Ionizing Radiation

Abstract

Abstract Ionizing radiation may be defined as electromagnetic (X‐rays and gamma rays) and particle radiation (alpha and beta particles, electrons, neutrons, and protons) with sufficient energy to disrupt an atom or a molecule. This is done by knocking out an electron, thereby “ionizing” the atom or molecule. Knowledge of radiation and safety problems associated with its use goes back more than 100 years, with the discovery, in 1895, of X‐rays by Wilhelm Roentgen. On the same day that Roentgen announced his discovery, Emile Grubbe, a physicist working in Chicago with an apparatus similar to Roentgen's, developed severe skin burns after handling an energized cathode ray tube similar to the one used by Roentgen. This was the first work‐related injury from radiation. In 1896, Antoine Henri Becquerel discovered radioactivity while working with an ore called pitchblende. Investigation revealed three different radiations that originated in the ore. Becquerel called these radiations alpha, beta, and gamma rays. (Later investigations showed that X‐rays and gamma rays were the same type of radiation.) The discovery of these radiations opened new fields of scientific investigation and uses for these radiations. Parallel with the studies of the physics and chemistry of radiation and radioactive materials were researches into their biomedical effects. With this expanded use of radiation there were further reports of harmful effects, such as skin burns and hair loss when X‐rays were used in medical diagnosis. In 1899 the first case of a cancer, a basal cell carcinoma on a woman's face was cured by X‐rays. In 1906, two French physiologists, Bergonie and Tribendeau, published their classical paper on the relative radiosensitivity of different cells and tissues. They found that the less differentiated a cell was, and the more frequently it divided, the more radiosensitive it was. From then until now, we have found nothing to contradict their observations. However, much is understood now about the molecular biology basis for their findings. Since then, an enormous amount of information on the nature of the interaction of radiation with living tissue, and on the dose–effect and dose–response relationships has been amassed. Sources of information, such as the experiences of the radium dial painters, early radiologists, and the uranium miners, showed that occupational overexposures led to harmful effects. Other major sources of information include the populations that had been medically exposed to diagnostic and therapeutic radiation, the survivors of the atomic bombings in Japan, radiation accidents, epidemiological studies of populations exposed to low level radiation from nuclear facilities and from natural background. This body of knowledge forms the scientific basis for the radiation safety standards currently in use. After radiation safety guidelines were developed, occupational exposures that were within the radiation safety guidelines did not lead to harmful biomedical effects.