What is the range over which the strong nuclear force is attractive?

From about 0.5 fm up to about 3 fm.

Why is the repulsive part of the strong force needed?

It stops the nucleons being pulled together and collapsing, giving a minimum separation of about 0.5 fm.

Why are very large nuclei unstable?

Electrostatic repulsion acts between all protons, but the strong force only acts between close neighbours.

What is an alpha particle?

A helium nucleus: 2 protons and 2 neutrons.

What happens in beta-minus decay?

A neutron changes into a proton, emitting an electron and an antineutrino.

How do Z and A change in beta-minus decay?

Z rises by 1 and A is unchanged.

What observation led to the neutrino hypothesis?

Beta electrons had a continuous range of energies up to a maximum, so energy seemed not to be conserved.

What does the neutrino do in beta decay?

It carries away the missing energy so that energy is conserved.

Which two quantities must balance in every nuclear equation?

Nucleon number and charge (proton number).

Stable and unstable nucleiAQA A-Level Physics: Flashcards

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Which force holds nucleons together?

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Which force holds nucleons together?: The strong nuclear force.
What is the range over which the strong nuclear force is attractive?: From about 0.5 fm up to about 3 fm.
At what separation does the strong force become repulsive?: Below about 0.5 fm.
Why is the repulsive part of the strong force needed?: It stops the nucleons being pulled together and collapsing, giving a minimum separation of about 0.5 fm.
Why are very large nuclei unstable?: Electrostatic repulsion acts between all protons, but the strong force only acts between close neighbours.
What is an alpha particle?: A helium nucleus: 2 protons and 2 neutrons.
How do Z and A change in alpha decay?: Z falls by 2 and A falls by 4.
What happens in beta-minus decay?: A neutron changes into a proton, emitting an electron and an antineutrino.
How do Z and A change in beta-minus decay?: Z rises by 1 and A is unchanged.
Write the equation for beta-minus decay of a neutron.: n → p + e⁻ + ν̄ₑ.
What observation led to the neutrino hypothesis?: Beta electrons had a continuous range of energies up to a maximum, so energy seemed not to be conserved.
What does the neutrino do in beta decay?: It carries away the missing energy so that energy is conserved.
Which two quantities must balance in every nuclear equation?: Nucleon number and charge (proton number).

Exam questions on Stable and unstable nuclei

A physics class is discussing why a nucleus, which contains positively charged protons packed very close together, does not fly apart.
Explain why it is important that the strong nuclear force becomes repulsive at very small separations.2 marks
Radium-226, $^{226}_{88}\mathrm{Ra}$ , is an unstable nucleus that decays by emitting an alpha particle to form an isotope of radon (Rn).
Write the nuclear equation for the alpha decay of radium-226.2 marks
Strontium-90, $^{90}_{38}\mathrm{Sr}$ , is a waste product of nuclear fission. It decays by beta-minus emission to yttrium (Y). When beta decay was first studied, the electrons emitted by a sample of a single beta-minus emitter were found to have a continuous range of kinetic energies up to a well-defined maximum, rather than all having the same energy.
Write a nuclear equation for the beta-minus decay of strontium-90.3 marks

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Written by the Exaim team, led by Shaun Daswani (Head of Upper Secondary, Improve ME Institute; MSc Financial Mathematics, Imperial College London; BSc, UCL) and Jason Daswani (operational lead, Improve ME Institute; LSE).