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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 217 records · Page 12
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

Heavy ion induced mutations in mammalian cells: Cross sections and molecular analysis

Our investigations of heavy ion-induced mutations in mammalian cells, which had been begun a few years ago, were systematically continued. For the first time, it was possible to cover a large LET range with a few kinds of ions. To do this, both UNILAC and SIS were used to yield comparable data for a large energy range. This is a necessary condition for a comprehensive description of the influence of such ion parameters as energy and LET. In these experiments, the induced resistance against the poison 6-thioguanin (6-TG), which is linked to the HPRT locus on the genome, is being used as mutation system. In addition to the mutation-induction cross-section measurements, the molecular changes of the DNA are being investigated by means of Multiplex PCR ('Polymerase Chain Reaction') gene amplification. From these experiments we expect further elucidation of the mutation-inducing mechanisms composing the biological action of heavy-ion radiation.

Stoll, U.↗
NASA NTRS1975

Energy spectra and charge states of H, He, and heavy ions observed in the earth's magnetosheath and magnetotail

Observations of pulses of H, He, and heavy ions of energies greater than 0.12 MeV per charge in the magnetotail and in the magnetosheath are reported. It was found that the relative ion abundances were about 9:1:0.04, their differential energy spectra were about 1 divided by the fourth power of E, and their atomic electrons were almost completely stripped. These results suggest that they were low-energy 'quiet-time' cosmic rays accelerated within the magnetotail and the magnetosheath to the observed energies.

Fan, C. Y.↗
NASA NTRS1982

The sputtering of insulating materials by fast heavy ions

In this paper recent experimental results on sputtering of UF4 and H2O (ice) by fast heavy ions are reviewed. Measurements have been made of the dependence of the sputtering yield on the incident ion type, charge state, and energy. In the case of UF4, the energy spectra of neutral sputtered particles have been obtained as well. There is a clear dependence of the sputtering yield on the electronic part of the stopping power, and the yield is strongly affected by the charge state of the incident ion, which shows that in the near-surface region from which sputtered particles arise, the charge state of the incident ion has not reached equilibrium. The shape of the energy spectra observed for UF4 targets is that expected from a thermal distribution rather than that of the collision cascade form typical of ordinary sputtering. A model of the sputtering-track registration process that has arisen from these data is shown to provide a framework of understanding the close relationship of these observations to the 'plasma desorption' of marcromolecules.

Seiberling, L. E.↗
NASA NTRS1984

SEU of complementary GaAs static RAMs due to heavy ions

The first measurement of single event upset (SEU) for complementary GaAs static RAMs caused by heavy ions is reported. Upset cross-sections of the circuits for 28 MeV oxygen ions are reported as well as the linear energy transfer (LET) threshold established by using 170 MeV oxygen ions at various angles of beam incidence.

Zuleeg, R.↗
NASA NTRS1989

Improved calculation of total cross section for pair production by relativistic heavy ions

A calculation of the total cross section for direct electron-positron pair production by heavy ions is described. It combines the use of the Weizsaecker-Williams method for low-energy transfers and existing calculations for high-energy transfers. Higher-order corrections to the total cross section are calculated based on the Weizsaecher-Williams method and existing results for pair production by photons.

Eby, P. B.↗
NASA NTRS1991

Benchmark solutions for the galactic heavy-ion transport equations with energy and spatial coupling

Nontrivial benchmark solutions are developed for the galactic heavy ion transport equations in the straightahead approximation with energy and spatial coupling. Analytical representations of the ion fluxes are obtained for a variety of sources with the assumption that the nuclear interaction parameters are energy independent. The method utilizes an analytical LaPlace transform inversion to yield a closed form representation that is computationally efficient. The flux profiles are then used to predict ion dose profiles, which are important for shield design studies.

Ganapol, Barry D.↗
NASA NTRS1972

Heavy ion passive dosimetry with silver halide single crystals

A method of detecting radiation damage tracks due to heavy particles in large single crystals of the silver halides is described. The tracks, when made visible with a simple electrical apparatus, appear similar to tracks in emulsions. The properties of the crystals, the technique of printing out the tracks, and evidence concerning the threshold energy for registering particles indicates that this method may find application in heavy ion dosimetry. The method has been found to be sensitive to stopping He nuclei and relativistic M group cosmic rays. Some impurities strongly influence the printout of the tracks, and the effects of these impurities are discussed.

Childs, C. B.↗
NASA NTRS2002

Heavy Ion Transient Characterization of a Photobit Hardened-by-Design Active Pixel Sensor Array

This paper presents heavy ion data on the single event transient (SET) response of a Photobit active pixel sensor (APS) four quadrant test chip with different radiation tolerant designs in a standard 0.35 micron CMOS process. The physical design techniques of enclosed geometry and P-channel guard rings are used to design the four N-type active photodiode pixels as described in a previous paper. Argon transient measurements on the 256 x 256 chip array as a function of incident angle show a significant variation in the amount of charge collected as well as the charge spreading dependent on the pixel type. The results are correlated with processing and design information provided by Photobit. In addition, there is a large degree of statistical variability between individual ion strikes. No latch-up is observed up to an LET of 106 MeV/mg/sq cm.

Marshall, Paul W.↗
NASA NTRS2004

Effects of Heavy Ion Exposure on Nanocrystal Nonvolatile Memory

We have irradiated engineering samples of Freescale 4M nonvolatile memories with heavy ions. They use Silicon nanocrystals as the storage element, rather than the more common floating gate. The irradiations were performed using the Texas A&M University cyclotron Single Event Effects Test Facility. The chips were tested in the static mode, and in the dynamic read mode, dynamic write (program) mode, and dynamic erase mode. All the errors observed appeared to be due to single, isolated bits, even in the program and erase modes. These errors appeared to be related to the micro-dose mechanism. All the errors corresponded to the loss of electrons from a programmed cell. The underlying physical mechanisms will be discussed in more detail later. There were no errors, which could be attributed to malfunctions of the control circuits. At the highest LET used in the test (85 MeV/mg/sq cm), however, there appeared to be a failure due to gate rupture. Failure analysis is being conducted to confirm this conclusion. There was no unambiguous evidence of latchup under any test conditions. Generally, the results on the nanocrystal technology compare favorably with results on currently available commercial floating gate technology, indicating that the technology is promising for future space applications, both civilian and military.

Oldham, Timothy R.↗
NASA NTRS1994

Multiple-scattering model for inclusive proton production in heavy ion collisions

A formalism is developed for evaluating the momentum distribution for proton production in nuclear abrasion during heavy ion collisions using the Glauber multiple-scattering series. Several models for the one-body density matrix of nuclei are considered for performing numerical calculations. Calculations for the momentum distribution of protons in abrasion are compared with experimental data for inclusive proton production.

Cucinotta, Francis A.↗
NASA NTRS2022

Mechanisms of Heavy Ion-, Focused X-Ray-, and Pulsed Laser-Induced Single Event Transients in an Epitaxial Silicon Diode

Heavy ion-, focused X ray-, and pulsed laser induced single event effects in an epitaxial silicon diode were simulated using Sentaurus Technology Computer Aided Design (TCAD). The variation of the potential with time in simulation agrees with previous experimental data, which suggests that the different radiation sources result in different amounts of potential modulation. The charge generation spatial profile strongly affects the potential modulation. The longitudinal range and starting location of generated charge most strongly impacts the amount of potential modulation, while the radial width has a slight effect, and the temporal duration of charge injection has negligible impact on potential modulation

Kaitlyn L. Ryder↗
NASA NTRS2007

Distribution of Micronuclei in Human Fibroblasts across the Bragg Curve of Light and Heavy Ions

The space environment consists of energetic particles of varying mass and energy, and understanding the :biological Bragg curve" is essential in optimizing shielding effectiveness against space radiation induced biological impacts. The "biological Bragg curve" is dependent on the energy and the type of the primary particle, and may vary for different biological endpoints. Previously, we studied the induction of micronuclei (MN) across the Bragg curve of energetic Fe and Si ions, and observed no increased yield of MN at the location of the Bragg peak. However, the ratio of mono- to bi-nucleated cells, which indicates inhibition of cell progression, was found higher at the Bragg peak location in comparison to the plateau region of the Bragg curve. Here, we report the induction of MN in normal human fibroblast cells across the Bragg curve of incident protons generated at Loma Linda University. Similar to Si and Fe ions, the ratio of mono- to bi-nucleated cells showed a clear spike as the protons reached the Bragg peak. Unlike the two heavy ions, however, the MN yield also increased at the Bragg peak location. These results confirm the hypothesis that severely damaged cells at the Bragg peak of heavy, but not light ions are more likely to go through reproductive death and not be evaluated for micronuclei.

Hada, M.↗
NASA NTRS1985

The heavy ion composition in 3HE-rich solar flares

The 3He-rich flares show a tendency to be enriched in heavy ions, and that this enrichment covers the charge range through Fe. The discovery of this association was responsible, in part, for the discarding of 3He enrichment models which involved spallation or thermonuclear reactions, since such models were unable to produce heavy nuclei enhancement. Results of a survey of heavy nucleus abundances observed in 66 3He-rich flares which occurred over the period October 1978 to June 1982 are presented.

Mason, G. M.↗
NASA NTRS2001

HZETRN: neutron and proton production in quasi-elastic scattering of GCR heavy-ions

The development of transport models for radiation shielding design and evaluation has provided a series of deterministic computer codes that describe galactic cosmic radiation (GCR), solar particle events, and experimental beams at particle accelerators. These codes continue to be modified to accommodate new theory and improvements to the particle interaction database (Cucinotta et al., 1994, NASA Technical Paper 3472, US Government Printing Office, Washington DC). The solution employed by the heavy-ion transport code HZETRN was derived with the assumption that nuclear fragments are emitted with the same velocity as the incident ion through velocity conserving nuclear interactions. This paper presents a version of the HZETRN transport code that provides a more realistic distribution of the energy of protons and neutrons emitted from GCR interactions in shields. This study shows that the expected GCR dose equivalent is lower than previously calculated for water shields that are less than 110 g cm-2 thick. Calculations of neutron energy spectra in low Earth orbit indicate substantial contributions from relativistic neutrons. c2001 Elsevier Science Ltd. All rights reseved.

NASA Center LaRC↗
NASA NTRS2004

A Plasmaspheric Mass Density Model and Constraints on its Heavy Ion Concentration

The first empirical model of the equatorial mass density of the plasmasphere is constructed using ground-based ULF wave diagnostics. Plasmaspheric mass density between L=l.7 and L=3.2 has been determined using over 5200 hours of data from pairs of stations in the MEASURE array of ground magnetometers. The least-squares fit to the data as a function of L shows that mass density falls logarithmically with L. Average ion mass as a function of L is also estimated by combining the mass density model with plasmaspheric electron density profiles determined from the IMAGE Radio Plasma Imager (RPI). Additionally, we use the RPI electron density database to examine how the average ion mass changes under different levels of geomagnetic activity. We find that average ion mass is greatest under the most disturbed conditions. This result indicates that heavy ion concentrations are enhanced during large geomagnetic disturbances, and therefore play an important role in storm-time plasmaspheric dynamics. The average ion mass is also used to constrain the concentrations of He(+) and O(+). Estimates of the He(+) concentration determined this way can be useful for interpreting IMAGE Extreme Ultraviolet Imager (EUV) images.

Berube, D.↗