Radioactivity — Prelims Strategy

Prelims Strategy

For decay questions, write the mass number and atomic number separately. An alpha particle removes four nucleons including two protons. Beta-minus changes a neutron into a proton, while gamma emission does not change these counts. Do not apply the same subtraction to both numbers simply because one particle is emitted.

For half-life arithmetic, count elapsed intervals and multiply by one half repeatedly. Three half-lives leave one eighth of the parent population. This is not an expiry clock for an individual nucleus and does not establish that the transformed parent fraction has disappeared as bulk mass. In a simple parent sample, activity follows the same proportional decline.

Check units before comparing readings. Becquerel is a rate, gray is energy per mass and sievert belongs to weighted protection quantities. A direct Bq-to-Gy claim without exposure information is incomplete. Finally, distinguish radiation from radioactive material and irradiation from contamination. A device producing radiation need not contain a radionuclide, and exposure alone does not establish deposited radioactive material.