2. Some nuclei – usually large ones – are unstable They cannot fit their neutrons and protons into a space small enough that that strong nuclear force can act on all of them When that happens, the atom changes its nucleus to become more stable Sometimes, atoms follow a long chain of decay reactions, until the atom is finally stable and will not decay any further

3. Helium nuclei – made up of two protons and two neutrons – can be ejected by the original nucleus This is alpha decay Alpha particles are relatively heavy and positively charged

4. In beta decay, a neutron decays to a proton and an electron The electron is ejected from the nucleus, while the proton stays in the nucleus Beta particles are very, very light and negatively charged

5. Gamma decay occurs if a nucleus is still excited (has too much energy) following another decay event Gamma decay ejects energy from the nucleus in the form of high energy electromagnetic radiation. It has no charge and no mass

6. Alpha particles are stopped by a sheet of paper. They have low penetrating power Beta particles are stopped by thin sheets of aluminium or other metals. They have medium penetrating power Gamma rays have high penetrating power. They can penetrate up to several cm of lead

7. In a magnetic field, different types of radiation move differently. Gamma radiation is uncharged and therefore undeflected Alpha radiation is positively charged and relatively heavy, so it curves a little one way Beta radiation is negatively charged and relatively light, so it curves a lot the other way

8. This shows the alpha decay of Uranium-238 The Mass number is always conserved, then the atomic number is also conserved. The element symbols are written on last

9. Because the electron has no mass number, and has an atomic (charge) number of -1, the overall effect is that a neutron changes to a proton in the nucleus Write the original atom, then the beta particle, then balance the mass number and atomic number

10. 226 Ra 88 Rn + 86 222 He 4 2 Step one: write down the things you know, that radium 226 is decaying to Radon 222 Step two: identify the decay taking place by balancing the mass numbers and atomic numbers on each side Step three: fill in the remaining gaps