Showing papers on "Proton published in 1976"

Nuclear Fireball Model for proton inclusive spectra from relativistic heavy-ion collisions

Abstract: A simple model is proposed for the emission of nucleons with velocities intermediate between those of the target and projectile. In this model, the nucleons which are mutually swept out from the target and projectile form a hot quasiequilibrated fireball which decays as an ideal gas. The overall features of the proton-inclusive spectra from 250- and 400-MeV/nucleon $^{20}\mathrm{Ne}$ ions and 400-MeV/nucleon $^{4}\mathrm{He}$ ions interacting with uranium are fitted without any adjustable parameters.

Efficiencies for production of atomic nitrogen and oxygen by relativistic proton impact in air

Abstract: Relativistic electron and proton impact cross sections are obtained and represented by analytic forms which span the energy range from threshold to 109 eV. For ionization processes, the Massey–Mohr continuum generalized oscillator strength surface is parametrized. Parameters are determined by simultaneous fitting to (1) empirical data, (2) the Bethe sum rule, and (3) doubly differential cross sections for ionization. Branching ratios for dissociation and predissociation from important states of N2 and O2 are determined. The efficiency for the production of atomic nitrogen and oxygen by protons with kinetic energy less than 1 GeV is determined using these branching ratio and cross section assignments.

Ion beam surface layer analysis

Abstract: of Volume 1.- I. Energy Loss and Straggling.- The Treatment of Energy-Loss Fluctuations in Surface-Layer Analysis by Ion Beams.- Evidence of Solid State Effects in the Energy Loss of 4He Ions in Matter.- Empirical Stopping Cross Sections for 4He Ions.- Determination of Stopping Cross Sections by Rutherford Backscattering.- Depth Profiling of Implanted 3He in Solids by Nuclear Reaction and Rutherford Backscattering.- Energy Loss Straggling of Protons in Thick Absorbers.- Energy Dependence of Proton Straggling in Carbon.- Energy Straggling of 4He Ions in Al and Cu in the Backscattering Geometry.- Energy Spreading Calculations and Consequences.- Analysis of Nuclear Scattering Cross Sections by Means of Molecular Ions.- II. Backscattering Analysis.- Determining Concentration vs. Depth Profiles from Backscattering Spectra without Using Energy Loss Values.- Comparative Analysis of Surface Layers by Backscattering and by Auger Electron Spectroscopy.- Analyzing the Formation of a Thin Compound Film by Taking Moments on Backscattering Spectra.- Computer Analysis of Nuclear Backscattering.- Some Practical Aspects of Depth Profiling Gases in Metals by Proton Backscattering: Application to Helium and Hydrogen Isotopes.- Depth Profiling of Deuterium and Helium in Metals by Elastic Proton Scattering: A Measurement of the Enhancement of the Elastic Scattering Cross Section over Rutherford Scattering Cross Section.- Near-Surface Investigation by Backscattering of N+ Ions and Grazing Angle Beam Incidence.- The Application of Low Angle Rutherford Backscattering to Surface Layer Analysis.- Measurement of Projected and Lateral Range Parameters for Low Energy Heavy Ions in Silicon by Rutherford Backscattering.- Range Parameters of Heavy Ions in Silicon and Germanium with Reduced Energies from 0.001 ? ? ? 10.- On Problems of Resolving Power in Rutherford Backscattering.- Studies of Surface Contaminations, Composition and Formation of Superconducting Layers of V, Nb3Sn and of Tunneling Elements Using High Energetic Protons Combined with Heavy Ions.- Determination of Implanted Carbon Profiles in NbC Single Crystals from Random Backscattering Spectra.- Pore Size from Resonant Charged Particle Backscattering.- Measurement of Thermal Diffusion Profiles of Gold Electrodes on Amorphous Semiconductor Devices by Deconvolution of Ion Backscattering Spectra.- Enhanced Sensitivity of Oxygen Detection by the 3.05 MeV (?,?) Plastic Scattering.- Progress Report on the Backscattering Standards Project (Abstract).- III. Applications of Backscattering and Combined Techniques.- Ion Beam Studies of Thin Films and Interfacial Reactions.- Studies of Tantalum Nitride Thin Film Resistors.- Investigation of CVD Tungsten Metallizations on Silicon by Backscattering.- Ion Beam Analysis of Aluminium Profiles in Heteroepitaxial Ga1-xAlxAs-Layers.- Analysis of Ga1-xA1xAs-GaAs Heteroepitaxial Layers by Proton Backscattering.- Interdiffusion Kinetics in Thin Film Couples.- Backscattering and T.E.M. Studies of Grain Boundary Diffusion in Thin Metal Films.- The Analysis of Nickel and Chromium Migration Through Gold Layers.- Applications of Ion Beam Analysis to Insulators.- Lithium Ion Backscattering as a Novel Tool for the Charac terization of Oxidized Phases of Aluminum Obtained from Industrial Anodization Procedures.- Investigation of an Amino Suger-Like Compound from the Cell Walls of Bacteria Using Backscattering of MeV Particles.- IV. Equipment.- Versatile Apparatus for Real-Time Profiling of Interacting Thin Films Deposited in Situ.- Application of a High-Resolution Magnetic Spectrometer to Near-Surface Materials Analysis.- Rutherford Backscattering Analysis with Very High Depth Resolution Using an Electrostatic Analysing System.- An Apparatus for the Study of Ion and Photon Emission from Ion Bombarded Surfaces: I. Some Preliminary Results.- Author Index.

Observations of magnetospheric bursts of high-energy protons and electrons at ∼35 RE with Imp 7

Abstract: A detailed study of energetic (Ep ≳ 0.29 MeV; Ee ≳ 0.22 MeV) proton and electron bursts in the vicinity of the magnetosphere over a 1-year period (day 270 of 1972 to day 270 of 1973) using the Johns Hopkins University/Applied Physics Laboratory (JHU/APL) experiment on board the near-circular (∼32 RE by ∼38 RE) orbiting Explorer 47 (Imp 7) satellite has been performed with greater sensitivity (jp ≳ 10−2 cm−2 s−1 sr−1 MeV−1) than has previously been possible at these energies. The results reveal that bursts of electrons and protons at these energies are a semipermanent feature of the near-earth environment both within and outside the magnetotail with intensities ranging from 10−2 to 104 (cm² s sr MeV)−1 for protons and 0.5 to 5 × 10³ (cm² s sr)−1 for electrons and energies up to 4.5 MeV and >1 MeV for protons and electrons, respectively. The proton energy spectrum is soft and characterized by spectral indices 5 ≲ γ ≲ 7. The bursts are found in and about the magnetosheath, plasma sheet, and magnetotail boundary layer and outside the bow shock; however, they rarely appear at large distances (≳ 10 RE) north or south of the neutral sheet. Dawn-dusk asymmetries are present in intensity (most intense proton bursts occur in the dusk magnetotail) but not necessarily in frequency of occurrence. Proton bursts are highly anisotropic (typical amplitude C ≳ 1) upstream from the bow shock and in the magnetosheath (moving away from the earth). In the magnetotail, proton anisotropies are somewhat reduced and are directed either toward or away from the earth but with a substantial dawn to dusk component. Electron bursts are anisotropic (and field aligned) only in the upstream solar wind, where differences in the proton and electron anisotropy vectors can exceed 90°. A unique class of ‘impulsive’ bursts has been identified in the dusk magnetotail having intensities of up to 105 (cm² s sr MeV)−1, a duration of 10–30 s, and field-aligned anisotropies of up to 5 × 104 to 1 (sunward to antisunward ratio) and exhibiting inverse velocity dispersion (i.e., low-energy protons arrive before higher-energy ones). No electrons are observed in association with these bursts. The observed bursts are consistent with a nonthermal origin, in association with other magnetospheric phenomena. The implications of the results with regard to the origin of the bursts, acceleration mechanisms, and magnetospheric processes in general are discussed.

Evidence for interplanetary acceleration of nucleons in corotating interaction regions

Abstract: Simultaneous measurements of protons and helium in the energy range 0.5-2 MeV per nucleon on IMP-8 (at 1 AU) and Pioneer-10 and Pioneer-11 (between 1 and 8 AU) have revealed a correlation which develops beyond about 2.5 AU between the positions of double peaks in recurring proton intensity increases and the leading and trailing edges of recurring regions of fast solar wind streams and enhanced magnetic field. From these correlations and the study of energy spectra and the proton-to-helium abundance ratios, it is concluded that there is local acceleration of nucleons, probably near the boundary regions where shocks are observed, even if the nucleons are injected initially at the sun.

Deep Inelastic Scattering of Polarized Electrons by Polarized Protons

Abstract: We report measurements of the asymmetry in deep inelastic scattering of longitudinally polarized electrons by longitudinally polarized protons. The antiparallel-parallel asymmetries are positive and large in agreement with predictions of quark-parton models of the proton. A limit is obtained on parity nonconservation in the scattering of longitudinally polarized electrons by unpolarized nucleons.

Protein rotational relaxation as studied by solvent 1H and 2H magnetic relaxation.

Abstract: Earlier studies of the magnetic field dependence of the nuclear spin magnetic relaxation rate of solvent protons in solutions of diamagnetic proteins have indicated that this dependence (called relaxation dispersion) is related to the rotational Brownian motion of solute proteins. In essence, the dispersion is such that 1/T1 (the proton spin-lattice relaxation rate) decreases monotonically as the magnetic field is increased from a very low value (approximately 10 Oe); the dispersion has a point of inflection at a value of magnetic field which depends on protein size, shape, concentration, temperature, and solvent composition. The value of the proton Larmor precession frequency nu(c) at the inflection field appears to relate to tau (R), the rotational relaxation time of the protein molecules. We have measured proton relaxation dispersions for solutions of various proteins that span a three-decade range of molecular weights, and for one sample of transfer ribonucleic acid. We have also measured deuteron relaxation dispersions for solutions of three proteins: lysozyme, carbonmonoxyhemoglobin, and Helix pomatia hemocyanin with molecular weight 900 000. A quantitative relationship between both proton and deuteron dispersion data and protein rotational relaxation is confirmed, and the point is made that magnetic dispersion measurements are of very general applicability for measuring the rotational relaxation rate of macromolecules in solution. It has been previously shown that the influence of proton motion on the relaxation behavior of the solvent is not due to exchange of solvent molecules between the bulk solvent and a hydration region of the protein. In the present paper, we suggest that the interaction results from a long range hydrodynamic effect fundamental to the situation of large Brownian particles in an essentially continuum fluid. The general features of the proposed mechanism are indicated, but no theoretical computations are presented.

Screening of a proton in an electron gas

Abstract: Calculations are reported of the nonlinear screening of a proton in an electron gas of densities corresponding to rs=1-6. Results for charge densities and total energies are presented from self-consistent Kohn-Sham ground-state calculations. The results differ markedly from the case of linear screening, particularly at low densities. The occurrence of a bound state around the proton for rs>1.9 indicates that hydrogen in jellium is in the form of a screened H- ion. It is also found that at metallic densities the induced polarization around the proton is insensitive to rs, and the screening length is almost constant (0.65) for 2

Theoretical studies of magnetic shielding in H2O and (H2O)2

Abstract: Magnetic shielding constants are calculated for the nuclei in H2O and (H2O)2 using a slightly extended$set of atomic functions modified by gauge factors. Calculated shielding results for the theoretical equilibrium structures of H2O and (H2O)2 lead to a value for the hydrogen bond shift of −2.95 ppm, which is in reasonable agreement with the available experimental data. The anisotropy of the magnetic shielding tensor associated with the hydrogen bonded proton is found to increase by 12 ppm on dimer fromation. This suggestes that proton magnetic shielding anisotropies may be more sensitive to features of hydrogen bonding than are isotropic values. An analysis of the theoretical results reveals that the downfield hydrogen bond shift arises (a) from a decrease of the electronic charge on the hydrogen bonded proton, and (b) from deshielding effects of the currents induced on the oxygen atom of the porton acceptor by the external magnetic field. For (H2O)2 these two types of contribution are of equal importance. The latter type of contribution (b) is found to be almost tottally responsible for the anisotropy changes produced on dimer formation. The sensitivity of the shielding tensor associated with the hydrogen bonded proton to changes in the intermolecular geometrical parameters of (H2O)2 is examined. The calculatted isotropic and anisotropic values of thius tensor show large changes of the O⋅⋅⋅O distance%is reduced below 3.5 A. In contrast, the sensitivity of this shielding tensor to the relative orientation of the water monomers in (H2O)2 is quite small. Finally, the results of relaxing the geometry of the proton donor are reported. The isotropic value of the shielding at the hydrogen bonding proton is found to decrease markedly as the O−H distance of O−H⋅⋅⋅O is increased slightly from its equilibrium value.

Measured radial distributions of dose and LET for alpha and proton beams in hydrogen and tissue-equivalent gas.

Abstract: Experimental measurements of the radial distribution of dose and radially restricted linear energy transfer (L/sub r/) are reported for alpha and proton beams of 1 to 3 MeV from a Van de Graaff accelerator. The method employs a large cylindrical ionization chamber filled with tissue-equivalent gas (or hydrogen) at variable low pressure for L/sub r/ measurement. For radial dose determination, a small movable ionization chamber of transparent mesh located inside the large cylinder is used to measure ionization by secondary electrons around the charged particle beam. Results are presented for simulated tissue radii from about 10 A to a few thousand angstroms. Comparison of the measured dose distributions with recent calculations by H. G. Paretzke indicates fair agreement except for large radii, where the local energy deposition is a small part of the total. (auth)

The inconsistency between proton charge exchange and the observed ring current decay

Abstract: The equatorial pitch-angle distributions of ring-current ions observed during a storm recovery phase at L values between 3 and 4 are compared with the pitch-angle distributions predicted by proton charge exchange with neutral hydrogen. Large disagreements are found, and three alternative explanations are explored. (1) A strong proton source acts to mask the effects of charge exchange. It is believed that the required strong continual source with a unique pitch-angle and energy dependence is unrealistic at these low L values. (2) Presently accepted neutral hydrogen density models have densities well over an order of magnitude too large for a storm recovery phase. No evidence is known to support the required large errors in the densities. (3) The ring current at particle energies not exceeding 50 keV was dominated by some ion species other than protons during the storm recovery phase. Such ions must have much longer lifetimes for charge exchange with hydrogen than do protons. This alternative is strongly favored, with He(+) being an attractive candidate.

Physical studies on the H3/H4 histone tetramer.

Abstract: High-resolution proton magnetic resonance spectroscopy (270 MHz), circular dichroism, and infrared spectroscopies and ultracentrifugation studies have been carried out on the salt-extracted (H3/H4)2 tetramer from calf thymus. The tetramer contains about 29% alpha helix and no beta structure. It is denatured in 6 M urea but can be renatured simply by dialysis to water. The proton spectrum shows a number of perturbed resonances which are not observed in the spectra of either H3 or H4 alone. The observation of these resonances demonstrates that the tetramer contains some elements of tertiary structure. The overall appearance of the spectrum however is close to that of a partially denatured protein. Sedimentation velocity studies show the tetramer to have a frictional ratio of 1.99 in 50 mM acetate/50 mM bisulfite and thus to be hydrodynamically quite different from a globular protein. Two possible structural models compatible with the data are discussed.

Mechanism for 180° Proton Production in Energetic Proton-Nucleus Collisions

Abstract: The energetic protons seen at 180\ifmmode^\circ\else\textdegree\fi{} in 600- and 800-MeV proton-nucleus collisions by Frankel et al. are accounted for by a single-scattering mechanism that incorporates a new phenomenological form for the momentum distribution in the nucleus.

Dimensionality of spin fluctuations in highly anisotropic TCNQ salts

Abstract: An anisotropic three‐dimensional random walk model is developed and used to describe the frequency dependence of proton spin–lattice relaxation rates in several TCNQ salts. The triplet exciton system (φ3AsCH3) (TCNQ)2 at 145 °K is shown to display two‐dimensional diffusive behavior. Measurements of the proton relaxation rate in NMP–TCNQ at room temperature are reported and interpreted as displaying two‐dimensional diffusive behavior with a transition to three‐dimensional behavior. These results suggest that the nuclear resonance time scale is so long as to preclude observing one‐dimensional behavior even in highly anisotropic one‐dimensional systems. The random walk model is extended to display the dependence of relaxation rate upon charge transfer and thus explain the unusually rapid relaxation in NMP–TCNQ.

Early Irradiation of Matter in the Solar System: Magnesium (Proton, Neutron) Scheme

Abstract: The occurrence of positive and negative 26Mg anomalies in inclusions of the Allende meteorite is explained in terms of proton bombardment of a gas of solar composition. A significant fraction of 26Mg in the irradiated gas is stored temporarily in the form of radioactive 26Al by the reaction 26Mg(p,n) 26Al. Proton fluxes of 1017 to 1019 protons per square centimeter per year at l million electron volts are inferred. Aluminum-rich materials condensing from the gas phase have positive 26Mg anomalies, whereas magnesium-rich materials have negative 26Mg anomalies. The proton flux required to account for the observed magnesium anomalies is used to investigate possible isotopic anomalies in the elements from oxygen to argon. Detectable isotopic anomalies are predicted only for neon. The anomalous neon is virtually pure 22Ne from 22Na decay. The predicted amount of anomalous 22Ne is about 10–8 cubic centimeter (at standard temperature and pressure) per milligram of sodium.