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| Question | Answer |
| How can the stability of a nuclide be determined? | By examining its neutron and proton content We can plot a graph of N (number of neutrons) against Z (number of protons) |
| What does the stability of a nucleus depend on? | The size and proton number |
| What are the features of an N-Z graph? | For proton numbers up to 20- N=Z so a straight line For all Nuclei with Z>20, stable nuclei have more neutrons then protons, so the line curves upwards. The extra neutrons help bind the nucleus without contributing to the coulomb repulsion |
| What are unstable nuclei above the stability curve called? | Neutron rich |
| What are unstable nuclei below the stability curve called? | Neutron poor |
| How can unstable neutron rich nuclei become more stable? | By loosing neutrons Do this by beta decay B- Z+1 N-1 |
| How can unstable neutron poor nuclei become more stable? | By gaining neutrons Do this by positron decay B+ Z-1 N+1 |
| When can electron capture occur? | In the regions on the curve where B+ happens Generally happens when there is not enough energy for B+ |
| What happens in electron capture? | The nucleus takes an electron from its lower shells Combines it with a proton and produces a neutron and electron neutrino |
| What effect does alpha decay have on the position of the nucleus relative to the stability curve and why? | Very little effect Because loss of an alpha particle is 2p and 2n so doesn't upset the N-Z ratio too much |
| What nuclei participate in Alpha decay? | Only large nuclei |
| Where does the effect of Alpha decay occur on the curve and why? | Only confined to the very top section of the curve Because the nucleus has become so large, the nuclear strong force can not across its whole width |
| What are decay chains? | A chain of decays that unstable nuclei will undergo in order to reach stability And in doing so will pass through being several different elements |
| What four decay chains naturally occur? | Thorium, Neptunium, Uranium and Actinium chains |
| What may happen after a nucleus has undergone a chain of reactions? | May find itself as a new element in an excited state |
| What must elements in an excited state do to reach its ground state? | Energy must be emitted as gamma radiation |
| What is a meta stable state? | A state which will be long lived but cannot be defined as indefinate |
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