### GCSE Physics Revision: Half-lives

#### 10th April 2017

GCSE Science – Physics – Radiation

KEY STAGE 4 – GCSE Physics Revision Guide - The Electromagnetic Spectrum

Then use this Revision Guide on radiation to remember all the key study points on your GCSE

Syllabus and get full marks in your GCSE Physics exam.

The emission of energy through space or other materials as:

 electromagnetic waves

 moving subatomic particles.

Materials and substances which emit radiation all the time are known as Radioactive materials.

There are 3 types of Nuclear Radiation:

 alpha

 beta

 gamma.

As Radiation travels, it can be absorbed by materials or substances which are in its path, causing the

intensity to decrease as it travels away from the source.

How the Radiation is absorbed will depend on the type of Radiation AND the type of material it

encounters.

This is because each type of Radiation has its own characteristics, and they are as follow:

ALPHA

 Travels only a few centimetres in air

 Cannot penetrate your hand or a sheet of paper

BETA

 Stronger than Alpha, but not as strong as Gamma

 Travels much further through air (many centimetres)

 Can penetrate a piece of paper and your hand

 Cannot penetrate a thin Aluminium sheet (a few millimetres thick)

GAMMA

 The strongest type of Radiation

 Can penetrate paper, your hand and a sheet of Aluminium

 Can only be stopped by very dense materials:

- a thick sheet (several centimetres) of Lead,

- thick concrete walls (several metres)

- water can also be used to stop Gamma rays.

 ALPHA: Smoke detectors

 BETA: In factories, to test the thickness of materials being produced (e.g. paper or plastic)

 GAMMA: hospitals / medical treatments.

The atomic nuclei of radioactive substances are unstable and change or break down into another

type of atom, this is known as “Radioactive Decay”.

For example:

Carbon-14 is unstable and decays - emitting Beta radiation

Nitrogen - 14 is produced as a result.

The Half-Life of a radioactive substance is the length of time it takes for half of the nuclei in that

substance to decay/be lost as radiation.

OR (another way of saying it)

The time it takes for the count rate of that sample of isotope to drop to half of its starting amount.

Examples of Half-Life:

 Carbon-14 = 5,715 years

 Francium-223 = 20 minutes

 Nitrogen-12 = 10 minutes

 Oxygen-20 = 13.5 seconds

How do we measure the activity of a radioactive source?

The unit of measurement is known as a Becquerel (Bq).

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