Page 299 - Radiochemistry and nuclear chemistry

CHAPTER 10

Cosmic Radiation and Elementary Particles

Contents

1 o. 1. Primary cosmic radiation 283
10.2. Secondary reactions in the earth's atmosphere 286
10.3. Elementary particles and forces of nature 287
10.4. Waves and particles 289
10.5. Formation and properties of some elementary particles 290
10.6. The neutrino 292
10.7. Quarks and the Standard model 294
10.8. Exercises 298
10.9. Literature 298

The early workers in nuclear science found that their measuring equipment had a constant
background level of radiation which could be eliminated only partially even with the aid of
thick shielding walls of iron and lead. It was assumed initially that this radiation had its
origin in naturaUy radioactive elements present in the materials in the laboratory. However,
in 1911 Hess carried measuring equipment into the atmosphere with the aid of balloons and
learned that this background radiation increase~ with altitude. Obviously, at least a
component of the laboratory background radiation had its origin in some extra-terrestrial
source. In recent years, test equipment carried outside of the earth's atmosphere by rockets
has given us data which provide a fairly accurate picture of the composition of the radiation
that comes to the earth from space.
The investigation of cosmic radiation has had a profound influence on nuclear science.
When Chadwick in 1932 discovered the neutron, the picture of matter seemed complete:
all matter appeared to be composed of four fundamental particles: protons, neutrons,
electrons, and photons. However, through studies of the cosmic radiation Anderson
discovered the positron (the first antiparticle) in the same year. Five years later Anderson
and Neddermeyer discovered another new particle with a mass about one-tenth of a proton
or about 200 times heavier than the electron. This particle is the muon, designated by/~.
Since that time a large number of subatomic particles have been discovered.

10.1. Primary cosmic radiation

A rather small fraction of the cosmic radiation consists of electromagnetic radiation and
electrons. The former vary in energy from a small percentage of ~-rays to a considerable
intensity of X-rays, to visible light and to radiation in the radiofrequency region. The types

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