True or False Alpha is the least penetrating form of radiation Betas particles are radioactive Up and Down are antimatter pairs of quarks Gamma is a highly penetrating form of radiation The radioactive sources in school are safe to use because they have a short half life. Alpha decay will increase the proton number by 2. A particle formed by beta+ emission will have a lepton number of 1. All hadrons consist of 3 quarks Only quarks are influenced by the nuclear strong force Marie Curie discovered radioactivity

A graph can be plotted showing the change in N, the N – Z Curves A graph can be plotted showing all known nuclides with N, the neutron number, plotted against Z, the proton number. This produces a graph which has a thin line of stable elements with a non-linear gradient slightly steeper than 1.0 (i.e. 1 proton for each neutron). We know this will be the case because the repulsive force experienced by the protons would be too great if the neutrons were not there to separate them. Each additional neutron increases the nuclear strong force whilst lessening the electrostatic repulsion due to separation of charges.

Z>83 Too many protons and neutrons: α emission Stable nuclei line Too many neutrons to be stable: β- emission Too many protons to be stable: β+ emission

Empirical rules deduced from the N – Z curve Lighter nuclides (Z < 20) have N approximately equal to Z Heavier nuclides require more neutrons than protons to be stable For all values of Z > 83, nuclei are unstable Most stable nuclei have even numbers of protons and neutrons

2 neutrons and 2 protons are given out What does an alpha decay look like on the N – Z graph? N Neutron no. Proton no. Z Alpha: 2 neutrons and 2 protons are given out

A neutron turns into a proton What does beta decay look like on the N – Z graph? N Neutron no. Proton no. Z Beta: A neutron turns into a proton

U - 238 will decay through a process of alpha and beta decays to form the stable isotope Pb - 206. Can you work out the decay chain?

U-238 DECAY CHAIN

gamma absorption emission penetration stable alpha unstable decay nucleus beta