Late effects of heavy charged particles on the fine structure of the mouse coronary artery.
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Animals↗
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Results for “Elementary Particles”
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Secondary particle contribution to LET spectra on LDEF.
Four experiments utilizing passive detectors (P0006, P0004, A0015, M0004) were flown on LDEF to study the radiation environment. These experiments have been summarized in a companion paper (Benton et al., 1996). One of the experimental goals was to measure LET spectra at different locations and shielding depths with plastic nuclear track detectors (PNTD). It was found that the LET spectra extended well above the LET cutoff imposed by the geomagnetic field on GCR particle penetration into LEO. The high LET particles detected were mostly short-range (range < 2000 m), indicating that they were secondaries produced locally within the PNTD. The presence of these high LET particle fluences is important for the determination of dose equivalent because of the high Quality Factors (Q) involved. A relatively small fraction of particle fluence can contribute a large fraction of dose equivalent. Short-range, inelastic secondary particles produced by trapped protons in the South Atlantic Anomaly (SAA) were found to be a major contributor to the LET spectra above 100 keV/micrometer. The LET spectra were found to extend beyond the approximately 137 keV/micrometer relativistic GCR Fe peak to over 1000 keV/micrometer. The high LET tail of the LET spectra was measured in CR-39 and polycarbonate PNTDs using different techniques. GCR made a relatively modest contribution to the LET spectra as compared to the contributions from short-range secondary particles and stopping protons. LET spectra intercomparisons were made between LDEF measurements and exposures to 154 MeV accelerated proton beams. The similarities support the role of nuclear interactions by trapped protons as the major source of secondary particles in the PNTDs. Also techniques were employed to reduce the range cutoff for detection of the short-range secondaries to approximately 1 micrometer, so that essentially all secondary particles were included in the LET spectra. This has allowed a more realistic assessment of secondary contribution to dose equivalent. Comparisons of measured and calculated LET spectra have been made that demonstrate the need for more accurate modeling of secondary particles in radiation transport codes. Comparisons include preliminary calculations in which attempts have been made to include secondary particles.
Atlantic Ocean↗
Analysis of dose-LET distribution in the human body irradiated by high energy hadrons.
For the purposes of radiological protection, it is important to analyse profiles of the particle field inside a human body irradiated by high energy hadrons, since they can produce a variety of secondary particles which play an important role in the energy deposition process, and characterise their radiation qualities. Therefore Monte Carlo calculations were performed to evaluate dose distributions in terms of the linear energy transfer of ionising particles (dose-LET distribution) using a newly developed particle transport code (Particle and Heavy Ion Transport code System, PHITS) for incidences of neutrons, protons and pions with energies from 100 MeV to 200 GeV. Based on these calculations, it was found that more than 80% and 90% of the total deposition energies are attributed to ionisation by particles with LET below 10 keV microm(-1) for the irradiations of neutrons and the charged particles, respectively.
Body Burden↗
[X-ray small angle scattering and x-ray wide angle scattering of single nucleosomes. Preliminary results].
The X-ray scattering diagram from single chromatin subunit particles is registered within a scattering vector intervall from s = 0 to s = 1 1/A. Preliminary results concerning the dimensions and the structure of the nucleosome core particle are communicated.
Chromatin↗
A new dynamical atmospheric ionizing radiation (AIR) model for epidemiological studies.
A new Atmospheric Ionizing Radiation (AIR) model is currently being developed for use in radiation dose evaluation in epidemiological studies targeted to atmospheric flight personnel such as civilian airlines crewmembers. The model will allow computing values for biologically relevant parameters, e.g. dose equivalent and effective dose, for individual flights from 1945. Each flight is described by its actual three dimensional flight profile, i.e. geographic coordinates and altitudes varying with time. Solar modulated primary particles are filtered with a new analytical fully angular dependent geomagnetic cut off rigidity model, as a function of latitude, longitude, arrival direction, altitude and time. The particle transport results have been obtained with a technique based on the three-dimensional Monte Carlo transport code FLUKA, with a special procedure to deal with HZE particles. Particle fluxes are transformed into dose-related quantities and then integrated all along the flight path to obtain the overall flight dose. Preliminary validations of the particle transport technique using data from the AIR Project ER-2 flight campaign of measurements are encouraging. Future efforts will deal with modeling of the effects of the aircraft structure as well as inclusion of solar particle events.
Aerospace Medicine↗
Charged particle emission from the capture of negative pions: energy spectra, LET distributions and W-value.
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Bone and Bones↗
Proposal for a program in particle-beam radiation therapy in the the United States. A report from the Committee for Radiation Oncology Studies (CROS) and its Particle Subcommittee.
The Program for Particle Therapy proposes utilization of hospital-based particle generators in a nationwide program to evaluate, through meaningful clinical trials, particle radiation therapy and the impact its utilization can have in cancer care. The scientific rationale for use of particle therapy compared to conventional radiation in the effort to achieve uncomplicated local control of cancer, to heal, cure and palliate the patient, indicates the advantages of particle therapy consist of either or both a) enhanced biological effect and b) physical properties leading to improvement in dose distribution. It has been estimated that in tho control local-regional cancer. Any new modality enabling the therapist to increase dose to tumor, while sparing critical normal tissue, can enhance local control and benefit systemic therapy. Limited clinical trials to date warrant further definitive clinical study of particle beams. Physical and biologic considerations of fast-neutron beams have been essentially completed; equipment design, availability, and predicted reliability are good; and the medical community has indicated support of further study. A major clinical investigation can be implemented to provide the scientific basis for judging clinical merit of use of high LET radiations. Concurrently, the first phase of work can be started with protons, negative pions, and heavy ions. It is anticipated that clinical results will accrue much more rapidly with hospital-based units for clinical trials; this Program proposes this transfer of particle technology from the laboratory to such hospital-based facilities in two phases, over a 10-year period.
Clinical Trials as Topic↗
LET spectra measurements on LDEF: variations with shielding and location.
LET spectra measurements made with passive plastic nuclear track detectors (PNTDs) were found to depend on detector orientation, shielding and experiment location. LET spectra were measured at several locations on LDEF as part of the P0006 LETSME experiment (Benton and Parnell, 1984), the P0004 Seeds in Space experiment (Parks and Alston, 1984), the A00l5 Free Flyer Biostacks and the M0004 Fiber Optics Data Link experiment (Taylor, 1984). Locations included the east, west and Earth sides of the LDEF satellite. The LET spectra measured with PNTDs deviated significantly from calculations, especially for high LET particles (LET infinity H2O > or = 100 keV/micrometer). At high LETs, short-range inelastic secondary particles produced by trapped proton interactions with the nuclei of the detector were found to be the principal contributor to LET spectra. At lower LETs, the spectra appeared to be due to short-range, inelastic and stopping primary protons, with primary GCR particles making a smaller contribution. The dependence of LET spectra on detector orientation and shielding was studied using the four orthogonal stacks in the P0006 experiment. Both measurements of total track density and LET spectra showed a greater number of particles arriving from the direction of space than from Earth. Measurements of LET spectra in CR-39 PNTD on the east (leading) and west (trailing) sides of LDEF showed a higher rate of production at the west side. This was caused by a larger flux of trapped protons on the west side as predicted by the east/west trapped proton anisotropy in the South Atlantic Anomaly (SAA). Track density measured in CR-39 PNTDs increased as a function of shielding depth in the detector stack. A similar measurement made in a thick stack of CR-39 interspersed with layers of Al and exposed to 154 MeV protons at a ground-based accelerator showed a similar result, indicating that a significant fraction of the particle events counted were from secondaries and that the total cross-section for production of proton-induced secondaries increased as the energy of primary protons attenuated. Little change was seen in either total differential or integral LET spectra as a function of shielding depth, indicating that the increase in cross section with decreasing proton energy affected mostly the shorter range secondary components. Similarity in the slopes of LET spectra from ground-based proton exposures and the A00l5 LET spectra showed that modeling of a monoenergetic proton beam transported through a 1-D geometry was a useful first step in modeling the production of secondary particles by trapped protons in the SAA.
Atlantic Ocean↗
Determination of charge states of single swift heavy projectiles by high-energy delta-electrons.
The effective charge state is an important particle parameter which is required for the calculation of many effects concerning the interaction between radiation and matter such as an estimate of the radial dose of swift heavy projectiles, stopping power and so on. A new method for the determination of effective charge states of heavy ions is based on the measurement of the number of high-energy delta-electrons which are ejected from a target by the penetrating ion. These electrons are detectable with a CCD-detector and their number can be correlated to the effective charge state of the projectile for known particle velocities. This method is even applicable to operation with single swift heavy ions within statistical bounds.
Computer Simulation↗
Cosmic ray particles with different LET values under various thicknesses of shielding in low altitude orbits: calculations and Cosmos-2044 measurements.
Fluxes of cosmic ray particles with different LET values were measured on board the Cosmos-2044 biosatellite under various thicknesses of shielding by stacks of CR-39 and nitrocellulose plastic nuclear track detectors (mounted outside the satellite). The component composition of the particles detected under shieldings of 0.1-2.5 g cm-2 is verified by comparing experimental data with the results of model simulations of the fluxes of galactic cosmic ray particles and of radiation belt protons.
Computer Simulation↗
Treatment planning for particle radiation therapy.
Fast neutrons beams from the new medically dedicated cyclotrons in the US have depth dose characteristics comparable to photon beams from a 6-MV linear accelerator, at best. Treatment planning will have specific difficulties related to the relatively increased radiosensitivities of the brain, spinal cord, lens of the eye, and salivary gland. Therefore, exploitation of the potential biologic advantages compared to high energy photons will extract the price of increased difficulties in treatment planning. Dosimetric advantages of protons and helium ions compared to high energy photons are real and make possible the high-dose irradiation of cancers immediately adjacent to sensitive critical normal structures. Treatment planning and delivery with a precision of less than 2 mm is necessary. Such methods are already operational. Particle radiation therapy facilities are national resources, which can help the clinical radiation oncologist in the unique management of a few, specific problems.
Elementary Particles↗
[Evaluation of biological effectiveness of high-energy accelerated particles based on the study of cytogenetic disorders in murine sex cells].
The frequency of reciprocal translocations in spermatogonia of F1(CBAxC57Bl6) mice irradiated with 50 MeV protons, 4.2 GeV deuterons, 1.8 GeV/nucleon helium ions or 60Co gamma-rays was investigated. The relative biological effectiveness of these particles calculated by comparing the equieffective doses of reference and experimental radiations was less than 1.0 under the assumption of the linear dose-effect relationship. The RBE of the particles calculated by means of the nonparametric method largely depended on the doses applied.
Animals↗
Possible biomedical applications of antiproton beams: focused radiation transfer.
A calculation of the energy lost by antiprotons stopping in water shows that the radiation transferred is localized within 1 mm of the stopping point. This "focusing" of the radiation is mainly due to heavily ionizing particles emitted from the nuclei on which the annihilation takes place. At present antiproton beams for medical purposes may not be cost effective compared to other charged particle beams, but the sharpness of their radiation transfer combined with antiprotonic radiography are highly attractive and unique features that may invite special applications.
Elementary Particles↗
Particle radiation therapy: requiem or reveille.
The 1960s and 1970s witnessed a surge of many institutions devoted to electron therapy. Currently, many facilities are adding or have added particle types of radiation to their armamentarium against cancer. The authors review the concepts, problems, and potentials of this form of therapy.
Elementary Particles↗
Errors in the particle flux measurement data relevant to solar energetic particle spectra.
Systematical errors of the spacecraft measured high-energy particle fluxes are analyzed. The errors are shown to be inherent to most of the measurements made to be the monitoring of the high-energy radiation in the space. The level of the systematic errors of the measurements varies with energy, thus resulting in distortions of the solar energetic particle spectra based on the measurement data. The erroneous experimental data have resulted in spurious estimates of space radiation environment and give rise to erroneous physical conclusions.
Cosmic Radiation↗
Dosimetry on the Spacelab missions IML1 and IML2, and D2 and on MIR.
Detector packages consisting of plastic nuclear track detectors, nuclear emulsions, and thermoluminescence detectors were exposed inside BIORACK during the Spacelab missions IML1 and IML2, in different sections of the MIR space station, and inside the Spacelab module at rack front panels or stowage lockers and in the Spacelab tunnel during D2. In addition, during D2, each Payload Specialist (PS) has worn three permanent detector packages; one at the neck; one at the waist; and one at the ankle. Total dose measurements, particle fluence rate and LET spectra, number of nuclear disintegrations and neutron dose from this exposure are given in this report. The results are compared to theoretical calculations and to previous missions results. The dose equivalent (total radiation exposure) received by the PSs were calculated from the measurements and range from 190 to 770 microSv d-1. Finally, a cursory investigation of results from a particle telescope from two silicon detectors, first used in the last BIORACK mission on STS76, is reported.
Atlantic Ocean↗
Multiple scattering distributions for therapeutic pion beams.
Accurate treatment planning for therapeutic beams of negative pions requires knowledge of the multiple scattering of pions in biologically relevant materials. Complete spatial and angular scattering distributions have been measured for pions in scatterers of carbon, water and calcium. Measurements were made for targets varying in thickness from 0.5 to 21 g cm-2 and for pions with ranges of approximately 12 and 20 g cm-2. An array of scintillators, multiwire drift and multiwire proportional chambers was used to record the scattering of individual particles. These data are compared with the results of Molière scattering theory. The implications for pion treatment planning are discussed.
Elementary Particles↗
Monte Carlo calculation of the angular distribution of cosmic rays at flight altitudes.
The angular distribution of the secondary radiation produced by the galactic component of cosmic rays has been determined by simulating the penetration of the primary spectra in the Earth's atmosphere. The simulations have been carried out with the latest version of the FLUKA code. Particles have been scored at various altitudes according to their angle of incidence for some significant values of vertical cut-off rigidity and solar modulation parameter. The calculated results at typical cruise altitudes for a civil aircraft are presented. The data at 10.7 km have been fitted with simple mathematical equations. It has been demonstrated that the major contribution to the doses at aviation altitudes arises from downward-directed particles. The isotropic irradiation usually assumed for the evaluation of aircrew exposure could be a very poor approximation.
Aircraft↗