Using the pie chart below, write a paragraph, Prepare to Learn Using the pie chart below, write a paragraph, summarising the main sources of background radiation.

Stable and Unstable Nuclei Text books Stable and Unstable Nuclei Homework: Read pages 4 & 5 Makes notes on the section ‘specific charge’

Objectives To know what keeps protons and neutrons together in the nucleus (knowledge) To understand why some nuclei are unstable (knowledge & application) To be able to complete decay equations for alpha and beta decay (analysis)

Recap from KS4

Present new information The strong nuclear force

Radioactive Decay

Present New Information Select 20 elements off the periodic table Record the number of protons (z) and the number of neutrons (N) in a table (you will need to make sure one of you elements has a proton number of 90+) Plot a graph of N against z and draw a line of best fit Label this line ‘line of stability’ Add a dotted line to your graph for N=z

Construct – Using the Graph Task 1 Area to the right of z = 84 Shade in blue This area represents elements that are all unstable. They decay by a decay – label the area ‘alpha decay’ Task 2 Colour the section above the line of stability red In this region, the nuclei are ‘neutron rich’ They decay by electron emission This is beta-minus decay Task 3 Colour the section below the line of stability green In this region, the nuclei are ‘proton rich’ They decay by positron emission This is beta-plus decay

Beta minus a neutron in an atom's nucleus turns into a proton Mini-review Alpha emitters Beta plus a proton in an atom's nucleus turns into a neutron

Alpha Decay

Copy the equation and label the: Parent nucleus Daughter nucleus Alpha particle

Mini Review Write the alpha decay equation for Polonium (208, 84)

What happens in beta-minus decay Some new particles here, but don’t worry too much – we do a separate lesson on antimatter in a few weeks!

What is the actual process? The isotope has too many neutrons A neutron changes into a proton + an electron (b-) This requires a down quark to change into an up

Copy the equation Label – parent nucleus, daughter nucleus, beta minus, anti-electron neutrino and energy Write the decay equations for a beta-minus decay from: Carbon (14,6) Oxygen (19,8)

Compare with beta-minus

Mini Review Write a general equation for beta plus decay Add the energy Label each section of the equation

What actually happens? The isotope has too many protons A proton changes into a neutron + a positron (b+) This requires an up quark to change into a down quark Write a beta-plus decay equation for Oxygen (15-8)

Mini Review Alpha Decay Beta Decay

Apply to demonstrate In the actinium series, uranium-235 (235,92) decays by the emission of 5 alpha particles and two beta-minus particles. Determine the proton and nucleon number of the nuclide formed when these decays have taken place.

Summary Stable nuclides Heavier nuclides have more neutrons than protons Most nuclides have an even no. of p and n Implies alpha is a stable combination O, Si and Fe account for over 75% of earth’s crust Unstable nuclides Disintegrations tend to produce new nuclides nearer the stability line A nuclide above the line decays to increase proton number i.e by β emission A nuclide below the line disintegrates so that Z decreases

Review of Objectives To know what keeps protons and neutrons together in the nucleus (knowledge) To understand why some nuclei are unstable (knowledge & application) To be able to complete decay equations for alpha and beta decay (analysis)