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NASA NTRS1974

Proton dose approximation in arbitrary convex geometry

An expansion is derived for the solution to the transport equation in two dimensions subject to boundary conditions given for an arbitrary convex region. Questions of high-energy transport are considered along with the properties of the dose response function. The expansion of the solution of the transport equation is presented in terms of a parameter which measures the lateral dispersion of an unidirectional beam. This parameter is usually small and the expansion is expected to converge rapidly. The dominant term in the expansion is related to fluence-to-dose conversion factors in a semiinfinite slab for normal incidence. A convenient parameterization of the conversion factors is provided along with numerical examples.

Wilson, J. W.↗

NASA NTRS1974

Justification of permissible doses of radiation during prolonged space flights

Maximum permissible radiation doses for astronauts are reported based on chronic radiation experiments with dogs and actual measurements during space flights. Observed were clinical conditions, peripheral blood and marrow, the state of the cardiovascular system, higher nervous activity, the state of the vestibular analyzer, the organ of vision, spermatogenic function and the ability to reproduce, the state of immunity and a number of biological indices in blood and tissues. The following maximum permissible doses are determined as preliminary values: 1 year of flight - 200 rem; 2 years of flight - 250 rem; 3 years of flight - 275 rem.

Grigoryev, Y. G.↗

NASA NTRS1975

Lymphoid cell kinetics under continuous low dose-rate gamma irradiation: A comparison study

A comparison study was conducted of the effects of continuous low dose-rate gamma irradiation on cell population kinetics of lymphoid tissue (white pulp) of the mouse spleen with findings as they relate to the mouse thymus. Experimental techniques employed included autoradiography and specific labeling with tritiated thymidine (TdR-(h-3)). The problem studied involved the mechanism of cell proliferation of lymphoid tissue of the mouse spleen and thymus under the stress of continuous irradiation at a dose rate of 10 roentgens (R) per day for 105 days (15 weeks). The aim was to determine whether or not a steady state or near-steady state of cell population could be established for this period of time, and what compensatory mechanisms of cell population were involved.

Foster, B. R.↗

NASA NTRS1976

Proton-tissue dose buildup factors

When an object is exposed to external radiation, the dose field within the object is a complicated function of the character of the external radiation, the shape of the object (including orientation), and the object's material composition. In this note, the dose conversion factors for protons in tissue are represented using buildup factors. A parametric form for the buildup factors is obtained. The values of the parameters are derived from Monte Carlo calculations of various authors. All the necessary information to estimate nuclear reaction effects in proton irration of convex objects of arbitrary shape is included.

Wilson, J. W.↗

NASA NTRS1977

Depth-dose relations for heavy ion beams

Radiation transport of heavy ions in matter is of interest to radiological protection in space and high-altitude aircraft. In addition, heavy ion beams are expected to be of advantage in radiotherapy since their characteristic Bragg curve allows a relative reduction of the dose in reaching a tumor site and the near elimination of exposure beyond the tumor region as the beam exits the body. Furthermore, the radioresistance of tumorous cells due to their hypoxic state may be reduced or eliminated by the high specific ionization of heavy ion beams. The depth-dose distribution of heavy ion beams consists of energy deposited by the attenuated primary beam with its characteristic Bragg curve and a relatively unstructured background due to secondary radiations produced in nuclear reactions. As the ion mass increases, the secondary contribution becomes more structured and may add significantly to the Bragg peak of the primary ions. The result for heavy ions (z greater than 20) is a greatly broadened Bragg peak region, especially in comparison to straggling effects, which may prove to be of importance in radiotherapy and biomedical research.

Wilson, J. W.↗

NASA NTRS1981

Total-dose radiation effects data for semiconductor devices, volume 2

Total ionizing dose radiation test data on integrated circuits are analyzed. Tests were performed with the electron accelerator (Dynamitron) that provides a steady state 2.5 MeV electron beam. Some radiation exposures were made with a Cobalt-60 gamma ray source. The results obtained with the Cobalt-60 source are considered an approximate measure of the radiation damage that would be incurred by an equivalent dose of electrons.

Price, W. E.↗

NASA NTRS1984

Total dose effects in the 54HC family of microcircuits

Motorola and National Semiconductor 54HC00 and 54HC74 microcircuits were evaluated using CO-60 to determine their total dose radiation hardness. The devices were found to be radiation soft failing parametrically between 5 and 10 K rads and functionally between 20 and 40 K rads. The failures were bias dependent, relatively insensitive to dose rate, and only annealed moderately when left unbiased at room temperature.

Ropiak, S.↗

NASA NTRS1986

Total-dose radiation effects data for semiconductor devices. 1985 supplement. Volume 2, part A

Steady-state, total-dose radiation test data, are provided in graphic format for use by electronic designers and other personnel using semiconductor devices in a radiation environment. The data were generated by JPL for various NASA space programs. This volume provides data on integrated circuits. The data are presented in graphic, tabular, and/or narrative format, depending on the complexity of the integrated circuit. Most tests were done using the JPL or Boeing electron accelerator (Dynamitron) which provides a steady-state 2.5 MeV electron beam. However, some radiation exposures were made with a Cobalt-60 gamma ray source, the results of which should be regarded as only an approximate measure of the radiation damage that would be incurred by an equivalent electron dose.

Martin, K. E.↗

NASA NTRS1986

Total-dose radiation effects data for semiconductor devices. 1985 Supplement. Volume 2, part B

Steady-state, total-dose radiation test data are provided in graphic format, for use by electronic designers and other personnel using semiconductor devices in a radiation environment. The data were generated by JPL for various NASA space programs. The document is in two volumes: Volume 1 provides data on diodes, bipolar transistors, field effect transistors, and miscellaneous semiconductor types, and Volume 2 (Parts A and B) provides data on integrated circuits. The data are presented in graphic, tabular, and/or narrative format, depending on the complexity of the integrated circuit. Most tests were done steady-state 2.5-MeV electron beam. However, some radiation exposures were made with a Cobalt-60 gamma ray source, the results of which should be regarded as only an approximate measure of the radiation damage that would be incurred by an equivalent electron dose. All data were generated in support of NASA space programs by the JPL Radiation Effects and Testing Group (514).

Martin, K. E.↗

NASA NTRS1986

Radiation dose prediction for Space Station

A detailed examination is conducted of the basis for the significant differences in Space Station radiation dose predictions that result from magnetic field model extrapolations into the future, with attention to the radiation attenuation effects of the residual atmospheric layer at altitudes of less than 1000 km. A model adjustment is proposed to supplant the arbitrary procedure of magnetic field extrapolation into the future. At altitudes below 500 km and low inclination, and with nominal module wall thicknesses, the new predictions for a 90-day Space Station tour are found to be well within current radiation dose limit guidelines.

Mccormack, Percival D.↗

NASA NTRS1987

Low altitude flux and dose measurements during two solar flare events

The dosimeter on board the low altitude polar orbiting DMSP/F7 satellite makes dose and flux measurements for electrons with energies greater than 1.0, 2.5, 5.0 and 10.0 MeV; and for protons with energies greater than 20, 35, 51, and 75 MeV. The characteristics and performance of the dosimeter are illustrated by presenting dose and flux data taken during the solar flare proton events of February 16 and April 26, 1984.

Brautigam, D. H.↗

NASA NTRS1990

Effects Of Dose Rates On Radiation Damage In CMOS Parts

Report describes measurements of effects of ionizing-radiation dose rate on consequent damage to complementary metal oxide/semiconductor (CMOS) electronic devices. Depending on irradiation time and degree of annealing, survivability of devices in outer space, or after explosion of nuclear weapons, enhanced. Annealing involving recovery beyond pre-irradiation conditions (rebound) detrimental. Damage more severe at lower dose rates.

Goben, Charles A.↗

NASA NTRS1989

Variation in SEU sensitivity of dose-imprinted CMOS SRAMs

The authors report on an experimental study of dose-induced changes in SEU (single-event-upset) sensitivity of CMOS static RAMs. Two time regimes were investigated following exposure of memories to cobalt-60 gamma rays: the near term, within a few hours after exposure, and the long term, after many days. Samples were irradiated both at room and at liquid nitrogen temperatures. The latter procedure was used in order to freeze in the damage state until SEU measurements could be made prior to annealing. Results show that memories damaged by dose are more sensitive to upsets by heavy ions. The induced changes are substantial: threshold linear energy transfer (LET) values decreased by as much as 46 percent and asymptotic cross sections increased by factors of two to four (unannealed samples).

Stassinopoulos, E. G.↗

NASA NTRS1991

Radiation dose estimates for typical piloted NTR lunar and Mars mission engine operations

The natural and manmade radiation environments to be encountered during lunar and Mars missions are qualitatively summarized. The computational methods available to characterize the radiation environment produced by an operating nuclear propulsion system are discussed. Mission profiles and vehicle configurations are presented for a typical all-propulsive, fully reusable lunar mission and for a typical all-propulsive Mars mission. Estimates of crew location biological doses are developed for all propulsive maneuvers. Post-shutdown dose rates near the nuclear engine are estimated at selected mission times.

Schnitzler, Bruce G.↗

NASA NTRS1992

Effects of fragmentation parameter variations on estimates of galactic cosmic ray exposure: Dose sensitivity studies for aluminum shields

Initial studies of the sensitivities of estimates of particle fluence, absorbed dose, and dose equivalent to fragmentation parameter variations are undertaken by using the LaRC galactic cosmic ray transport code (HZETRN). The new results, presented as a function of aluminum shield thickness, include upper and lower bounds on dose/dose equivalent corresponding to the physically realistic extremes of the fragmentation process and the percentage of variation of the dose/dose equivalent as a function of fragmentation parameter variation.

Townsend, Lawrence W.↗

NASA NTRS1993

Depth-dose equivalent relationship for cosmic rays at various solar minima

Galactic cosmic rays (GCR) pose a serious radiation hazard for long-duration missions. In designing a lunar habitat or a Mars transfer vehicle, the radiation exposure determines the GCR shielding thickness, and hence the weight of spacecraft. Using the spherically symmetric diffusion theory of the solar modulation of GCR, and data on the differential energy spectra of H, He, O, and Fe, from 1965 to 1989, it has been shown that (1) the flux is determined by the diffusion parameter which is a function of the time in the solar cycle, and (2) the fluxes in the 1954 and 1976-1977 solar minima were similar and higher than those in 1965. In this paper, we have extended the spherical solar modulation theory back to 1954. The 1954-1955 GCR flux was nearly the same as that from 1976 to 1977; the 1965 flux values were nearly the same as those in 1986. Using this theory we have obtained the GCR spectra for all the nuclei, and calculated the depth dose as a function of Al thickness. It is shown that the shielding required to stay below 0.5 Sv is 17.5 -3/+8 g/sq cm of Al, and 9 -1.5/+5 g/sq cm to stay below 0.6 Sv. The calculated dose equivalent using the ICRP 60 values for quality factors is about 15 percent higher than that calculated using the ICRP 26 value.

Badhwar, G. D.↗

NASA NTRS1994

The use of displacement damage dose to correlate degradation in solar cells exposed to different radiations

It has been found useful in the past to use the concept of 'equivalent fluence' to compare the radiation response of different solar cell technologies. Results are usually given in terms of an equivalent 1 MeV electron or an equivalent 10 MeV proton fluence. To specify cell response in a complex space-radiation environment in terms of an equivalent fluence, it is necessary to measure damage coefficients for a number of representative electron and proton energies. However, at the last Photovoltaic Specialist Conference we showed that nonionizing energy loss (NIEL) could be used to correlate damage coefficients for protons, using measurements for GaAs as an example. This correlation means that damage coefficients for all proton energies except near threshold can be predicted from a measurement made at one particular energy. NIEL is the exact equivalent for displacement damage of linear energy transfer (LET) for ionization energy loss. The use of NIEL in this way leads naturally to the concept of 10 MeV equivalent proton fluence. The situation for electron damage is more complex, however. It is shown that the concept of 'displacement damage dose' gives a more general way of unifying damage coefficients. It follows that 1 MeV electron equivalent fluence is a special case of a more general quantity for unifying electron damage coefficients which we call the 'effective 1 MeV electron equivalent dose'.

Summers, Geoffrey P.↗

NASA NTRS1995

Heavy ion track-structure calculations for radial dose in arbitrary materials

The delta-ray theory of track structure is compared with experimental data for the radial dose from heavy ion irradiation. The effects of electron transmission and the angular dependence of secondary electron ejection are included in the calculations. Several empirical formulas for electron range and energy are compared in a wide variety of materials in order to extend the application of the track-structure theory. The model of Rudd for the secondary electron-spectrum in proton collisions, which is based on a modified classical kinematics binary encounter model at high energies and a molecular promotion model at low energies, is employed. For heavier projectiles, the secondary electron spectrum is found by scaling the effective charge. Radial dose calculations for carbon, water, silicon, and gold are discussed. The theoretical data agreed well with the experimental data.

Cucinotta, Francis A.↗