Atomic structure & radioactivity
The nuclear model of the atom, isotopes, radioactive decay and nuclear equations, half-life and the hazards of radiation.
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Atomic structure & radioactivity, explained point by point
Everything the GCSE specification expects you to be able to do, and how to actually do it - the same lesson a signed-in student studies from.
Describe the nuclear atom and isotopes
An atom has a tiny nucleus of protons and neutrons, with electrons in shells around it - and the nucleus holds almost all the mass. Isotopes are atoms of the same element (same protons) with different numbers of neutrons. Some isotopes have unstable nuclei that break down and give out radiation; these are radioactive.
Describe alpha, beta and gamma radiation and their penetration
Unstable nuclei emit three main types of radiation. Alpha is a helium nucleus, highly ionising but stopped by paper or skin. Beta is a fast electron, stopped by a few millimetres of aluminium. Gamma is a high-energy wave, very penetrating, needing thick lead or concrete. Penetrating power runs opposite to ionising power.
Write and balance nuclear equations
In radioactive decay the nucleus changes, and the mass and atomic numbers must balance on both sides. Alpha decay removes 2 protons and 2 neutrons (mass down 4, atomic number down 2). Beta decay turns a neutron into a proton, so the atomic number rises by 1 while the mass number stays the same.
Explain half-life and use it in calculations
Radioactive decay is random, but on average the activity falls steadily. The half-life is the time for half the unstable nuclei - and so the activity - to decay. After two half-lives, a quarter of the original remains; after three, an eighth. Counting the halvings from a graph tells you how long has passed.
Compare irradiation and contamination, and describe safety
Irradiation is being exposed to radiation from an outside source; it stops when the source is removed and does not make you radioactive. Contamination is getting radioactive material on or in you, which keeps exposing you until it is removed. Handling sources with tongs, shielding and limiting exposure time all reduce the risk.
Describe uses of radioactivity
Different radiations suit different jobs. Gamma sources sterilise medical equipment and can treat cancer, and tracers with short half-lives help doctors follow processes inside the body. The type and half-life are chosen carefully so the source does its job while keeping exposure as low as possible.
Atomic structure & radioactivity key terms
The words the specification and the mark schemes use, each defined the way an examiner wants it.
- Radioactive decay
- The random process in which an unstable nucleus releases radiation to become more stable. It cannot be predicted or influenced.
- Activity
- The rate at which a radioactive source decays, measured in becquerels (1 Bq is one decay per second).
- Half-life
- The time it takes for the number of unstable nuclei in a sample, or its activity, to halve.
- Alpha particle
- Two protons and two neutrons (a helium nucleus) emitted from a nucleus. Strongly ionising, but stopped by a sheet of paper or a few centimetres of air.
- Beta particle
- A high-speed electron emitted from the nucleus when a neutron turns into a proton. Stopped by a few millimetres of aluminium.
- Gamma ray
- Electromagnetic radiation emitted from the nucleus. Weakly ionising but very penetrating: it takes thick lead or metres of concrete to absorb it.
- Irradiation
- Exposing an object to radiation. The object does not become radioactive itself.
- Contamination
- Unwanted radioactive atoms getting onto or into an object. The object stays hazardous until the atoms decay or are removed.
Practice
Try a Atomic structure & radioactivity question
A GCSE-style original question from this topic. Have a go before you open the working - deciding on an answer first is what makes the working stick.
Radon-220 has atomic number 86. A radon-220 nucleus decays by emitting an alpha particle. What is the atomic number of the nucleus formed?
- 84
- 85
- 88
- 82
Show the answer and the working
Answer: 84
An alpha particle carries away 2 protons, so the atomic number falls by 2: 86 − 2 = 84.
- An alpha particle is 2 protons and 2 neutrons, so its atomic number is 2.
- In alpha decay the atomic number drops by 2.
- 86 − 2 = 84.