Radioactivity

Contents Atomic Structure Atomic Structure Isotopes Isotopes Background Radiation Background Radiation Alpha, Beta, Gamma Alpha, Beta, Gamma Uses of Radiation Uses of Radiation Nuclear Fission Nuclear Fission Chain Reactions Chain Reactions

Atomic Structure Electron: negative, mass nearly nothing Proton: positive, same mass as neutron (“1”) Neutron: neutral, same mass as proton (“1”)

Isotopes The atomic number controls which element it is. e.g. Oxygen must always have 8 protons Isotopes are the same element with a different mass number. Isotopes have different numbers of neutrons Radiation occurs when the mass number of an element changes

Background Radiation Radon gas Food Cosmic rays Gamma rays Medical Nuclear power 13% are man-made

Alpha, Beta, Gamma Alpha (α): atom decays into a new atom & emits an alpha particle (2 protons and 2 neutrons: the nucleus of a helium atom) Beta ( β ): atom decays into a new atom by changing a neutron into a proton & electron. The fast moving, high energy electron is called a beta particle Gamma (γ): after α or β decay, surplus energy is sometimes emitted. This is called gamma radiation & has a very high frequency with short wavelength. The atom is not changed Unstable nucleus New nucleus Alpha particle Beta particle Gamma radiation

Uses of Radiation β passes through paper, card etc. β passed through sheets to a detector When β count slows  material is too thick α  γ Sheet of paperThin foil Few cm of lead γ kills microbes Medical instruments sterilised Food keeps fresh for longer No damage to substances Half-life short so no radiation afterwards

Nuclear Fission Nuclear fission occurs when the mass number of an element splits. The product is a new element and released neutrons Nuclear fission releases heat energy This heat is harnessed in nuclear power stations to boil water, which is used to drive turbines and machinery The amount of energy produced by each reaction is very small billions of reactions occur every second The waste products from these reactions are radioactive, which is why many people worry about nuclear power plants

Uranium nucleus Unstable nucleus New nuclei (e.g. barium and krypton) More neutrons Neutron Nuclear Fission

Chain Reactions Each fission reaction releases neutrons that are used in further (chain) reactions

Summary Nucleus = protons and neutrons; electrons are in shells Nucleus = protons and neutrons; electrons are in shells Isotopes = same element with different mass number Isotopes = same element with different mass number Background radiation = many causes, some man-made Background radiation = many causes, some man-made Alpha (highly ionising, low penetration), Beta (stopped by a few mm of foil), Gamma (high penetration  v dangerous) Alpha (highly ionising, low penetration), Beta (stopped by a few mm of foil), Gamma (high penetration  v dangerous) Uses of radiation (Beta: quality assurance, Gamma: medical instruments & food freshness) Uses of radiation (Beta: quality assurance, Gamma: medical instruments & food freshness) Nuclear fission = atom divides  releases neutrons Nuclear fission = atom divides  releases neutrons Chain reactions = result of released neutrons Chain reactions = result of released neutrons