SEARCH · PubMed Health

Results for “Elementary Particles”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 127 records · Page 7Linked to original sources

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↗

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↗

PubMed1982

Energy deposition spectra of pi- calculated from pion nucleus interaction data.

Distributions of absorbed dose in linear energy transfer (LET) and in lineal energy (y) are calculated for beams of negatively charged pions in a water phantom. The calculation is based on a comprehensive set of experimental data. The production of delta-ray electrons by fast particles is taken into account semiempirically. The results are compared with experimentally obtained spectra of ionization yields. The equivalence of data derived from pion nucleus interaction and taken from microdosimetry is clearly revealed. The distribution of absorbed dose is given in a sequence of contributions from the various secondary particles, i.e., the so-called 'star' particles emitted following a nuclear capture process or the recoil nuclei from pion scatterings. This unique feature of calculated spectra will be useful for a characterization of the beam quality in view of the existing dependence of biological effects on track structure properties.

Animals↗

PubMed1985

Electronic excitations in condensed biological matter.

In living matter, electronic excitations may have a collective character which is reviewed here in simple physical terms. In liquids and ordered solids the collective excitations appear as plasmons or excitons. Plasmons are delocalized electronic perturbations of a huge number of oscillating electrons decaying very quickly into localized electronic perturbations, mainly low-energy ionizations. Excitons are very light, moving quantum quasi-particles carrying energy, charge and information in structured biological systems. In deformable soft structures collective excitations appear as solitons behaving as rather massive quasi-particles of combined quantum and classical character. Solitons are relatively stable micro-objects able to transfer energy, charge, mass, and biological information along such biological structures as (chains of) macromolecules, fibres, membranes and surfaces. Some photobiological and radiation biological consequences of collective electronic excitations are suggested.

Animals↗

PubMed1981

The influence of ionization density on the DNA synthetic phase and survival of irradiated mammalian cells.

Depression of the DNA synthetic rate of exponentially growing V79 cells was transient with a dose-dependent maximum at 1 hour after exposure to sparsely or densely ionizing radiation. The dose-effect curves were biphasic for 241Am alpha-particles as well as for 60Co gamma-rays, being partly congruent if inhibition of DNA synthesis was expressed per S-phase cell. The lesions responsible caused a prolongation of the DNA synthetic period (S-phase) after sparsely ionizing X- or 60Co gamma-rays. However, no such effect was observed during the first 4 hours after exposure to densely ionizing alpha particles, peak pions and high LET neon ions. The effect was dose-rate independent. The inhibition of the DNA synthetic rate seems to be only partly related to survival.

Americium↗

PubMedDate not supplied

Recent advances in radiation therapy of head and neck cancer.

The major advances in radiation oncology in this century was the development of megavoltage radiation in the 1950s, which greatly expanded the clinical utility of ionizing radiation in the treatment of many forms of cancer, including cancers of the head and neck. The combination of radiation and surgery for improved control of local and regional cancers followed. The use of interstitial implant therapy is growing rapidly because of new materials and techniques, thus expanding the radiotherapeutic options available to the oncologist. Investigations into several other therapeutic modalities currently are being carried out. These modalities include the use of particle radiation, oxygen-mimicking drugs, and hyperthermia, primarily in efforts to overcome the need for the oxygen effect in tumors. New uses of chemotherapy in combination with radiation also are being explored. Details of these activities within the field of radiation oncology are discussed.

Antineoplastic Agents↗

PubMed1985

Neoplastic cell transformation by heavy charged particles.

With confluent cultures of the C3H10T1/2 mammalian cell line, we have investigated the effects of heavy-ion radiation on neoplastic cell transformation. Our quantitative data obtained with high-energy carbon, neon, silicon, argon, iron, and uranium particles show that RBE is both dose- and LET-dependent for malignant cell transformation. RBE is higher at lower doses. There is an increase of RBE with LET, up to about 100-200 keV/micron, and a decrease of RBE with beams of higher LET values. Transformation lesions induced by heavy particles with LET values greater than 100 keV/micron may not be repairable in nonproliferating cells. RBE for slow and nonproliferating cells may be much higher than for actively growing cells.

Animals↗

PubMed1975

Visual sensations induced by Cerenkov radiation.

Pulses of relativistic singly charged particles entering the eyeball induce a variety of visual phenomena by means of Cerenkov radiation generated during their passage through the vitreous. These phenomena are similar in appearance to many of the visual sensations experienced by Apollo astronauts exposed to the cosmic rays in deep space.

Dark Adaptation↗

PubMed1977

Particle radiation therapy: current status and future potential.

Radiation therapy with "heavy" particles offers potential biological and physical advantages compared to irradiation with low LET photons. Clinical studies are in progress with proton beams, which have dosimetric advantages, and fast neutron beams, which have potential biologic advantages. Clinical studies with negative pi mesons and heavy nuclei, which have combined dosimetric and biologic advantages are about to start.

Elementary Particles↗

PubMed1989

Size of lethality target in mouse immature oocytes determined with accelerated heavy ions.

Mouse immature oocytes were irradiated in vivo with highly charged, heavy ions from the Bevalac accelerator at the Lawrence Berkeley Laboratory. The particles used were 670-MeV/nucleon Si14+, 570-MeV/nucleon Ar18+, and 450-MeV/nucleon Fe26+. The cross-sectional area of the lethality target in these extremely radiosensitive cells was determined from fluence-response curves and information on energy deposition by delta rays. Results indicate a target cross-section larger than that of the nucleus, one which closely approximates the cross-sectional area of the entire oocyte. For 450-MeV/nucleon Fe26+ particles, the predicted target cross-sectional area is 120 +/- 16 microns2, comparing well with the microscopically determined cross-sectional area of 111 +/- 12 microns2 for these cells. The present results are in agreement with our previous target studies which implicate the oocyte plasma membrane.

Animals↗

PubMed1985

Cellular fast-mixing techniques: possible applications with particle beams.

In the past cellular fast-mixing techniques have been used to investigate the time resolution of radiation processes that lead to modification of radiation response in bacterial and mammalian cellular systems. So far, published studies have been confined to effects with low-LET electron beams. The brief for this paper was to discuss where, and under what conditions, such a technique could be used to advantage with high-LET particle beams. Criteria for the experimental design, including conditions of flow rate, dose rate, and mixing times, are discussed. Radiobiological problems appropriate for applications of fast-particle beams are also discussed. These include studies to reveal possible multicomponents in cellular sensitization by oxygen and electron-affinic radiation sensitizers, studies designed to assist in the resolution of direct and indirect effects, and resolution of intracellular DNA damage.

Animals↗

PubMed1978

[Radiobiological bases and clinical aspects of radiation therapy with heavy particles (author's transl)].

Our present radiobiological knowledge gives rise to the hope of an amelioration of the local results in radiation therapy by means of new categories of radiations. Neutrons are clinically used to a larger extent already, protons occasionally. The physical characteristics of pi-meson beams are especially favorable. Even considerable ameliorations, however, of the percentage of local healing would increase the survival rate by some few per-cent only.

Elementary Particles↗

PubMed1985

W value measurements for 241Am alpha particles in various gases.

Measurements of W, the mean energy expended per ion pair formed, have been performed for 241Am alpha particles stopping in a number of the gases commonly used in ionisation chambers. Both absolute and relative measurements were made with nitrogen used as the reference gas for the relative measurements. The absolute method entailed a simultaneous measurement of a quantity of charge and the number of alpha particles which produced that charge, whilst the relative approach simply required a determination of the ratio of ion currents. Results were obtained for methane-based tissue-equivalent gas, for its constituents, i.e. methane, carbon dioxide and nitrogen, for argon, and also for a gas mixture with a composition approximately equivalent to A-150 plastic.

Americium↗

PubMed1975

An approach to microdosimetry in a pi- meson beam using nuclear emulsions.

K5 emulsions 10 mum thick were exposed at various depths in a perspex phantom to a 70 MeV pi- meson beam and counts taken of the tracks in emulsion volumes 7x7x10 mum3. Data are presented on the number of track events and also the total number of grains associated with each event in each of four categories spanning the LET range of the secondary particles. The number of heavy tracks (category 4) shows an increased incidence in the region of the stopping pi- mesons (14-5 cm in perspex) while the number of single grains (category 1) decreases with depth. Categories 2 and 3 (grain clusters and light tracks) are approximately constant with depth. An estimate of the grain sensitivity is obtained by taking the proton as representative of the whole range of secondary particles. This procedure gives a value of 5 keV per grain in the pi- peak. The LET of light tracks was therefore in the range 1-10 keV mum-1 in emulsion, scaling to 0-4-4 keV mum-1 in water. Heavy tracks have LET values in excess of 4 keV mum-1 in water.

Cobalt Radioisotopes↗

PubMedDate not supplied

Measurements and calculations of the influence of thin inhomogeneities on charged particle beams.

The predictions of an analytic technique for calculating fluence and dose distributions beneath thin inhomogeneities are presented for a number of structures, including a rectangular cavity or bar, a cylinder, a disk, and an angled or diffuse edge. Experiments with both electrons and protons for several geometries are presented and compared with predictions based on this technique. We offer some clinical guidelines for avoiding large perturbations due to scattering effects.

Elementary Particles↗

PubMed1982

Molecular and cellular radiobiology of heavy ions.

Quantitative studies at the BEVALAC have demonstrated some of the physical and radiobiological factors that promise to make accelerated heavy ions important for the therapy of cancer. The measured physical dose-biological effect relationships allow the safe and effective delivery of therapeutic schedules of heavy ions. Among the charged particle beams available, carbon, neon and helium ions in the "extended Bragg peak mode" have optimal physical and biological effectiveness for delivery of therapy to deep seated tumors. The depth-dose profiles of these beams protect intervening and adjacent tissues as well as tissues beyond the range of the particles. For the treatment of hypoxic tumors, silicon and argon beams are being considered because they significantly depress the radiobiological oxygen effect in the region of the extended Bragg ionization peak. The depth-effectiveness of the argon beam is somewhat limited, however, because of primary particle fragmentation. Silicon beams have a depth-dose profile which is intermediate between that of neon and argon, and are candidates to become the particle of choice for maximizing high LET particle effects. Heavy accelerated ions depress enzymatic repair mechanisms, decrease variations of radiosensitivity during the cell division cycle, cause greater than expected delays in cell division, and decrease the protective effects of neighboring cells in organized systems. Near the Bragg peak, enhancement of heavy particle effects are observed in split dose schedules. Late and carcinogenic effects are being studied. With the newly developed Repair-Misrepair theory we can quantitatively model most observations.

Animals↗

PubMed1980

Radiolysis of CoIII-EDTA solution by charged particles through 6Li(n,a)3H reaction.

This experiment was to study the radiolysis of CoIII-EDTA solution in 0.8N H2SO4 saturated with air by charged particles produced through 6Li(n,a)3H reaction. The experimental results show that the G(-CoIII-EDTA) decreases as the absorbed dose rate increases. For the same absorbed dose rate, the values of G(-CoIII-EDTA) are practically independent of absorbed dose. The effects of concentration and temperature are also studied.

Cobalt↗

PubMedDate not supplied

[Nonparametric method of determining the RBE coefficients of accelerated charged particles by the incidence of neoplasms in rats].

The nonparametric method was used to determine RBE coefficients of accelerated charged particles (helium ions of 4 GeV/nucleon and 645 MeV protons) by the incidence of tumors localized in different rat organs or by the absence of tumors. The nonparametric method permitted to find the dose dependence of the RBE coefficients and to make statistical analysis of the results obtained with due regard for come features of developing damages which were not revealed by conventional methods of determining RBE coefficients.

Animals↗