UPSC Prelims 1995 · General Studies
Question 106: Science and Technology
Which one of the following can be used to confirm whether drinking water contains a gamma-emitting isotope or not?
AnswerThe answer is (c).
Gamma rays produce tiny flashes of light in certain crystals, which a scintillation counter detects and counts, so water can be tested for gamma-emitting isotopes. A microscope cannot see radiation, a lead plate only shields against it, and a spectrophotometer measures how a sample absorbs light. Remember: scintillation counter, Geiger counter and film badge detect radiation.
Why each option is right or wrong
- (a) A microscope magnifies things; it cannot detect gamma radiation.
- (b) A lead plate absorbs gamma rays, so it shields but does not detect.
- (c) Right: a scintillation counter.
- (d) A spectrophotometer measures how a sample absorbs light, not radioactivity.
Explanation: written by UPSC Grade, not by UPSC.
Source: UPSC, Civil Services (Preliminary) Examination 1995, General Studies. UPSC's own paper isn't online; the words are from a published compilation. The paper on upsc.gov.in.