Radiation

The harmful effects of radiological and nuclear agents (i.e. radionuclides) results from the radiation they emit. This gives rise to two types of radiological hazard: from external exposure through absorption of radioactive material into the body.

There are three main types of radiation: alpha or beta particles and gamma rays, which have differing abilities to penetrate matter both between a person and the source and within the body.

• Alpha particles (2 protons + 2 neutrons ≈ He core) can scarcely penetrate the dead, outer layer of human skin and are, therefore, not hazardous unless they are taken into the body through breathing or eating or through a skin wound.
  
  
• Beta particles (negative electrons or also positrons) are much more penetrating than alpha particles and can penetrate the outer layers of skin and may penetrate a centimetre or so of tissue, depending on their energy. Beta particles are therefore hazardous to superficial tissues of the body but not to internal organs unless they are taken into the body (e.g. through inhalation or ingestion).
  
  
• Gamma rays (electromagnetic rays) can pass through the body, so radionuclides that emit them may be hazardous whether on the outside or inside of the body. Gamma rays can penetrate most materials, requiring a substantial thickness of earth, lead, concrete or water to provide an effective barrier.