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Date November 2017 Marks available 3 Reference code 17N.2.HL.TZ0.3
Level Higher level Paper Paper 2 Time zone Time zone 0
Command term Outline Question number 3 Adapted from N/A

Question

The Feynman diagram shows electron capture.

Particles can be used in scattering experiments to estimate nuclear sizes.

Electron diffraction experiments indicate that the nuclear radius of carbon-12 is 2.7 x 10–15 m. The graph shows the variation of nuclear radius with nucleon number. The nuclear radius of the carbon-12 is shown on the graph.

State and explain the nature of the particle labelled X.

[3]
a.i.

Outline how these experiments are carried out.

[2]
b.i.

Outline why the particles must be accelerated to high energies in scattering experiments.

[3]
b.ii.

State and explain one example of a scientific analogy.

[2]
c.

Determine the radius of the magnesium-24 nucleus.

[2]
d.i.

Plot the position of magnesium-24 on the graph.

[1]
d.ii.

Draw a line on the graph, to show the variation of nuclear radius with nucleon number.

[2]
d.iii.

Markscheme

«electron» neutrino

it has a lepton number of 1 «as lepton number is conserved»

it has a charge of zero/is neutral «as charge is conserved»
OR
it has a baryon number of 0 «as baryon number is conserved»

Do not allow antineutrino

Do not credit answers referring to energy

a.i.

«high energy particles incident on» thin sample

detect angle/position of deflected particles

reference to interference/diffraction/minimum/maximum/numbers of particles

Allow “foil” instead of thin

b.i.

λ \( \propto \frac{1}{{\sqrt E }}\) OR λ \( \propto \frac{1}{E}\)

so high energy gives small λ

to match the small nuclear size

Alternative 2

E = hf/energy is proportional to frequency

frequency is inversely proportional to wavelength/c = fλ

to match the small nuclear size

Alternative 3

higher energy means closer approach to nucleus

to overcome the repulsive force from the nucleus

so greater precision in measurement of the size of the nucleus

Accept inversely proportional

Only allow marks awarded from one alternative

b.ii.

two analogous situations stated

one element of the analogy equated to an element of physics

eg: moving away from Earth is like climbing a hill where the contours correspond to the equipotentials

Atoms in an ideal gas behave like pool balls

The forces between them only act during collisions

c.

R = 2.7 x 10–15 x \({2^{\frac{1}{3}}}\)

3.4 – 3.5 x 10–15 «m»

Allow use of the Fermi radius from the data booklet

d.i.

correctly plotted

Allow ECF from (d)(i)

d.ii.

single smooth curve passing through both points with decreasing gradient

through origin

d.iii.

Examiners report

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

Syllabus sections

Additional higher level (AHL) » Topic 12: Quantum and nuclear physics » 12.2 – Nuclear physics
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