Mass–Energy & Nuclear Physics — practice questions

A nucleus has a mass defect of $\Delta m = 0.0250$ u.

Calculate the binding energy in MeV, using $1$ u $= 931.5$ MeV/c².

A lithium-7 nucleus (mass $7.0154$ u) contains 3 protons ($1.0073$ u each) and 4 neutrons ($1.0087$ u each).

Calculate the binding energy per nucleon, in MeV.

Explain, in terms of the strong nuclear force and mass–energy equivalence, why the mass of a stable nucleus is always less than the sum of the masses of its separate protons and neutrons, and explain what the binding energy physically represents.

In a nuclear reaction, the total mass before is $240.1173$ u and the total mass after is $240.0968$ u.

Calculate the energy released, in MeV.

A uranium-235 nucleus (mass $235.0439$ u) absorbs a neutron ($1.0087$ u) and fissions into barium-141 ($140.9144$ u), krypton-92 ($91.9262$ u), and 3 free neutrons ($1.0087$ u each).

Calculate the Q-value of this reaction in MeV, and state what happens to this energy.

Explain why fission of a heavy nucleus such as uranium-235 releases energy, and explain how the free neutrons produced allow the process to sustain itself as a chain reaction.

In a fusion reaction, the total mass before is $4.0282$ u and the total mass after is $4.0248$ u.

Calculate the energy released, in MeV.

Using the binding energy per nucleon curve, explain why fusing two light nuclei into a heavier one releases energy, referring to how binding energy per nucleon changes.

Using the binding energy per nucleon curve, explain why BOTH fission of a heavy nucleus and fusion of light nuclei release energy, and explain why fusion or fission of nuclei near iron (A ≈ 56) would not release energy.