S-Cool Revision Summary

S-Cool Revision Summary

Radioactivity

Some nuclei are unstable - they have too many or too few neutrons. This can result in the nuclei spontaneously and randomly splitting up and giving out energy to stabilise themselves. This is radioactive decay and isotopes of atoms that do this are called radioisotopes. It can't be affected by any process.

Background Radiation

We constantly receive radiation from a number of sources in our environment. Learn them! At this low level, the radiation is not damaging to us.

What is ionising radiation?

Alpha, beta and gamma

Ionising radiation comes in three varieties:

α (alpha) particles

β (beta) particles

γ (gamma) rays.

Properties of alpha, beta and gamma radiation

Type of radiation: Symbol: Formula: Penetrating power: Mass: Charge: Speed:
Alpha particle:

α

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Stopped by paper or skin 4 + 2 Slow
Beta particle:

β

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topped by thin metal Negligible - 1 Fast
Gamma rays:

γ

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Reduced by many cms of lead or a few metres of concrete No mass No charge Speed of light

Separating alpha, beta and gamma

Electric Fields

The effect of the field depends on the charge of the radiation.

Alpha particles are positively charged and are therefore attracted to the negative plate in an electric field.

Beta particles are negatively charged and are therefore attracted to the positive plate in an electric field.

Gamma rays are unaffected.

Magnetic Fields

Use Fleming's Left Hand Rule to predict behaviour in magnetic fields. The "current" (second finger flow of charged particles) is the beam of radiation. Remember, the second finger shows conventional current so for beta particles point it in the reverse direction to the beam. For alpha particles it points in same direction as beam. Gamma rays have no charge so experience no force.

Note: alpha and beta particles follow circular paths in magnetic fields. The force due to the magnetic field is a centripetal force (see circular motion).

Cloud and bubble chambers

In order to study subatomic particles you need a method of detecting them. Over the years physicists have developed devices that can show the presence of particles and reveal their properties by the tracks that they leave. Two of the most important early detecting devices were cloud and bubble chambers. In modern high-energy research these devices are now obsolete. Spark and drift chambers are used as faster alternatives.

All of these devices work on a common principle: charged particles that pass through leave a path of detectable ionised particles. The technical details of each detector are slightly different but this principle is true nonetheless.

Uses of radioactive particles

Radioactive nuclides are made use of in many completely different ways. In whatever way they are used, it is always necessary to take precautions so the user is well protected from any radiation.

Four main uses of radioactive particles are: tracers, medical treatment, archaeological dating and scattering experiments.