing the algorithm based on the data conditioning and results of the Excel analyses. A custom LabView control interface was developed and is capable of graphing dose rate and dose equivalent rate along with providing total integrated dose and dose equivalent. In conclusion, hardware requirements specified by NASA for this technology have either been met or exceeded: tissue equivalent sensor, omni-directional response, LET response between 0.2 and 300 keV/µm, detects maximum credible SPE without saturation, measures dose rate to required level of precision and time resolution, very low power consumption (about 0.75 W), low mass (about 250 g), and adaptable to either a personal dosimeter or area monitor. Additional software work is required to improve yD calculations, and more tests are required to better define lower limit of detection, important for ambient dose-equivalent rates in space. More »

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This is a historic project that was completed before the creation of TechPort on October 1, 2012. Available data has been included. This record may contain less data than currently active projects.