Within a nucleus, the nucleons are subject to two main forces which compete against each other.
(a) What are these two forces?
(b) Outline how the two forces compete against each other.
(c) Generally, that is for the majority of nuclides, which of the two forces remains dominant?
d. Alpha decay occurs only in the nuclei with the very largest number of nucleons.
(d) Explain why the strong force is not always dominant in the nuclides with the largest number of nucleons.
e. Americium-241, 95241Am , an isotope of americium used extensively in classrooms for demonstrating α -decay, decays into neptunium-237.
(e) Write a nuclear decay equation for the α -decay of americium-241 into neptunium-237.
(f) The following table shows the nuclear masses, in unified atomic mass units, for americium-241, neptunium-237 and an alpha-particle.
Particle
Mass (amu)
Americium-241
241.004579
Neptunium-237
236.99702
α -particle
4.00151
(i) Show that, energetically, this decay is possible.
(ii) Hence, calculate the energy released by the decay process.
(iii) What fraction of the available energy released would you expect to be taken away as kinetic energy by the α -particle?
(iv) In fact, the α -particle carries away 5.49 MeV of kinetic energy. Suggest a reason for this.
(g) Show that it is not possible for
(i) the americium nucleus to emit a proton only.
(Mass of proton = 1.00728 u; mass of 94240Pu = 240.00211 u )
(ii) The americium nucleus to emit a neutron only.
(Mass of neutron = 1.00867 u; mass of americium 240 = 240.00305 u)
(h) Suggest why it is almost always the case that heavy nuclei decay by alpha-decay and not by emitting a single proton or neutron.