Radioactivity

Compare the same property across the three types rather than mixing unrelated facts. Alpha carries charge +2e, beta-minus carries −e, and gamma is uncharged. This explains why gamma is not deflected by electric or magnetic fields in the standard treatment. Paper stops alpha, suitable aluminium shielding strongly reduces beta, and thick lead or concrete reduces gamma intensity. The shielding comparison depends on radiation energy and material thickness, so gamma should not be described as absolutely unstoppable or completely removed by one universal sheet thickness.

A graph starting above zero does not automatically represent source activity alone. If background is present, half of the total initial reading is not the correct target. Subtract background to isolate the source contribution, halve that contribution, then add background back when locating the target on the original total-count graph. Draw clear horizontal and vertical guides to read times. A long straight segment drawn between noisy points is less informative than a sensible decay trend, and an apparent small variation between half-life estimates may reflect measurement uncertainty.

The exam explanation links penetration to detection: radiation stopped entirely inside the body would not reach an external detector effectively. A useful tracer must also travel to the region being investigated, so its chemistry and biological handling cannot be ignored in real applications. “Short half-life” is relative to the measurement time; an isotope that decays almost completely before it arrives would not be useful. Gamma exposure still requires controlled use. An external detector records only some emitted photons, so the measured count rate also depends on detector efficiency and geometry.

The number that decays during successive equal half-life intervals becomes smaller because there are fewer undecayed nuclei available. This is why a decay curve gradually becomes less steep rather than forming a straight line to zero. Individual nuclei remain unpredictable: a particular nucleus might decay early or persist through many half-lives. In a finite sample, the very last event is a random question, whereas the smooth curve describes statistical behaviour of a large population. Match the remaining fraction to the number of halving steps before calculating the elapsed time.

An object can be irradiated without acquiring any radioactive material. For example, an external source can send radiation towards a sample and then be moved away. By contrast, radioactive dust on a surface remains a source wherever the dust is carried, so it can spread the problem. The distinction matters when explaining protective measures: shielding and distance reduce exposure, while preventing ingestion, inhalation or transfer of material addresses contamination. Do not automatically conclude that every object exposed to radiation becomes radioactive; that is not what ordinary irradiation means.

The total count of nucleons stays fixed because one neutron becomes one proton; a nucleon has changed type rather than being removed. The emitted electron carries negative charge, balancing the increase in the daughter nucleus’s positive charge. At IGCSE level, decay equations track nucleon and proton numbers using this relationship. Full nuclear descriptions include an antineutrino, beyond some syllabus treatments. A separate process removing an outer electron would produce an ion of the same element, whereas beta-minus decay changes the proton number and therefore the element.