Comparing Radiation Shielding Potential of Liquid Propellants to Water for Application in Space

• Main Author: Czaplewski, John
• Format: Others
• Published: DigitalCommons@CalPoly 2021
• Subjects: FLUKA; Liquid-Propellant; Radiation; Engineering Physics; Other Aerospace Engineering; Statistical Methodology; Structures and Materials
• Online Access: https://digitalcommons.calpoly.edu/theses/2357; https://digitalcommons.calpoly.edu/cgi/viewcontent.cgi?article=3795&context=theses

The radiation environment in space is a threat that engineers and astronauts need to mitigate as exploration into the solar system expands. Passive shielding involves placing as much material between critical components and the radiation environment as possible. However, with mass and size budgets, it is important to select efficient materials to provide shielding. Currently, NASA and other space agencies plan on using water as a shield against radiation since it is already necessary for human missions. Water has been tested thoroughly and has been proven to be effective. Liquid propellants are needed for every mission and also share similar characteristics to water such as their density and hydrogenous composition. This thesis explores the shielding potentials of various liquid propellants as they compare to water for the purpose of providing an additional parameter when choosing propellants for any given mission. Testing propellants is done by first creating an experimental setup involving radioisotope sources Cs-137 and Co-60, a column of liquid with variable depths, and a Geiger-Mueller tube. Water and three other liquids: acetone, 70% isopropyl alcohol, and 12% hydrogen peroxide are physically tested and their linear attenuation coefficients are calculated. Then, the test setup is replicated in CERN’s Monte Carlo base radiation transport code, FLUKA. Although the calculated linear attenuation outputs from FLUKA are discrepant from experimental results by an average of 34%, they produce the same trends. FLUKA is used to expand upon experimental results by simulating a multitude of liquid propellants and comparing them all to water. FLUKA has the ability to simulate all propellants including hydrogen, oxygen, hydrazine, and dinitrogen tetroxide. Most of the tested propellants are found to have similar, to within 35%, gamma radiation linear attenuation coefficients as compared to water. The gamma radiation in this thesis’s experiment and simulations comes from Cs-137 and Co-60 radioisotope sources. For gamma radiation from the Co-60 source, liquid hydrogen provides 90% less attenuation than water and nitric acid and AF-M315E provide 35% and 38% more attenuation than water respectively. For gamma radiation emitted by Cs-137, liquid hydrogen, isopropyl alcohol, and methane have 90%, 35%, and 29% less attenuation than water respectively. Dinitrogen tetroxide, hydrogen peroxide, AF-M315E, and nitric acid have 34%, 41%, 46%, and 52% greater attenuation coefficients than water respectively. The liquids that are similar to water for the Cs-137 source have linear attenuation coefficients within 20% of water’s. Ultimately, most of the tested liquid propellants are shown to shield against radiation at a similar rate to water. Thus, an additional parameter for choosing liquid propellants on any given mission should be their radiation shielding capabilities.