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PubMed1998

Liquid drop model considerations in HZE particle fragmentation by hydrogen.

The fragmenting of high energy, heavy ions by hydrogen targets is an important physical process in several areas of space radiation protection research. Quantum mechanical, optical model methods for calculating cross sections for particle fragmentation by hydrogen have been developed from a modified abrasion-ablation collision formalism. The abrasion stage is treated as a knockout process which leaves the residual prefragment in an excited state. In the ablation stage the prefragment excitation to produce the final fragment. The prefragment excitation energies are estimated from a combination of liquid drop model considerations and frictional-spectator interaction processes. Estimates of elemental and isotopic production cross sections are in good agreement with published cross section measurements.

Cosmic Radiation↗

PubMed2001

Neutron environments on the Martian surface.

Radiation is a primary concern in the planning of a manned mission to Mars. Recent studies using NASA Langley Research Center's HZETRN space radiation transport code show that the low energy neutron fluence on the Martian surface is larger than previously expected. The upper atmosphere of Mars is exposed to a background radiation field made up of a large number of protons during a solar particle event and mixture of light and heavy ions caused by galactic cosmic rays at other times. In either case, these charged ions interact with the carbon and oxygen atoms of the Martian atmosphere through ionization and nuclear collisions producing secondary ions and neutrons which then interact with the atmospheric atoms in a similar manner. In the past, only these downward moving particles have been counted in evaluating the neutron energy spectrum on the surface. Recent enhancements in the HZETRN code allow for the additional evaluation of those neutrons created within the Martian regolith through the same types of nuclear reactions, which rise to the surface. New calculations using this improved HZETRN code show that these upward moving neutrons contribute significantly to the overall neutron spectrum for energies less than 10 MeV.

Computer Simulation↗

PubMed1994

[Particle state: divided solids and functionality].

Physical and physico-mechanical properties of powder particles, in the field of pharmacy, as drugs, excipients, microparticles and so on... are one of the main element in quality of dosage forms. The aim of this work is to insist on the importance of packing and rheological properties of divided solids and on his influence on compacting behaviour in drug development and industrial process, to avoid difficulties due to the variability of physical properties batch to batch. But as the physical quality of material raw is induced up to the crystallization operation, it is necessary to know, before, what use it will be done.

Elementary Particles↗

PubMed1988

Physical considerations relevant to HZE-particle transport in matter.

High-energy, highly charged (HZE) heavy nuclei may seem at first sight to be an exotic type of radiation, only remotely connected with nuclear power generation. On closer examination it becomes evident that heavy-ion accelerators are being seriously considered for driving inertial confinement fusion reactors, and high-energy heavy nuclei in the cosmic radiation are likely to place significant constraints on satellite power system deployment and space-based power generation. The use of beams of heavy nuclei in an increasing number of current applications, as well as their importance for the development of the state of the art of the future, makes it necessary to develop at the same time a good understanding of their transport through matter.

Cosmic Radiation↗

PubMed1997

Heavy fragment production cross sections from 1.05 GeV/nucleon 56Fe in C, Al, Cu, Pb, and CH2 targets.

We have obtained charge-changing cross sections and partial cross sections for fragmentation of 1.05 GeV/nucleon Fe projectiles incident on H, C, Al, Cu, and Pb nuclei. The energy region covered by this experiment is critical for an understanding of galactic cosmic ray propagation and space radiation biophysics. Surviving primary beam particles and fragments with charges from 12 to 25 produced within a forward cone of half-angle 61 mrad were detected using a silicon detector telescope to identify their charge and the cross sections were calculated after correction of the measured yields for finite target thickness effects. The cross sections are compared to model calculations and to previous measurements. Cross sections for the production of fragments with even-numbered nuclear charges are seen to be enhanced in almost all cases.

Aluminum↗

PubMed2001

A reference radiation facility for dosimetry at flight altitude and in space.

A reference facility for the intercomparison of active and passive detectors in high-energy neutron fields is available at CERN since 1993. A positive charged hadron beam (a mixture of protons and pions) with momentum of 120 GeV/c hits a copper target, 50 cm thick and 7 cm in diameter. The secondary particles produced in the interaction are filtered by a shielding of either 80 cm of concrete or 40 cm of iron. Behind the iron shielding, the resulting neutron spectrum has a maximum at about 1 MeV, with an additional high-energy component. Behind the concrete shielding, the neutron spectrum has a pronounced maximum at about 70 MeV and resembles the high-energy component of the radiation field created by cosmic rays at commercial flight altitudes. The facility is used for a variety of investigations with active and passive neutron dosimeters. Its use for measurements related to the space programme is discussed.

Altitude↗

PubMed1997

Cosmic ray radiation effects caused by proton-induced fragmentation.

In space, radiation effects in which a large amount of energy is transferred by a single particle are observed. These effects can be caused by either the direct ionization of a cosmic ray heavy ion or alternatively by the ionization of short range target fragments which are produced inside the material by interactions of cosmic ray particles. Protons of the lower radiation belt contribute significantly to target fragmentation; especially in the South Atlantic Anomaly (SAA). To allow predictions of possible radiation hazards the characteristics of these interactions at energies below 100 MeV must be understood in detail. We have performed an experiment to measure the proton induced fragmentation cross sections for carbon target nuclei at about 70 MeV/nucleon and to determine some characteristics of the kinematics of the target fragments. For this purpose experimental setups with CR-39 track detectors were used. In this paper we describe the experimental technique and present some preliminary results.

Beryllium↗

PubMed2003

Optically induced multispin entanglement in a semiconductor quantum well.

According to quantum mechanics, a many-particle system is allowed to exhibit non-local behaviour, in that measurements performed on one of the particles can affect a second one that is far away. These so-called entangled states are crucial for the implementation of most quantum information protocols and, in particular, gates for quantum computation. Here we use ultrafast optical pulses and coherent techniques to create and control spin-entangled states in an ensemble of non-interacting electrons bound to donors (at least three) and at least two Mn2+ ions in a CdTe quantum well. Our method, relying on the exchange interaction between localized excitons and paramagnetic impurities, can in principle be applied to entangle an arbitrarily large number of spins.

Cadmium↗

PubMed1978

A heavy particle comparative study. Part I: depth-dose distributions.

The results of a comparative study of heavy particles of interest in radiotherapy, with peaks spread over a depth of 10 cm, are reported in four parts. The introduction to this study and the depth-dose distributions of the particles, (n, pi-, p, He, C, Ne, and Ar ions) are reported herein. The results indicate that protons give the best localization of dose. The degree of localization of dose with heavy ions is reduced with increasing charge on the ion. For ranges less than 15cm, heavier ions such as neon and argon still have favourable dose localization; however, for ranges in excess of 15 cm, heavy ions such as argon are unfavourable but superior to fast neutrons because penetration can be controlled by modulation of energy or range.

Argon↗

PubMed2001

A Monte Carlo code for a direct estimation of radiation risk.

An example of pragmatic approach for predicting mixed field effects is presented. The method was initially applied adopting the following, commonly used, assumptions: a) radiation risk (typically cancer) is correlated with chromosome aberration induction; b) radiation-induced chromosome-exchange yield can be well described by a linear-quadratic dependence on particle fluences (mostly linear with high-LET radiation), with parameters depending on particle types and energies. Information on monochromatic field radiobiological effects was integrated in a condensed-history Monte Carlo transport code (FLUKA), able to simulate nuclear interactions. The integrated code provides the chromosome aberration yield (and thus an estimation of radiation risk) in each voxel of any irradiated volume, given any external mixed-field irradiation; in the present work, the method was tested for neutron irradiation of a water phantom. FLUKA was then coupled with a geometrical human phantom provided with different radiation shielding, in order to apply this approach to estimate radiation risk in manned space missions.

Chromosome Aberrations↗

PubMed1995

Measurements of the secondary particle energy spectra in the Space Shuttle.

Measurements of the energy spectra of secondary particles produced by galactic cosmic rays and trapped protons due to the nuclear interactions of these particles with the Shuttle shielding provide a powerful tool for validating radiation transport codes. A code validated in this way can be used to better estimate the dose and dose equivalent to body organs, measurements that cannot be made directly. The principal cause of single event upsets in electronic devices in the region of the South Atlantic Anomaly is secondary particles, and even in the region of galactic cosmic radiation a significant fraction is produced by secondary particles. In this paper, we describe the first direct measurements of the energy spectra of secondary protons, deuterons, tritons, 3He and 4He produced by galactic cosmic rays inside the Space Shuttle using a charged particle spectrometer. A comparison of these spectra with radiation transport code HZETRN showed reasonably good agreement for secondary protons. However, the code seriously underestimated the flux of all other light ions. The code has been modified to include pick-up and knock-on processes. The modified code leads to good agreement for deuterons and 3He but not for other light ions. This revised code leads to about 10% higher dose equivalent than the original code under moderate shielding, if we assume that higher charge ion fluxes are correctly predicted by the model.

Atlantic Ocean↗

PubMed1983

Neutron doses in negative pion radiotherapy.

Absorbed neutron doses in regions outside the treatment volume from negative pion radiotherapy are presented, based on neutron spectral measurements for pions stopping in a tissue-equivalent target. A Monte Carlo neutron transport computer code was developed and used to calculate the absorbed dose as a function of the distance from the centre of the treatment volume. The Monte Carlo code, which is a modification of a neutron detector efficiency code, follows neutrons and gamma rays as they interact with either hydrogen or oxygen nuclei in a phantom. The code includes neutron elastic scattering on both hydrogen and oxygen as well as five inelastic nuclear reactions on oxygen. The recoil charged particles which provide the absorbed dose are considered until the neutron escapes the phantom or its kinetic energy falls below 1 ke V. Calculations of absorbed dose are compared with earlier dose calculations and measurements. Measurements of the neutron spectrum from a tissue-equivalent target indicate that the total kinetic energy carried away by neutrons is about 76 MeV, which is a significantly higher value than that used in earlier estimates of the neutron dose. The calculations presented here suggest that the neutron dose outside large treatment volumes may limit the use of negative pions for some therapeutic applications.

Elementary Particles↗

PubMed2001

Calculation of the radiation environment caused by galactic cosmic rays for determining air crew exposure.

The spectra of secondary particles resulting from interactions of primary galactic cosmic rays with the nuclei in the atmosphere have been calculated using the Monte Carlo transport code FLUKA. The simulations have been carried out at solar minimum and solar maximum activity, for several values of the vertical geomagnetic cut-off. The effective dose rate and the ambient dose equivalent rate as a function of geomagnetic cut-off and altitude have been obtained using appropriate sets of conversion coefficients. The calculated results are discussed and compared with experimental data and other calculations. A simple method is proposed to calculate the radiation exposure at aircraft altitudes.

Aircraft↗

PubMed1977

Recent advances in radiotherapy.

Significant recent achievement in radiotherapy are presented, with brief discussions of brachytherapy, clinical dose-rate effects, ultrafractionation, and total and half-body irradiation. Reports on radiation modifiers, including hyperbaric oxygen, chemical radiosensitizers, and normal tissue protective agents are briefly summarized, while the potential of local and systemic hyperthermia is discussed in greater detail. Recent reports of local tumor control in so-called "radioresistant tumors," such as salivary gland tumors, adenocarcinomas of the breast, prostate and pancreas, malignant melanoma and malignant carcinoid, are summarized. Current status of heavy particle radiotherapy is discussed in detail. Results of initial clinical trials of neutron beam therapy are summarized, and a brief review of proton beam clinical trials and pion beam facilities is included. Recent reports defining the role of combined irradiation and surgery in rectal and breast cancer, and in soft tissue sarcomas, are discussed. Reports of enhanced radiation toxicity seen with concomitant or sequential chemotherapy and radiotherapy are detailed, including CNS toxicity seen with methotrexate and cytosine arabinoside, cardiotoxicity with adriamycin, and pulmonary toxicity with bleomycin. New or improved diagnostic techniques with special relevance to radiotherapy treatment planning, including CT scanning, histerography, internal mammary lymphoscintigraphy, and upper extremity lymphangiography are described.

Breast Neoplasms↗

PubMed2001

Problems of modern cosmology: how dominant is the vacuum?

It would be hard to find a cosmologist today who does not believe that the vast bulk of the Universe (95% or more) is hidden from our eyes. We review the evidence for this remarkable consensus, and for the latest proposal, that the mysterious dark matter consists of as many as four separate ingredients: baryons, massive neutrinos, new "exotic" dark matter particles, and vacuum energy, also known as the cosmological constant (lambda). Of these, only baryons fit within standard theoretical physics; the others, if their existence is confirmed, will mean rewriting textbooks. Fresh experimental evidence has recently appeared for and against all four components, so that the subject is in a state of turmoil and excitement. The past 3 years in particular have seen the fourth (vacuum) component come into new prominence, largely at the expense of the third (exotic dark matter). We conclude our review by exploring the possibility that the energy density of the vacuum is in fact so dominant as to leave little room for significant amounts of exotic dark matter.

Astronomy↗

PubMed1992

Risk analyses for the solar particle events of August through December 1989.

The solar particle events of August through December 1989, among the largest ever recorded, are analyzed to assess the potential hazards to humans on interplanetary missions from events of these types. Using the coupled neutron-proton space radiation transport computer code, BRYNTRN, risk estimates for the effects of exposures to the skin, ocular lens, and bone marrow are made for nominal thicknesses of the spacecraft aluminum shielding. Risk assessment in terms of absorbed dose is made for each event. Also presented are estimates of organ absorbed dose and dose equivalent for pairs of events which occurred within 30-day periods, and for the cumulative August through December 1989 period.

Elementary Particles↗

PubMed2002

Bystander-induced apoptosis and premature differentiation in primary urothelial explants after charged particle microbeam irradiation.

The ureter primary explant technique was developed to study bystander effects under in vivo like conditions where stem and differentiated cells are present. Irradiation was performed with a 3He2+ charged particle microbeam available at the Gray Cancer Institute, with high (approximately 2 microns) precision. Tissue sections from porcine ureters were pre-irradiated with the microbeam at a single location with 10 3He2+ particles (5 MeV; LET 70 keV.micron-1). After irradiation, the tissue section was incubated for 7 days, thus allowing the explant outgrowth to form. Total cellular damage (total fraction of micronucleated and apoptotic cells) was measured according to morphological criteria. Apoptosis was also assessed using a 3'-OH DNA end-labelling technique. Premature differentiation was estimated using antibodies to uroplakin III, a specific marker of terminal urothelial differentiation. Results of our experiments demonstrated a significant bystander-induced differentiation and a less significant increase in apoptotic and micronucleated cells. A hypothesis based on the protective nature of the bystander effect is proposed.

Animals↗

PubMedDate not supplied

A technique for calculating the influence of thin inhomogeneities on charged particle beams.

A method has been developed for calculating the fluence and dose perturbations which occur in the shadow of inhomogeneous structures exposed to beams of charged particles. It is shown that differences in scattering power in adjacent portions of irradiated material can give rise to fluence perturbations which, in turn, are responsible for dose perturbations. A quantitative analysis of this process is developed which permits calculation of both the perturbed primary fluence and dose distributions. Results of these calculations are given for a square-faced edge discontinuity. The analytic technique, however, can be applied to more complicated interfaces and the general formulae are developed in this paper. They include provisions for the important modifying effects of beam divergence, of overlying or underlying homogeneous material, and of nonuniform beam profiles. In a companion paper, more complex geometries are analyzed and comparisons between calculations and experiments are presented.

Elementary Particles↗