Overview
This lecture provides a crash course on radiation for GAMSAT Section 3, covering radioactive decay, types of radiation, half-lives, and concepts of radiation dosage relevant to medical imaging.
Radioactive Decay Basics
- Radioactive decay occurs due to an unstable ratio of neutrons to protons in an atomic nucleus.
- Atoms decay to stabilize their mass and charge, emitting radiation in the process.
Types of Radiation
- Alpha Radiation: Emits an alpha particle (two protons, two neutrons), decreasing atomic number by 2 and mass number by 4.
- Beta Radiation: Two types:
- Beta-minus emits an electron, converting a neutron to a proton, increasing the atomic number by 1.
- Beta-plus emits a positron, converting a proton to a neutron, decreasing the atomic number by 1.
- Gamma Radiation: Emission of energy (not particles) to stabilize the nucleus’s energy state; usually follows alpha or beta decay.
Radioactive Decay Equations
- The sum of atomic and mass numbers must balance on both sides of decay equations.
- Changes in atomic or mass numbers identify the decay type and the resulting element.
Half-Life and Decay Curves
- Half-life is the time it takes for half of a radioactive sample to decay.
- After each half-life, 50% of the remaining sample decays, creating an exponential decay curve.
- Both activity and remaining mass/particles decrease exponentially over time.
Measuring Radiation Dosage
- Absorbed Dose: Energy absorbed per mass of tissue; measured in grays (Gy) or milligrays (mGy).
- Equivalent Dose: Absorbed dose adjusted for tissue sensitivity using tissue weighting factors; measured in sieverts (Sv).
- Effective Dose: Sum of equivalent doses from all affected tissues; also in sieverts.
Applications and Sample Problems
- Medical imaging applications include PET scans (positron emission tomography, using beta-plus decay), X-rays, and CT scans.
- Sample GAMSAT questions may involve decay sequence calculations, half-life math, and dosage estimations.
Key Terms & Definitions
- Radioactive Decay — Process by which an unstable atomic nucleus loses energy by emitting radiation.
- Alpha Particle — A helium nucleus (2 protons, 2 neutrons) emitted during alpha decay.
- Beta-minus Particle — An electron emitted when a neutron turns into a proton.
- Beta-plus Particle — A positron emitted when a proton turns into a neutron.
- Gamma Radiation — High-energy photons released to stabilize a nucleus’s energy state.
- Half-life — Time for half a radioactive sample to decay.
- Absorbed Dose (Gy) — Energy deposited per kilogram of tissue.
- Equivalent Dose (Sv) — Absorbed dose adjusted for radiation type and tissue sensitivity.
- Effective Dose (Sv) — Combined equivalent doses for all exposed tissues.
Action Items / Next Steps
- Review provided sample questions and solutions to reinforce understanding.
- Prepare for the next lecture on waves and light.
- Check the linked resources page for more sample questions and video walkthroughs.
- (Optional) Sign up for the Thursday Thoughts newsletter for Section 2 reading and writing practice.