John W Wilson
Old Dominion University, Department of mathematics, Department Member
- KsSU 1962, William and Mary 1969, 1975, NASA Langley Research Center 1963-2007, Old Dominion University Research Foundation 2012-presentedit
Extension of the high charge and energy (HZE) transport computer program HZETRN for angular transport of neutrons is considered. For this paper, only light ion transport, Heâ´ and lighter, will be analyzed using a pure solar proton... more
Extension of the high charge and energy (HZE) transport computer program HZETRN for angular transport of neutrons is considered. For this paper, only light ion transport, Heⴠand lighter, will be analyzed using a pure solar proton source. The angular transport calculator is the ANISN/PC program which is being controlled by the HZETRN program. The neutron flux values are compared for straight-ahead transport and angular transport in one dimension. The shield material is aluminum and the target material is water. The thickness of these materials is varied; however, only the largest model calculated is reported which is 50 gm/cm² of aluminum and 100 gm/cm² of water. The flux from the ANISN/PC calculation is about two orders of magnitude lower than the flux from HZETRN for very low energy neutrons. It is only a magnitude lower for the neutrons in the 10 to 20 MeV range in the aluminum and two orders lower in the water. The major reason for this difference is in the transport modes: ...
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Past space missions beyond the confines of the Earth’s protective magnetic field have been of short duration and protection from the effects of solar particle events was of primary concern. The extension of operational infrastructure... more
Past space missions beyond the confines of the Earth’s protective magnetic field have been of short duration and protection from the effects of solar particle events was of primary concern. The extension of operational infrastructure beyond low-Earth orbit to enable routine access to more interesting regions of space will require protection from the hazards of the accumulated exposures of Galactic Cosmic Rays (GCR). There are significant challenges in providing protection from the long-duration exposure to GCR: the human risks to the exposures are highly uncertain and safety requirements places unreasonable demands in supplying sufficient shielding materials in the design. A vigorous approach to future radiation health-risk mitigation requires a triage of techniques (using biological and technical factors) and reduction of the uncertainty in radiation risk models. The present paper discusses the triage of factors for risk mitigation with associated materials issues and engineering design methods.
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The purpose of this work is an assessment of the lunar lava tubes physical characteristics and an evaluation of the their actual safety features from the point of view of the ionizing radiation environment as potential habitats for future... more
The purpose of this work is an assessment of the lunar lava tubes physical characteristics and an evaluation of the their actual safety features from the point of view of the ionizing radiation environment as potential habitats for future lunar exploration crews.
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One major obstacle to human space exploration is the possible limitations imposed by the adverse effects of long-term exposure to the space environment. Even before human spaceflight began, the potentially brief exposure of astronauts to... more
One major obstacle to human space exploration is the possible limitations imposed by the adverse effects of long-term exposure to the space environment. Even before human spaceflight began, the potentially brief exposure of astronauts to the very intense random solar energetic particle (SEP) events was of great concern. A new challenge appears in deep space exploration from exposure to the low-intensity heavy-ion flux of the galactic cosmic rays (GCR) since the missions are of long duration and the accumulated exposures can be high. Because cancer induction rates increase behind low to rather large thickness of aluminum shielding according to available biological data on mammalian exposures to GCR like ions, the shield requirements for a Mars mission are prohibitively expensive in terms of mission launch costs. Preliminary studies indicate that materials with high hydrogen content and low atomic number constituents are most efficient in protecting the astronauts. This occurs for two...
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Research Interests: Physics and Astrobiology
An optical model description of momentum transfer in relativistic heavy ion collisions, based upon composite particle multiple-scattering theory, is presented. The imaginary component of the complex momentum transfer, which comes from the... more
An optical model description of momentum transfer in relativistic heavy ion collisions, based upon composite particle multiple-scattering theory, is presented. The imaginary component of the complex momentum transfer, which comes from the absorptive part of the optical potential, is shown to be the main contributor to the momentum loss of the projectile. Within the context of the Goldhaber formalism, predictions of fragment momentum distribution observables are made and compared with experimental data. Use of the model as a tool for estimating collision impact parameters is also discussed.
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A solar cycle statistical model has been developed to project sunspot numbers which represent the variations in the space radiation environment The resultant projection of sunspot numbers in the near future were coupled to space-related... more
A solar cycle statistical model has been developed to project sunspot numbers which represent the variations in the space radiation environment The resultant projection of sunspot numbers in the near future were coupled to space-related quantities of interest in radiation protection such as the galactic cosmic radiation GCR deceleration potential phi and the mean occurrence frequency of solar particle events SPEs Future GCR fluxes have been derived from a predictive model in which GCR temporal dependence represented by phis was derived from GCR flux and ground-based Climax neutron monitor rate measurements over the last four decades Results showed that the point dose equivalent inside a typical spacecraft in interplanetary radiation fields was influenced by solar modulation up to a factor of three One important characteristic of sporadic SPEs is their mean frequency of occurrence which depends on solar activity Projections of future mean frequency of SPE occurrence were estimated fr...
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The understanding of the risk from exposure to cosmic rays to personnel and electronic equipment in spaceflight and in the upper atmosphere is confounded by the high energy nuclear interactions and the track structure of fast ions. The... more
The understanding of the risk from exposure to cosmic rays to personnel and electronic equipment in spaceflight and in the upper atmosphere is confounded by the high energy nuclear interactions and the track structure of fast ions. The Langley Research Center has developed several radiation transport codes and associated nuclear interaction data bases for describing the passage of high energy protons, neutrons, and light and heavy ions through materials and tissue. We present and overview these transport codes and databases including comparisons to laboratory and spaceflight experiments. Several risk assessment models are considered in order to study the attenuation properties of selected shielding candidates. These comparisons show that in contrast to conventional risk models based on linear energy transfer (LET), track structure models indicate that only hydrogen rich materials are effective in reducing risk. The contrasting conclusions of the conventional and track structure based approaches are shown to be due to differences in the assessment of the effectiveness of secondary ions such as neutrons, protons, alphas, and heavy ion target fragments. Microdosimetric measurements with proton and heavy ion beams are also discussed and as reported earlier in this session by Dicello, reach the same conclusions as the track models on the importance of target fragmentation.
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We calculate the probability that large size ejecta from a major collision on a planet in an extrasolar planetary system find their way to our solar system and collide with the Earth. The production rate of ejecta is estimated from the... more
We calculate the probability that large size ejecta from a major collision on a planet in an extrasolar planetary system find their way to our solar system and collide with the Earth. The production rate of ejecta is estimated from the conditions in Our Solar System, and the evolution of the environment of the Sun is derived on the assumption
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The Langley cosmic ray transport code and the Langley nucleon transport code (BRYNTRN) are used to quantify the transport and attenuation of galactic cosmic rays (GCR) and solar proton flares through the Martian atmosphere. Surface doses... more
The Langley cosmic ray transport code and the Langley nucleon transport code (BRYNTRN) are used to quantify the transport and attenuation of galactic cosmic rays (GCR) and solar proton flares through the Martian atmosphere. Surface doses are estimated using both a low density and a high density carbon dioxide model of the atmosphere which, in the vertical direction, provides a
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In view of manned missions targeted to Mars for which radiation exposure is one of the greatest challenges to be tackled it is of fundamental importance to have available a tool which allows the determination of the particle flux and... more
In view of manned missions targeted to Mars for which radiation exposure is one of the greatest challenges to be tackled it is of fundamental importance to have available a tool which allows the determination of the particle flux and spectra at any time at any point of the Martian surface With this goal in mind a new model for
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A model of the chemical kinetics of the n-C3F7I solar-simulator-pumped iodine laser is utilized to study the major kinetic processes associated with the threshold behavior of this experimental system. Excited-state diffusion to the cell... more
A model of the chemical kinetics of the n-C3F7I solar-simulator-pumped iodine laser is utilized to study the major kinetic processes associated with the threshold behavior of this experimental system. Excited-state diffusion to the cell wall is the dominant limiting factor below 5 torr. Excited-state diffusion to the cell wall is the dominant limiting factor below 5 torr. Excited-state recombination with
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Stacks consisting of thin CR-39 sheets sandwiched between thick Lucite and water absorbers were perpendicularly bombarded by 12C ions at 200 and 244 MeV/u. Track radius distributions representing the charge composition of the fragmented... more
Stacks consisting of thin CR-39 sheets sandwiched between thick Lucite and water absorbers were perpendicularly bombarded by 12C ions at 200 and 244 MeV/u. Track radius distributions representing the charge composition of the fragmented beams were automatically measured by a particle track analysis system. After analysis of the nuclear charge distributions, the total charge removal cross sections and elemental production cross sections of fragments with atomic numbers from 5 to 3, were obtained down to the lower energies (~ 50 and 100
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Two methods of calculating the transition of galactic heavy ions in the Earth's atmosphere are compared with respect to accuracy, generality, and computer efficiency. The most general method is shown to have the highest accuracy... more
Two methods of calculating the transition of galactic heavy ions in the Earth's atmosphere are compared with respect to accuracy, generality, and computer efficiency. The most general method is shown to have the highest accuracy and is a simple numerical procedure.
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A repair/misrepair kinetic model for multiple radiation-induced lesions (mutation inactivation) is coupled to a two-mutation model of initiation-promotion in tissue to provide a parametric description of tumour prevalence in the mouse... more
A repair/misrepair kinetic model for multiple radiation-induced lesions (mutation inactivation) is coupled to a two-mutation model of initiation-promotion in tissue to provide a parametric description of tumour prevalence in the mouse Harderian gland from high-energy and charge radiations. Track-structure effects are considered using an action-cross section model. Dose-response curves are described for gamma rays and relativistic ions, and good agreement with experiment is found. The effects of nuclear fragmentation are also considered for high-energy proton and alpha-particle exposures. The model described provides a parametric description of age-dependent cancer induction for a wide range of radiation fields. Radiosensitivity parameters found in the model for an initiation mutation (sigma 0 = 7.6 x 10(-10) cm2 and D0 = 148.0 Gy) are somewhat different than previously observed for neoplastic transformation of C3H10T1/2 cell cultures (sigma 0 = 0.7 x 10(-10) cm2 and D0 = 117.0 Gy). We consider the two hypotheses that radiation acts solely as an initiator or as both initiator and promoter and make model calculations for fractionation exposures from gamma rays and relativistic Fe ions. For fractionated Fe exposures, an inverse-dose-rate effect is provided by a promotion hypothesis with an increase of 30% or more, dependent on the dose level and fractionation schedule, using a mutation rate for promotion similar to that of single-gene mutations.
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Recently (R.K. Tripathi, J.W. Wilson, F.A. Cucinotta, Nucl. Instr. and Meth. B 145 (1998) 277; R.K. Tripathi, F.A. Cucinotta, J.W. Wilson, NASA-TP-1998-208438), we have extracted nucleon-nucleon (N-N) cross-sections in the medium directly... more
Recently (R.K. Tripathi, J.W. Wilson, F.A. Cucinotta, Nucl. Instr. and Meth. B 145 (1998) 277; R.K. Tripathi, F.A. Cucinotta, J.W. Wilson, NASA-TP-1998-208438), we have extracted nucleon-nucleon (N-N) cross-sections in the medium directly from experiment. The in-medium N-N cross-sections form the basic ingredients of several heavy-ion scattering approaches including the coupled-channel approach developed at the NASA Langley Research Center. Here, we investigate the ratio of real to imaginary part of the two-body scattering amplitude in the medium. These ratios are used in combination with the in-medium N-N cross-sections to calculate total proton-nucleus cross-sections. The agreement is excellent with the available experimental data. These cross-sections are needed for the radiation risk assessment of space missions.
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It has long been recognized that galactic cosmic rays are of such high energy that they tend to pass through available shielding materials resulting in exposure of astronauts and equipment within space vehicles and habitats. Any... more
It has long been recognized that galactic cosmic rays are of such high energy that they tend to pass through available shielding materials resulting in exposure of astronauts and equipment within space vehicles and habitats. Any protection provided by shielding materials results not so much from stopping such particles but by changing their physical character by interaction with shielding material nuclei to hopefully less dangerous species. Clearly, the fidelity of nuclear cross sections is essential to correct specification of shield design and sensitivity to cross section error is important in guiding experimental validation of cross section models and database. We examine the Boltzmann transport equation which is used to calculate a radiation dose equivalent, with units (cSv/year), associated with various depths of shielding materials. The equivalent radiation dose is a weighted sum of contributions from protons, alpha particles, light ions , medium ions, heavy ions and neutrons....
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... A transverse cross section of the system is shown in Fig. 1. The fluorescent gas for the present study is taken to be mixtures of Ar, Kr, and F2. ... The photoab-Neutron Moderator 3He/Ar/Kr/F sorption cross section is shown in Fig. ...
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Research Interests: Physics, Nuclear Physics, Biomedical Engineering, Environmental modeling, Radiation Protection, and 15 moreCosmic Rays, Comparative Study, Medicine, Aluminum, Models, Digital Systems, Fragmentation, Prediction Model, Radiation Monitoring, Mathematical Model, Radiation Effect, Radiation Transport, Low Earth Orbit, Cosmic Radiation, and High energy
The US Lab module of the International Space Station (ISS) is a primary working area where the crewmembers are expected to spend majority of their time. Because of the directionality of radiation fields caused by the Earth shadow, trapped... more
The US Lab module of the International Space Station (ISS) is a primary working area where the crewmembers are expected to spend majority of their time. Because of the directionality of radiation fields caused by the Earth shadow, trapped radiation pitch angle distribution, and inherent variations in the ISS shielding, a model is needed to account for these local variations in the radiation distribution. We present the calculated radiation dose (rem/yr) values for over 3,000 different points in the working area of the Lab module and estimated radiation dose values for over 25,000 different points in the human body for a given ambient radiation environment. These estimated radiation dose values are presented in a three dimensional animated interactive visualization format. Such interactive animated visualization of the radiation distribution can be generated in near real-time to track changes in the radiation environment during the orbit precession of the ISS.
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The most challenging radiation in space consists of fully ionized atomic elements with high energy for which only the few lowest energy ions can be stopped in shielding materials. The health risk from exposure to these ions and their... more
The most challenging radiation in space consists of fully ionized atomic elements with high energy for which only the few lowest energy ions can be stopped in shielding materials. The health risk from exposure to these ions and their secondary radiations generated in shield materials is poorly understood since there are few human data and a systematic study in relevant animal model systems has not been made. The accuracy of risk prediction is described as the major limiting factor in the management of space radiation risk. The expected impact of systematic studies is examined using the limited available biological data and models. Given the limitations of current predictions, models must be developed that are able to incorporate the required fundamental scientific data into accurate risk estimates. The important radiation components that can be provided for laboratory testing are identified. The use of ground-based accelerator beams to simulate space radiation is explained and quant...
Research Interests: Physics, Radiation Protection, Risk assessment, Medicine, Probability, and 13 moreBiological Sciences, Humans, Space flight, Aerospace Medicine, Female, Male, Physical sciences, Risk Assessment, Relative Biological Effectiveness, Cosmic Radiation, Particle Accelerators, Heavy Ions, and Medical and Health Sciences
For the first time track structure theory has been applied to radiobiological effects in a living organism. Data for lethal mutagenesis in Caenorhabditis elegans, obtained after irradiation with nine different types of ions of atomic... more
For the first time track structure theory has been applied to radiobiological effects in a living organism. Data for lethal mutagenesis in Caenorhabditis elegans, obtained after irradiation with nine different types of ions of atomic number 1-57 and gamma rays have yielded radiosensitivity parameters (E0, sigma 0, kappa, m = 68 Gy, 2.5 x 10(-9) cm2, 750, 2) comparable with those found for the transformation of C3HT10 1/2 cells (180 Gy, 1.15 x 10(-10) cm2, 750, 2) but remote from those (E0 and sigma 0 = approximately 2 Gy, approximately 5 x 10(-7) cm2) for mammalian cell survival.
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The recoil spectrum of nuclei in polymers for incident protons below 10 MeV in energy is calculated by using the Rutherford cross-section with screening corrections. Employing the work of McKinley and Feshbach on the Coulomb scattering of... more
The recoil spectrum of nuclei in polymers for incident protons below 10 MeV in energy is calculated by using the Rutherford cross-section with screening corrections. Employing the work of McKinley and Feshbach on the Coulomb scattering of relativistic electrons by nuclei, the recoil spectrum of the nuclei is also calculated for electron energies varying from threshold to 10 MeV. The partitioning of energy between electronic excitation and ionization and nuclear recoil is then studied to search for possible difference in polymer radiation response as a function of radiation energy and type.
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A parameter-free geometric model for nuclear absorption is derived from microscopic theory. The expression for the absorption cross section in the eikonal approximation taken in integral form is separated into a geometric contribution,... more
A parameter-free geometric model for nuclear absorption is derived from microscopic theory. The expression for the absorption cross section in the eikonal approximation taken in integral form is separated into a geometric contribution, described by an energy-dependent effective radius, and two surface terms which are shown to cancel in an asymptotic series expansion. For collisions of light nuclei, an expression for the effective radius is derived using harmonic-oscillator nuclear density functions. A direct extension to heavy nuclei with Woods-Saxon densities is made by identifying the equivalent half density radius for the harmonic-oscillator functions. Coulomb corrections are incorporated and a simplified geometric form of the Bradt-Peters type obtained. Results spanning the energy range of 1 MeV/nucleon to 1 GeV/nucleon are presented. Good agreement with experimental results are obtained.
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An analysis of radiation safety issues on lunar lava tubes as potential manned habitats has been performed. Lava tubes are formed when an active low-viscosity lava flow develops a continuous and hard crust, which thickens and forms a roof... more
An analysis of radiation safety issues on lunar lava tubes as potential manned habitats has been performed. Lava tubes are formed when an active low-viscosity lava flow develops a continuous and hard crust, which thickens and forms a roof above the still flowing lava stream. At the end of the extrusion period, an empty flow channel free from molten magma
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In view of manned missions targeted to the Moon for which radiation exposure is one of the greatest challenges to be tackled it is of fundamental importance to have available a tool which allows the determination of the particle flux and... more
In view of manned missions targeted to the Moon for which radiation exposure is one of the greatest challenges to be tackled it is of fundamental importance to have available a tool which allows the determination of the particle flux and spectra at any time and at any point of the lunar surface With this goal in mind a new model of the Moon s radiation environment due to Galactic Cosmic Rays GCR and Solar Particle Events SPE has been developed Primary particles reach the lunar surface and are transported all throughout the subsurface layers with backscattering patterns taken into account The surface itself has been modeled as regolith and bedrock with composition taken from the results of the instruments flown on the Apollo missions namely on the Apollo 12 from the Oceanus Procellarum landing site Subsurface environments like lava tubes have been considered in the analysis Particle transport has been performed with both deterministic and Monte Carlo codes with an adaptation for plan...
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Radiation risk cross sections (i.e. risks per particle fluence) are discussed in the context of estimating the risk of radiation-induced cancer on long-term space flights from the galactic cosmic radiation outside the confines of the... more
Radiation risk cross sections (i.e. risks per particle fluence) are discussed in the context of estimating the risk of radiation-induced cancer on long-term space flights from the galactic cosmic radiation outside the confines of the earth's magnetic field. Such quantities are useful for handling effects not seen after low-LET radiation. Since appropriate cross-section functions for cancer induction for each particle species are not yet available, the conventional quality factor is used as an approximation to obtain numerical results for risks of excess cancer mortality. Risks are obtained for seven of the most radiosensitive organs as determined by the ICRP [stomach, colon, lung, bone marrow (BFO), bladder, esophagus and breast], beneath 10 g/cm2 aluminum shielding at solar minimum. Spectra are obtained for excess relative risk for each cancer per LET interval by calculating the average fluence-LET spectrum for the organ and converting to risk by multiplying by a factor proportional to R gamma L Q(L) before integrating over L, the unrestricted LET. Here R gamma is the risk coefficient for low-LET radiation (excess relative mortality per Sv) for the particular organ in question. The total risks of excess cancer mortality obtained are 1.3 and 1.1% to female and male crew, respectively, for a 1-year exposure at solar minimum. Uncertainties in these values are estimated to range between factors of 4 and 15 and are dominated by the biological uncertainties in the risk coefficients for low-LET radiation and in the LET (or energy) dependence of the risk cross sections (as approximated by the quality factor). The direct substitution of appropriate risk cross sections will eventually circumvent entirely the need to calculate, measure or use absorbed dose, equivalent dose and quality factor for such a high-energy charged-particle environment.
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An energy-dependent parameterization of the total absorption (reaction) cross sections for heavy ion (Z > or = 2) collisions at energies above 25 MeV per nucleon is presented. The formula will be especially useful in heavy-ion... more
An energy-dependent parameterization of the total absorption (reaction) cross sections for heavy ion (Z > or = 2) collisions at energies above 25 MeV per nucleon is presented. The formula will be especially useful in heavy-ion transport applications.
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A comprehensive physical model for galactic heavy ion propagation is presented. The nuclear fragmentation model is a simplified physical model but contains the major processes of importance to galactic ions. Comparison is made to... more
A comprehensive physical model for galactic heavy ion propagation is presented. The nuclear fragmentation model is a simplified physical model but contains the major processes of importance to galactic ions. Comparison is made to measurements of atmospheric ion fluence and the limitations of these comparisons are discussed.
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The propagation of primary cosmic rays through the Earth's atmosphere and the energy spectra of the resulting secondary particles have been calculated using the Monte Carlo transport code FLUKA with several novel auxiliary... more
The propagation of primary cosmic rays through the Earth's atmosphere and the energy spectra of the resulting secondary particles have been calculated using the Monte Carlo transport code FLUKA with several novel auxiliary methods. Solar-modulated primary cosmic ray spectra were determined through an analysis of simultaneous proton and helium measurements made on spacecraft or high-altitude balloon flights. Primary protons and helium ions are generated within the rigidity range of 0.5 GV-20 TV, uniform in cos2theta. For a given location, primaries above the effective angle-dependent geomagnetic cut-off rigidity, and re-entrant albedo protons, are transported through the atmosphere. Helium ions are initially transported using a separate transport code called HEAVY to simulate fragmentation. HEAVY interfaces with FLUKA to provide interaction starting points for each nucleon originating from a helium nucleus. Calculated cosmic ray neutron spectra and consequent dosimetric quantities for locations with a wide range of altitude (atmospheric depth) and geomagnetic cut-off are presented and compared with measurements made on a high-altitude aeroplane. Helium ion propagation using HEAVY and inclusion of re-entrant albedo protons with the incident primary spectra significantly improved the agreement of the calculated cosmic ray neutron spectra with measured spectra. These cosmic ray propagation calculations provide the basis for a new atmospheric ionising radiation (AIR) model for air-crew dosimetry, calculation of effects on microelectronics, production of cosmogenic radionuclides and other uses.
Research Interests: Algorithms, Radiation Protection, European Union, Risk assessment, Computer Simulation, and 12 moreAtmosphere, Risk factors, Neutrons, Radiometry, Theoretical Models, Public health systems and services research, Spectrum analysis, Reproducibility of Results, Risk Factors, Risk Assessment, Sensitivity and Specificity, and Cosmic Radiation
The use of Green's function has played a fundamental role in transport calculations for high-charge high-energy (HZE) ions. Two recent developments have greatly advanced the practical aspects of implementation of... more
The use of Green's function has played a fundamental role in transport calculations for high-charge high-energy (HZE) ions. Two recent developments have greatly advanced the practical aspects of implementation of these methods. The first was the formulation of a closed-form solution as a multiple fragmentation perturbation series. The second was the effective summation of the closed-form solution through nonperturbative techniques. The nonperturbative methods have been recently extended to an inhomogeneous, two-layer transport media to simulate the lead scattering foil present in the Lawrence Berkeley Laboratories (LBL) biomedical beam line used for cancer therapy. Such inhomogeneous codes are necessary for astronaut shielding in space. The transport codes utilize the Langley Research Center atomic and nuclear database. Transport code and database evaluation are performed by comparison with experiments performed at the LBL Bevalac facility using 670 A MeV 20Ne and 600 A MeV 56Fe ion beams. The comparison with a time-of-flight and delta E detector measurement for the 20Ne beam and the plastic nuclear track detectors for 56Fe show agreement up to 35%-40% in water and aluminium targets, respectively.
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The energy-dependent, semiempirical, surface transparency factor of Kox et al. is accurately represented by a simple analytical expression. Total reaction cross sections obtained using this parametrization agree with Kox's... more
The energy-dependent, semiempirical, surface transparency factor of Kox et al. is accurately represented by a simple analytical expression. Total reaction cross sections obtained using this parametrization agree with Kox's predictions to within four percent.
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ABSTRACT We present calculations of the tensor moments of deuteron polarization in neutron-deuteron scattering between 77 and 300 MeV lab kinetic energy in the hope that they will motivate measurements in this currently neglected area.... more
ABSTRACT We present calculations of the tensor moments of deuteron polarization in neutron-deuteron scattering between 77 and 300 MeV lab kinetic energy in the hope that they will motivate measurements in this currently neglected area. The moments are found to be large compared with their maximum possible values, in contrast with the experience at lower energies. The reaction model on which the calculations are based is a form of single scattering. We evaluate the single scattering integral numerically and utilize a novel method for obtaining the necessary off-shell two-nucleon amplitudes based on relativistic considerations. We compare our results with the results obtained using a more complete model wmploying nucleon exchange and a phenomenological s-wave representing higher-order multiple scattering. In this way we demonstrate that our results are relatively independent of the less known contributions to the scattering amplitude, if we restrict our attention to the forward hemisphere. We also discuss sensitivity of these results to the D-state percentage of the deuteron.
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Abtract The use of Green's function has played a fundamental role in transport calculations for high-charge high-energy (HZE) ions. Two recent developments have greatly advanced the practical aspects of implementation of these... more
Abtract The use of Green's function has played a fundamental role in transport calculations for high-charge high-energy (HZE) ions. Two recent developments have greatly advanced the practical aspects of implementation of these methods. The first was the formulation of a closedform solution as a multiple fragmentation perturbation series. The second was the effective summation of the closedform solution through nonperturbative
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A parameter-free geometric model for nuclear ab-sorption is derived herein from microscopic theory. The expression for the absorption cross section in the eikonal approximation, taken in integral form, is separated into a geometric... more
A parameter-free geometric model for nuclear ab-sorption is derived herein from microscopic theory. The expression for the absorption cross section in the eikonal approximation, taken in integral form, is separated into a geometric contribution that is de-scribed by an energy-...
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Research Interests: Mechanical Engineering, Aerospace Engineering, Nuclear Physics, Quantum Theory, Radiation Protection, and 15 moreRisk assessment, Space, Aerospace Medicine, Atmosphere, Human Body, Nuclear Reactions, Neutrons, Theoretical Models, Aircraft, Risk Assessment, Alpha Particles, Spacecraft, Penetration Depth, Cosmic Radiation, and Elementary Particles
Crews of manned interplanetary missions may accumulate significant radiation exposures from the galactic cosmic ray (GCR) environment in space. Estimates of how these dose levels are affected by the assumed temporal and spatial variations... more
Crews of manned interplanetary missions may accumulate significant radiation exposures from the galactic cosmic ray (GCR) environment in space. Estimates of how these dose levels are affected by the assumed temporal and spatial variations in the composition of the GCR environment, and by the effects of the spacecraft and body self-shielding on the transported radiation fields are presented. In this work, the physical processes through which shielding alters the transported radiation fields are described. We then present estimates of the effects on model calculations of (1) nuclear fragmentation model uncertainties, (2) solar modulation, (3) variations between solar cycles, and (4) proposed changes to the quality factors which relate dose equivalent to absorbed dose.