1999 General Studies, all questions
UPSC Prelims 1999 · General Studies
Question 125: Science and Technology
Cobalt-60 is commonly used in radiation therapy because it emits
aalpha rays
bbeta rays
cgamma rays
dX-rays
AnswerThe answer is (c).
Cobalt-60 is a radioactive isotope that emits penetrating gamma rays, which reach tumours deep inside the body and destroy cancer cells. This is why it is used in radiation therapy (the cobalt bomb). It also emits beta particles, but the gamma rays do the treatment. Remember: cobalt-60 therapy uses gamma rays.
Why each option is right or wrong
- (a) Wrong. Alpha rays are stopped by skin and cannot reach deep tumours.
- (b) Wrong. Beta rays penetrate little and are not what treats deep tumours.
- (c) Right. Gamma rays penetrate deep tissue.
- (d) Wrong. X-rays are produced by machines, not emitted by cobalt-60.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 1999, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.