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Date November 2021 Marks available 2 Reference code 21N.2.SL.TZ0.5
Level Standard level Paper Paper 2 Time zone 0 - no time zone
Command term Draw 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.

[1]
a.i.

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.

[2]
a.ii.

Identify, with a cross, on the graph in (a)(ii), the region of greatest stability.

[1]
a.iii.

Show that the energy released in this decay is about 6 MeV.

[3]
b.i.

The plutonium nucleus is at rest when it decays.

Calculate the ratio kinetic energy of alpha particlekinetic energy of uranium.

[2]
b.ii.

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.

a.i.

curve rising to a maximum between 50 and 100 ✓

curve continued and decreasing ✓

 

Ignore starting point.

Ignore maximum at alpha particle

a.ii.

At a point on the peak of their graph ✓

a.iii.

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.

b.i.

«KEαKEU=»p22mαp22mU  OR  mUmα ✓

«2344=» 58.5 ✓

 

Award [2] marks for a bald correct answer.

Accept 1172 for MP2.

b.ii.

Examiners report

[N/A]
a.i.
[N/A]
a.ii.
[N/A]
a.iii.
[N/A]
b.i.
[N/A]
b.ii.

Syllabus sections

Core » Topic 7: Atomic, nuclear and particle physics » 7.2 – Nuclear reactions
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