ý

Half-life – WJECHalf-lives of isotopes used in GCSE questions

Radioactive isotopes are used for blood flow monitoring, cancer treatment, paper mills, carbon dating and smoke alarms. Each isotope used in these applications has a characteristic half-life.

Part of Physics (Single Science)Forces, space and radioactivity

Half-lives of isotopes commonly used in GCSE questions

IsotopeHalf-life
Thorium-23214,000 million years
Uranium-235704 million years
Plutonium-23924,110 years
Carbon-145,730 years
Caesium-13730 years
Cobalt-605.27 years
Polonium-210138 days
Technetium-99m6 hours
Polonium-2183 minutes
IsotopeThorium-232
Half-life14,000 million years
IsotopeUranium-235
Half-life704 million years
IsotopePlutonium-239
Half-life24,110 years
IsotopeCarbon-14
Half-life5,730 years
IsotopeCaesium-137
Half-life30 years
IsotopeCobalt-60
Half-life5.27 years
IsotopePolonium-210
Half-life138 days
IsotopeTechnetium-99m
Half-life6 hours
IsotopePolonium-218
Half-life3 minutes

Example

Every 5.27 years, the mass of cobalt-60 halves. The number of cobalt-60 atoms halves. The activity of cobalt-60 halves.

Every 5,730 years, the mass of carbon-14 halves. The number of carbon-14 atoms halves. The activity of carbon-14 halves.

If an isotope has a half-life of 6 days, after 6 days the number of parent nuclei will halve, the isotope’s activity will halve and its mass will halve.

Question

The half-life of a radioactive isotope is 27 years. How long will its mass take to fall from 2 g to 0.25 g?

Question

The activity of an isotope falls from 600 Bq (becquerel) to 150 Bq in 10 days. What is its half-life?

Question

An isotope has a half-life of 30 years. Estimate how long it will take for the number of nuclei to decay to below 200 if the starting number is 8,000?

Next page
Using a decay curve to find the half-life
Previous page
Radioactive half-life

More guides on this topic

Related links