The table shows information about three isotopes of uranium.
| Isotope | Proton number | Neutron number | Half-life | Abundance in natural uranium |
|---|---|---|---|---|
| Uranium-234 | 92 | 142 | 246,000 years | 0.005% |
| Uranium-235 | [A] | 143 | 704 million years | 0.72% |
| Uranium-238 | 92 | [B] | 4.5 billion years | 99.27% |
State the values that should replace [A] and [B] to complete the table.
Explain what is meant by the term half-life of a radioactive isotope.
Suggest why uranium-238 is the most common isotope of uranium found in nature.
Uranium-235 can be used as a fuel in fission reactors. State the products resulting from the induced nuclear fission of a single uranium-235 nucleus.
What is the purpose of the thick concrete shielding that surrounds a nuclear reactor vessel?
Describe what happens in the reactor core when the control rods are partially withdrawn from (raised out of) the core.
Following a serious nuclear accident, radioactive isotopes such as Caesium-137 (with a half-life of approximately 30 years) are deposited in the surrounding environment. Explain why isotopes with a medium half-life of this scale make the area difficult to make safe, compared to those with extremely short or extremely long half-lives.
