TNAG-1776-FCO40-2530-Daya-Bay-nuclear-power-station-project-safety-concerns-in-Ho-1988 — Page 133

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RADIATION

3.1 Introduction

The term 'radiation' embraces electromagnetic waves (such as light, radiowaves and X-rays) and particles emitted by radioactive materials as they decay to reach a stable, non-radioactive state (such as alpha and beta particles). These particles and the more energetic electromagnetic waves produce electrically charged particles called 'ions' in the materials they strike. This ionisation can result in chemical changes which, in living tissue, can lead to injury in the organism. The non-ionising radiations such as those produced by lasers and radio transmitters may be hazardous in some circumstances, but this is generally due to heating effects.

Radioactivity is not a modern phenomenon. The earth has been radioactive throughout its 4 billion year history and man has successfully evolved in this environment of constant exposure to low levels of radiation. Exposure to man-made radiations has only occurred since 1895 when Roentgen discovered that penetrating rays were emitted from some high voltage equipment he was experimenting with. He named this radiation 'X-rays'. In 1896 Henri Becquerel discovered natural radioactivity in pitchblende (an ore of uranium) and later the Curies extracted radium. from pitchblende.

There were many early injuries as a result of high exposure, particularly to X-rays. As early as January 1896 E H Grubbe had developed acute dermatitis of his hands as a result of experimenting with crude X-ray tubes. The first volume of 'American X-ray Journal' was published in 1897, and included in it was a compilation of 69 cases of X-ray injury. By March 1902 at least 147 cases of radiation injury had been reported in the literature.

Over the ninety years since the discovery of the harmful effects of ionising radiations a vast amount of research has been carried out and coincident with that research safety standards have been developed. The detrimental properties of high levels of ionising radiations are now generally well understood, and application of the recommendations of the International Commission on Radiological Protection (ICRP) ensure a high degree of protection for workers and members of the public.

Notwithstanding the knowledge that has been gained over the last ninety years there is still confusion in many. people's minds about the effects of radiation. This has not been helped by having strange and wonderful properties attributed to radiation in science fiction novels, films, television programmes and occasionally the popular press. The purpose of this chapter is to describe the properties of ionising radiations and to dispel some of the myths surrounding the topic.

3.2 Types of Radiation

There are a number of different types of ionising radiation, each has its own properties.

Alpha Particles

These are positively charged particles formed of two protons and two neutrons. They are easily stopped and do not penetrate the skin. Radioactive materials that emit alpha particles can only be hazardous if they enter the body, for example by inhalation or ingestion.

Beta Particles

These are negatively charged electrons and are much lighter than alpha particles. They can be stopped by, for example, a sheet of glass, or aluminium. They can penetrate the skin but again the main hazard is associated with the intake of beta emitting materials into the body.

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