Americium-241 is a radioactive isotope commonly used in domestic ionization smoke detectors. It has the symbol:
95241Am95241Am \vphantom{}^{241}_{95}\text{Am} \hskip{1em} ^{241}_{95}\text{Am} 95241Am95241Am(i) How many protons are in an americium-241 nucleus? A: 95, B: 146, C: 241, D: 336.
(ii) How many neutrons are in an americium-241 nucleus? A: 95, B: 146, C: 241, D: 336.
(iii) How many electrons are in a neutral americium-241 atom? A: 95, B: 146, C: 241, D: 336.
When americium-241 decays, it emits alpha (α\alphaα) particles to form neptunium-237 (Np\text{Np}Np). Complete the nuclear equation by finding the values of xxx, yyy, and zzz:
95241Am⟶x237Np+zyα ^{241}_{95}\text{Am} \longrightarrow ^{237}_{x}\text{Np} + ^{y}_{z}\alpha 95241Am⟶x237Np+zyαAfter the decay, the neptunium-237 nucleus may emit a gamma (γ\gammaγ) ray. State what happens to the number of protons and neutrons in the nucleus as a result of gamma emission.
The diagram shows a cross-section of a domestic ionization smoke detector.
In normal operation, the americium-241 alpha source emits alpha particles into the air gap between the two charged metal plates. This ionizes the air, allowing a steady current to flow between the plates.
Explain how the alpha particles are able to ionize the air to allow a current to flow.
(i) Describe what is meant by the term half-life.
(ii) Americium-241 has a half-life of 432 years. Explain why Americium-242 (which has a half-life of 16 hours and is an alpha emitter) is not suitable for this application, and why a long-lived beta emitter is also not suitable.
