Physics & Astronomy ETDs

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Two tissue-equivalent ionization chambers were flown behind 0.4 gram/cm.2 and 2.5 grams/cm.2 of shielding inside the Gemini-6 spacecraft. The instruments measured the radiation levels resulting from primary cosmic radiation and the trapped particle environment of the earth's Van Allen belts. Each sensor was constructed from a special tissue-equivalent plastic with radiation cross sections that closely match standard muscle tissue for the many complex types and energies of radiation encountered in space. The design of the sensor and logarithmic electrometer preamplifier are described in detail. The calibration and directional sensitivity of the sensors with cobalt-60 and cesium-137 gamma radiation and 60 Mev. protons are discussed completely. Cosmic radiation levels up to 1.0 millirad/hour were recorded on revolutions 10 and 13 of the mission. The average cosmic radiation dose rate for all orbits was 0.2 millirad/hour, The total cosmic radiation dose was 4.8 millirad for the 24 hour mission. The maximum radiation dose rate behind the lightly shielded sensor in the Van Allen belts was 73 millirad/hour on revolution 6. The shielded sensor recorded 42 millirad/hour during the same time period. The total dose measured behind light shielding in the radiation belts was 19 millirad for the mission. The total radiation dose for the mission behind the 2.5 gram/cm.2 shield was 12.6 millirad, Radiation surveys conducted on the fifth revolution in the radiation belt indicated that the dose recorded by the lightly shielded sensor was reduced by 50%, to 73% for various astronaut and spacecraft shielding locations. Measurements show that electrons contributed up to 34 percent of the radiation dose during spacecraft passage through the radiation belts. It was also found that the electron contribution to the total mission dose was only 26%. Excellent agreement was found between the predicted and measured dose levels on the Gemini-4 spacecraft using the same type of instruments as flown on the Gemini-6 mission. Both the Gemini-4 and Gemini-6 radiation measurements indicate that there is no significant hazard to astronauts operating in the orbital and shielding configurations of the Gemini-4 and 6 missions. Useful conversion factors from proton flux to dose are generated for use in determining the hazards associated with manned spaceflight operations during solar flare charged particle events.

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Level of Degree


Department Name

Physics & Astronomy

First Committee Member (Chair)

John Lee Howarth

Second Committee Member

Philip Montgomery Campbell

Third Committee Member

Christopher Pratt Leavitt

Fourth Committee Member

Christopher Dean



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