Radioactivity — Scientific Principles

Scientific Principles

Track nuclear identity

Atomic number counts protons; mass number counts protons plus neutrons. Isotopes share the first number but differ in the second. Alpha emission reduces mass number by four and atomic number by two. Beta-minus decay leaves mass number unchanged and increases atomic number by one. Gamma emission changes nuclear energy without changing either number.

Apply repeated halving

In the simple decay model, a large parent population falls by half during each half-life. An illustrative 800-unit parent population with a five-year half-life becomes 400, 200 and 100 after five, ten and fifteen years. The remaining fraction is one eighth, not zero. Transformed parents should not be confused with vanished bulk sample mass.

Match the unit to the quantity

One becquerel is one nuclear transformation per second. One gray is one joule of deposited energy per kilogram. Sievert is used for relevant protection-weighted dose quantities. Activity alone does not determine a person's dose; the radiation and exposure circumstances also matter.

Separate exposure from material presence

Irradiation is exposure to radiation. Contamination means radioactive material is present where it is not intended. Exposure does not automatically establish contamination or activation. Similarly, visible light and radio waves are radiation but are not evidence of radioactive decay. Use the process and measured quantity to interpret the term rather than relying on its everyday associations.