Date | November 2021 | Marks available | 1 | Reference code | 21N.2.SL.TZ0.5 |
Level | Standard level | Paper | Paper 2 | Time zone | 0 - no time zone |
Command term | State | Question number | 5 | Adapted from | N/A |
Question
Plutonium-238 (Pu) decays by alpha (α) decay into uranium (U).
The following data are available for binding energies per nucleon:
plutonium 7.568 MeV
uranium 7.600 MeV
alpha particle 7.074 MeV
State what is meant by the binding energy of a nucleus.
Draw, on the axes, a graph to show the variation with nucleon number AA of the binding energy per nucleon, BEABEA. Numbers are not required on the vertical axis.
Identify, with a cross, on the graph in (a)(ii), the region of greatest stability.
Show that the energy released in this decay is about 6 MeV.
The plutonium nucleus is at rest when it decays.
Calculate the ratio kinetic energy of alpha particlekinetic energy of uraniumkinetic energy of alpha particlekinetic energy of uranium.
Markscheme
the energy needed to «completely» separate the nucleons of a nucleus
OR
the energy released when a nucleus is assembled from its constituent nucleons ✓
Accept reference to protons AND neutrons.
curve rising to a maximum between 50 and 100 ✓
curve continued and decreasing ✓
Ignore starting point.
Ignore maximum at alpha particle
At a point on the peak of their graph ✓
correct mass numbers for uranium (234) and alpha (4) ✓
234×7.600+4×7.074-238×7.568234×7.600+4×7.074−238×7.568 «MeV» ✓
energy released 5.51 «MeV» ✓
Ignore any negative sign.
«KEαKEU=KEαKEU=»p22mαp22mUp22mαp22mU OR mUmαmUmα ✓
«2344=2344=» 58.558.5 ✓
Award [2] marks for a bald correct answer.
Accept 11721172 for MP2.