Edexcel A-Level Physics A2 4.5 Nuclear and Particle Physics Questions

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 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 $B=p/(rQ)=0.0028\,\mathrm{T}$ .

[Maximum number: 2]

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.

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

Figure for Question 4 — Edexcel A-Level Physics A2

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

[Maximum number: 2]

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.

The diagram shows part of a simplified linac.

Figure for Question 5 — 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.

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

Explain why.

[Maximum number: 3]

In 1932, Carl Anderson published this photograph of a track in a cloud chamber. The cloud chamber contained a lead plate. There was a magnetic field perpendicular to the plane of the track.

Figure for Question 6 — Edexcel A-Level Physics A2

The photograph shows the track of a positron from cosmic rays and is the first photographic record of the existence of an antiparticle.

In the upper part of the photograph the positron had an energy of 23 MeV .

For relativistic particles such as this positron, momentum obeys the relationship

E=pc

where E = particle energy, p = particle momentum and c = speed of light.

Determine the magnetic flux density of the magnetic field.

Radius of curvature of path = $3.7\,\mathrm{cm}$

Magnetic flux density =

Use of E=p c (ecf for E from (c)(i))

- Use of r=p / B q

- $B=2.1 \mathrm{~T}$

Do not award MP1 if p=m v calculated using v from part (i)

Example of calculation
$\begin{aligned} & 3.7 \times 10^{-12} \mathrm{~J}=p \times 3.00 \times 10^{8} \mathrm{~m} \mathrm{~s}^{-1} & p=1.2 \times 10^{-20} \mathrm{~N} \mathrm{~s} & 0.037 \mathrm{~m}=1.2 \times 10^{-20} \mathrm{~N} \mathrm{~s} / B \times 1.6 \times 10^{-19} \mathrm{C} & B=2.1 \mathrm{~T} \end{aligned}$

[Maximum number: 4]

Actinium-225 is a radioactive isotope. It decays to francium by emitting alpha particles. Actinium-225 has a short half-life, which makes it suitable for medical applications.

The francium nucleus and the alpha particle move away from each other after the decay.

Explain why the kinetic energy given to the alpha particle is just less than 5.9 MeV . mass decrease for the decay $=6.35 \times 10^{-3} u$

[Maximum number: 1]

The structure of nucleons can be investigated using high energy electrons.
Which of the following is the reason high energies are needed?

to cause annihilation

to produce individual quarks

to produce short de Broglie wavelengths

to overcome the repulsive electrostatic forces

[Maximum number: 4]

In 1932, Carl Anderson published this photograph of a track in a cloud chamber. The cloud chamber contained a lead plate. There was a magnetic field perpendicular to the plane of the track.

Figure for Question 9 — Edexcel A-Level Physics A2

The photograph shows the track of a positron from cosmic rays and is the first photographic record of the existence of an antiparticle.

A positron travelling at a non-relativistic speed of $1.5 \times 10^{7} \mathrm{~m} \mathrm{~s}^{-1}$ collides with an electron travelling at the same speed in the opposite direction. This collision results in the production of gamma radiation.

Calculate the frequency of the gamma radiation produced.

Frequency =

Use $E_k=\frac12mv^2$ , $\Delta E=c^2\Delta m$ , and E=hf.

For the electron and positron, total kinetic energy is $2.0\times10^{-16}\,\mathrm{J}$ , and rest energy is $1.64\times10^{-13}\,\mathrm{J}$ . Each of the two gamma photons has energy $8.2\times10^{-14}\,\mathrm{J}$ .

$8.2\times10^{-14}=6.63\times10^{-34}f$

Therefore $f=1.2\times10^{20}\,\mathrm{Hz}$ .

[Maximum number: 3]

In 1932, Carl Anderson published this photograph of a track in a cloud chamber. The cloud chamber contained a lead plate. There was a magnetic field perpendicular to the plane of the track.

Figure for Question 10 — Edexcel A-Level Physics A2

The photograph shows the track of a positron from cosmic rays and is the first photographic record of the existence of an antiparticle.

In the upper part of the photograph the positron had an energy of 23 MeV .

Show that the positron must have been travelling at a relativistic speed. Assume that all of its energy is kinetic energy.

Use of conversion factor $1.6 \times 10^{-19} \mathrm{C}$

- Use of $E_{\mathrm{k}}=1 / 2 m v^{2}$

- Calculated speed $=2.8 \times 10^{9}\left(\mathrm{~m} \mathrm{~s}^{-1}\right)$ , which is greater than the speed of light (so it must be relativistic)

Example of calculation
$\begin{aligned} & E_{\mathrm{k}}=23 \times 10^{6} \mathrm{eV} \times 1.6 \times 10^{-19} \mathrm{C}=3.7 \times 10^{-12} \mathrm{~J} & 3.7 \times 10^{-12} \mathrm{~J}=0.5 \times 9.11 \times 10^{-31} \mathrm{~kg} \times v^{2} & v=2.8 \times 10^{9} \mathrm{~m} \mathrm{~s}^{-1} \end{aligned}$

[Maximum number: 3]

A spark chamber consists of a set of parallel metal plates. It can reveal the path of a high energy particle as shown.

Figure for Question 11 — Edexcel A-Level Physics A2

A potential difference of 10.5 kV is applied across two adjacent plates as shown below.

Most of the particles detected in the spark chamber are muons. The muons were created in the upper atmosphere. Muons normally have a very short lifetime and should have decayed before they reach the surface of the Earth.

Explain why these muons reach the surface of the Earth.

[Maximum number: 2]

Experiments with muons are taking place at Fermilab in the USA to improve our understanding of the standard model.

The muon belongs to the same family of particles as the electron.

State how the muon is classified in the standard model.

[Maximum number: 3]

In 1932, Carl Anderson published this photograph of a track in a cloud chamber. The cloud chamber contained a lead plate. There was a magnetic field perpendicular to the plane of the track.

Figure for Question 13 — Edexcel A-Level Physics A2

The photograph shows the track of a positron from cosmic rays and is the first photographic record of the existence of an antiparticle.

State the properties of a positron that show it is the antiparticle to the electron.

[Maximum number: 3]

A muon will decay into a neutrino, an antineutrino and an electron or a positron.
A positron is the antiparticle of an electron.

Explain whether the following decay would be possible.

You should consider conservation of charge and lepton number.

\mu^{-} \rightarrow e^{-}+v_{e}+\bar{v}_{\mu}

[Maximum number: 2]

Experiments with muons are taking place at Fermilab in the USA to improve our understanding of the standard model.

A muon $\mu^-$ can be produced by the decay shown in this nuclear equation.

$\pi^-\rightarrow\mu^-+\bar{\nu}_{\mu}$

State the names of the two other particles involved.

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Covered syllabus points

Question 1

Question 2

Question 3

Question (a)

Question (b)

Question (i)

Question (ii)

Question (c)

Question 4

Question 5

Question 6

Question 7

Question 8

Question 9

Question 10

Question 11

Question 12

Question 13

Question 14

Question 15