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 | Identify | 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 A of the binding energy per nucleon, BEA. 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 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+4×7.074-238×7.568 «MeV» ✓
energy released 5.51 «MeV» ✓
Ignore any negative sign.
«KEαKEU=»p22mαp22mU OR mUmα ✓
«2344=» 58.5 ✓
Award [2] marks for a bald correct answer.
Accept 1172 for MP2.