Showing papers on "Proton published in 1986"

Binary collision rates of relativistic thermal plasmas. II: Spectra

Abstract: Spectra of importance for the analysis of relativistic thermal plasmas are numerically calculated assuming a thermal form for the particle distribution functions. Complete sets of optically thin thermal electron-proton, electron-electron, and electron-positron bremsstrahlung spectra are calculated throughout the transrelativistic regime of electron temperatures and compared with approximate expressions for the spectra in the nonrelativistic and extreme relativistic regimes of temperature. A method for calculating accurate secondary particle production spectra in proton-proton collisions from threshold to the highest energies is presented based on an isobaric model near threshold and scaling representations at high energies. The production spectra of charged and neutral pions resulting from proton-proton collisions in relativistic proton plasmas are calculated, and the resultant electron, positron, and gamma-ray spectra from the decay of secondary pions are presented.

Energy Dependence of Proton-Induced Displacement Damage in Silicon

Abstract: Calculations of nonionizing energy deposition in silicon as a function of proton energy between 1-1000 MeV have been reviewed, a new calculation made, and the results compared with experimental data. Major observations are the following: 1) Only one of the calculations reported in the literature was found to contain all of the interactions necessary to qualitatively and quantitatively describe the energy dependence over the full energy range. 2) The new calculation agreed well with the single complete calculation using different input data and an approach that differed in detail. 3) The two complete calculations and the experimental data were not found to support the frequently reported "plateau" in damage production or energy loss at proton energies above 10 MeV. 4) An extensive set of experimental solar cell data (1-200 MeV) showed an almost perfect linear dependence of the silicon damage coefficient for diffusion length on nonionizing energy deposition. 5) New measurements of bipolar transistor displacement damage factors were also found to exhibit a similar dependence. 6) Ratios of proton energy loss to neutron energy loss compared well with experimental ratios of displacement damage factors.

Single and double ionization of helium by fast antiproton and proton impact.

Abstract: The first ion-atom--collision data obtained with antiprotons are presented. We measured the single- and double-ionization cross section for 0.5-5-MeV antiprotons and protons colliding with helium. For ion energies above --2 MeV, the single-ionization cross section is the same for protons and antiprotons. However, surprisingly, the double-ionization cross section for antiprotons is approximately a factor of 2 larger than that for protons. The present data constitute a challenge for future theoretical models of charged-particle--atom collisions.

Hydration dynamics of protons from photon initiated acids

Abstract: Proton transfer from the excited states of 1-naphthol and 2-naphthol to the water solvent is studied in water/alcohol mixtures. In pure water, the deprotonation rate of 1-naphthol is insensitive to temperature (..delta..H* approx. O), while that of 2-naphthol exhibits an activation energy of about 2600 cal mol/sup -1/. The deprotonation rates in both molecules decrease nonlinearly as the alcohol concentration increases, becoming effectively zero in pure alcohol. Variation of solvent concentrations in the mixed solvent thus serves as a probe for studying the local reaction environment. Using a Markov random walk theory, a water cluster, (H/sub 2/O)/sub 4 +/- 1/, is identified as the effective acceptor for both molecules, indicating that the structure H/sub 9/O/sub 4//sup +/ plays a direct role in the proton hydration dynamics. At high water concentrations the proton hydration rate is reaction controlled while at high alcohol concentrations it can become diffusion controlled. Proton transfer dynamics in the naphthol systems are similar to the dynamics measured for electron photoionization into water, with the rates having low or zero activation barrier but being entropically inhibited to various degrees. The approx. 1:3 deuterium effect on the rates is in fact derived almost entirely from entropic considerations. A correspondencemore » between the thermodynamic quantities ..delta..H/sup 0//sub i/ and ..delta..S/sup 0//sub i/ and the rate parameters ..delta..H/sup + +/ and ..delta..S/sup + +/ for acid dissociation processes is suggested.« less

A test of Lee's quasi-linear theory of ion acceleration by interplanetary traveling shocks

Abstract: Lee's (1983) quasi-linear theory of ion acceleration is tested using ISEE-3 measurements of the November 12, 1978 quasi-parallel interplanetary shock. His theory accounts with varying degrees of precision for the energetic proton spatial profiles; the dependence of the spectral index of the power law proton velocity distribution upon the shock compression ratio; the power law dependence of the upstream proton scalelength upon energy; the absolute magnitude of the upstream proton scale length; the behavior of the energetic proton anisotropy upstream and downstream of the shock; the behavior of the alpha-particle proton ratio upstream; the equality of the spatial scale lengths at the shock of the upstream waves and of the protons that resonate with them; and the dependence of the integrated wave energy density upon the proton energy density at the shock. However, the trace magnetic field frequency spectra disagree with his theory in two ways. The part of the spectrum that can resonate with the observed protons via first-order cyclotron resonance is flat, whereas Lee's theory predicts an f exp - 7/4 frequency dependence for the November 12 shock. Higher frequency waves, which could not resonate with the observed upstream protons, increased in amplitude as the shock approached, suggesting that they too were generated by the shock.

Energetic photons from intermediate energy proton- and heavy-ion-induced reactions

Abstract: The cross section for emitting high energy gamma rays in heavy-ion collisions is calculated in a model based on the Boltzmann-Uehling-Uhlenbeck equation. The elementary production cross section is assumed to be neutron-proton bremsstrahlung. Comparison is made with experimental data at bombarding energies from 20 to 84 MeV/nucleon. The calculations are found to roughly reproduce the energy spectrum, bombarding energy dependence, and angular distribution. From the numerical analysis we conclude that the production of high-energy \ensuremath{\gamma} rays is limited to the very early stage of the collision.

Measurement of elastic electron scattering from the proton at high momentum transfer.

Abstract: We have performed absolute measurements of the differential cross section for elastic e−p scattering in the range of momentum transfer from Q2=2.9 to 31.3 (GeV/c)2. Combined statistical and systematic uncertainties in the cross-section measurements ranged from 3% at low Q2 to 19% at high Q2. These data have been used to extract the proton magnetic form factor GMp(Q2). The results show a smooth decrease of Q4GMp with momentum transfer above Q2=10 (GeV/c)2. These results are compared with recent predictions of perturbative QCD.

Structural characterization of proton exchanged LiNbO3 optical waveguides

Abstract: This paper reports the results of structural analysis of proton‐exchanged lithium niobate optical waveguides fabricated in Z‐, X‐, and Y‐cut substrates immersed in pure benzoic acid Rutherford backscattering spectrometry, nuclear reactions, secondary ion mass spectrometry, scanning electron microscopy, and x‐ray diffraction were used to measure atomic composition profiles and the marked lattice distortion induced by the proton exchange process in the waveguiding layer H and Li concentration measurements indicate an exchange of about 70% of the Li atoms are present in the virgin LiNbO3 crystal

The magnetosphere of Uranus: Hot plasma and radiation environment

Abstract: Inferences are drawn on the morphology and composition of the Uranus magnetosphere based on low-energy charged particle data collected by Voyager 2. Proton and electron energies in the magnetosphere attained energies of 4 and 1.2 MeV, respectively, although electron intensities surpassed the proton intensities at most energy levels. Protons dominated in the ion energy regime 0.6-1.0 MeV. The ion and electron spectra were Maxwellian below about 200 keV and had a power law distribution at energies over 590 keV. The power law was reduced by a factor of nearly three inside the orbit of Miranda. The proton population is dense enough to polymerize CO and CH4 ice surfaces within 10,000-100,000 yr. The data indicated that the particles are swept out at least to the orbit of Titania by the satellites. The morphology of the magnetosphere closely resembles that around Jupiter, except that plasma sheet distorsion from particle loading is negligible in regions within 15 Uranus radii.

Angular and energy dependence of cross sections for ejection of electrons from water vapor. II. 15--150-keV proton impact

Abstract: Absolute values of cross sections for electron ejection by protons of 15--150 keV energy have been measured as a function of the angle and energy of the electrons. The range of angles was 10\ifmmode^\circ\else\textdegree\fi{} to 160\ifmmode^\circ\else\textdegree\fi{} and the electron energy range was 1--300 eV. The doubly differential cross sections were also integrated over energy or angle to obtain singly differential and total cross sections and also average ejected electron energies. Good agreement is obtained with Senger's DDCS-MT (doubly differential cross section--mixed treatment) theoretical treatment using the Salin factor.

Ab initio determination of the proton affinities of small neutral and anionic molecules

Abstract: The proton affinity of a molecule in the gas phase is a fundamental measure of its basicity and is the factor controlling the course of many ion-molecule reactions. In this article, ab initio molecular orbital theory at the MP4/6-311 ++ G(3df, 3pd) level of theory is demonstrated to predict proton affinities (PA's) for small neutral and anionic bases to within 2 kcal mol-1. Furthermore, the errors are random, indicating that there are likely no systematic errors in either the experimental or theoretical PA's. Also, this level of theory is used to calibrate less sophisticated theoretical models which are suitable for larger molecules; the MP4/6-311 ++ G(2d, 2p) and MP2/6-311 ++ G(d, p) theoretical models should be particularly useful. A procedure for predicting the vibrational frequencies for anion is proposed and applied to CH3-, NH2-, OH-, and CN-.

Axion bremsstrahlung by an electron beam

Abstract: Compact expressions for energy-angle distribution and energy distribution for axion from electron scattering on an atomic target are derived using the generalized Weizsacker-Williams method. The axion flux from an electron beam dump is estimated. It is also shown that even in a proton beam dump, the mechanism of producing axions is still predominantly due to electrons in the dump.

Localized lifetime control in insulated-gate transistors by proton implantation

Abstract: The application of localized carrier lifetime control to power devices is explored. A new type of power device, the insulated-gate transistor, was chosen for this study. Proton implantation was used as an agent of lifetime control by varying energy (1 to 3.8 MeV) and dose. Most of the proton damage in silicon, and therefore most of the lifetime reduction, occurs near the proton end-of-range, resulting in a localized band of low lifetime. Proton energy determines the depth at which the region of minimum lifetime is placed within the device structure. The effect of localized lifetime reduction on forward voltage, turn-off time, and leakage current was studied. The results lead to an understanding of the proper choice of depth at which to place a region of low lifetime, and illustrate the advantages of localization. With this choice, a significantly better tradeoff curve of forward voltage versus turn-off time is shown to be realized with proton implantation compared to the unlocalized but common technique of electron irradiation.

Biological effectiveness of low energy protons. I. Survival of Chinese hamster cells.

Abstract: SummaryThe biological effectiveness of monoenergetic protons was investigated with the track-segment method. Protons were accelerated by a Tandem Van de Graaff accelerator and their final energies were 3·0 and 7·4 MeV. The biological system used was Chinese hamster V-79 cells and their survival ability following proton irradiation was investigated. Cobalt-60 γ-rays were used as reference radiation to assess proton relative biological effectiveness (RBE). Survival curves were obtained for the γ-ray and proton irradiations, and the relation S = exp (−αD − βD2) was fitted to the data and the parameters α and β were determined. The RBE values, calculated on the basis of the mean inactivation dose D¯ and other pertinent parameters, were found to be 1·7 ± 0·1 and 2·8 ± 0·2 for 7·4 and 3·0 MeV protons, respectively. Comparisons were made with the results published by other investigators and it was concluded that in this low energy range the biological effectiveness increases substantially with decreasing proton ...