10.3.1 Radioactive Emission

3 Types of Radioactive Emission

Alpha Particle


  • carries positive charge.
  • most strongly ionizing of the nuclear radiations. 
  • least penetrating. Range in air is only a few centimetres, and can be stopped by a thick sheet of paper.

Beta Particle


  • carry a negative charge. 
  • much less ionizing than alpha emission.
  • more penetrating than alpha emission..
  • have a range of a metre or so in air,
  • can be stopped by a few millimetres of Perspex or aluminium.

Gamma Radiation


  • often emitted at the same time as an alpha or beta particle.
  • least ionizing of the nuclear radiations, 
  • most penetrating.
  • their intensity is greatly reduced by several centimetres of lead, but they are never completely absorbed.

Ionising Effect

  • All alpha, beta and gamma emission can cause ionising effect.
  • Alpha particle has high ionizing power.Beta particle has low ionizing power.
  • Gamma ray has very low ionizing power.

Penetrating Power


Deflection in Electric Field

Deflection in Magnetic Field


  • Alpha and beta emission can be deflected by a magnetic field.
  • The direction of deflection can be determined by using Fleming’s Left Hand Rule.
  • Beta particle deflected more compare to alpha particle due to its much smaller mass.

Summary

Characteristic
Alpha Particle
Beta Particle
Gamma Ray
Symbol
α
β
γ
Nature
Nucleus of Helium
High speed electron Electromagnetic wave
Charge
+2
-1
Neutral
Ionizing Effect
strong
weak
Very weak
Absorted by Sheet of writing paper
About 5mm of aluminium
Never fully absorded. 25mm of lead reduces intensity to half
Deflection in Electric Field
Can be deflected
Can be deflected
Not deflected
Deflection in magnetic Field
Can be deflected
Can be deflected
Not deflected
Speed
Up to 10% of the speed of light
Up to 90% of the speed of light
Speed of light

Series Decay

  1. Sometimes after a radioactive decay, the daughter nuclide formed is still unstable.
  2. It will further decay into another nuclide which may also unstable.
  3. This process continues until a stable nuclide is reached. This is called a series decay.
  4. Each decay will emit either an alpha particle or a beta particle and may be gamma ray.
  5. Figure below shows a series decay started from plutonium-241 to formed Thallium-205 eventually.
(This image is created by Johantheghost under creative common licence)