61 research outputs found
Gamma ray line production from cosmic ray spallation reactions
The gamma ray line intensities due to cosmic ray spallation reactions in clouds, the galactic disk and accreting binary pulsars are calculated. With the most favorable plausible assumptions, only a few lines may be detectable to the level of 0.0000001 per sq. cm per sec. The intensities are compared with those generated in nuclear excitation reactions
Implications of cross section errors for cosmic ray propagation
Errors in nuclear interaction cross sections are the single most important limitation on the analysis of cosmic ray composition data. At the 18th International Cosmic Ray Conference, the potential importance of correlations in cross section errors in determining cosmic ray source abundances was demonstrated. In this paper the magnitude of cross section error correlation is estimated. Analysis suggests that cross section errors are essentially uncorrelated for nuclei with Z 29 and that the actual errors may be less than the nominal 35%
Calculation of improved spallation cross sections
Several research groups have recently carried out highly precise measurements (to about 10 percent) of high-energy nuclear spallation cross sections. These measurements, above 5 GeV, cover a broad range of elements: V, Fe, Cu, Ag, Ta and Au. Even the small cross sections far off the peak of the isotopic distribution curves have been measured. The semiempirical calculations are compared with the measured values. Preliminary comparisons indicate that the parameters of our spallation relations (Silberberg and Tsao, 1973) for atomic numbers 20 to 83 need modifications, e.g. a reduced slope of the mass yield distribution, broader isotopic distributions, and a shift of the isotopic distribution toward the neutron-deficient side. The required modifications are negligible near Fe and Cu, but increase with increasing target mass
Propagation of cosmic rays and new evidence for distributed acceleration
The origin and propagation of cosmic rays in terms of conventional and supplementary newer assumptions were explored. Cosmic rays are considered to be accelerated by supernoava shock waves and to traverse clouds in the source region. After rigidity-dependent escape from these clouds into interstellar space, cosmic rays are further accelerated by the weakened shocks of old supernova remnants and then pass through additional material. The distributed acceleration hypothesis is discussed with emphasis on recent data on the abundances of cosmic-ray isotopes of N above 1 GeV/u and of He near 6 GeV/u
Considerations on the Unruh Effect: Causality and Regularization
This article is motivated by the observation, that calculations of the Unruh
effect based on idealized particle detectors are usually made in a way that
involves integrations along the {\em entire} detector trajectory up to the
infinitely remote {\em future}. We derive an expression which allows
time-dependence of the detector response in the case of a non-stationary
trajectory and conforms more explicitely to the principle of causality, namely
that the response at a given instant of time depends only on the detectors {\em
past} movements. On trying to reproduce the thermal Unruh spectrum we are led
to an unphysical result, which we trace down to the use of the standard
regularization t\to t-i\eps of the correlation function. By consistently
employing a rigid detector of finite extension, we are led to a different
regularization which works fine with our causal response function.Comment: 19 pages, 2 figures, v2: some minor change
Vacuum polarization on the spinning circle
Vacuum polarization of a massive scalar field in the background of a
two-dimensional version of a spinning cosmic string is investigated. It is
shown that when the `radius of the universe' is such that spacetime is globally
hyperbolic the vacuum fluctuations are well behaved, diverging though on the
`chronology horizon'. Naive use of the formulae when spacetime is nonglobally
hyperbolic leads to unphysical results. It is also pointed out that the set of
normal modes used previously in the literature to address the problem gives
rise to two-point functions which do not have a Hadamard form, and therefore
are not physically acceptable. Such normal modes correspond to a locally (but
not globally) Minkowski time, which appears to be at first sight a natural
choice of time to implement quantization.Comment: 3 pages, no figures, REVTeX4, published versio
Particle detectors, geodesic motion, and the equivalence principle
It is shown that quantum particle detectors are not reliable probes of
spacetime structure. In particular, they fail to distinguish between inertial
and non-inertial motion in a general spacetime. To prove this, we consider
detectors undergoing circular motion in an arbitrary static spherically
symmetric spacetime, and give a necessary and sufficient condition for the
response function to vanish when the field is in the static vacuum state. By
examining two particular cases, we show that there is no relation, in general,
between the vanishing of the response function and the fact that the detector
motion is, or is not, geodesic. In static asymptotically flat spacetimes,
however, all rotating detectors are excited in the static vacuum. Thus, in this
particular case the static vacuum appears to be associated with a non-rotating
frame. The implications of these results for the equivalence principle are
considered. In particular, we discuss how to properly formulate the principle
for particle detectors, and show that it is satisfied.Comment: 14 pages. Revised version, with corrections; added two references.
Accepted for publication in Class. Quantum Gra
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