Proton

About: Proton is a research topic. Over the lifetime, 31263 publications have been published within this topic receiving 573472 citations. The topic is also known as: p & ¹H⁺.

PAMELA Measurements of Cosmic-Ray Proton and Helium Spectra

Abstract: Protons and helium nuclei are the most abundant components of the cosmic radiation Precise measurements of their fluxes are needed to understand the acceleration and subsequent propagation of cosmic rays in our Galaxy We report precision measurements of the proton and helium spectra in the rigidity range 1 gigavolt to 12 teravolts performed by the satellite-borne experiment PAMELA (payload for antimatter matter exploration and light-nuclei astrophysics) We find that the spectral shapes of these two species are different and cannot be described well by a single power law These data challenge the current paradigm of cosmic-ray acceleration in supernova remnants followed by diffusive propagation in the Galaxy More complex processes of acceleration and propagation of cosmic rays are required to explain the spectral structures observed in our data

Optical-Model Analysis of Proton Elastic Scattering in the Range of 9 to 22 MeV

Abstract: For incident proton energies between 9 to 22 Mev, 35 elastic scattering angular distributions were analyzed with the optical model using a least-square criteria over the complete angular range of the data. The observed increase of the real well depth as a function of mass number is explained by the presence of a nuclear symmetry term in the potential and by the momentum dependence of the potential. The polarization and reaction cross-section data are in good agreement with the calculations. The effect of core excitations on the parameters of the optical model are studied, and the relative importance of volume and surface imaginary potentials is discussed. Formulas are given to obtain the value of the parameters of the optical model as a function of mass number and energy. (auth)

Detection of the characteristic pion-decay signature in supernova remnants

Abstract: Cosmic rays are particles (mostly protons) accelerated to relativistic speeds. Despite wide agreement that supernova remnants (SNRs) are the sources of galactic cosmic rays, unequivocal evidence for the acceleration of protons in these objects is still lacking. When accelerated protons encounter interstellar material, they produce neutral pions, which in turn decay into gamma rays. This offers a compelling way to detect the acceleration sites of protons. The identification of pion-decay gamma rays has been difficult because high-energy electrons also produce gamma rays via bremsstrahlung and inverse Compton scattering. We detected the characteristic pion-decay feature in the gamma-ray spectra of two SNRs, IC 443 and W44, with the Fermi Large Area Telescope. This detection provides direct evidence that cosmic-ray protons are accelerated in SNRs.

The nature and transport mechanism of hydrated hydroxide ions in aqueous solution

Abstract: Compared to other ions, protons (H+) and hydroxide ions (OH-) exhibit anomalously high mobilities in aqueous solutions1. On a qualitative level, this behaviour has long been explained by ‘structural diffusion’—the continuous interconversion between hydration complexes driven by fluctuations in the solvation shell of the hydrated ions. Detailed investigations have led to a clear understanding of the proton transport mechanism at the molecular level2,3,4,5,6,7,8. In contrast, hydroxide ion mobility in basic solutions has received far less attention2,3,9,10, even though bases and base catalysis play important roles in many organic and biochemical reactions and in the chemical industry. The reason for this may be attributed to the century-old notion11 that a hydrated OH- can be regarded as a water molecule missing a proton, and that the transport mechanism of such a ‘proton hole’ can be inferred from that of an excess proton by simply reversing hydrogen bond polarities11,12,13,14,15,16,17,18. However, recent studies2,3 have identified OH- hydration complexes that bear little structural similarity to proton hydration complexes. Here we report the solution structures and transport mechanisms of hydrated hydroxide, which we obtained from first-principles computer simulations that explicitly treat quantum and thermal fluctuations of all nuclei19,20,21. We find that the transport mechanism, which differs significantly from the proton hole picture, involves an interplay between the previously identified hydration complexes2,3 and is strongly influenced by nuclear quantum effects.