A-LevelPhysicsNuclear physics9702/42 · May/June 2020 · Q128 Marks

Some masses are shown in Table 12.1. [Table 12.1]

(a)State what is meant by the mass defect of a nucleus.[2]
(b)(i)Show that: the energy equivalence of 1.00 u is 934 MeV[2]
(b)(ii)Show that: the binding energy per nucleon of a helium-4 nucleus is 7.09 MeV.[2]
(c)Isotopes of hydrogen have binding energies per nucleon of less than 3 MeV. Suggest why a nucleus of helium-4 does not spontaneously break down to become nuclei of hydrogen.[2]

Mark scheme

Marking points from the official mark scheme (May/June 2020). The mark or mark type is shown in brackets.

[1] difference between mass of nucleus and mass of (constituent) nucleons
[1] where nucleons are separated to infinity
[1] E = mc²
[1] = 1.66 × 10⁻²⁷ × (3.00 × 10⁸)² / (1.60 × 10⁻¹³) = 934 MeV
[1] mass defect = 2 × (1.007276 + 1.008665) – 4.001506
[1] (= 0.030376)
[1] binding energy per nucleon = (0.030376 × 934)/4 = 7.09 MeV
[1] binding energy per nucleon is much greater
[1] so would require a large amount of energy to separate the nucleons in helium
[1] amount of energy released in forming hydrogen isotopes
[1] is less than energy required to break apart helium nucleus

On Oracle Prep you can write or photograph your own answer and have it marked by AI against this mark scheme, with feedback on what you missed.