Free Biological and Medical Uses of Radiation MCQs with Answers

1. Cobalt 60 is used in hospitals mainly as a source of

• A. alpha particles for imaging
• B. gamma rays for treating cancer
• C. neutrons for sterilising instruments
• D. X rays for dental work

Explanation: Its penetrating gamma radiation can be focused on a deep tumour from outside the body, and because dividing cells are more sensitive, the cancer is damaged more than the surrounding tissue. The same gamma source is also used to sterilise medical equipment. Alpha particles cannot penetrate the skin and so are useless for external imaging or therapy.

2. A radioactive tracer used for medical diagnosis should ideally have

• A. a long half life and emit alpha particles
• B. a short half life and emit gamma rays that escape the body for detection
• C. a very long half life and emit beta particles
• D. no radiation at all

Explanation: Gamma radiation escapes the body so an external camera can detect it, and a short half life means the activity falls quickly once the scan is done, limiting the patient's dose. Technetium 99m, with a six hour half life, is the workhorse of nuclear medicine for exactly these reasons. Alpha emitters would deposit all their energy inside the tissue and be detected by nothing.

3. Radiation damages living tissue mainly because it

• A. heats the tissue significantly
• B. ionises molecules, including DNA, producing reactive fragments
• C. makes the tissue radioactive
• D. changes the pH of the cells

Explanation: Ionisation breaks chemical bonds and generates free radicals that go on to damage DNA, which may kill the cell or, if it is repaired imperfectly, cause a mutation and later a cancer. The energy deposited is far too small to matter as heat. Exposure to gamma or X rays does not make the patient radioactive, which is a common public misconception.

4. The equivalent dose that accounts for the different biological effects of different radiations is measured in

• A. gray
• B. sievert
• C. becquerel
• D. joule

Explanation: The sievert multiplies the absorbed dose in grays by a quality factor, which is 1 for beta and gamma but about 20 for alpha particles, because alpha deposits its energy in a very short track and does far more local damage. Legal exposure limits for workers and the public are therefore set in millisieverts. The becquerel describes the source rather than the dose received.