Ionising Radiation A2 Waves and Radiation

Radioactive Decay Law Time characteristics of radioactive decay depend upon two important ideas Radioactive decay is a completely random process Nuclei have no memory The first of these ideas means you cannot tell if a nuclei will decay in a given time period. There is a probability that it will decay within the time period, not no certainty. The second point shows that if the half life of a sample had decayed in 4.5 seconds, it would be thought that all would decay in 9 seconds. This isn't true as the nuclei have no memory of its previous decay and therefore doesn't mean that it is anymore likely to decay in the second instance as it is in the first.

Alpha Decay Certain heavier elements emit alpha particles in order to become more stable. The alpha particle consists of 2 protons and 2 neutrons and is the nucleus of a Helium atom. Alpha particles are very tightly bound and these are the only multi particle systems that occur in radioactive decay. Unstable nucleus New nucleus Alpha particle

Beta decay In a beta negative decay a neutron in the radioisotope will decay leaving behind a proton, an electron and an anti-neutrino. Anti-neutrino New nucleus Beta - particle Unstable nucleus

Gamma decay Gamma decay only usually takes place when another form of radioactive decay takes place. It takes the form of a high energy electromagnetic wave which takes away any left over energy from the original decay. From this Gamma decay doesn't have an effect on the mass number or the atomic number of the element. Unstable nucleus New nucleus Gamma radiation

Penetration Properties If a substance is capable of ALWAYS emitting radiation under any conditions we say it is ____________. There are three types of radiation: ALPHA, _____ and GAMMA. These types of radiation are always given off by rocks, _____, building materials, air and cosmic rays around us – this is called BACKGROUND RADIATION. Each type is capable of penetrating different materials:    Sheet of paper Few mm of _________ Few cm of lead Words – aluminium, beta, food, radioactive

Ionisation When radiation collides with neutral atoms or molecules it alters their structure by knocking off electrons. This will leave behind IONS – this is called IONISING RADIATION.  particle Electron

Dangers of Ionising Radiation Radiation will ionise atoms in living cells – this can damage them and cause cancer or leukaemia. Alpha Beta Gamma OUTSIDE the body  and  are more dangerous as  radiation is blocked by the skin. INSIDE the body an  source causes the most damage because it is the most ionising.