Overview
This lecture explains radioactive decay, its types (alpha, beta, gamma, and neutron emission), the effects on atomic structure, and properties of each radiation type.
Radioactive Decay Basics
- Unstable atomic nuclei undergo radioactive decay to become more stable by emitting radiation.
- The decay process is random and results in the emission of various particles or waves.
Alpha Decay
- Occurs when an atom has too few neutrons.
- Releases an alpha particle (2 protons and 2 neutrons), also called a helium nucleus.
- Atomic number decreases by 2, mass number decreases by 4.
- Changes the element because the number of protons changes (e.g., oxygen-17 to carbon-13).
- Alpha radiation has low penetrating power (stopped by skin or a few cm of air) but high ionizing power.
Beta Decay
- Happens when an atom has too many neutrons.
- A neutron transforms into a proton and a high-speed electron (beta particle).
- Atomic number increases by 1, mass number stays the same.
- Changes the element (e.g., oxygen-17 to fluorine-17).
- Beta radiation penetrates air and skin but is stopped by thick aluminum; has lower ionizing power than alpha.
Gamma Decay
- Unstable nuclei emit gamma rays to lose excess energy.
- Gamma rays are high-energy electromagnetic waves from the nucleus.
- Atomic number and mass number do not change.
- Highest penetrating power (stopped by thick lead) but lowest ionizing power.
Neutron Emission
- Atoms can emit neutrons naturally or artificially (e.g., James Chadwick’s experiment).
- Emitting a neutron decreases the mass number by 1 but does not change the element.
- Example: oxygen-17 emits a neutron and becomes oxygen-16.
Key Terms & Definitions
- Radioactive decay — Random process where an unstable nucleus emits radiation to become stable.
- Alpha particle — 2 protons and 2 neutrons; same as a helium nucleus.
- Beta particle — High-speed electron emitted from the nucleus during beta decay.
- Gamma ray — High-energy electromagnetic radiation from the nucleus.
- Ionizing power — Ability of radiation to ionize atoms; alpha has the highest, gamma the lowest.
- Penetrating power — Ability of radiation to pass through materials; gamma the highest, alpha the lowest.
Action Items / Next Steps
- Practice the provided decay questions.
- Review how atomic and mass numbers change with each decay type.