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PubMed2001

Neutron dosimetric measurements in shuttle and MIR.

Detector packages consisting of thermoluminescence detectors (TLD), nuclear emulsions and plastic track detectors were exposed at identical positions inside MIR space station and on shuttle flights inside Spacelab and Spacehab during different phases of the solar cycle. The objectives of the investigations are to provide data on charge and energy spectra of heavy ions, and the contribution of events with low-energy deposit (protons, electrons, gamma, etc.) to the dose, as well as the contribution of secondaries, such as nuclear disintegration stars and neutrons. For neutron dosimetry 6LiF (TLD600) and 7LiF (TLD700) chips were used both of which have almost the same response to gamma rays but different response to neutrons. Neutrons in space are produced mainly in evaporation and knock-on processes with energies mainly of 1-10 MeV and up to several 100 MeV, respectively. The energy spectrum undergoes continuous changes toward greater depth in the attenuating material until an equilibrium is reached. In equilibrium, the spectrum is a wide continuum extending down to thermal energies to which the 6LiF is sensitive. Based on the difference of absorbed doses in the 6LiF and 7LiF chips, thermal neutron fluxes from 1 to 2.3 cm-2 s-1 are calculated using the assumption that the maximum induced dose in TLD600 for 1 neutron cm-2 is 1.6 x 10(-10) Gy (Horowitz and Freeman, Nucl. Instr. and Meth. 157 (1978) 393). It is assumed that the flux of high-energy neutrons is at least of that quantity. Tissue doses were calculated taking as a mean ambient absorbed dose per neutron 6 x10(-12) Gy cm2 (for a10 MeV neutron). The neutron equivalent doses for the above-mentioned fluxes are 52 micro Gy d-1 and 120 micro Gy d-1. In recent experiments, a personal neutron dosimeter was integrated into the dosimeter packages. First results of this dosimeter which is based on nuclear track detectors with converter foils are reported. For future measurements, a scintillator counter with anticoincidence logic is under development.

Cosmic Radiation↗
PubMed1996

Effects of target fragmentation on evaluation of LET spectra from space radiations: implications for space radiation protection studies.

We present calculations of linear energy transfer (LET) spectra in low earth orbit from galactic cosmic rays and trapped protons using the HZETRN/BRYNTRN computer code. The emphasis of our calculations is on the analysis of the effects of secondary nuclei produced through target fragmentation in the spacecraft shield or detectors. Recent improvements in the HZETRN/BRYNTRN radiation transport computer code are described. Calculations show that at large values of LET (> 100 keV/micrometer) the LET spectra seen in free space and low earth orbit (LEO) are dominated by target fragments and not the primary nuclei. Although the evaluation of microdosimetric spectra is not considered here, calculations of LET spectra support that the large lineal energy (y) events are dominated by the target fragments. Finally, we discuss the situation for interplanetary exposures to galactic cosmic rays and show that current radiation transport codes predict that in the region of high LET values the LET spectra at significant shield depths (> 10 g/cm2 of Al) is greatly modified by target fragments. These results suggest that studies of track structure and biological response of space radiation should place emphasis on short tracks of medium charge fragments produced in the human body by high energy protons and neutrons.

Aluminum↗
PubMed1996

Model calculations of the radiation dose and LET spectra on LDEF and comparisons with flight data.

Ionizing radiation environment models, a 3-D spacecraft mass model, and radiation transport codes have been used to predict the radiation dose and linear energy transfer (LET) spectra measured at various locations on the LDEF satellite. The predictions are compared with thermoluminescent dosimeter measurements of the trapped proton and electron doses and with LET spectra measured by plastic nuclear track detectors. The predicted vs observed comparisons indicate some of the uncertainties of present ionizing radiation environment models for low Earth-orbit missions.

Anisotropy↗
PubMed1986

Hot hydrogen atom reactions moderated by H2 and He.

Photolysis experiments were performed on the H2-CD4-NH3 and the He-CD4-NH3 systems. The photolysis (1849 angstoms) involved only NH3. Mixtures of H2:CD4:NH3 included all combinations of the ratios (200,400,800):(10,20,40):4. Two He:CD4:NH3 mixtures were examined where the ratios equalled the combinations 100:(10,20):4. Abstraction of a D from CD4 by the photolytically produced hot hydrogen from ammonia was monitored by mass spectrometric determination of HD. Both experiment and semiempirical hot-atom theory show that H2 is a very poor thermalizer of hot hydrogens with excess kinetic energy of about 2 eV. Applications of the hard-sphere collision model to the H2-CD4-NH3 system results in predicted ratios of net HD production to NH3 decomposition that were two orders of magnitude smaller than the experimental ratios. On the other hand, helium is found to be a very efficient thermalizer; here, the classical model yields reasonable agreement with experiments. Application of a semiempirical hot-atom program gave quantitative agreement with experiment for either system.

Ammonia↗
PubMedDate not supplied

The multi-disciplinary role of 'pion factories'.

The multi-disciplinary role of intermediate energy proton accelerators in pure and applied nuclear physics is discussed with particular reference to the experimental programmes at LAMPF (Los Alamos Meson Physics Facility) and SIN (Swiss Institute for Nuclear Research, Zurich).

Elementary Particles↗
PubMed1996

The history of the galaxies.

Astronomical observations now reach far enough back in time, in enough depth and detail, to reveal the history of galaxies since their formation. The early Universe contained a network of gas clouds that filled much of the space between the young galaxies, where stars were forming at a high rate. Since then, intergalactic space has been swept clean, and galaxies have continued to convert the dwindling supply of gas slow into stars.

Astronomical Phenomena↗
PubMed1994

The evolution of the universe.

Some 15 billion years ago the universe emerged from a hot, dense sea of matter and energy. As the cosmos expanded and cooled, it spawned galaxies, stars, planets and life.

Astronomical Phenomena↗
PubMed2002

Magnetic fields and radical reactions: recent developments and their role in nature.

Recombination of pairs of radicals is exceptional in being affected by magnetic fields. The mechanism has been known for some thirty years, but recently new applications have appeared and research has been extended to very high fields (up to 30 Tesla). Claims that low electromagnetic fields damage health have led to extensive medical, chemical and physical research: no firm evidence of hazards has emerged; on the other hand, migrating birds orient themselves in the earth's field (50 microT): radical pairs may provide the mechanism.

Animals↗
PubMed1976

Bone scanning with 99m-Tc-phosphates: a comparison and problems in the detection of tumor metastasis.

A comparative study on 99m-Tc-phosphate compounds (TcPP) in detecting tumor metastasis to bone and problems accompanying it are reported. TcPP revealed metastatic foci which are unrecognized by conventional bone survey. To recognize these foci, exclusion of following problems is necessary: Accumulation at front of neck, asymmetrical image of joint, increased bone density of the aged, Tc-photon absorption and radiotherapy effect. The mechanism of TcPP accumulation is discussed.

Absorption↗
PubMed1976

[Biomedical use and dosimetry of pions of the sin 590 MeV isochrone cyclotrone. VII. Radiation therapy using negative pions (author's transl)].

The scheme of radiation of Schumacher for high energy electrons is investigated. In it 3 high individual doses are given at first. In the second phase which follows immediately, weekly single doses of 500 rad are given until the tumor is completely destroyed. Reoxygenation and transformation of anoxic cells are important here for the number of surviving tumor cells but unfortunately still rather unknown. This uncertainty can be removed with the Pion therapy in which transformation does not take a large part. About 10 single doses of negative pions of 150-200 rad should be clearly superior to 5000 rad electron doses (D1 = 500 rad) and should not exceed the limits of tolerance with a weekly treatment. Finally the importance of contamination with electrons of the pionrays is examined. Exact measurement of this contamination is necessary.

Bronchial Neoplasms↗
PubMed1977

Radiation damage in mouse embryos exposed to 1 rad x-rays or negative pions.

Pregnant mice of two different strains (F/A and NMRI) were exposed to 1 rad of whole-body pion- or X-irradiation at day 8 of gestation. Lucanthone (Miracil D), a known radiosensitizer in various biological systems, was applicated 30 min before irradiation. Five days after treatment the fetuses were observed for developmental anomalies. In both strains of mice it was found that the radiation dose as low as 1 rad results in a significant increase in the rate of abnormal fetuses compared to nonirradiated, but restrained fetuses. Comparing the effectiveness of negative pions (peak irradiation) with X-rays for teratogenic effects, the RBE was between 1.7 and 1.9. The application of Lucanthone increased the number of damaged fetuses and led to various degrees of sensitization depending on the mouse strain and dosage used. Differences between the strains as regards the frequency of damages are explained by different development stages at the time of treatment.

Animals↗