Which one of the following element's isotope is used in the treatment of cancer?
- (a)Uranium
- (b)Cobalt
- (c)Sodium
- (d)Iodine
Correct — B, Cobalt. The radioactive isotope cobalt-60 is widely used in cancer radiotherapy: it emits high-energy gamma rays (about 1.17 and 1.33 MeV) that penetrate tissue and destroy the DNA of rapidly dividing tumour cells in external-beam ('teletherapy') treatment. So cobalt is the element whose isotope is used to treat cancer.
- (a)Uranium — Uranium (U-235) is used as fuel in nuclear reactors and weapons, not as a therapeutic source for cancer.
- (c)Sodium — Radioactive sodium-24 is used as a tracer to study blood flow and locate clots, not as a mainstream cancer-treatment source.
- (d)Iodine — Iodine-131 is used for thyroid disorders (including thyroid cancer) because the thyroid absorbs iodine, but the standard isotope for general external-beam cancer radiotherapy is cobalt-60.
Radioisotopes have many medical uses. Cobalt-60 is the classic external-beam radiotherapy source because it emits deeply penetrating gamma rays. Other isotopes have distinct roles - iodine-131 for the thyroid, sodium-24 as a blood-flow tracer, and uranium-235 as reactor fuel.
Distinguish a therapeutic gamma source from a nuclear fuel and from diagnostic tracers. The isotope used to irradiate and kill tumour cells in general radiotherapy is cobalt-60.
- Cobalt-60 emits penetrating gamma rays and is used in external-beam radiotherapy to kill cancer cells.
- Cobalt-60 has a half-life of about 5.27 years.
- Iodine-131 is used for thyroid disorders, sodium-24 as a blood-flow tracer, and uranium-235 as reactor fuel.
- Gamma radiation damages the DNA of fast-dividing tumour cells more than that of normal cells.
- Picking uranium because it is the most famous radioactive element - it is a fuel, not a therapy.
- Choosing iodine, which is correct only for the thyroid, whereas cobalt-60 is the general radiotherapy source.
- Confusing diagnostic tracers (sodium-24, technetium-99m) with therapeutic sources.
NDA and UPSC ask which radioisotope treats cancer (cobalt-60) or which serves as a tracer or fuel - match the isotope to its use.
Cobalt-60 is commonly used in radiation therapy because it emits
- (a) alpha rays
- (b) beta rays
- (c) gamma rays
- (d) X-rays
Answer(c) gamma rays
The same cobalt-60 fact from the other angle - UPSC asks WHY it treats cancer (its penetrating gamma rays); here NDA asks WHICH element's isotope is used.
- practice — not a real PYQ
Cobalt-60 is used in cancer therapy because it emits
- (a)alpha rays
- (b)beta rays
- (c)gamma rays
- (d)sound waves
Answer(c) gamma rays - penetrating radiation that destroys tumour-cell DNA.
- practice — not a real PYQ
Which radioisotope is commonly used to treat disorders of the thyroid gland?
- (a)Cobalt-60
- (b)Iodine-131
- (c)Uranium-235
- (d)Carbon-14
Answer(b) Iodine-131 - the thyroid takes up iodine, concentrating the isotope there.