What is the binding energy of a nucleus?

The energy needed to separate the nucleus completely into its individual nucleons.

How is binding energy found from the mass deficit?

E = c²Δm, with the mass deficit in kg and the energy in J.

How big is the atomic mass unit in kg?

1 u = 1.66 × 10⁻²⁷ kg, one twelfth of the mass of a carbon-12 atom.

What is binding energy per nucleon?

The binding energy divided by the number of nucleons; it shows how tightly bound a nucleus is.

Which nucleus has the highest binding energy per nucleon?

Iron-56, at about 8.8 MeV per nucleon, near the peak of the curve.

What is nuclear fission?

The splitting of a heavy nucleus into two medium-mass nuclei, releasing energy.

What is nuclear fusion?

The joining of two light nuclei to form a heavier nucleus, releasing energy.

Why does fission of uranium release energy?

The fragments have a higher binding energy per nucleon, so the total binding energy increases and energy is released.

Why does fusion need a very high temperature?

Nuclei repel each other, so they need high kinetic energy to get close enough for the attractive force to fuse them.

Why does fusion need a very high density?

It keeps the nuclei close together so collisions are frequent enough to sustain the reaction.

Why does a fusion reactor need a hotter plasma than the Sun's core?

Its density is far lower than the Sun's, so a higher temperature is needed to make up for the lower collision rate.

Binding energy, fusion and fissionEdexcel International A Level Physics: Flashcards

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What is the mass deficit of a nucleus?

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What is the mass deficit of a nucleus?: The total mass of its separate nucleons minus the mass of the nucleus.
What is the binding energy of a nucleus?: The energy needed to separate the nucleus completely into its individual nucleons.
How is binding energy found from the mass deficit?: E = c²Δm, with the mass deficit in kg and the energy in J.
How big is the atomic mass unit in kg?: 1 u = 1.66 × 10⁻²⁷ kg, one twelfth of the mass of a carbon-12 atom.
How do you convert an energy in J to MeV?: Divide by 1.60 × 10⁻¹³ J.
What is binding energy per nucleon?: The binding energy divided by the number of nucleons; it shows how tightly bound a nucleus is.
Which nucleus has the highest binding energy per nucleon?: Iron-56, at about 8.8 MeV per nucleon, near the peak of the curve.
What is nuclear fission?: The splitting of a heavy nucleus into two medium-mass nuclei, releasing energy.
What is nuclear fusion?: The joining of two light nuclei to form a heavier nucleus, releasing energy.
Why does fission of uranium release energy?: The fragments have a higher binding energy per nucleon, so the total binding energy increases and energy is released.
Why does fusion need a very high temperature?: Nuclei repel each other, so they need high kinetic energy to get close enough for the attractive force to fuse them.
Why does fusion need a very high density?: It keeps the nuclei close together so collisions are frequent enough to sustain the reaction.
Why does a fusion reactor need a hotter plasma than the Sun's core?: Its density is far lower than the Sun's, so a higher temperature is needed to make up for the lower collision rate.

Exam questions on Binding energy, fusion and fission

A student is analysing the helium-4 nucleus, which contains 2 protons and 2 neutrons. She is given the following data: mass of a proton = 1.00728 u; mass of a neutron = 1.00867 u; mass of a helium-4 nucleus = 4.00151 u.
Calculate the mass deficit of the helium-4 nucleus, in u.2 marks
A nuclear physicist is converting between units for a nucleus whose mass deficit is 0.0580 u. Use: 1 u = 1.66 × 10⁻²⁷ kg; c = 3.00 × 10⁸ m s⁻¹; 1 MeV = 1.60 × 10⁻¹³ J.
Calculate the binding energy of the nucleus in MeV.2 marks
The binding energy per nucleon of the nuclei rises steeply from about 1 MeV for hydrogen-2 to about 7 MeV for helium-4, reaches a maximum of about 8.8 MeV near iron-56, and then falls slowly to about 7.6 MeV for uranium-235. A uranium-235 nucleus can absorb a neutron and split into two fragments of medium mass, each with a binding energy per nucleon of about 8.5 MeV.
Explain, with reference to the binding energy per nucleon curve, why energy is released when two light nuclei such as hydrogen-2 undergo fusion to form helium-4.3 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).