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Benton, E. V.

Publications and source records attributed to Benton, E. V..

At least 109 records · Page 6
All sourcesNASA NTRSDOE OSTI
NASA NTRS1990

Radiation experiments on Cosmos 2044: K-7-41, parts A, B, C, D, E

The Cosmos 2044 biosatellite mission offered the opportunity for radiation measurements under conditions which are seldom available (an inclination of 82.3 deg and attitude of 294 x 216 km). Measurements were made on the outside of the spacecraft under near-zero shielding conditions. Also, this mission was the first in which active temperature recorders (the ATR-4) were flown to record the temperature profiles of detector stacks. Measurements made on this mission provide a comparison and test for modeling of depth doses and LET spectra for orbital parameters previously unavailable. Tissue absorbed doses from 3480 rad (252 rad/d) down to 0.115 rad (8.33 mrad/d) were measured at different depths (0.0146 and 3.20 g/sq cm, respectively) with averaged TLD readings. The LET spectra yielded maximum and minimum values of integral flux of 27.3 x 10(exp -4) and 3.05 x 10(exp -4)/sq cm/s/sr, of dose rate of 7.01 and 1.20 mrad/d, and of dose equivalent rate of 53.8 and 11.6 mrem/d, for LET(sub infinity)-H2O is greater than or equal to 4 keV/micron. Neutron measurements yielded 0.018 mrem/d in the thermal region, 0.25 mrem/d in the resonance region and 3.3 mrem/d in the high energy region. The TLD depth dose and LET spectra were compared with calculations from the modeling codes. The agreement is good but some further refinements are in order. In comparing measurements on Cosmos 2044 with those from previous Cosmos missions (orbital inclinations of 62.8 deg) there is a greater spread (maximum to minimum) in depth doses and an increased contribution from GCRs, and higher LET particles, in the heavy particle fluxes.

Frank, A. L.↗
NASA NTRS1990

Ionizing radiation exposure of LDEF

The Long Duration Exposure Facility (LDEF) was launched into orbit by the Space Shuttle 'Challenger' mission 41C on 6 April 1984 and was deployed on 8 April 1984. The original altitude of the circular orbit was 258.5 nautical miles (479 km) with the orbital inclination being 28.5 degrees. The 21,500 lb NASA Langley Research Center satellite, having dimensions of some 30x14 ft was one of the largest payloads ever deployed by the Space Shuttle. LDEF carried 57 major experiments and remained in orbit five years and nine months (completing 32,422 orbits). It was retrieved by the Shuttle 'Columbia' on January 11, 1990. By that time, the LDEF orbit had decayed to the altitude of 175 nm (324 km). The experiments were mounted around the periphery of the LDEF on 86 trays and involved the representation of more than 200 investigators, 33 private companies, 21 universities, seven NASA centers, nine Department of Defense laboratories and eight foreign countries. The experiments covered a wide range of disciplines including basic science, electronics, optics, materials, structures, power and propulsion. The data contained in the LDEF mission represents an invaluable asset and one which is not likely to be duplicated in the foreseeable future. The data and the subsequent knowledge which will evolve from the analysis of the LDEF experiments will have a very important bearing on the design and construction of the Space Station Freedom and indeed on other long-term, near-earth orbital space missions. A list of the LDEF experiments according to experiment category and sponsor is given, as well as a list of experiments containing radiation detectors on LDEF including the LDEF experiment number, the title of the experiment, the principal investigator, and the type of radiation detectors carried by the specific experiment.

Benton, E. V.↗
NASA NTRS1990

Experiment K-6-24, K-6-25, K-6-26. Radiation dosimetry and spectrometry

Radiation experiments flown by the University of San Francisco on the Cosmos 1887 spacecraft were designed to measure the depth dependence of both total dose and heavy particle flux, dose and dose equivalent, down to very thin shielding. Three experiments were flown and were located both inside and outside the Cosmos 1887 spacecraft. Tissue absorbed dose rates of 264 to 0.028 rad d(-1) under shielding of 0.013 to 3.4 g/sq cm of (7)LiF were found outside the spacecraft and 0.025 rad d(-1) inside. Heavy particle fluxes of 3.43 to 1.03 x 10 to the minus 3rd power cm -2 sub s -1 sub sr -1 under shielding of 0.195 to 1.33 g/sq cm plastic were found outside the spacecraft and 4.25 times 10 to the minus 4th power cm -2 sub s -1 sub sr -1 inside (LET infinity H2O greater than or equal to 4 keV/micron m). The corresponding heavy particle dose equivalent rates outside the spacecraft were 30.8 to 19.8 mrem d(-1) and 11.4 mrem d(-1) inside. The large dose and particle fluxes found at small shielding thicknesses emphasize the importance of these and future measurements at low shielding, for predicting radiation effects on space materials and experiments where shielding is minimal and on astronauts during EVA. The Cosmos 1887 mission contained a variety of international radiobiological investigations to which the measurements apply. The high inclination orbit (62 degrees) of this mission provided a radiation environment which is seldom available to U.S. investigators. The radiation measurements will be compared with those of other research groups and also with those performed on the Shuttle, and will be used to refine computer models employed to calculate radiation exposures on other spacecraft, including the Space Station.

Benton, E. V.↗
NASA NTRS1990

Linear energy transfer (LET) spectra of cosmic radiation in low Earth orbit

Integral linear energy transfer (LET) spectra of cosmic radiation (CR) particles were measured on five Cosmos series spacecraft in low Earth orbit (LEO). Particular emphasis is placed on results of the Cosmos 1887 biosatellite which carried a set of joint U.S.S.R.-U.S.A. radiation experiments involving passive detectors that included thermoluminescent detectors (TLDs), plastic nuclear track detectors (PNTDs), fission foils, nuclear photo-emulsions, etc. which were located both inside and outside the spacecraft. Measured LET spectra are compared with those theoretically calculated. Results show that there is some dependence of LET spectra on orbital parameters. The results are used to estimate the CR quality factor (QF) for the Cosmos 1887 mission.

NASA Discipline Radiation Health↗
NASA NTRS1990

Differential neutron energy spectra measured on spacecraft in low Earth orbit

Two methods for measuring neutrons in the range from thermal energies to dozens of MeV were used. In the first method, alpha-particles emitted from the 6Li(n,alpha)T reaction are detected with the help of plastic nuclear track detectors, yielding results on thermal and resonance neutrons. Also, fission foils are used to detect fast neutrons. In the second method, fast neutrons are recorded by nuclear photographic emulsions (NPE). The results of measurements on board various satellites are presented. The neutron flux density does not appear to correlate clearly with orbital parameters. Up to 50% of neutrons are due to albedo neutrons from the atmosphere while the fluxes inside the satellites are 15-20% higher than those on the outside. Estimates show that the neutron contribution to the total equivalent radiation dose reaches 20-30%.

Cosmos 1887 Project↗
NASA NTRS1990

Radiobiological experiments with plant seeds aboard the biosatellite Kosmos 1887

The effects of spaceflight factors on the seeds of Arabidopsis thaliana and Crepis capillaris were studied provided with various protective measures: the seeds were located inside the satellite and in open space, protected with aluminium foil and also exposed without the foil cover. When the seeds were in open space without any protection, their viability was found to be suppressed; the survival rate and fertility of plants grown from these seeds were also diminished. An increase in the frequency of chromosome aberrations (CA) and in the number of multiple injuries was registered in this case. Experiments with the aluminium foil shielding showed a decrease in the suppression of the seeds' viability, but mutational changes were found to be even more increased, while the survival and fertility of the plants decreased. An increase in the thickness of shielding resulted in a decrease in the effects up to the level of the control, except for the effects connected with CA and fertility of the plants. Analysis of the results shows that these impairments can be ascribed to the action of single heavy charged particles (HCP). The seeds can be thus regarded as an integral biological 'dosimeter' which allows estimation of the total effects of radiation, ecological and biological factors.

Cosmos 1887 Project↗
NASA NTRS1990

Depth distribution of absorbed dose on the external surface of Cosmos 1887 biosatellite

Significant absorbed dose levels exceeding 1.0 Gy day-1 have been measured on the external surface of the Cosmos 1887 biosatellite as functions of depth in stacks of thin thermoluminescent detectors (TLDs) of U.S.S.R. and U.S.A. manufacture. The dose was found to decrease rapidly with increasing absorber thickness, thereby indicating the presence of intensive fluxes of low-energy particles. Comparison between the U.S.S.R. and U.S.A. results and calculations based on the Vette Model environment are in satisfactory agreement. The major contribution to the dose under thin shielding thickness is shown to be from electrons. The fraction of the dose due to protons and heavier charged particles increases with shielding thickness.

NASA Discipline Number 04-10↗
NASA NTRS1990

Multiplicities of secondaries in interactions of 1.8 GeV/nucleon 56Fe nuclei with photoemulsion and the cascade evaporation model

A nuclear photographic emulsion method was used to study the charge-state, ionization, and angular characteristics of secondaries produced in inelastic interactions of 56Fe nuclei at 1.8 GeV/nucleon with H, CNO, and AgBr nuclei. The data obtained are compared with the results of calculations made in terms of the Dubna version of the cascade evaporation model (DCM). The DCM has been shown to satisfactorily describe most of the interaction characteristics for two nuclei in the studied reactions. At the same time, quantitative differences are observed in some cases.

Non-NASA Center↗
NASA NTRS1989

Fragmentation cross sections of 28Si at 14.5 GeV/nucleon

We used CR39 plastic nuclear track detectors (C12H18O7) in combination with automatic track measurement techniques to determine total charge changing and partial cross sections for the production of fragments of charge ZF = 6 to ZF = 13 in collisions of 28Si beam nuclei at 14.5 GeV/nucleon in targets H, C, CR39, (C18H38O), Al, Cu, Ag, and Pb. By application of factorization rules, measured partial cross sections are separated into pure nuclear and electromagnetic components. The cross sections for electromagnetic dissociation agree with theoretical models. The results are consistent with a Z2 dependence of virtual photon spectra.

NASA Discipline Number 04-10↗
NASA NTRS1989

Model analysis of Space Shuttle dosimetry data

An extensive model analysis of plastic track detector measurements of high-LET particles on the Space Shuttle has been performed. Three Shuttle flights: STS-51F (low-altitude, high-inclination), STS-51J (high-altitude, low-inclination), and STS-61C (low-altitude, low-inclination) are considered. The model includes contributions from trapped protons and Galactic cosmic radiation, as well as target secondary particles. Target secondaries, expected to be of importance in thickly shielded space environments, are found to be a significant component of the measured LET (linear energy transfer) spectra.

Letaw, J. R.↗
NASA NTRS1988

Search for projectile fragments with fractional charge in relativistic heavy ion collisions

We measured the charge of about 35000 projectile fragments with Z > or = 5e produced by 14.5 GeV/nucleon and 200 GeV/nucleon 16O beams in a Pb target using CR39 plastic nuclear track detectors. A minimum track length of 3 mm in the detector without nuclear interaction was required. No evidence for fragments carrying a fractional charge was found.

NASA Discipline Number 22-70↗
NASA NTRS1986

Summary of radiation dosimetry results on U.S. and Soviet manned spacecraft

Measurements of the radiation environment aboard U.S. and Soviet manned spacecraft are reviewed and summarized. Data obtained mostly from passive and some active radiation detectors now exist for the case of low-earth-orbit missions. Major uncertainties still exist for space exposure in high-altitude, high-inclination geostationary orbits, in connection with solar effects and that of shielding. Data from active detectors flown in Spacelabs 1 and 2 suggest that a variety of phenomena must be understood before the effects of long-term exposure at the Space Station type of orbit and shielding can be properly assessed.

Benton, E. V.↗
NASA NTRS1986

The measured radiation environment within Spacelabs 1 and 2 and comparison with predictions

A set of passive and active radiation detectors was flown as part of the verification flight instrumentation (VFI) in an attempt to measure the radiation environment in the Spacelab (SL) module and on the pallet. SL 1 carried 4 passive and 2 active detector packages which were used to evaluate the radiation environment within the spacecraft and SL 2 carried 2 passive VFI units on the pallet. Dose equivalents of 330 + or - 70 mrem and 537 + or - 37 mrem were measured in the SL 1 module and SL 2 pallet, respectively.

Parnell, T. A.↗
NASA NTRS1985

Search for anomalous fragments produced in collisions with heavy target nuclei and in delta Z = 1 peripheral interactions

We exposed a stack of CR39 track detectors containing Ag foils to a 1.7-GeV/nucleon 56Fe beam and investigated the anomalous mean-free-path effect. Neither the whole set of 7517 nor a subset of 2542 interacting fragments produced probably in the Ag target show an effect. By combining the data of this and an earlier experiment we can also exclude an effect for 3219 interacting fragments produced in delta Z = 1 collisions.

Polyethylene Glycols↗
NASA NTRS1985

Radiation mapping on Spacelab 1: Experiment no. INS006

The first attempt at mapping the radiation environment inside Spacelab is described. Measurements were made by a set of passive radiation detectors distributed throughout the volume inside the Spacelab 1 module, in the access tunnel and outside on the pallet. Measurements of the low linear energy transfer (LET) component obtained from the TLD thermoluminescent detectors (TLD) ranged from 92 to 134 mrad, yielding an average low LET dose rate of 10.0 mrads/day inside the module. Because of the higher inclination orbit, substantial fluxes of highly ionizing (HZE particles) high charge and energy galactic cosmic rays were observed for the first time on an STS flight, yielding an overall average mission dose-equivalent of 295 mrem, or 29.5 mrem/day, which is about three times higher than that measured on previous STS missions. Little correlation is found between measured average dose rates or HZE fluences and the estimates shielding throughout the volume of the module.

Benton, E. V.↗
NASA NTRS1985

Radiation environment of Spacelab-1

The results of passive and active radiation measurements on Spacelab-1 are reported. Spacelab-1 was flown on the STS-9 mission, orbited at an altitude of 241 km, with an inclination of 57 deg and 240 hours of flight time. Approximately thirty passive detectors deployed inside the module, in the access tunnel, and outside on the pallet made possible the radiation measurements. The various forms of radiation measured were a low linear energy transfer component ranging from 94 to 133 mrads inside the module (average dose rate of 10.0 mrads/day; about twice the rate of earlier shuttle flights), an average mission dose-equivalent rate of about 18.5 mrem/day (six times higher than earlier flights), accumulated doses of 125 and 128 mrads and a yield of 17 and 12 mrads for passages through the South Atlantic Anomaly. Spacelab-1, because of its low altitude and short duration, was relatively benign in terms of total radiation dose. Some of the measurements such as high-LET particles and neutrons have biological significance and potential effects on future experiments.

Benton, E. V.↗
NASA NTRS1985

The effect of high energy (HZE) particle radiation (Ar-40) on aging parameters of mouse hippocampus and retina

Eight month old C57BL6 mice were exposed (head only) to 0.5 rad or 50 rads of Argon particles at the Lawrence Berkeley Radiation Facility, CA. Neuromotor performance was assessed monthly for six months beginning twelve weeks post-irradiation using a 'string test'. The decline in motor performance was dose-related and none of the animals was able to complete the task after four months of testing. Morphological changes were monitored six and twelve months post-irradiation by light and electron microscopy. The synaptic density in the CA-1 area of the hippocampus decreased six and twelve months after irradiation. The decrease after twelve months was less than after six months. The width of the outer nuclear layer (ONL) of the retina increased with increasing dose. The number of blood vessels between the ONL and the ganglion layer decreased twelve months after irradiation and this area did not show significant accumulation of age pigment.

Philpott, D. E.↗