Radioactivity — Revision Notes

⚡ 30-Second Revision

Bq is rate; Gy is energy per mass. Alpha: A−4, Z−2. Beta-minus: A unchanged, Z+1. Gamma: A and Z unchanged. Three half-lives leave 1/8 of the parent population. Radiation is broader than radioactivity; irradiation is different from contamination.

2-Minute Revision

Becquerel's 1896 discovery anchors the history, but the mechanism is unstable nuclear transformation. Isotopes share proton number, not necessarily stability. Decay is probabilistic for individuals and predictable statistically for large populations.

Repeated halving gives 800→400→200→100 in three intervals. The transformed parent fraction has not simply vanished as bulk mass. Activity counts transformations per second, absorbed dose measures deposited joules per kilogram, and protection-weighted doses use sievert.

Exposure circumstances are needed to connect a source reading to dose.

5-Minute Revision

Start with A=210 and Z=84. After one alpha emission obtain A=206 and Z=82. Explain why 210/85 belongs to a different decay pattern. Next, divide fifteen years by a five-year half-life and calculate the one-eighth remaining fraction. Finally, compute 2 joules deposited in 0.5 kg as 4 Gy and explain why the answer is not 4 Bq. For each step, state what is being counted or measured. End by distinguishing an irradiated object from one carrying radioactive contamination.

Vyyuha Quick Recall

Rate, energy, weighting: Bq counts transformations; Gy counts deposited energy per mass; Sv expresses relevant weighted dose quantities.