AQA GCSE Radioactive Decay

Radioactive Decay

The nuclei of some atoms are unstable, so they undergo radioactive decay to try to become more stable.

Remember the term isotope?

Isotopes are atoms of the same element, with the same number of protons, but different numbers of neutrons.

Some isotopes have stable nuclei, others unstable.

Stable nuclei: This has the correct ratio of protons to neutrons, so the nucleus is stable

Unstable nuclei: This has an incorrect ratio of protons to neutrons, so the nucleus is unstable and will undergo radioactive decay

Hydrogen has three isotopes. The first two isotopes are stable, but the third isotope is unstable. So, hydrogen-3 will undergo radioactive decay to become more stable

What happens during radioactive decay?

During radioactive decay an unstable nucleus will emit radiation to try to become more stable.

The radiation emitted could be one of the following:

1.Alpha particle (Helium nucleus: 2 protons and 2 neutrons)

2.Beta particle (an electron)

3.Gamma wave (electromagnetic wave)

4. Neutron

Emission of a gamma wave

Some nuclei will emit a gamma wave (electromagnetic wave) during radioactive decay.

Fluorine-18 is a gamma emitter

During the gamma decay, the particles in the nucleus do not change, but a gamma wave is emitted and the nucleus now has less energy than before, so it is more stable.

Emission of an Alpha, Beta or Neutron particle.

During some types of radioactive decay a particle can be emitted such as alpa, beta or a neutron.

Alpha Emission

An alpha particle is a helium nucleus, so it contains 2 protons and 2 neutrons. Polonium-210 commonly undergoes alpha decay to emit an alpha particle (helium nucleus)

Notice that due to the loss of the alpha particle, the nucleus has changed. As the number of protons have decreased by two, the element has changed from Polonium(Po) to Lead(Pb).

Beta Emission

A beta particle is an electron. During a beta decay a neutron turns into a proton and an electron is emitted.

Beta decay tends to occur when there are too many neutrons in the nucleus.

Remember what we said earlier, nuclei are unstable if the ratio of protons to neutrons is not correct!

During the beta decay a neutron turns into a proton and an electron is released.This means that the nucleus has changed as there is now one more proton and one less neutron.

Neutron emission

Neutron emission can occur in nuclear reactors. where neutrons are released through nuclear fission.

However, there are other ways that neutron emission can occur such as an alpha particle colliding with a nucleus to make the nucleus unstable and then emit a neutron.

An example of neutron emission is an alpha particle colliding with beryllium-9 to form carbon-12 and emit a neutron.