Radioactive Decay (OCR GCSE Physics A, Combined (Gateway Science Suite)): Revision Notes

Some atomic nuclei are unstable. The nucleus gives out radiation as it changes to become more stable. This is a random process called radioactive decay.

Through emitting radiation, we can change the nucleus of an atom.

There are two ways in which the nucleus of an atom can be changed:

1. Charge. We can increase or decrease the charge of an atom through nuclear radiation.
2. Mass. We can decrease the mass of an atom through nuclear radiation.

• A sample with high activity has a fast rate of decay
• Measured in Becquerel, Bq

Count-rate is the number of decays recorded by a detector per second.

E.g. a Geiger-Muller Tube

1. Example:

• A helium nucleus has been emitted. Since a helium nucleus has been emitted, we know that this is alpha decay. The helium nucleus is made up of 2 protons and 2 neutrons, and it is the alpha particle.

• Mass and atomic numbers have changed. From the equation, we can see that both the mass number and the atomic numbers have changed. The mass number has decreased by 4, whilst the atomic number has decreased by 2. Beta Minus β (electron)

• Medium ionising

• Medium penetration (~50cm of air, sheet of paper)

2. Example:

• An electron has been emitted. Since an electron has been emitted, we know that this is beta decay. The electron is the beta particle.
• Only the atomic number has changed. From the equation, we can see that only the atomic number has changed. The mass number does not change, since the electron has a negligible mass. Gamma γ (radiation)

• Low ionising
• Highly penetrating (very far in air, few cm of lead)