Engineering topics
Publications and source records attributed to Burrell, M. O..
Preliminary charged particle dose rates are presented for the LST orbit. The trapped proton component appears to dominate the total dose for the expected shielding available. Typical dose rates should range from 400 to 800 millirads/day.
When high energy protons from solar proton events or trapped radiation belts impinge on spacecraft structures, secondary particles are emitted. The most pernicious secondaries, from either a biological or physical standpoint, are the cascade and evaporation neutrons because of their reaction with matter leading to radioactive materials in the spacecraft structures. Empirically determined cascade and evaporation neutron emission spectra for protons of energy between 20 and 500 MeV incident on all materials at or above carbon in mass number are presented.
This study is concerned with approximation methods that can be readily applied to estimate the absorbed dose rate from cosmic rays in rads - tissue or rems inside simple geometries of aluminum. The present work is limited to finding the dose rate at the center of spherical shells or behind plane slabs. The dose rate is calculated at tissue-point detectors or for thin layers of tissue. This study considers cosmic-rays dose rates for both free-space and earth-orbiting missions.
The total dose in rads-tissue from solar protons was tabulated for weekly time intervals, and the number of weeks which gave a dose above 25 rads behind 10 g/sq cm of aluminum for the active 6 years of the 19th cycle were called dangerous or large event weeks. The number of such event weeks was found to be only 3 weeks for the past 20 years. Even though the chance for smaller events is examined, it was found that for any reasonable, high confidence level (95%), the smaller events could be ignored. Consequently, the total particle flux for the 19th cycle was divided by a factor of 3 and determined a single large event week. Using this spectrum, the tissue dose in rads is calculated at the center of an aluminum spherical shell.
Various techniques for the calculation of electron and bremsstrahlung dose deposition are described. Energy deposition, transmission, and reflection coefficients for electrons incident on plane slabs are presented, and methods for their use in electron dose calculations were developed. A method using the straight-ahead approximation was also developed, and the various methods were compared and found to be in good agreement. Both accurate and approximate methods of calculating bremsstrahlung dose were derived and compared. Approximation is found to give a good estimate of dose where the electron spectrum falls off exponentially with energy.
Probability models for risk of solar proton events to space missions
Calculation of electron and bremsstrahlung dose deposition with energy deposition, transmission, and reflection coefficients for electrons
Charged particle dose rates for men and radiation sensitive materials during long-duration flights in low orbit
Method for simulating Van Allen belt proton energy spectra
Design and analysis of radiation shields for nuclear rocket systems
Energetic space radiation and galactic cosmic radiation measured for radiation hazards in manned space flight
Monte Carlo generation of plane isotropic buildup factors for bremsstrahlung calculations
Electron and bremsstrahlung dose rate calculations from Monte Carlo energy transfer method and bremsstrahlung production method
Gamma ray isotropic dose, energy flux, and energy current buildup factors by Monte Carlo methods for bremsstrahlung calculations
Gamma-ray isotropic dose, energy flux and energy current buildup factors for finite slabs calculated by Monte Carlo techniques
Energetic space radiation and dose rate analysis
Flux and energy spectra code for orbital calculations and trapped radiation mapping
Calculation of proton penetration and dose rates for tissue, aluminum, and other shielding materials