Today’s Title: CW: Ionising radiation 21 April 2017 Today’s Title: CW: Ionising radiation Learning Question: What makes some isotopes radioactive? Starter – Name the two parts that make up the nucleus of an atom

Key words… Radiation Ion Radioactive Penetration distance Alpha and beta particles Gama rays

Atoms Atoms are made up of two main parts, the nucleus and orbiting electrons. Electrons can be lost or gained and this forms charged particles - ions. The nucleus contains two types of particles called neutrons and protons. As protons, neutrons and electrons are the building blocks of atoms they're called sub-atomic particles. Electron (e-) proton (p+) Neutron (n+)

Ions Since the number of electrons and protons in an atom are equal, there is no overall charge. If an atom gains or loses an electron, its charge will change and it becomes an ion Particle Relative mass Relative charge Proton 1 +1 Neutron Electron Almost zero -1

Ionising radiation Ionising radiation has enough energy to cause atoms to lose electrons and become ions A radioactive substance has an unstable nucleus. The unstable nucleus decays to become more stable by losing energy when certain types of ionising radiation are emitted from the nucleus. The types of radiation t hat can do this are: Alpha particles Beta particles and Gamma radiation You cannot predict when a nucleus will decay – it is a random process!

Ionising radiation – alpha particles Alpha particles contain 2 protons and 2 neutrons, just like the nucleus of He. Alpha particles have NO electrons, so have an overall charge of +2. Alpha particles travel at high speeds, so lose energy quickly. This means that they only travel short distances and have a short penetration distance. They can be stopped by a sheet of paper.

Alpha particle summary equivalent to the nucleus of a helium atom – contains 2 protons and 2 neutrons charge of +2 stopped by a few cm of air or a few sheets of paper most ionising type of radiation

Ionising radiation – beta particles Beta particles are electrons that are given out from an unstable nucleus These particles are much less ionising than alpha particles, so can travel further into an object. Beta particles can be stopped by a thin layer of aluminium or by an even smaller layer of lead

Beta particle summary Beta particle electron emitted from nucleus charge of –1 stopped by a few mm of aluminium moderately ionising

Ionising radiation – gamma rays Gamma rays are high frequency electromagnetic waves that are given out by some unstable nuclei and so travel at the speed of light. Gamma rays do not have an electrical charge. Gamma rays are x10 less ionising that beta particles. This means they can travel further and penetrate matter very easily. Gamma rays can be stopped by a few centimetres of lead and absorbed by many meters of concrete.

Gamma ray summary Gamma ray electromagnetic wave not charged stopped by a few cm of lead or many metres of concrete least ionising form of radiation

http://www.bbc.co.uk/learningzone/clips/alpha-beta-and-gamma-radiation-pt-1-2/4561.html

A: An atom with an electrical charge. 1 What is an ion? A: An atom with an electrical charge. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original.

2. A fluorine atom has seven electrons 2 A fluorine atom has seven electrons. It gains an electron when it becomes an ion. What charge does a fluoride ion have? A: –1. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original.

3 What is the mass number of an alpha particle? A: 4 © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original.

4 What materials will absorb and stop beta particles? A: A few millimetres of aluminium or a smaller thickness of lead . © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original.

5 The reactor in a nuclear power station is surrounded by large amounts of concrete. Why is this necessary? A: To stop gamma rays. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original.

6 Draw up a table to summarise the form, charge, penetration and ionisation properties of the three types of radiation. A: Alpha particle Beta particle Gamma ray equivalent to the nucleus of a helium atom – contains 2 protons and 2 neutrons electron emitted from nucleus electromagnetic wave charge of +2 charge of –1 not charged stopped by a few cm of air or a few sheets of paper stopped by a few mm of aluminium stopped by a few cm of lead or many metres of concrete most ionising type of radiation moderately ionising least ionising form of radiation

7 What changes take place in a nucleus when it emits an alpha particle? A: Its mass number goes down by 4 and its atomic number goes down by 2 – it becomes a different element. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original.

8 Explain how an oxygen molecule in the air might become an ion by being near a radioactive source. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original.

Ionising radiation collides with oxygen atom. A: Radioactive source emits ionising radiation (e.g. alpha particles, beta particles or gamma rays). Ionising radiation collides with oxygen atom. Collision knocks an electron out of the oxygen atom. Charge in the nucleus is now not balanced by the charge on the electrons. The atom has a net charge and so is an ion. © Pearson Education Ltd 2011. Copying permitted for purchasing institution only. This material is not copyright free. This document may have been altered from the original.