Cobalt-60 is commonly used in radiation therapy because it emits

1. The question asks why Cobalt-60 is commonly used in radiation therapy. 2. Radiation therapy (radiotherapy) uses ionizing radiation to kill cancer cells and shrink tumors. 3. Cobalt-60 (⁶⁰Co) is a radioactive isotope of cobalt that undergoes beta decay. 4. During its decay process, Cobalt-60 emits a beta particle (beta rays) and then the resulting excited nucleus of Nickel-60 releases energy in the form of high-energy photons, which are gamma rays. 5. It is these penetrating gamma rays (with energies of 1.17 MeV and 1.33 MeV) that are primarily used in external beam radiation therapy (teletherapy) machines, often called Cobalt therapy units. 6. Alpha rays have very low penetration. Beta rays have moderate penetration but gamma rays are highly penetrating, making them suitable for targeting deep-seated tumors. 7. X-rays are also used in radiotherapy but are produced differently (typically via electron bombardment in an X-ray tube or linear accelerator), not emitted by Cobalt-60 decay.