Low frequency fields Chapter 10 in the book: Radiation at Home, Outdoors and in the Workplace, Ed: DBrune, RHellborg, BRRPersson, RPääkkönen, Scandinavian Science Publisher, 2001 ISBN 82-91833-02-8 Arnt Inge Vistnes, Department of Physics, University of Oslo, Norway 101 Introduction The word radiation is often taken as a synonym to electromagnetic waves All electromagnetic waves are solutions of Maxwells equations, but the waves have very different properties when they interact with matter, depending on the frequency (and wavelength) of the waves In figure 1 the so-called electromagnetic spectrum is given, and we see that very high frequency electromag- netic fields appear as γ-rays (gamma radiation), X-rays and ultraviolet (UV) radiation These ex- amples of waves are called ionizing radiation, since such radiation may knock out electrons from atoms or molecules so that the molecule is left with an net electric charge (becomes an ion, at least for a short time) and a more or less permanent radiation damage may be created Waves with lower frequencies can not ionize atoms or molecules directly, and are called non- ionizing radiation Waves with slightly lower frequencies than UV are visible light Then follows infrared radiation, microwaves and radio waves As one moves to even lower frequencies, the common solutions of Maxwells equations are no longer ordinary electromagnetic waves Thus, when we come down to eg 50 or 60 Hz, we rather talk about low frequency electric and magnetic fields, in short, electromagnetic fields, and they are no longer an integral part of the electro- magnetic spectrum For that reason, power line radiation is not a natural part of Figure 10-1, and is consequently put in a parenthesis When we discuss the intensity, dose and biological effects from ionizing radia- tion or light, it is relatively easy at least to characterize the radiation: Type of particles, the photon frequency or particle energy spectrum, the intensity at various positions in space, and the Figure 10-1 The electromagnetic spec- trum with the various manifestations of electromagnetic waves, depending on their frequency The product of fre- quency and wavelength is always the speed of light NOTE: The latest changes in the manuscript (due to the editors and publisher) are not included in this file Go to the book if you want the final version
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