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At least 235 records · Page 13Linked to original sources
PubMed2005

Hunting for Dark Matter particles with new detectors.

Although first hints of the existence of Dark Matter were observed by the Swiss astronomer Zwicky already in the 1930s, only in recent years has it become known that the universe, in fact, is dominated by particles whose nature is almost unknown and which have never been directly observed. Meanwhile, as the existence of these particles is postulated not only by astronomy, but also cosmology and theoretical particle physics, there is significant effort to detect them in a laboratory experiment and determine their physical properties. However, as the interaction rate between Dark Matter particles and ordinary matter is extremely low, detectors have to be extremely sensitive. Low temperature detectors have been available for more than a decade and have now reached the highest sensitivity for direct Dark Matter detection. In this article, we give a short overview of observational results that suggest the existence of Dark Matter particles and what physicists have learned so far about their properties. The main focus is on the experimental challenges and effort for their direct detection.

Astronomical Phenomena↗
PubMed1981

A review and comparative analysis of the biological damage induced during space flight by HZE particles and space hadrons.

We have studied the somatic and genetic effects of heavy ions (HZE particles) and the very high energy hadrons of space radiation on various organisms ranging in complexity from bacteriophage to man. Experimental data were obtained in space, on high mountains and in a proton accelerator at energies of 76 GeV. In all these experiments local micro- and macroradiational damage was observed. This damage was characterized by severity over large local regions and for the most part was due to cascades of secondary particle bundles resulting from the collision of very high energy space hadrons with atomic nuclei rather than from cellular hits from relatively low energy single HZE particles. At present there does not appear to be any effective way to provide shielding against these cosmic hadrons.

Animals↗
PubMed2002

Nuclear model calculations and their role in space radiation research.

Proper assessments of spacecraft shielding requirements and concomitant estimates of risk to spacecraft crews from energetic space radiation requires accurate, quantitative methods of characterizing the compositional changes in these radiation fields as they pass through thick absorbers. These quantitative methods are also needed for characterizing accelerator beams used in space radiobiology studies. Because of the impracticality/impossibility of measuring these altered radiation fields inside critical internal body organs of biological test specimens and humans, computational methods rather than direct measurements must be used. Since composition changes in the fields arise from nuclear interaction processes (elastic, inelastic and breakup), knowledge of the appropriate cross sections and spectra must be available. Experiments alone cannot provide the necessary cross section and secondary particle (neutron and charged particle) spectral data because of the large number of nuclear species and wide range of energies involved in space radiation research. Hence, nuclear models are needed. In this paper current methods of predicting total and absorption cross sections and secondary particle (neutrons and ions) yields and spectra for space radiation protection analyses are reviewed. Model shortcomings are discussed and future needs presented.

Cosmic Radiation↗
PubMed1980

Lung clearance of particles in two strains of rats.

Two strains of commonly used experimental rats were compared with regard to lung clearance of TiO2 particles. The Fisher 344 inbred rats retained predictably fewer particles after a 7-hr exposure than the larger outbred Long-Evans rats. This fact can be expected in view of the different lung size of the two strains. In addition, clearance of the retained particles was significantly slower in Fisher 344 rats. Differences in lung clearance capacity of different animal strains should be considered when experiments in inhalation toxicology are performed.

Aerosols↗
PubMed2002

[Meta-analyses of quarks, baryons and mesons--a "Cochrane Collaboration" in particle physics].

Within the last 20 years meta-analysis has become an important research technique in medicine for integrating the results of independent studies. Meta-analytical techniques, however, are much older. In particle physics for 50 years now the properties of huge numbers of particles have been assessed in meta-analyses. The Cochrane Collaboration's counterpart in physics is the Particle Data Group. This article compares methodological and organisational aspects of meta-analyses in medicine and physics. Several interesting parallels exist, especially with regard to methodology.

Elementary Particles↗
PubMed1983

Response of colony-forming units-spleen to heavy charged particles.

Survival of colony-forming units-spleen (CFU-S) was measured after single doses of photons or heavy charged particles from the BEVALAC. The purposes were to define the radiosensitivity to heavy ions used medically and to evaluate relationships between relative biological effectiveness (RBE) and dose-averaged linear energy transfer (LET infinity). In in vitro irradiation experiments. CFU-S suspensions were exposed to 220 kVp X rays or to 20Ne (372 MeV/micron) or 40Ar (447 MeV/micron) particles in the plateau portion of the Bragg curve. In in vivo irradiation experiments, donor mice from which CFU-S were harvested were exposed to 12C (400 MeV/micron). 20Ne (400 or 670 MeV/micron), or 40Ar (570 MeV/micron) particles in Bragg peaks spread to 4 or 10 cm by spiral ridge filters. Based on RBE at 10 survival, the maximum RBE of 2.1 was observed for 40Ar particles characterized by an LET infinity of approximately 100 keV/micron. Lower RBEs were determined at lower or higher estimated values of LET infinity and ranged from 1.1 for low energy 40Ar particles to 1.5-1.6 for low energy 12C and 20Ne. The responses of CFU-S are compared with responses of other model systems to heavy charged particles and with the reported sensitivity of CFU-S to neutrons of various energies. The maximum RBE reported here, 2.1 for high energy 40Ar particles, is somewhat lower than values reported for fission-spectrum neutrons, and is appreciably lower than values for monoenergetic 0.43-1.8 MeV neutrons. Low energy 12C and 20Ne particles have RBEs in the range of values reported for 14.7 MeV neutrons.

Animals↗
PubMed1981

New modalities in cancer treatment: heavy charged particles.

Heavy charged particles represent the ultimate that the physicist can contribute to the development of radiation sources for therapy. Of the heavy charged particles, protons are the least expensive to accelerate and can be manipulated to give a sharply defined high-dose volume with a rapid fall-off of dose outside the target area. The biological properties of protons do not differ significantly from X or gamma rays. Negative pi mesons require an elaborate accelerator for their production. Pions offer the possibility of concentrating energy, some of it densely ionizing with a reduced oxygen enhancement ratio and elevated biological effectiveness within the designated tumour volume, while minimizing the dose of sparsely ionizing radiation to the normal tissues traversed. High-energy heavy ions offer the greatest flexibility and allow localized dose distributions and also, with the higher Z particles, a substantial reduction of the oxygen enhancement ratio can be achieved. The ultimate choice of particle depends upon what turns out to be the most important factor in radiotherapy--an improved localization of dose or a reduction in the dependence of cell killing on the presence of molecular oxygen.

Elementary Particles↗
PubMed1998

Distribution of energetic particles and secondary radiation according to orbital station "MIR" data obtained in 1991.

A set of instruments for measuring energetic particle fluxes, containing two neutron detectors under different plexiglas shielding thicknesses, a scintillation detector, measuring energy release >0.1 MeV and 0.5 MeV and a Geiger counter were launched onboard OS 'MIR'. The latitude dependencies of the cosmic ray measurements were obtained and studied. The distributions of primary particle fluxes (protons and elections) as well as secondary particle fluxes (bremsstrahlung gamma-rays and neutrons) produced in interactions of radiation belt particles with the station materials were obtained. The electron belt, generated during the storm of March 24 1991, is studied.

Cosmic Radiation↗
PubMedDate not supplied

Basic and applied research at the TRIUMF meson factory.

The TRIUMF 520 MeV H- cyclotron produces intense beams of protons, pions and muons supporting basic research in nuclear, particle and solid-state physics, nuclear chemistry and biomedicine, and applied research in electromagnetic breeding of nuclear fuel, proton radiography, radioisotope production and cancer treatment.

Animals↗
PubMed1987

Influence of the physical state and straggling on the computation of the radiation dose due to radon daughters deposited in the lung.

The effect of the physical state (phase) of the absorbing medium and the energy straggling of the alpha particles on the calculation of the radiation dose due to the daughter products of radon deposited in the lung have been studied in detail. The stopping power data for alpha particles in water and water vapour have been used. It has been found that the effect of straggling on the stopping power calculations is small, and therefore its contribution to dose calculations is negligible. The phase effect has been found to be dependent on the energy of the alpha particles and the depth in the medium. If the stopping power of water vapour is used instead of that for liquid water, the dose may be overestimated by 5-20 and 1-11% for 6 and 7.7 MeV alpha particles, respectively, at the beginning of alpha range, and underestimated by 15 and 40% respectively for the above energies at the end of the range.

Dose-Response Relationship, Radiation↗
PubMed2001

Monte Carlo simulation of charged particle transport in biomatter.

Knowledge of the microscopic distribution of interactions in irradiated matter is of fundamental importance for a mechanistic understanding of subsequent effects. This may be obtained by Monte Carlo codes which simulate event-by-event the transport of charged particles in matter. The development of such codes necessitates accurate interaction cross-sections for all the important collision processes. A semi-theoretical formalism has been developed and implemented in a Monte Carlo code which fairly accurately predicts energy-loss spectra for charged particle impact on water molecules. The extension of the formalism for establishing the necessary cross-sections for liquid/solid water (i.e. more realistic biomatter) is discussed and preliminary results are presented.

Carbon↗
PubMed2001

An overview of recent charged-particle radiation biology in Italy.

Radiobiology with charged particles is being carried out in Italy since several decades, starting with the experiments with protons in Milan. Later, also other groups entered the field, such as those in Naples, in Legnaro (LNL) and in Rome. In the last 10-15 years the activities in the field began to grow in a significant way. This happened in concomitance with the involvement of various researchers and Institutions in European and international projects devoted to radiation protection aspects, such as those aimed at elucidating and modelling radiation action mechanisms (EC/EU) and those aimed at radiation protection in space (NASA). A special role has been played since then by the Laboratori Nazionali di Legnaro of the INFN, where a radiobiology facility for low energy light ions was set up and operated in 1985. A formidable stimulus for charged-particle radiobiology was more recently given by the onset of plans for developing hadrontherapy Centres in Italy. The TERA Foundation first, and than the TOP Project at the Istituto Superiore di Sanità, at the same time favoured the spreading in Italy of radiobiology research with charged particles and encouraged co-operation among various groups. The Italian radiobiology community, though relatively small, developed a number of valuable activities with charged particles, mostly at the cellular and molecular levels, that span from mechanisms of radiation action to radiation protection in space and to therapy with charged hadrons. In this article, due to space limitations, we have just been able to list the present activities and to briefly review some research that forms a common background for the various areas. This includes the work on Chinese hamster V79 cells irradiated with light ions at LNL, that provided extensive data on the relationships between radiation quality, molecular damage and cellular effects, and the related work aimed at possible interpretation by mechanistic models. It appears that the multiplicity of objectives does not represent a factor of weakness for the relatively small Italian radiobiology community. Synergistic effects have been found because the basic radiobiology is the same for different areas such as radiation protection and hadrontherapy, and because the expertise and the methods developed for a given purpose may find useful applications in others. Though it is difficult to forecast the future development in Italy of the various areas that will take advantage of charged-particle radiobiology, it is expected that hadrontherapy and space radiation protection together, independently of their relative weight, will be important driving forces for the future development of the field in our Country.

Animals↗
PubMed1986

Induction of proline prototrophs in CHO-K1 cells by heavy ions.

Using an established mammalian cell line, Chinese hamster ovary cells (CHO-K1), we have observed the induction of prototrophs by various heavy ions. This cell line requires proline for normal growth in medium with low serum concentration. X-rays, three types of heavy particles (600 MeV/u iron, 670 MeV/u neon, and 320 MeV/u silicon ions), ethylmethane sulphonate and 5-azacytidine were used to induce revertants which were proline independent. Log-phase cells treated with 5-azacytidine showed a very high reversion frequency. The induction frequency per viable cell appears to be dose dependent for these four types of radiation, and the dose-response curves are approximately linear. Our results also indicate that the effectiveness of high-LET particles in inducing proline prototrophs is much greater than that of low-LET radiation. The RBE value for the induction of prototrophs was calculated for neon, silicon, and iron particles and found to be about 1.3, 1.7 and 4.5, respectively. At equal survival level, the reversion frequency for X-rays and EMS was about the same.

Animals↗
PubMed2004

Averaged particle dose conversion coefficients in air crew dosimetry.

The MCNPX Monte Carlo code was used to calculate energy-dependent fluence-to-effective dose conversion coefficients for neutrons, protons, electrons, photons, charged pions and muons. The FLUKA Monte Carlo code was used to calculate the spectral particle fluences of secondary cosmic rays for different altitudes, and for different combinations of solar modulation and vertical cut-off rigidity parameters. The energy-averaged fluence-to-dose conversion coefficients were obtained by folding the particle fluence spectra with the conversion coefficients for effective dose and ambient dose equivalent. They show a slight dependence on altitude, solar activity and location in the geomagnetic field.

Aircraft↗
PubMed1994

An inductive assessment of radiation risks in space.

Procedures for the assessment of risks or vulnerabilities from radiation in space are evaluated in terms of model-independent inductive approaches. The reliability of risks calculated for space applications on the basis of accelerator-based physical and biological data is examined from a microdosimetric perspective. Probability distributions for energy deposition in biologically significant sites extend over several decades in lineal energy even for monoenergetic high-energy particles of relatively high atomic number. Because the response depends on a large number of variables and because of the difficulty of incorporating all such factors into calculations, a precise correlation between a physical descriptor of the field and observed effects in space is not feasible. For the same reasons, it is equally difficult to estimate the accuracies of such risk assessments. We use recently published microdosimetric spectra for HZE particles and biological weighting functions, including those derived from biological measurements with maximum entropy techniques, to illustrate some problems associated with the evaluations of risks from radiation fields in space.

Animals↗
PubMed1986

Predicting charmonium and bottomonium spectra with a quark harmonic oscillator.

We present a simple application of the three-dimensional harmonic oscillator which should provide a very nice particle physics example to be presented in introductory undergraduate quantum mechanics course. The idea is to use the nonrelativistic quark model to calculate the spin-averaged mass levels of the charmonium and bottomonium spectra.

Elementary Particles↗
PubMed1994

Secondary radiations in spacecraft shieldings.

Some problems are discussed which relate to the generation of secondary radiation under the effects of heavy charged cosmic ray particles in spacecraft shielding and in biological tissue. Methods for obtaining the total and differential inelastic interaction cross sections are recommended for use in the calculation of heavy charged particle transport in the shielding. The most extensively used methods for calculating heavy charged particle passage through matter are appraised. The results of calculating cosmic ray doses in biological tissue behind shielding, which allow for the secondary particle contribution, are presented. All the calculations have been made using the set of radiation protection standards approved by the Russian State Committee for Standards. The set of standards has been verified experimentally on board satellites of the Cosmos series.

Cosmic Radiation↗
PubMedDate not supplied

Measurement of the effect of inhomogeneities and compensating bolus in clinical pion beams.

Measurement of the effects of Telfon and air inhomogeneities on the ionization distributions of clinical negative-pion beams have been made at the Los Alamos Meson Physics Facility. Inhomogeneity location and pion-beam energy vary the effect of multiple coulomb scattering on the dose distribution lying in the penumbra of the inhomogeneity. CH2 bolus adequately corrects for the effects of these inhomogeneities. Bolus misalignment less than 0.5 cm does not seem critical because of large multiple coulomb scattering of the pion beam. However, this and secondary particles emitted from pion stars prevent the pion beam from being precisely shaped with sharp edges, as demonstrated by measurements under a patient bolus.

Elementary Particles↗