The table shows information about three isotopes of thorium.
| Isotope | Proton number | Neutron number | Half-life | Amount in natural thorium |
|---|---|---|---|---|
| Thorium-228 | 90 | 138 | 1.9 years | trace |
| Thorium-230 | [A] | 140 | 75,000 years | 0.02% |
| Thorium-232 | 90 | [B] | 14 billion years | 99.98% |
State the values that should replace [A] and [B] to complete the table.
Explain what is meant by the term half-life.
Suggest why thorium-232 is the most common isotope of thorium found in nature.
Plutonium-239 can also be used as a nuclear fuel in some reactors. What are the products of the nuclear fission of a plutonium-239 nucleus?
What is the purpose of the thick concrete shielding that surrounds the nuclear reactor vessel?
Describe what happens in the reactor when the control rods are lowered further into the reactor core.
There have been several serious accidents at nuclear power stations, causing explosions that spread radioactive materials over surrounding regions. Explain why it is difficult to make the surrounding areas safe again after such an accident.