Edexcel A-Level Physics Nuclear and Particle Physics

Practise Edexcel A-Level Physics nuclear and particle physics through alpha scattering, accelerator fields, quarks and particle laws.

Exam points

explain alpha-scattering evidence for nuclear charge, empty space and concentrated mass
apply charge, baryon, lepton, energy and momentum conservation to particle interactions
use mass-energy, particle units and magnetic-track equations in accelerator contexts

Covered syllabus points

4.5.111 - Nucleon number and proton number 4.5.112 - Alpha scattering and the nuclear atom 4.5.113 - Thermionic emission and acceleration 4.5.114 - Fields in particle accelerators and detectors 4.5.115 - Charged-particle radius in a magnetic field 4.5.116 - Particle interaction conservation laws 4.5.117 - High energies and nucleon structure 4.5.118 - Mass-energy equivalence 4.5.119 - Particle energy and mass units 4.5.120 - Relativistic lifetime increase 4.5.121 - Standard quark-lepton model 4.5.122 - Particles and antiparticles 4.5.123 - Charge, baryon and lepton number conservation 4.5.124 - Particle equations

[Maximum number: 1]

Which of the following is the number of neutrons in a nucleus of ${ }_{51}^{121} \mathrm{Sb}$ ?

121

172

[Maximum number: 6]

In the early 20th century, experiments were carried out in which alpha particles were directed towards thin gold foil.

A simplified diagram of the apparatus used is shown.

Figure for Question 4.5 - Nuclear and Particle Physics question 2 — Edexcel A-Level Physics A2

State three observations and the corresponding conclusions made from the alpha particle scattering experiment.

Most alpha particles were undeviated

Or Most particles pass through with little or no deviation

Most of the atom is empty space

(MP2 with reference to lack of deviation)

Few alpha particles were scattered by small angles

There is a concentration of charge in the atom

(MP4 with reference to scattering)

Very few alpha particles were deviated by more than $90^{\circ}$

Most of the mass is concentrated in a small region of the atom

Or Most of the mass is concentrated in nucleus

(Accept Mass of nucleus much greater than mass of alpha particle)

(MP6 with reference to back scattering)

[Maximum number: 11]

The photograph shows a hospital radiotherapy machine that contains a linear accelerator (linac). The linac accelerates electrons to very high speeds for use in treating cancer.

(c) Alexander Tihonov/Pearson Asset Library)

(a)

The electrons used in the linac are produced by the filament in an electron gun, as shown in the diagram.

Figure for Question (a) — Edexcel A-Level Physics A2

Name and describe the process in which electrons are produced by the filament.

[ 2 ]

(b)

The diagram shows part of a simplified linac.

Figure for Question (b) — Edexcel A-Level Physics A2

An electron enters the linac from the electron gun with a speed of $2.5 \times 10^{6} \mathrm{~m} \mathrm{~s}^{-1}$ . The electron passes through 60 drift tubes before emerging from the other end.

[ 5 ]

(i)

Calculate the energy of the electron as it emerges.
potential difference between adjacent drift tubes =80 kV
(3)
Energy of the electron =

[ 3 ]

(ii)

For very high energy electrons, successive drift tubes have the same length.

Explain why.

[ 2 ]

(c)

Electrons emerging from a standing-wave linac are rotated through $270^\circ$ by magnets. Determine the required magnetic flux density.

electron energy $=2.5\,\mathrm{keV}$ ; path radius $=61\,\mathrm{mm}$ .

Figure for Question (c) — Edexcel A-Level Physics A2

[ 4 ]

Convert $2.5\,\mathrm{keV}$ to joules and use $E_k=p^2/(2m_e)$ , giving $p=2.70\times10^{-23}\,\mathrm{kg\,m\,s^{-1}}$ . Then r=p/(BQ) gives $B=p/(rQ)=0.0028\,\mathrm{T}$ .

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Covered syllabus points

4.5 - Nuclear and Particle Physics question 1

4.5 - Nuclear and Particle Physics question 2

4.5 - Nuclear and Particle Physics question 3

Question (a)

Question (b)

Question (i)

Question (ii)

Question (c)