Recall which radioisotope is often used in radiotherapy machines as a source of gamma rays.

The radioisotope often used in radiotherapy machines as a source of gamma rays is Cobalt-60 (Co-60). Cobalt-60 is a synthetic isotope that emits two high-energy gamma photons during its decay process, making it highly effective for killing cancer cells in tumor treatment.

In radiotherapy, the gamma rays produced by Cobalt-60 are directed towards the cancerous tissues. The high energy of these gamma rays allows them to penetrate the body and damage the DNA of cancer cells, leading to cell death or the inability for the cells to further divide and proliferate.

Cobalt-60 has been widely used since the 1950s due to its effectiveness and the relatively low cost of obtaining it. Its half-life is approximately 5.27 years, which allows for practical usage in medical applications, though it requires regular replenishment in treatment facilities. Overall, Cobalt-60 plays a crucial role in radiation therapy and has significantly contributed to cancer treatment advancements.