|Cobalt sources and radium needles|
Cobalt bombs, powerful sources of gamma rays, are still used in radiotherapy for cancer, although they are gradually being replaced by small accelerators. After use, these sources, the power of which only decreases by half every five years, have to be recovered. More than 3300 objects for medical uses, such as these radium needles, have been recovered. Radium was used in brachytherapy in the first half of the 20th Century in the form of needles and tubes. It has been replaced by caesium-137 and iridium-192, which have much shorter half-lives than radium (the half-life of radium is 1600 years).