Radionuclides

Radionuclides can be grouped into three categories, according to their half-lives.

The categories are:

• Very short-lived radionuclides with half-lives of less than a day (e.g. Technetium-99m and iodine-120). Even if a very large quantity were released, it would decay away within days.
  
  
• Short-lived radionuclides with half-lives of up to 3 weeks (e.g. phosphorus-32, molybdenum-99, iodine-131). Even a substantial amount of radioactivity of this kind would decay away within months.
  
  
• Radionuclides with half-lives longer than 3 weeks. These will take at least years to decay away. Radionuclides in this category may be grouped according to whether their hazard is predominantly gamma, beta or alpha emissions:
  
  
  • Gamma emitters (such as caesium-137 and iridium-192);
  • Beta emitters (e.g. strontium-89 and strontium-90);
  • Alpha emitters (such as plutonium-238 and curium-242).