SHIELDING PROBLEMS IN MANNED SPACE VEHICLES. Annual Report-1960

Technical Report · Fri Sep 01 04:00:00 EDT 1961

OSTI ID:4798769

Allen, R; Bly, F T; Dessler, A J; Douglass, C C; Perkins, J F; Price, H C; Schofield, W M; Smith, E C; Tolan, J.H. ed.

Results are presented that were obtained in the first phase of a study of the shielding requirements for manned space vehicles, as imposed by the natural radiations to be encountered in space flight and with consideration of the radiations from auxiliary nuclear power sources. The penetrating radiations known to exist in space are discussed and the reliabilities of various data are considered. Intensity, energy spectra, and spatial and time dependence of the various types of radiation are summarized in graphical and tabular form. Spatial distribution of trapped protons and electrons are presented in the form of contours of constant flux. Significance and general shielding implications of the more important penetrating radiations are treated. Computational methods for predicting dose rates due to high energy protons and electrons are formulated and results of calculations are presented. Proton dose rate calculations are based on the energy spectrum as determined by Freden and White; bremsstrahlung dose rates are calculated on the basis of the low-altitude electron spectrum measurements of Walt et al and of Holly and Johnson. It is found that attenuation of protons in shields of moderate thickness is governed largely by ionization energy losses while inelastic nuclear collisions result in attenuation of the primary flux of protons and in the production of secondary radiations, which become significant for very thick shields. Proton dose rates at the center of the proton belt range from 20 rad/hr behind a 2 gm/cm/sup 2/ shield to about 1 rad/hr behind a 100 gm/cm/sup 2/ carbon shield. Light elements are most effective for proton shields, as they offer combined advantages of large stopping power and relatively small production of low-energy secondary radiation. Carbon is a particularly effective element for proton shielding; its stopping power is exceeded only by those of hydrogen and helium. Hydrogeneous compounds may prove to be suitable, as the stopping power of hydrogen is more than twice that of any other element; and such compound; offer advantages of attenuation of both protons and secondary neutrons by nuclear collisions. Production of bremsstrahlung by electrons stopped in the vehicle exterior can be minimized by use of a thin layer of low-Z material. Bremsstrahlung dose rates in a lightly shielded vehicle reach values of several r/hr but are reduced to acceptable levels by 3 or 4 gm/cm/sup 2/ of lead or uranium. High energy protons accompanying solar flares present an imposing special case of shield design. Shields adequate for short transit flight through the belt of trapped protons offer meager protection against flare protons. Prediction of flare activity and temporary use of non-structural elements for shfelding are dfscussed as remedial measures for protection during space flight. Uncertainties in the spectra of proton radiations and in the relative-biologic-effect of these radiations are discussed. A method of evaluating the biologic significance of an exposure by protons is suggested. (auth)

• Research Organization: Lockheed Georgia Co., Marietta, Ga.
• NSA Number: NSA-16-014351
• OSTI ID: 4798769
• Report Number(s): LNP-NR-140
• Country of Publication: United States
• Language: English

Related Subjects

ABSORPTION
BREMSSTRAHLUNG
CARBON
COLLISIONS
COMPUTERS
COSMIC RADIATION
DIAGRAMS
DISTRIBUTION
ELECTRONS
ENERGY
FILMS
IONIZATION
LEAD
LOSSES
MAN
METALS
PROTON BEAMS
PROTONS
QUANTITATIVE ANALYSIS
RADIATION DOSES
RADIATION PROTECTION
RADIATIONS
RADIOISOTOPES
REACTORS
SAFETY
SHIELDING
SHIELDING MATERIALS
SPACE APPLICATIONS AND TECHNOLOGY
SPACE FLIGHT
SPACE VEHICLES
SPECTRA
STANDARDS
SUN
TABLES
THERMONUCLEAR REACTIONS
THICKNESS
URANIUM