The chemical composition of galactic and solar cosmic rays.
Chemical composition of galactic and solar cosmic rays, discussing differences from universal cosmic abundances, using Cerenkov counters, emulsions, etc
Mcdonald, F. B.↗
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The heliospheric intensity gradients of the anomalous He4 and the galactic cosmic-ray components
Measurements made with Pioneers 10 and 11 over the radial range of 1 to about 25 AU from 1972 to 1981 are presented to show that at solar minimum (1972-1977), the radial gradient for the anomalous helium component from 11 to 20 MeV/n is about 14%/AU. This result is significantly smaller than that predicted for either charge state of the component based on the observed spectrum and assumptions of conventional solar modulation for particles propagating inward from the heliospheric boundary. It is confirmed that the solar modulation mechanism that determines the level and distribution of low-energy galactic cosmic rays in the heliosphere, also modulates the He(A) spectrum. With increasing modulation between solar minimum and maximum, the 10-20 MeV/n He(A) flux decreases below the flux of modulated galactic He first at 1 AU and then progressively outward to 22-25 AU over an approximately two year period.
Mckibben, R. B.↗
Designing Spacecraft and Mission Operations Plans to Meet Flight Crew Radiation Dose Requirements: Why is this an "Epic Challenge" for Long-Term Manned Interplanetary Flight
Outline of presentation: (1) Radiation Shielding Concepts and Performance - Galactic Cosmic Rays (GCRs) (1a) Some general considerations (1b) Galactic Cosmic Rays (2)GCR Shielding I: What material should I use and how much do I need? (2a) GCR shielding materials design and verification (2b) Spacecraft materials point dose cosmic ray shielding performance - hydrogen content and atomic number (2c) Accelerator point dose materials testing (2d) Material ranking and selection guidelines (2e) Development directions and return on investment (point dose metric) (2f) Secondary particle showers in the human body (2f-1) limited return of investment for low-Z, high-hydrogen content materials (3) GCR shielding II: How much will it cost? (3a) Spacecraft design and verification for mission radiation dose to the crew (3b) Habitat volume, shielding areal density, total weight, and launch cost for two habitat volumes (3c) It's All about the Money - Historical NASA budgets and budget limits (4) So, what can I do about all this? (4a) Program Design Architecture Trade Space (4b) The Vehicle Design Trade Space (4c) Some Near Term Recommendations
Koontz, Steven↗
Galactic Cosmic-Ray-Produced Thermoluminescence Profiles in Meteorites Lunar Samples and a Terrestrial Analog
The long-term radiation shielding properties of common extraterrestrial materials are poorly known, although these materials are the most likely structural elements on airless worlds such as the Moon. We report on radiation dose profiles in meteorites and lunar soil cores using specific minerals as naturally-occurring "dosimeters". We find that radiation profiles are fairly flat in typical meteoroid bodies (less than 85 cm radius) and drop by only about 40% through about 2.5 m of lunar soil. These profiles are produced by primary galactic cosmic rays and the secondary proton cascade but with a significant contribution by secondary neutrons at depths of about 2 m (300 g/sq cm).
Benoit, Paul H.↗
A perturbation calculation of the dynamical effects of cosmic rays and interstellar gas on the solar wind
The modulation of galactic cosmic rays and other energetic particles by the solar wind produces a gradient in their pressure, which in turn influences the wind dynamics. The basic equations describing this interaction are presented in the 'hydrodynamic' approximation. A perturbation solution of the equations is presented for the case in which both the galactic cosmic ray pressure, and the pressure of the anomalous cosmic ray component accelerated at the wind termination shock, are small compared with the wind ram pressure. Analytical expressions for the deceleration of the wind and the modification of the shock and its location are derived in this case. These effects are estimated to have a relative magnitude of several percent in the solar wind. The interstellar neutral gas which penetrates the heliosphere is ionized, predominantly by photoionization and charge exchange with the wind, and may also have a significant dynamical effect on the wind. The basic equations describing this interaction are also presented, A perturbation solution is presented under the assumption that the mass loading and momentum-loading of the wind by the interstellar pickup ions is small compared with the wind ram pressure. Analytical expressions for the deceleration of the wind, the contribution of the pickup ions to the wind pressure, and the modification of the termination shock location are derived. Again, with the exception of pickup ion pressure which is large compared with solar wind thermal pressure, the effects are estimated to be several percent in relative magnitude in the solar wind.
Lee, M. A.↗
Numerical Simulation of the Anomalous Transport of High-Energy Cosmic Rays in Galactic Superbubble
A continuous-time random-walk (CTRW) model to simulate the transport and acceleration of high-energy cosmic rays in galactic superbubbles has recently been put forward (Barghouty & Schnee 2102). The new model has been developed to simulate and highlight signatures of anomalous transport on particles' evolution and their spectra in a multi-shock, collective acceleration context. The superbubble is idealized as a heterogeneous region of particle sources and sinks bounded by a random surface. This work concentrates on the effects of the bubble's assumed astrophysical characteristics (cf. geometry and roughness) on the particles' spectra.
Barghouty, A. F.↗
Influence of Dust Loading on Atmospheric Ionizing Radiation on Mars
Measuring the radiation environment at the surface of Mars is the primary goal of the Radiation Assessment Detector on the NASA Mars Science Laboratory's Curiosity rover. One of the conditions that Curiosity will likely encounter is a dust storm. The objective of this paper is to compute the cosmic ray ionization in different conditions, including dust storms, as these various conditions are likely to be encountered by Curiosity at some point. In the present work, the Nowcast of Atmospheric Ionizing Radiation for Aviation Safety model, recently modified for Mars, was used along with the Badhwar & O'Neill 2010 galactic cosmic ray model. In addition to galactic cosmic rays, five different solar energetic particle event spectra were considered. For all input radiation environments, radiation dose throughout the atmosphere and at the surface was investigated as a function of atmospheric dust loading. It is demonstrated that for galactic cosmic rays, the ionization depends strongly on the atmosphere profile. Moreover, it is shown that solar energetic particle events strongly increase the ionization throughout the atmosphere, including ground level, and can account for the radio blackout conditions observed by the Mars Advanced Radar for Subsurface and Ionospheric Sounding instrument on the Mars Express spacecraft. These results demonstrate that the cosmic rays' influence on the Martian surface chemistry is strongly dependent on solar and atmospheric conditions that should be taken into account for future studies.
Norman, Ryan B.↗
Capability Demonstration of a 3D CdZnTe Detector on a High-Altitude Balloon Flight
In collaboration between the University of Michigan and Los Alamos National Laboratory, a 3D position-sensing CdZnTe (CZT) detector prototype was built and integrated into a high-altitude balloon platform to evaluate its performance in a space-like mixed-radiation environment. The detector prototype, Orion Eagle, was designed to operate in near-vacuum environments without any temperature regulation. Orion Eagle was hand-launched from NASA’s Columbia Scientific Balloon Facility (CSBF) at Fort Sumner, NM on September 26, 2021, and successfully operated throughout a 9-hour flight, which reached 38.5 km in altitude. The flight met its objectives, successfully detecting atmospheric gamma rays and galactic cosmic rays, and raising the Technical Readiness Level from 4 to 6 for large-volume 3D CZT detector technology for space applications. Ionization tracks produced by charged particles create spatial signatures in the detector that are distinguishable from discrete gamma-ray interactions. Therefore, the 3D position-sensing capabilities using pixelated electrodes on a CZT detector can help enable discrimination of background charged particles from gamma-ray events without an anticoincidence shield. The potential for background rejection capability, ambient-temperature operation, gamma-ray coded-aperture and Compton imaging, and near High Purity Germanium (HPGe) energy resolution motivate the use of large-volume 3D CZT imaging spectrometers in future space missions.
46 INSTRUMENTATION RELATED TO NUCLEAR SCIENCE AND ↗
Charged particle radiation exposure of geocentric satellites
The near-earth radiation environment is characterized, summarizing published data on trapped and transient charged particles and their potential effects on hardware systems and the crews of manned missions. Topics examined include the role of the magnetosphere, the five radiation domains, cyclic and sporadic variations in the radiation environment, the potential effect of a high-altitude nuclear explosion, NASA empirical models for predicting trapped proton and electron fluxes, and the South Atlantic anomaly and the estimation of flux-free periods. Consideration is given to solar cosmic rays and heavy ions, Galactic cosmic rays, geomagnetic shielding, secondary radiation, the design of shielding systems, variables affecting dose evaluations, and ionizing-radiation doses. Extensive diagrams, graphs, and tables of numerical data are provided.
Stassinopoulos, E. G.↗
Shielding materials for highly penetrating space radiations
Interplanetary travel involves the transfer from an Earth orbit to a solar orbit. Once outside the Earth's magnetosphere, the major sources of particulate radiation are solar cosmic rays (SCR's) and galactic cosmic rays (GCR's). Intense fluxes of SCR's come from solar flares and consist primarily of protons with energies up to 1 GeV. The GCR consists of a low flux of nuclei with energies up to 10(exp 10) GeV. About 70 percent of the GCR are protons, but a small amount (0.6 percent) are nuclei with atomic numbers greater than 10. High energy charged particles (HZE) interact with matter by transferring energy to atomic electrons in a Coulomb process and by reacting with an atomic nucleus. Energy transferred in the first process increases with the square of the atomic number, so particles with high atomic numbers would be expected to lose large amounts of energy by this process. Nuclear reactions produced by (HZE) particles produce high-energy secondary particles which in turn lose energy to the material. The HZE nuclei are a major concern for radiation protection of humans during interplanetary missions because of the very high specific ionization of both primary and secondary particles. Computer codes have been developed to calculate the deposition of energy by very energetic charged particles in various materials. Calculations show that there is a significant buildup of secondary particles from nuclear fragmentation and Coulomb dissociation processes. A large portion of these particles are neutrons. Since neutrons carry no charge, they only lose energy by collision or reaction with a nucleus. Neutrons with high energies transfer large amounts of energy by inelastic collisions with nuclei. However, as the neutron energy decreases, elastic collisions become much more effective for energy loss. The lighter the nucleus, the greater the fraction of the neutron's kinetic energy that can be lost in an elastic collision. Thus, hydrogen-containing materials such as polymers are most effective in reducing the energy of neutrons. Once neutrons are reduced to very low energies, the probability for undergoing a reaction with a nucleus (the cross section) becomes very high. The product of such a reaction is often radioactive and can involve the release of a significant amount of energy. Thus, it is important to provide protection from low energy neutrons during a long duration space flight. Among the light elements, lithium and boron each have an isotope with a large thermal neutron capture cross section, Li-6 and B-10. However, B-10 is more abundant in the naturally-occurring element than Li-6, has a thermal neutron capture cross section four times that of Li-6, and produces the stable products, He-4 and Li-7 in the interaction while Li-6 produces radioactive tritium (H-3). Thus, boron is the best light-weight material for thermal neutron absorption in spacecraft. The work on this project was focused in two areas: computer design where existing computer codes were used, and in some cases modified, to calculate the propagation and interactions of high energy charged particles through various media, and materials development where boron was incorporated into high performance materials.
Kiefer, Richard L.↗
Confinement and acceleration of cosmic rays in galactic superbubbles
The role of the newly discovered galactic superbubbles on the confinement and acceleration of cosmic rays is examined. It is shown that these structures naturally account for the lifetime and the local origin of the cosmic rays, as well as for the location of galactic gamma-ray sources not associated with pulsars.
Kafatos, M.↗
Two classes of cosmic ray decrease
In a study of galactic cosmic ray intensity variations it had been found that there are two distinct classes of transient intensity decrease, which have been called type I and type II. Type I events are flare-associated Forbush decreases. Type II events appear to be associated with 27-day recurrences. It is suggested, on the basis of several characteristics of the decreases, that type II events are simply the subsequent evolution of type I events or quasi-stationary 'corotating' structures loosely associated with active regions.
Verschell, H. J.↗
The isotopic composition of cosmic ray chlorine
The isotopic composition of galactic cosmic ray chlorine (approx. = 225 MeV/amu) has been studied using the high energy cosmic ray experiment on the International Sun Earth Explorer 3 (ISEE-3) spacecraft. The abundances of 35C1 and 37C1 are found to be consistent with the secondary production expected from a propagation model developed to account for both light and subiron secondaries. An upper limit on the abundance of the radioactive isotope 36C1 (halflife approx. = 0.3 Myr) is used to set a lower limit on the confinement time of cosmic rays of approximately 1 Myr.
Wiedenbeck, M. E.↗
Galactic cosmic-ray intensity 0.99 to 5.26 astronomical units from the sun
The intensity of galactic cosmic radiation in interplanetary space has been observed over the heliocentric radial range 0.99 to 5.26 AU with five Geiger-Mueller tubes on Pioneer 10 and over the range 1.00 to 3.59 AU with three similar tubes on Pioneer 11. The observations span the time period 1972 March 3 to 1974 April 29, near the epoch of minimum solar activity. The contributions of solar energetic particles are eliminated. The effect of temporal trends is removed in a variety of ways - by comparison of simultaneous measurements on the two spacecraft; by comparison with data from Explorer 35 at 1.0 AU; and by comparison with terrestrial neutron monitor data. The radial gradient of the intensity of particles with energies greater than 80 MeV/nucleon is zero to within an experimental uncertainty of less than 2 per cent per AU over the range 0.99 to 5.26 AU. Hence, it is less than the theoretically expected value by at least a factor of 5.
Thomsen, M. F.↗
Cosmic rays and their formation of a galactic halo.
Cosmic rays leading to inflation of galactic magnetic fields produce halo of cosmic rays and field around galaxy
COSMIC RADIATION↗
Comment on 'The origin of transient cosmic ray intensity variations' by S. P. Duggal and M. A. Pomerantz
Transient Forbush decreases in galactic cosmic ray intensity have generally been linked to interplanetary shocks and solar flares. However, Duggal and Pomerantz (1977) have concluded that the majority of transient intensity variations of galactic cosmic rays cannot be assigned directly to specific solar flares. The object of the present paper is to show that the observations of Duggal and Pomerantz are in fact consistent with the solar flare origin of most transient cosmic ray reductions (i.e., with the solar flare hypothesis). The consistency of the Duggal-Pomerantz observations with the flare hypothesis is demonstrated on the basis of a statistical model of modulation which reproduces the essential features of their observations. In response to the present analysis (by Parker), Duggal and Pomerantz have presented additional arguments to the effect that the majority of transient intensity modifications (not necessarily Forbush decreases) during the period 1964-1974 were indeed related to the central meridian passage of active centers rather than to any other visible solar feature.
Parker, G. D.↗
Cosmic-ray variations and magnetic field fluctuations in the outer heliosphere
We have formally confirmed that galactic cosmic ray intensity variations measured by Voyager 2 during recovery from solar maximum are caused by travelling compressions and rarefactions in the mean interplanetary magnetic field. We used Voyager's nearly continuous magnetic field data as input to a time-independent, spherically-symmetric, cosmic ray transport equation in the force-field approximation. The solutions closely followed the count rate of cosmic rays greater than 75 MeV/nucleon over four years. This strongly supports prior theoretical assertions that turbulent interaction regions travelling with the solar wind are the major cause of the solar-cycle variation of galactic cosmic rays in the ecliptic region.
Perko, J. S.↗
Interstellar propagation of galactic cosmic-ray nuclei 2 less than or equal to Z less than or equal to 8 in the energy range 10 to 1000 MeV per nucleon.
Analysis of the differential kinetic energy per nucleon spectra of galactic cosmic-ray He, Li, Be, B, C, N, and O with the University of Chicago cosmic-ray telescope on board the IMP-5 satellite in 1969-1970. The ratios He/(C + N + O) and (Li + Be + B)/(C + N + O) obtained from these spectra are found, within errors of about 20%, to be energy-independent over the energy range 10-1000 MeV per nucleon, and equal to about 15 and about 0.25, respectively. These results are compared with discrepancies existing among other measurements of these ratios, and with predictions of a class of steady-state models of cosmic-ray propagation which assume that Li, Be, and B are absent in cosmic-ray sources. The best fits for the present measurements are obtained for models with a source spectrum in the form of a power law in total energy per nucleon, but even these fits are outside the error limits at energies below 100 MeV per nucleon. In the context of the propagation models examined, it is concluded that the observed behavior of these ratios requires an additional mechanism operative at low energies. This mechanism may be adiabatic deceleration of cosmic rays in the solar wind. In order for this mechanism to be adiabatic deceleration, the deceleration in 1969 must have been such that particles observed at 10 to 20 MeV per nucleon had energies greater than 100 to 150 MeV per nucleon in the local interstellar space.
Mason, G. M.↗