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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 343 records · Page 19
All sourcesNASA NTRSDOE OSTI
NASA NTRS2001

Rejoining of isochromatid breaks induced by heavy ions in G2-phase normal human fibroblasts

We reported previously that exposure of normal human fibroblasts in G2 phase of the cell cycle to high-LET radiation produces a much higher frequency of isochromatid breaks than exposure to gamma rays. We concluded that an increase in the production of isochromatid breaks is a signature of initial high-LET radiation-induced G2-phase damage. In this paper, we report the repair kinetics of isochromatid breaks induced by high-LET radiation in normal G2-phase human fibroblasts. Exponentially growing human fibroblasts (AG1522) were irradiated with gamma rays or energetic carbon (290 MeV/nucleon), silicon (490 MeV/nucleon), or iron (200 MeV/nucleon) ions. Prematurely condensed chromosomes were induced by calyculin A after different postirradiation incubation times ranging from 0 to 600 min. Chromosomes were stained with Giemsa, and aberrations were scored in cells at G2 phase. G2-phase fragments, the result of the induction of isochromatid breaks, decreased quickly with incubation time. The curve for the kinetics of the rejoining of chromatid-type breaks showed a slight upward curvature with time after exposure to 440 keV/microm iron particles, probably due to isochromatid-isochromatid break rejoining. The formation of chromatid exchanges after exposure to high-LET radiation therefore appears to be underestimated, because isochromatid-isochromatid exchanges cannot be detected. Increased induction of isochromatid breaks and rejoining of isochromatid breaks affect the overall kinetics of chromatid-type break rejoining after exposure to high-LET radiation.

NASA Center JSC↗
NASA NTRS1972

Source and identification of heavy ions in the equatorial F layer.

Further evidence is presented to show that the interpretation of some Ogo 6 retarding potential analyzer (RPA) results in terms of ambient Fe+ ions is correct. The Fe+ ions are observed only within dip latitudes of plus or minus 30 deg, and the reason for this latitudinal specificity is discussed in terms of a low-altitude source region and F region diffusion and electrodynamic drift. It is shown that the polarization field associated with the equatorial electrojet will raise ions to 160 km out of a chemical source region below 100 km but it will do so only in a narrow region centered on the dip equator. Subsequent vertical ExB drift, coupled with motions along the magnetic fields, can move the ions to greater heights and greater latitudes. There should be a resultant fountain of metallic ions rising near the equator that subsequently descends back to the E and D layers at tropical latitudes.

Hanson, W. B.↗
NASA NTRS1971

Heavy ion plasma confinement in an RF quadrupole trap

The confinement of an electron free plasma in a pure quadrupole RF electric trap was considered. The ultimate goal was to produce a large density of mercury ions, in order to realize a trapped ion frequency standard using the hyperfine resonance of 199 Hg(+) at 40.7 GHz. An attempt was made to obtain an iodine plasma consisting of equal numbers of positive and negative ions of atomic iodine, the positive iodine ions, being susceptible to charge-exchange with mercury atoms, will produce the desired mercury ions. The experiment showed that the photoproduction of ions pairs in iodine using the necessary UV radiation occurs with a small cross-section, making it difficult to demonstrate the feasibility of space charge neutralization in a quadrupole trap. For this reason it was considered expedient to choose thallium iodide, which has a more favorable absorption spectrum (in the region of 2000 to 2100 A). The results indicate that, although the ionic recombination is a serious limiting factor, a considerable improvement can be obtained in practice for the density of trapped ions, with a considerable advantage in lifetimes for spectroscopic purposes. The ion pair formation by photoionization is briefly reviewed.

Schermann, J.↗
NASA NTRS1974

Heavy ion beam probe measurements of radial potential profiles in the Modified Penning discharge

The reported measurements were conducted with the primary beam of an ion beam probe in a plasma discharge in which the space potential represents a large fraction of the primary beam energy. A Lewis ion beam probe similar to the device employed by Jobes et al. (1969) was used in the investigation. The apparatus used in the experiments is discussed along with the experimental procedure. The approximate radial potential profile was obtained by observing the effect of the plasma on the trajectory of the primary beam.

Kambic, G. X.↗
NASA NTRS1975

Behavior of some singly ionized, heavy-ion impurities during compression in a theta-pinch plasma

The introduction of a small percentage of an impurity gas containing a desired element into a theta-pinch plasma is a standard procedure used to investigate the spectra and atomic processes of the element. This procedure assumes that the mixing ratio of impurity-to-fill gases remains constant during the collapse and heating phase. Spectroscopic investigations of the constant-mixing-ratio assumption for a 2% neon and argon impurity verifies the assumption only for the neon impurity. However, for the 2% argon impurity, only 20 to 25% of the argon is in the high-temperature compressed plasma. It is concluded that the constant-mixing-ratio assumption is not applicable to the argon impurity.

Jalufka, N. W.↗
NASA NTRS1975

Acceleration of H, He, and heavy ions observed in the magnetosheath, magnetotail, and near-by interplanetary space

Pulses of electrons and ions composed of H, He, and heavier elements were observed in the magnetosheath, magnetotail, and near-by interplanetary space. From the spatial positions where these particles were detected and the ion flow directions, it is concluded that they were accelerated at the bow shock near the sub-solar point and in the near-earth region of the neutral sheet of the magnetotail.

Fan, C. Y.↗
NASA NTRS1975

Abundances, charge states, and energy spectra of helium and heavy ions during solar particle events

Carbon and oxygen energy spectra observed during several solar events indicate a systematic deviation of these spectra from a simple power law: the spectra bend down below about 100 keV/nuc and the amount of this bending is highly correlated with the size of the flare, as measured by the 'event averaged' flux of 130-220 keV protons. The energy spectra of helium computed for the same time periods do not show a similar feature. A large variability of the alpha/CNO ratio is found from event to event (from 2 to about 20 at 40 keV/nuc), and in all cases examined the carbon and oxygen nuclei are nearly fully stripped. These results are interpreted as evidence for storage of energetic ions in hot coronal regions, followed by strong adiabatic deceleration.

Gloeckler, G.↗
NASA NTRS1976

Heavy ions from the Galilean satellites and the centrifugal distortion of the Jovian magnetosphere

The Galilean satellites constitute a potentially significant source of plasma to the Jovian atmosphere. The paper examines the distortion of the Jovian magnetosphere that would result from injection of ions at the Galilean satellites. The magnetic distortion produced is a localized perturbation near the equatorial plane, in contrast to the large-scale distortion produced by Jovian atmospheric ions. The study estimates the relative perturbation currents resulting from the two sources in terms of the unknown ion production rate at the satellites. It is found that the two perturbations would be of comparable magnitudes if the ion source flux at all of the Galilean satellites were comparable to the photo-ion escape flux from Jupiter's atmosphere. More specifically, ions produced by the Galilean satellites should be confined near the equatorial plane of Jupiter's magnetosphere in a sheet whose thickness is determined by a centrifugal scale height given essentially by the ion thermal speed divided by the corotation frequency.

Hill, T. W.↗