Non-ionizing Radiation Protection

Summary of Research and Policy Options

Andrew W. Wood, Ken Karipidis, Andrew W. Wood, Ken Karipidis

• Éditeur: Wiley
• Année: 2017
• ISBN:
  9781119284208
• Édition: 1
• Sujet: Technology & Engineering
• Sous-sujet: Electrical Engineering & Telecommunications

A comprehensive review of non-ionizing radiation and its public health and environmental risks, for researchers, policy makers, and laymen

This book explains the characteristics of all forms of electromagnetic non-ionizing radiation (NIR) and analyzes the relationship between exposure and its biological effects, as well as the known dose-response relationships associated with each. Taking a uniquely holistic approach to the concept of health that builds upon the WHO definition to include not only absence of disease, but the physical, mental and social well-being of individuals and the population, it reviews established and potential risks and protections, along with regulatory issues associated with each.

The risks to public health of NIR, whether in the form of UV light, radio waves from wireless devices, or electric and magnetic fields associated with electrical power systems, is currently a cause of great concern among members of the public and lawmakers. But in order to separate established science from speculation and make informed decisions about how to mitigate the risks of NIR and allocate precious resources, policymakers, manufacturers, and individuals need a comprehensive source of up-to-date information based on the current scientific evidence. Written by a team of experts in their fields, this book is that source. Among other things, it:

• Summarizes scientific findings on the safety of different forms of NIR and the rationale behind current standards
• Describes devices for monitoring NIR along with the established and potential hazards of each form
• Explores proper protections against UV light and lasers, RF radiation, ELF fields and other forms of NIR
• Discusses how to avoid injuries through occupational training or public awareness programs, and how to perform medical assessments in cases of suspected NIR injuries
• Considers how to decide whether or not to spend money on certain mitigation measures, based on cost-benefit analyses

Offering expert reviews and analyses of the latest scientific findings and public policy issues concerning the risks to public health and the environment of NIR, Non-ionizing Radiation Protection is an indispensable source of information for manufacturers, government regulators, and regulatory agencies, as well as researchers, concerned laypersons, and students.

Chapter 1
Overview: The Electromagnetic Spectrum and Nonionizing Radiation

Andrew Wood¹ and Colin Roy²

¹Department of Health and Medical Sciences, Faculty of Health, Arts and Design, Swinburne University of Technology, Hawthorn, Victoria, Australia

²Australian Radiation Protection and Nuclear Safety Agency, Melbourne, Australia

1.1 What Is Nonionizing Radiation (NIR)?

By definition, nonionizing radiation (NIR) does not cause atoms and molecules to be ionized, that is, electrons are not removed from the atom or molecule leaving it with an electrical charge. Before describing the particular features of NIR, it is instructive to consider some of the general properties of electromagnetic radiation, which comprises both NIR and ionizing radiation.

Radiation can be thought of being both wave-like and particulate (this is often referred as the “wave-particle duality”). Ionization occurs when the energy in individual particles (or “quanta”) is sufficiently high to remove an electron, by transferring all of the energy of an individual quantum. Because of the “wave-particle duality” just referred to, each quantum can be associated with a particular wavelength. The wavelength of X-rays (a form of ionizing radiation) is approximately a nanometer (or a millionth of a millimeter), and other forms of ionizing radiation have wavelengths even shorter. NIR is regarded primarily as electromagnetic radiation whose wavelength is longer than 100 nm or 0.1 µm (see Figure 1.1). This is in the ultraviolet (or UV) part of the spectrum. To get this into perspective, a biological cell is around 10 µm in diameter and a single molecule of hemoglobin is 6 nm in diameter. Other forms of NIR have longer wavelengths, several thousands of kilometers in the case of waves associated with the domestic electricity supply. The wave itself is made up of two components, an electrical field (E-field) and a magnetic field (H-field), at right angles to each other and both of these quantities at right angles to the direction of propagation (see Figure 1.2). The wavelength is the physical distance between one peak and the next for either the E or the H field. The speed of propagation in vacuum is the same for all forms of electromagnetic radiation, whether ionizing or NIR, and is 300,000 km/second (or 3 × 10⁸ m/second). It should perhaps be remembered that in media (such as human tissue), the speed will be somewhat less than this value and will contribute to the phenomenon of refraction or deviation in the direction of propagation when going from one medium to another (e.g., air to tissue). This phenomenon is most familiar in the case of visible light (optical radiation), but applies to NIR generally. In a vacuum, the ratio of the magnitude of the E-field to that of the H-field has a fixed value for positions more than a few wavelengths from the generator. The fields are said to be coupled. When the wavelengths are of the order of kilometers, most positions of interest are much closer than one wavelength, and the fields are then said to be uncoupled.

Figure 1.1 The electromagnetic spectrum, from power frequencies through to γ-rays. Top: wavelength in meters; middle: relative sizes of wavelengths, names, and typical sources; bottom: frequency in waves per second or hertz (Hz) and the relative energy of each type. Source: K. Karipidis, ARPANSA, Australia.

Figure 1.2 A propagating electromagnetic wave, showing electric (E) and magnetic (H) vectors (arrows), the direction of propagation (k), and the wavelength (λ). Note that the E and H vectors are at right angles to each other and also to the direction of propagation. See diagram as supplied for location of all of these symbols (λ, E, k).

The fundamental unit of measurement of E-field is the volt per meter (or V/m) and of H-field is amperes per meter (A/m). The ratio E/H has units of resistance (ohms) and for a vacuum has the value 377 Ω, which is related to fundamental electrical constants. In a medium such as body tissue, the value reflects more complex interactions and is referred to as impedance. In fact, 377 Ω is usually referred to as the impedance of free space.

The E/H ratio is analogous to Ohms law (i.e., that electrical resistance is the ratio of voltage to current), so in the same way that the power dissipated by a resistor is the product of the voltage and the current (in W), the product of E × H is a measure of power density of the fields in watts per meter squared (W/m², see Figure 1.3). These measures have relevance throughout the spectrum of NIR, but at the longest wavelengths, the individual E and H field values are more important than power density and at the shortest wavelengths the opposite applies.

Figure 1.3 The relationship between power density and power. The sphere represents an expanding wavefront from the origin. Alternatively, it can represent an imaginary spherical surface across which the radiated power is flowing. Power density is expressed as power per unit area, so if the area considered is A in the diagram, proportion of the total power P crossing A will be P⋅A/(4πr²) watts, since 4πr² is the surface area of the entire sphere. Dividing by A gives the power density in W/m².

In general, the quantal nature of electromagnetic radiation is less important for NIR, but for the very shortest wavelengths of the NIR spectrum (UV and visible light), more quantal energy-specific modes of interaction (photoreactions) become very important. Unlike the ionizing radiation case, where an electron can leave a molecule, specific wavelengths of NIR can induce electron transitions to produce excited molecular states. Thus, as well as power density, the precise wavelengths of the radiation are very important in determining the precise bio...