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At least 1,297 records · Page 72Linked to original sources
PubMed1996

Galactic cosmic ray flux simulation and prediction.

A dynamic galactic cosmic ray model is proposed to quantitatively describe the z=1-28 ions and electrons of E=10-10(5) MeV/nucleon and their particle flux variations around the Earth's orbit and beyond the Earth's magnetosphere due to diverse large-scale variations of solar activity factors. The variations of large-scale heliospheric magnetic fields and the galactic cosmic ray flux variation time delays relative to solar activity variations are simulated. The lag characteristics and sunspot number predictions having been determined in detail, the model can be used to predict galactic cosmic ray flux levels.

Cosmic Radiation↗
PubMed1996

Shielding against galactic cosmic rays.

Ions of galactic origin are modified but not attenuated by the presence of shielding materials. Indeed, the number of particles and the absorbed energy behind most shield materials increases as a function of shield thickness. The modification of the galactic cosmic ray composition upon interaction with shielding is the only effective means of providing astronaut protection. This modification is intimately connected with the shield transport properties and is a strong function of shield composition. The systematic behavior of the shield properties in terms of microscopic energy absorption events will be discussed. The shield effectiveness is examined with respect to conventional protection practice and in terms of a biological endpoint: the efficiency for reduction of the probability of transformation of shielded C3H10T1/2 mouse cells. The relative advantage of developing new shielding technologies is discussed in terms of a shield performance as related to biological effect and the resulting uncertainty in estimating astronaut risk.

Aluminum↗
PubMed1996

Light ion components of the galactic cosmic rays: nuclear interactions and transport theory.

Light nuclei are present in the primary galactic cosmic rays (GCR) and are produced in thick targets due to projectile or target fragmentation from both nucleon and heavy ion induced reactions. In the primary GCR, 4He is the most abundant nucleus after 1H. However, there are also a substantial fluxes of 2H and 3He. In this paper we describe theoretical models based on quantum multiple scattering theory for the description of light ion nuclear interactions. The energy dependence of the light ion fragmentation cross section is considered with comparisons of inclusive yields and secondary momentum distributions to experiments described. We also analyze the importance of a fast component of lights ions from proton and neutron induced target fragmentation. These theoretical models have been incorporated into the cosmic ray transport code HZETRN and will be used to analyze the role of shielding materials in modulating the production and the energy spectrum of light ions.

Cosmic Radiation↗
PubMed1996

Calculations of depth-dose distributions, cross sections and momentum loss.

The ability to know with precision the depth-dose, dose average LET, fluence and energy distributions is of great importance in many research fields, including therapeutic and diagnostic medicine when using heavy ion beams, as well as in space research. We have therefore developed a model and a computer code for calculating these distributions when using high energy proton or heavy ion beams. In this model, we use semi-empirical total reaction and partial cross section formulas developed by us and a new prescription to take into account the energy and momentum loss of the secondary nuclei. In this paper, we will also present an empirical equation for the total inelastic 4He-p cross section, as well as the partial cross sections for the production of 3He, 3H, 2H, p and n.

Algorithms↗
PubMed1996

Century scale solar variability imprinted in the 44Ti activity in meteorites.

The measurements of gamma-activity of the 44Ti (T1/2 = 66.6 years) produced by spallation reaction of galactic cosmic rays (GCR) in Alfianello, Olivenza, Rio Negro, Dhajala and Torino meteorites, which fell in the time interval 1883 AD (Alfianello)-1988 AD (Torino), show a century scale modulation, connected to long-term solar-wind flux variations in the interplanetary space. The variation of the 44Ti activity with the time of fall of meteorites is qualitatively consistent with the Gleissberg solar cycle, but the amplitude is three-four times higher than expected (about 5%) for GCR flux modulated by solar activity, as determined solely by the sunspot number. The cosmogenic 44Ti is a suitable radioisotope for this investigation, but its activity in meteorites is very low. We performed these measurements in the underground low level counting station of Monte dei Cappuccini in Torino, by means of a big hyperpure Ge crystal (approximately 2 kg) in selective coincidence with a heavy NaI (T1) scintillation detector (approximately 28 kg). This system allows a reliable and non destructive measurement of 44Ti (44Sc) in meteorites of 200-1200 g in weight. The background is about 1 count per day in the gamma-peak at 1157 keV of 44Sc in equilibrium with its parent 44Ti. The high stability of the performance allows long-lasting runs (approximately 10(7) s) in order to attain results with a standard deviation up to about 10%.

Cosmic Radiation↗
PubMed1996

Low energy ions in the heavy ions in space (HIIS) experiment on LDEF.

We present data from the Lexan top stacks in the Heavy Ions In Space (HIIS) experiment which was flown for six years (April 1984-Jan 1990) onboard the LDEF spacecraft in 28.5 degrees orbit at about 476 km altitude. HIIS was built of passive (i.e. no timing resolution) plastic track detectors which collected particles continuously over the entire mission. In this paper we present data on low energy heavy ions (10 < or = Z, 20MeV/nuc < E < 200 MeV/nuc). These ions are far below the geomagnetic cutoff for fully ionized ions in the LDEF orbit even after taking into account the severe cutoff suppression caused by occasional large geomagnetic storms during the LDEF mission. Our preliminary results indicate an unusual elemental composition of trapped particles in the inner magnetosphere during the LDEF mission, including both trapped anomalous cosmic ray species (Ne, Ar) and other elements (such as Mg and Fe) which are not found in the anomalous component of cosmic rays. The origin of the non-anomalous species is not understood, but they may be associated with the solar energetic particle events and geomagnetic disturbances of 1989.

Argon↗
PubMed1996

On the origin of trapped heavy ions at L = 1.4-1.6.

Aboard the NASA satellite Long Duration Exposure Facility (LDEF) heavy ions of nuclear charge Z = 8-26 were detected with energies between 15 and 50 MeV/nuc which are far below the cutoff energy required of fully stripped ions to reach the LDEF orbit. The arrival directions and the falling energy spectra of these particles are consistent with a trapped component incident in the South Atlantic Anomaly at L = 1.4-1.6. The trapped oxygen, neon and argon ions probably originate from the anomalous cosmic rays, whereas the origin of the other particles like magnesium, silicon and iron is not yet solved but may be associated with the October 89 solar energetic particle events.

Argon↗
PubMed1996

Damage to the photoreceptor cells of the rabbit retina from 56Fe ions: effect of age at exposure, 1.

Optic and proximate tissues of New Zealand white (NZW) rabbits at ages (approximately 3.5 years) near the middle of their median lifespan (5-7 years) were given 0.5-3.5 Gy of 465 MeV u-1 56Fe ions in the Bragg plateau region of energy deposition at a linear energy transfer (LET infinity) of 220 +/- 31 keV micrometer-1. Dose-dependent losses of retinal photoreceptor cells (rods) occurred until 1-2 years after irradiation, the period of this interim report. Similar cumulative losses of photoreceptor cells were seen during the period 1-2 years post-irradiation for rabbits given comparable exposures when young (6-9 weeks old). Since losses of photoreceptor cells at early times had not been determined previously, the current experiment, which was designed to simulate the responses of mature astronauts, redressed that deficiency.

Age Factors↗
PubMed1996

The effect of track structure on cell inactivation and chromosome damage at a constant LET of 120 keV/micrometer.

The influence of track structure on chromosome damage and cell inactivation are being investigated. Plateau-phase normal human fibroblast cultures were irradiated with gamma rays, and He, Ne and Ar ions. Particle velocities were chosen so that all beams had an LET of 120 keV/micrometer. In this constant-LET experimental design, the radial distribution of excitations and ionizations about the particle track is the most significant variable. Using premature chromosome condensation, chromatin breaks were measured at two time points, promptly after irradiation and after a prolonged incubation to allow for repair. These measurements give an indication of both initial chromosomal damage and also residual damage that is either not repaired or is misrepaired. Survival was measured under the same conditions. Results indicate that the RBEs for both cell inactivation and, to a lesser extent, chromosome damage decrease as particle energy increases.

Alpha Particles↗
PubMed1979

Solar cycles and malignant melanoma.

There has been a sixfold increase in the incidence of malignant melanoma in the State of Connecticut during the past forty years. Superimposed on a steady incidence rise are cycles of markedly increased incidence rates which follow periods of maximum sunspot activity. We propose that the effect of sunspot cycles on human melanoma occurrence is mediated by modulation of stratospheric ozone and thus indirectly affects UV flux at the earth's surface. This hypothesis would predict a time lag in melanoma incidence cycles, relative to sunspot activity, with increasing distance from polar caps. This appears to be the case. The increase in melanoma incidence related to a given reduction in ozone depletion in this hypothesis, is in great excess of existing models relating anthropogenic ozone depletion and skin cancer.

Connecticut↗
PubMed1990

Spallation processes and nuclear interaction products of cosmic rays.

Most cosmic-ray nuclei heavier than helium have suffered nuclear collisions in the interstellar gas, with transformation of nuclear composition. The isotopic and elemental composition at the sources has to be inferred from the observed composition near the Earth. The source composition permits tests of current ideas on sites of origin, nucleosynthesis in stars, evolution of stars, the mixing and composition of the interstellar medium and injection processes prior to acceleration. The effects of nuclear spallation, production of radioactive nuclides and the time dependence of their decay provide valuable information on the acceleration and propagation of cosmic rays, their nuclear transformations, and their confinement time in the Galaxy. The formation of spallation products that only decay by electron capture and are relatively long-lived permits an investigation of the nature and density fluctuations (like clouds) of the interstellar medium. Since nuclear collisions yield positrons, antiprotons, gamma rays and neutrinos, we shall discuss these topics briefly.

Astronomical Phenomena↗
PubMed1986

Theoretical contributions to coherent pion production in subthreshold and relativistic heavy-ion collisions.

The analytic results from a microscopic calculation for pion production in heavy-ion collisions at intermediate to relativistic energies both above and below pion threshold are presented and the most important terms that contribute to the pion spectrum are determined. The energy dependence and the effects on the pion spectrum due to the various parameters in the theory are examined. The model is applied to coherent pion-production in 16O + 12C collisions.

Carbon↗
PubMed1990

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.

Bromides↗
PubMed1993

Determination of high LET cosmic particles' trajectories for space radiobiological studies.

During IML-1 mission, we carried out space experiments on radiobiological effect of a single HZE cosmic particle. In the experiment, the precise determination of the distance between the center of the particle trajectory and the individual biological objects around it is an indispensable condition. For the detection of HZE particles CR-39 track detectors were used and analyzed by the video image processing. The positions of biological objects in relation to a particle trajectory were measured by referring to the laser grid marks which were printed on the surface of CR-39 detector. We describe such an experimental method and report the applicability of this method.

Bacillus subtilis↗
PubMed1994

HZE beam transport in multilayered materials.

A nonperturbative analytic solution of the high charge and energy (HZE) Green's function is used to implement a computer code for laboratory ion beam transport in multiple-layered materials. The code is established to operate on the Langley nuclear fragmentation model used in space engineering applications. Computational procedures are established to generate linear energy transfer (LET) distributions for a specified ion beam and target for comparison with experimental measurement. Comparison with 56Fe ion with Pb-Al and Pb-(CH2)x targets shows reasonable agreement.

Aluminum↗
PubMed1990

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.

Cosmic Radiation↗
PubMed1990

Charge state distribution of anomalous oxygen ions in low Earth orbit during solar quiescence.

A new method of evaluating the charge state distribution of cosmic ray heavy ions, using a measured ratio of particle fluxes observed in two different satellite orbits passing through the Earth's magnetosphere, is described. The measurements of heavy ions were performed simultaneously on the Cosmos 1882 (orbital inclination 82 degrees) and Cosmos 1887 (inclination 62.3 degrees) satellites during September-October 1987. Solid state nuclear track detector stacks were used for the registration of C, N, O and heavier ions. After comparing the data of the two experiments with theoretical calculations, the charge state of galactic and anomalous heavy ions was derived.

Collodion↗
PubMed1992

A new method for internal calibration of nuclear track detectors.

A new technique is proposed for an internal calibration of a two-layer detector assembly. Spatially coincident pairs of conical tracks on one surface and overetched tracks on the adjacent surface are selected for measurement. Both the etch rate ratio and the particle range can be obtained from the minor and major diameters of the elliptical track and the radii of the circular tracks for two etching steps. This technique was applied to CR-39 detectors exposed to fast neutrons and those flown on a high altitude balloon in order to evaluate the proton response. An improvement by using multi-step etching was also carried out. It was found that not only a single set of the etch rate ratio and the range but also the response curve could be estimated in an extended region by analyzing combined growth curves.

Calibration↗