Atoms and nuclear radiation

Radioactive decay and nuclear radiation

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

Activity is the rate at which a source of unstable nuclei decays.

Activity is measured in becquerel (Bq)

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

• an alpha particle (α) – this consists of two neutrons and two protons.

• a beta particle (β) – a high speed electron ejected from the nucleus as a neutron turns into a proton.

• a gamma ray (γ) – electromagnetic radiation from the nucleus

• a neutron (n).

Ionisation-when radiations collides with atoms, that can cause the atoms to lose electrons and form ions.

Nuclear equations

*The emission of a gamma ray does not cause the mass or the charge of the nucleus to change.

Half-lives and the random nature of radioactive decay

The half-life of a radioactive isotope is the time it takes for the number of nuclei of the isotope in a sample to halve

Half life is also the time it takes for the count rate from a sample containing the isotope to fall to half its initial level.

  • It cannot be predicted when one nucleus will decay, but the half-life is constant that enables the activity of a very large number of nuclei to be predicted during the decay.

A short half-life -The source presents less of a risk, as it does not remain strongly radioactive

- This means initially it is very radioactive, but quickly dies down

- So presents less of a long-term risk

Long half-life - The source remains weakly radioactive for a long period of time

- Americium has a half-life of 432 years

  1. It is an alpha emitter, and used in smoke alarms

  2. It is emitted into the air around the alarm, and does not reach far because alpha is weakly penetrating

  3. If smoke reaches the alarm, the amount of alpha particles in the surrounding air drops

  4. This causes the alarm to sound

-It is suitable because it will not need to be replenished, and its weak activity means it won’t be harmful to anyone.

Radioactive contamination