NEWTONINE
THE IB PHYSICS LAB
Fission: A heavy nucleus (e.g., uranium‑235) absorbs a neutron, becomes unstable, and splits into two smaller nuclei plus 2‑3 neutrons and energy. The neutrons go on to cause further fissions → chain reaction. Control rods absorb neutrons to regulate the reaction.
Fusion: Two light nuclei (e.g., hydrogen isotopes) combine at very high temperatures and pressures. This releases more energy than fission but is technically difficult to sustain on Earth.
Past papers often ask for the advantages and disadvantages of nuclear power (Criteria D).
In an ‘evaluate’ question, present both sides: reliable, low CO₂ vs radioactive waste, accidents, decommissioning costs.
Do not confuse chemical reactions with nuclear – nuclear changes the nucleus, chemical involves electrons only.
Diagrams of chain reactions must show neutrons splitting other nuclei.
Radioactive sources are chosen based on half‑life and type of radiation.
Medical tracers: beta or gamma emitters with short half‑lives (hours) so they decay quickly after diagnosis. Iodine‑131 (beta/gamma, 8 days) is used for thyroid scans.
Radiotherapy: gamma rays (e.g., cobalt‑60) focused on tumours to kill cancer cells.
Industrial tracers: gamma sources to detect leaks in pipes; half‑life must be long enough for the process.
Thickness monitoring: beta particles – amount transmitted indicates paper thickness.
Always link the choice of isotope to its properties (penetrating power, half‑life).
Alpha sources are not used inside the body because they are too ionising and cannot penetrate tissue to be detected externally.
When ‘justifying’ an isotope choice, use data: half‑life, decay type.
For ‘suggest’ questions, think about safety: short half‑life reduces exposure time, penetrating radiation can be detected outside the body.
Q1. Which process powers the Sun?
Q2. Why is a radioactive tracer used in medicine?
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