|
Items in cart [0] |
Questions? Call 888-624-8373 |
| Copyright © 2009. National Academy of Sciences. All rights reserved. Terms of Use and Privacy Statement |
Below are the first 10 and last 10 pages of uncorrected machine-read text (when available) of this chapter, followed by the top 30 algorithmically extracted key phrases from the chapter as a whole.
Intended to provide our own search engines and external engines with highly rich, chapter-representative searchable text on the opening pages of each chapter.
Because it is UNCORRECTED material, please consider the following text as a useful but insufficient proxy for the authoritative book pages.
Do not use for reproduction, copying, pasting, or reading; exclusively for search engines.
OCR for page 111
IV
Cosmic Rays
OCR for page 112
OCR for page 113
Cosmic rays provide our only direct sample of material from outside
the solar system. Their composition reflects the nature of the
nucleosynthetic processes by which all the elements of the periodic
table are being constructed in the galaxy. In addition the cosmic rays
are accelerated to relativistic speeds by processes in which nature
concentrates vast amounts of energy in relatively few particles. These
acceleration processes apparently take place on a wide variety of
scales in astrophysical plasmas. Because some cosmic rays have
energies higher than man-made beams of particles, they are also of
interest for studying interactions of protons and atomic nuclei at
ultrahigh energy.
Cosmic-ray physics is thus in essence an interdisciplinary field,
touching astronomy and high-energy astrophysics, nuclear physics,
plasma physics, and elementary-particle physics. It began as the study
of energetic particles in the atmosphere, which we now know to be the
products of nuclear interactions between the primary cosmic rays and
air nuclei. In the past 35 years high-altitude balloons and spacecraft
have carried instruments above most of the atmosphere, and the focus
of cosmic-ray studies has shifted to the composition and energy spectra
of the primary particles themselves, which includes atomic nuclei and
electrons. The highest-energy cosmic rays, however, are still accessi-
ble only to surface experiments that can overcome the exceedingly low
rate of these cosmic rays by exposing detectors of large area for long
times. In addition, secondary neutrinos and muons are of great current
interest for deep underground experiments, and there is an intense
search for magnetic monopoles in the cosmic rays.
A major opportunity of the present decade is the ability provided by
the Space Shuttle to place large detectors in space and to visit them
subsequently for repair. By the early l990s this capability will be
supplemented by the Space Station, which will provide a permanent
manned presence in space and permit routine maintenance and modi-
fication of orbiting instruments as well as assembly of instruments that
otherwise would be too large to lift into orbit. The combination of
Shuttle and Station will permit us to place new kinds of instruments in
113
OCR for page 114
1 14 COSMIC RA YS
space, leading to new levels of precision of cosmic-ray instruments and
extension of direct observation of the major cosmic-ray components by
several orders of magnitude in energy. Ground-based detectors will
remain the only source of information in the highest-energy regime,
where galactic acceleration and confinement mechanisms probably fail,
and one expects a transition to particles from outside our own galaxy.
In both space and ground-based observations, instruments are now
possible that will be capable of addressing some of the key astrophys-
ical questions of processes of nucleosynthesis and particle accelera-
tion, as well as questions of the physics of particle interactions at
extremely high energies.
Representative terms from entire chapter:
atomic nuclei
