Engineering topics
Publications and source records attributed to Mast, T. S..
New high-energy cosmic-ray Be data indicate that the ratio Be-7/Be drops by approximately a factor of two between 200 and 1500 MeV/nucleon. This result may provide a severe constraint for theories of cosmic-ray acceleration.
Measurements of primary cosmic-ray composition and energy spectra made with a balloon-borne superconducting magnetic spectrometer are described. Results for both 6.7 g/sq cm equivalent vertical atmospheric depth and the top of the atmosphere are presented for the absolute and relative integral abundances, the differential energy spectra, and the spectral indices for cosmic-ray nuclei from Li to Fe and energies of 2 to 50 GeV/n. It is found that propagation effects can explain essentially all the elemental abundances, that the abundances of Li, Be, and B for rigidities below 10 GV/c are consistent with an energy-independent mean interstellar path length of 4.5 + or - 0.5 g/sq cm for the 'leaky box' propagation model, that the abundances of all elements above 10 GV/c are consistent with a path length that decreases as the inverse n-th power of rigidity, and that n equals 0.6 (+0.4, -0.3) for the simplest assumptions made in fitting the source spectra.
A balloon-borne superconducting magnetic spectrometer was used in the measurement of cosmic-ray isotopic abundances from lithium through oxygen in the energy range 200-1500 MeV per nucleon. Except for Be-7 all isotopic composition is essentially energy-independent. Be-10 is nearly absent, indicating a mean cosmic-ray age of 6(-3, +10) x 10 to the 6th years. Above about 500 MeV per nucleon, Be-7 drops dramatically in abundance relative to Be-9 and C. By 1500 MeV per nucleon, the relative abundance of Be-7 has become one-half of its lower-energy value. Since Be-7 is the only isotope measured which decays by electron capture, this result is interpreted as indicating that higher-energy Be-7 had an appreciable probability of not being stripped of all its electrons before entering interstellar space where electron pickup is negligible.
The cosmic-ray Be-7/Be ratio was observed to be 0.6 below 500 MeV/nucleon, as expected from spallation reactions, but then to drop sharply to 0.4 by 1500 MeV/nucleon. This measurement suggests that primary cosmic rays traverse some material at their sources, producing Be-7 which picks up electrons and decays by K capture during or after the acceleration to relativistic energies. All cosmic rays then enter interstellar space, where further pickup is negligible.
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Measurements in liquid Xe are reported of the characteristic function that describes the avalanche, the first Townsend coefficient. An electron avalanche occurs when the drifting electrons attain sufficient kinetic energy from the electric field to cause additional ionization. Data on the avalanche were obtained by studying the pulses in a liquid-filled proportional chamber as a function of applied voltage and anode diameter. The results of the investigation show that the avalanche of free electrons in purified liquid Xe is adequately described by the same formalism used for the avalanche of electrons in gases.
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