Date of Award

5-2015

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Master of Engineering (ME)

Department

Engineering Physics

Advisor

C.T. Hess

Second Committee Member

Samuel Hess

Third Committee Member

George Bernhardt

Abstract

Cosmogenic particles interacting with spacecraft shielding materials results in a constant neutron flux inside inhabited low earth orbiting spacecraft and is one of the primary radiative exposure mechanisms for astronauts. Neutron dose rate caused by impinging cosmic radiation is predicted to increase with spacecraft size and therefore as longer range space travel becomes a reality and the necessary structural size of spacecraft is increased, the effect of neutron flux 011 astronauts living inside such structures becomes more important. Also becoming increasingly of concern are the cumulative effects of neutron exposure received by astronauts over extended periods of time. Because neutron radiation has relatively high LET characteristics and is difficult to attenuate using conventional techniques, the hazard it poses to human life in space is expected to be significant. Much work has been done using particle accelerators to study the effect of neutron radiation 011 cell populations however the energies typically generated in these experiments are several billion times larger than would be seen in a low earth orbiting spacecraft. Although very useful in radiation therapy research, the large order of magnitude discrepancy makes these experiential results difficult to apply to human exposure conditions in spacecraft. This research took a low dose approach to neutron exposure using a Pu-Be neutron howitzer to deliver the exposure neutron flux thereby more closely approximating current reports of spacecraft neutron dose rates. NIH-3T3 mouse fibroblast cells were bombarded with neutrons for a period of 5 hours and the propagation and doubling times post exposure were tracked over time. This research found that with an overall neutron dose of 5000 mrem delivered at a dose rate of 1000 mrem/hr and an effective dose rate of 10 mSv hr fibroblast population doubling times were decreased an average of 1.15 hours as compared with the control group and growth rates were decreased by .0014 cells hr.

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