Overview
This lecture covers the basics of radioactivity, types of radioactive decay, properties of radiation, uses of radioisotopes, safety precautions, and example exam questions.
Introduction to Radioactivity
- Radioactive substances emit radiation from unstable atomic nuclei as they decay.
- Radiation exposure can occur through contamination (ingesting radioactive material) or irradiation (exposure to emitted radiation).
- Natural radiation sources include radon gas, cosmic rays, and building materials; artificial sources include x-rays and nuclear reactors.
- Radiation is detected using devices like Geiger counters, with the count rate measuring the amount of radiation.
Types of Radioactive Decay and Radiation
- Radioactive decay is a random process that changes an unstable nucleus into a more stable one.
- The three main types of radiation are alpha particles (2 protons, 2 neutrons), beta particles (electrons), and gamma rays (electromagnetic radiation).
- Alpha radiation is the least penetrating (stopped by paper), beta is intermediate (stopped by aluminum), and gamma is the most penetrating (stopped by thick lead).
- Ionizing power: alpha is most ionizing, beta is moderate, and gamma is least ionizing.
Properties and Identification of Radiation
- Alpha particles are positively charged, beta particles negative, and gamma rays have no charge.
- Radiation types can be identified using electric or magnetic fields: alpha is attracted to negative plates, beta to positive plates, gamma is unaffected.
- Radioactive decay results in the transformation of one element into another.
Half-Life and Activity
- Activity measures the rate of decay of a radioactive substance and decreases over time as nuclei decay.
- Half-life is the average time it takes for half of the radioactive atoms in a sample to decay.
- Example calculations involve determining how many half-lives elapse for a count rate to fall to a given value.
Uses of Radioisotopes
- Smoke detectors use alpha particles to ionize air and detect smoke.
- Beta radiation is used to measure thickness in manufacturing (e.g., paper mills).
- Gamma rays are used for cancer treatment and food sterilization due to their high penetration.
- Radioactive tracers help diagnose medical conditions and detect leaks in pipes.
- Carbon dating uses carbon-14 half-life to estimate the age of organic remains.
Safety Precautions with Radioactive Materials
- Radiation can kill cells, cause cancer by mutating DNA, or cause genetic changes.
- Precautions include protective clothing, remote handling, shielded storage, radiation badges, and limiting exposure time.
Key Terms & Definitions
- Radioactive decay — Spontaneous transformation of an unstable nucleus emitting radiation.
- Half-life — Time required for half the atoms of a radioactive material to decay.
- Alpha particle — Helium nucleus (2 protons, 2 neutrons), highly ionizing, low penetration.
- Beta particle — High-speed electron, moderately ionizing, medium penetration.
- Gamma ray — High-energy electromagnetic wave, weakly ionizing, strong penetration.
- Ionization — Process where radiation removes electrons from atoms, forming ions.
- Activity — Rate at which radioactive decays occur, measured in becquerels.
Action Items / Next Steps
- Review example calculations involving half-life and activity.
- Practice identifying radiation types using their properties.
- Read about additional uses of radioisotopes in medicine and industry.