Results 1 - 10 of 4348
Results 1 - 10 of 4348. Search took: 0.033 seconds
|Sort by: date | relevance|
[en] Cosmic-ray proton and helium spectra have been measured with the balloon-borne Cosmic Ray Energetics And Mass experiment flown for 42 days in Antarctica in the 2004-2005 austral summer season. High-energy cosmic-ray data were collected at an average altitude of ∼38.5 km with an average atmospheric overburden of ∼3.9 g cm-2. Individual elements are clearly separated with a charge resolution of ∼0.15 e (in charge units) and ∼0.2 e for protons and helium nuclei, respectively. The measured spectra at the top of the atmosphere are represented by power laws with a spectral index of -2.66 ± 0.02 for protons from 2.5 TeV to 250 TeV and -2.58 ± 0.02 for helium nuclei from 630 GeV nucleon-1 to 63 TeV nucleon-1. They are harder than previous measurements at a few tens of GeV nucleon-1. The helium flux is higher than that expected from the extrapolation of the power law fitted to the lower-energy data. The relative abundance of protons to helium nuclei is 9.1 ± 0.5 for the range from 2.5 TeV nucleon-1 to 63 TeV nucleon-1. This ratio is considerably smaller than the previous measurements at a few tens of GeV nucleon-1.
[en] The structure of particle populated regions approximately 200 Rsub(E) upstream from the Earth's bow shock is investigated using three-dimensional low-energy proton observations in the energy range 35-1600 keV onboard ISEE-3. The structure of the regions reveals itself at the onsets and ends of upstream proton events when the boundaries of the regions are carried past the spacecraft by the solar wind. During such crossings we observe i) a characteristic change in the energy spectrum which in some cases is a turnover towards lower energies and ii) characteristic gradient anisotropies which are directed oppositely to each other at the onset and end of the event. These observations are consistent with a model where upstream particles propagate in sheets or slabs from the Earth's bow shock out to ISEE-3
[en] Protons from 252Cf fission have been studied to determine their origin by using a ΔE, E detector particle telescope. Both fission- and nonfission-related events are discussed as possible sources of the observed proton energy spectrum. The increased yield of low-energy protons, which peak at approximately 3.2 MeV, seems to be due mainly to background (α,p) reactions. Evidence of polar proton emission is discussed and gives an estimated polar proton emission yield of 2.83 +- 0.18 x 10-5 per fission, with a most probable energy of 10.0 +- 0.2 MeV and full-width at half-maximum (FWHM) of 7.6 +- 0.2 MeV. The yield of tripartition fission-related protons was then estimated to be 3.50 +- 0.20 x 10-5 per fission, with a most probable energy of 6.6 +- 0.2 MeV and an FWHM of 7.0 +- 0.2 MeV
[en] Spectral lines from metabolites of interest, such as lactate, may be obscured because of the signal from a variety of protonated metabolites within the volume of interest (VOI). To eliminate interfering peaks, the authors combined localized proton spectroscopy in vivo with a method for volume-localized lactate editing that uses zero-quantum coherence created in a stimulated-echo (STEAM) pulse sequence with a 1.5-T clinical MR unit. H-1 spectra of the human brain in vivo were obtained in five normal volunteers and seven patients. All spectra were obtained for a VOI of 3x3x3 cm. In normal volunteers, neither the baseline spectrum nor the lactate editing spectrum exhibited a lactate peak. In patients with cerebral infarction ( n = 4) or brain tumors (n = 3), complex spectra were found before lactate editing due to interfering peaks in four of seven patients. With the lactate editing method, interfering lipid peaks could be removed from the lactate resonances in all four patients. The authors conclude that volume-localized lactate editing with zero-quantum coherence is useful in eliminating interfering peaks that may obscure the spectral line of lactate
[en] A method to unfold neutron spectra from experimental proton recoil data in form of a multichannel pulse height analyzer is developed and tested. The method takes into account, distortions due to multiple scattering and edge effects. It has been applied to a stilbene scintillation spectrometer using experimentally determined response functions but should equally well be applicable to other types of proton recoil spectrometers. The method is tested by application to experimental data produced with a stilbene fast neutron spectrometer system. Spectra of reactor neutron and that transmitted through water and iron barriers are unfolded. The unfolded measured spectra are compared with that calculated and a reasonable agreement was found between the two. Moreover, the maxima and depths which are observed in the spectra behind these barriers are checked against the depths and maxima in the total cross sections
[en] Complete text of publication follows. The ESA Standard Radiation Environment Monitor (SREM) is the second generation of instruments in a program established by ESA's European Research and Technology Centre (ESTEC) to provide minimum intrusive particle radiation detectors for space science and applications. SREM is a solid state particle detector consisting of three silicon diode detectors in a two-detectors-head configuration. All the pre-amplified detector pulses are scrutinized by a set of fifteen fast comparators. In order to determine proton and electron flux spectra without the need of pre-assuming their spectral form we have implemented a regularized unfolding method which is based on the Singular Value Decomposition (SVD) of SREM calibration matrix. The method includes proper schemes that treat the numerical issues arising by the electron-proton contamination, the energy range overlapping and the low number of SREM counters. First test studies show that this method can be successful for the unfolding of both monotonic and non-monotonic spectra of energetic particles using SREM data.
[en] Using data taken by the Pamela experiment during 5 years of operation we studied the anisotropy in the arrival direction distribution of cosmic ray protons with rigidity above 40 GV. In this survey we used two different and independent techniques to investigate the large and medium anisotropy patterns in the proton spectrum. With both methods the observed distribution of arrival directions is consistent with the isotropic expectation and no significant evidence of strong anisotropies has been observed