Cloud chamber observations of cosmic rays at 4300 meters elevation and near sea-level

Cloud chamber photographs at 4300 meters elevation show positive and negative electron tracks similar to those observed at sea-level, but positive-negative electron showers occur more frequently and, in general, consist of more numerous tracks. Showers of 2-4 tracks, 5-10 tracks, and 11-100 tracks occur respectively, 8.6, 21 and 29 times as frequently per unit time at 4300 meters as they do near sea-level. Further measurements on the energy loss in lead of electrons up to 400 MEV, are given. They show that in this range of energies the energy loss in lead is roughly proportional to the incident energy. About one percent of the exposures on Pike's Peak reveal the presence of strongly ionizing particles which in most cases seem to be protons. The proportion of such tracks is considerably greater than at Pasadena. These heavy tracks in general bear only little relation in direction to that of the incoming beam, and usually arise from a type of nuclear disintegration not heretofore observed. The energies of these heavily ionizing particles may rise to values so high as 150 MEV, thus indicating that the source of the particle energies is in the cosmic rays

Energy spectra of positrons ejected by artificially stimulated radioactive substances

Curie and Joliot (1) have reported that under the bombardment by α-particles from Po, several of the light elements, viz., B, Mg, Al undergo transmutations which result in the production of radioactive isotopes which have half-lives of the order of several minutes and disintegrate by the ejection of positrons

Cosmic-ray particles of intermediate mass

A Geiger-counter placed inside a cloud chamber and coupled by means of a coincidence circuit to a second counter placed above the chamber has been employed to increase the probability of observing cosmic-ray particles near the ends of their ranges, and thus to provide information concerning the mass and stability properties of the particles of intermediate mass

The relation of the positron energy spectrum to the decay constant and to the energy of the bombarding protons

We have reported(1) approximate energy distributions of the positrons emitted by various substances activated by proton or deuton bombardment. A typical photograph is reproduced in Fig. 1. To find whether a relation exists between the maximum energy of the bombarding particles and the energies of the disintegration positrons we have studied numerous samples of carbon bombarded by protons at peak voltages of 900,000 and 700,000, supplied us by Dr. Lauritsen and Mr. Crane

Note on the nature of cosmic-ray particles

Measurements (1) of the energy loss of particles occurring in the cosmic-ray showers have shown that this loss is proportional to the incident energy and within the range of the measurements, up to about 400 Mev, is in approximate agreement with values calculated theoretically for electrons by Bethe and Heitler. These measurements were taken using a thin plate of lead (0.35 cm), and the observed individual losses were found to vary from an amount below experimental detection up to the whole initial energy of the particle, with a mean fractional loss of about 0.5

Activation and Isomerization of n-Butane on Sulfated Zirconia Model Systems - An Integrated Study Across the Materials and Pressure Gaps

Butane activation has been studied using three types of sulfated zirconia materials, single-crystalline epitaxial films, nanocrystalline films, and powders. A surface phase diagram of zirconia in interaction with SO3 and water was established by DFT calculations which was verified by LEED investigations on single-crystalline films and by IR spectroscopy on powders. At high sulfate surface densities a pyrosulfate species is the prevailing structure in the dehydrated state; if such species are absent, the materials are inactive. Theory and experiment show that the pyrosulfate can react with butane to give butene, H2O and SO2, hence butane can be activated via oxidative dehydrogenation. This reaction occurred on all investigated materials; however, isomerization could only be proven for powders. Transient and equilibrium adsorption measurements in a wide pressure and temperature range (isobars measured via UPS on nanocrystalline films, microcalorimetry and temporal analysis of products measurements on powders) show weak and reversible interaction of butane with a majority of sites but reactive interaction with < 5 µmol/g sites. Consistently, the catalysts could be poisoned by adding sodium to the surface in a ratio S/Na=35. Future research will have to clarify what distinguishes these few sites

Statistical Mechanical Calculation of Anisotropic Step Stiffness of a Two-Dimensional Hexagonal Lattice Gas Model with Next-Nearest-Neighbor Interactions: Application to Si(111) Surface

We study a two-dimensional honeycomb lattice gas model with both nearest- and next-nearest-neighbor interactions in a staggered field, which describes the surface of stoichiometrically binary crystal. We calculate anisotropic step tension, step stiffness, and equilibrium island shape, by an extended random walk method. We apply the results to Si(111) 7$\times$7 reconstructed surface and high-temperature Si(111) 1$\times$1 surface. We also calculate inter-step interaction coefficient.Comment: revised on May 29 1999: RevTeX v3.1, 10 pages with 9 figures (one figure added