the splitting of large nuclei to form pairs of smaller nuclei and some free neutrons, with the release of energy

the smaller nuclei produced during nuclear fission

a series of nuclear fission events, with each one triggered by a neutron from a previous nuclear fission

the combining of small nuclei at very high temperatures with the release of energy

Nuclear fission and fusion

Physics

In A-level physics, some pupils will build on this knowledge to learn about probability and half-life equations, nuclear instability, Einstein’s equation E = mc2 that links mass and energy, and controlled nuclear fission.

In the Periodic table unit, in chemistry, pupils learnt about the nuclear model of the atom, the atomic number and mass number, and about isotopes of elements.

Nuclear physics

Breaking down electrons into protons and neutrons.

Splitting a heavy nucleus into smaller nuclei, releasing energy.

Emitting radiation from a substance without changing the nucleus.

Combining two light nuclei to form a heavier nucleus.

Which of the following nuclear equations could represent the fission of a uranium–235 nucleus?

A U–235 nucleus absorbs a neutron, becoming a U–236 nucleus.

The U–236 nucleus is unstable and splits into two, smaller nuclei.

As well as the smaller nuclei, 2 or 3 neutrons are released.

Energy, in the form of gamma radiation, is also released.

More U-235 atoms absorb the released neutrons.

A chain reaction occurs when more U–235 nuclei split releasing more neutrons.

Put the following stages of fission in the correct order, starting with a uranium–235 nucleus (U–235) absorbing a neutron.

Spontaneous fission needs external triggers; induced happens by itself.

Induced fission occurs naturally; spontaneous requires a neutron to be absorbed.

Spontaneous fission occurs naturally; induced requires a neutron to be absorbed.

Both types of fission occur due to temperature changes and external triggers.

What is the key difference between spontaneous fission and induced fission?

It is too dangerous, producing large amounts of harmful radiation.

It only works with special fuels not found on Earth.

It requires extremely high temperatures and pressure, hard to recreate on Earth.

It generates less energy than nuclear fission.

Nuclear fusion powers stars by combining light nuclei, such as hydrogen, into heavier elements. Why isn’t nuclear fusion currently a viable method for generating electricity on Earth?

Which of the following particles are found in the nucleus of an atom? 

an atom of the same element with a different number of neutrons.

an atom of a different element with the same number of neutrons.

an atom of the same element with a different number of protons.

an atom with the same atomic number but different mass number.

they have different chemical reactivities

some isotopes are more stable than others

What are the possible differences between substances that contain isotopes of the same element?

protons affect the stability of a nucleus

neutrons affect the stability of a nucleus

a nucleus is stable with more protons than neutrons

a nucleus is stable when the neutron–to–proton ratio is balanced

Which particle affects the stability of a nucleus, and what factors determine if a nucleus is stable or unstable?

Which of these can be released during nuclear reactions such as nuclear decay?

Decay always emits gamma rays with no change in the nucleus.

Decay can emit alpha/beta particles or gamma rays, changing atomic no/mass no.

Decay only emits particles, with no nucleus changes or energy release.

Which of the following statements accurately describes the changes that occur in the nucleus during radioactive decay?

This lesson will be removed by end of Summer Term 2025.

Nuclear fission and fusion

Lesson outcome

This lesson will be removed by end of Summer Term 2025.