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

Cobalt‑60 is used in radiation therapy because it emits highly penetrating gamma rays rather than alpha or beta particles or diagnostic X‑rays. Gamma radiation penetrates deeply into tissue and can treat internal, deep‑seated tumours, whereas alpha particles are stopped by paper or skin and beta particles have much more limited penetration [1]. The radioactive decay of 60Co produces two high‑energy gamma photons (commonly cited near 1.3 MeV), which is the megavoltage radiation exploited in cobalt teletherapy units and industrial irradiators [3]. These properties—strong penetration and well‑defined high energies—make 60Co gamma emission suitable for external beam radiotherapy.

Sources

1. [1] Environment, Shankar IAS Acedemy .(ed 10th) > Chapter 5: Environmental Pollution > 5.9.3. Tlpes of radiation particles > p. 82
2. [2] https://egyankosh.ac.in/bitstream/123456789/101501/1/Unit-6.pdf
3. [3] https://www.doh.wa.gov/Portals/1/Documents/Pubs/320-078_co60_fs.pdf