Introduction

Cosmic rays are individual high energy particles which travel through space from sources both within our galaxy and in other galaxies. Most of these `primary' particles are charged nuclei but there is also an important neutral component, particularly the gamma-rays. The latter, and perhaps most of the cosmic rays, come from objects which may also produce gravitational signals. We note that it is possible that primary neutrons or gamma-rays could carry the same periodicity in their signal.

The spectrum of cosmic ray energies conventionally extends from about 1GeV up to 100EeV (1EeV is eV). These are practical observational limits and may bear little correspondence to the real energy limits of charged cosmic particles. Between these limits, the energy spectrum is a steep power-law with an integral index somewhat below -2.

The primary cosmic rays are ultra-relativistic with, generally, much more kinetic energy than rest mass energy. As a result, when they interact with the atmosphere of the Earth, many energetic secondary particles are produced which may themselves produce further particles so that a fraction of the original energy and momentum of the cosmic ray is carried to ground level and may be deposited in the gravitational wave system. The major question is whether or not this deposition of energy and momentum, almost random in time, represents a significant source of noise to the gravitational system and a further question is whether or not such noise may be economically eliminated. The literature addresses these issues and we discuss here some of the principles involved (see Amaldi and Pizzella 1986, Ricci 1987, Giazotto 1988, Chiang et al. 1992).

© Copyright Astronomical Society of Australia 1997