Atoms always contain:
- Protons (+)
- Neutrons (+-)
- Electrons (-)
Atoms always have the same number of protons however isotopes have different numbers of neutrons
A radioactive substance always contains an unstable nuclei - they emit radiation and turn into other elements
Radioactive decay is a random process - it is not effected by external conditions
Alpha is a helium nucleus made up of 2 protons and 2 neutrons
The particles are quite large which results in lots of collisions - this means they cannot penetrate far into a material
- Human skin
- Few centimetres of air
Aplha particles are most dangerous if they are in the body - they are strongly ionising
Because of their positive charge they are deflected by electric and magnetic fields
A beta particle is a high speed electron found in the nucleus.
The particles are a lot smaller than alpha particles resulting in less collisions - this makes them less ionising and more penetrating
- Thin sheet of aluminium
- Few metres of air
Beta particles have a negative charge
They are deflected by electric and magnetic fields oppositely to alpha particles
Gamma radiation has a very short wavelength and is emitted from the nucleus.
As gamma rays are electromagnetic waves, they will travel a long time before colliding with an atom - not very ionising and very penetrating.
- Thick piece of lead ( few centimetres)
- Several metres of concrete
- Unlimited range of air
Gamma rays are not deflected by electric or magnetic fields.
Effects of Radiation on the Body
The danger of a radiaactive substance on the body depends on whether the radiation is in or outside of the body.
Inside the Body
- Alpha is most dangerous - it is easily absorbed by the cells
- Beta & Gamma aren't very dangerous - they are unlikely to be absorbed and would usually pass straight through the cells
Outside the Body
- Alpha isn't very dangerous - it is unlikely to reach cells inside the body
- Beta & Gamma are most dangerous - both are very penetrating so can penetrate the skin and damage the inside of cells.
Using Radiation in Industry
Radiation plays a big part in industry - depending upon its half life and the type of radiation it gives outs.
- Smoke detectors (alpha)
- Mearugin the thickness of materials, e.g. paper (beta)
- Tracers for medical diagnosis (gamma/beta)
- Sterilising medical treatment (gamma)
- Killing cancer cells (gamma)
The half life of these radiations are very important. For example, medical tracers need a half life of only a few hours so that the radiation is not exposed to the body for too long.
The radioactivity of a material decreases gradually over time till it falls to nearly zero.
The idea of half life is used to measure how quickly this radioactivity decreases.
Definitions for half life:
The time in which it takes for the count rate of a substance to fall to half its initial value
The time it takes for the number of nuclei in an isotope to halve.
Example - a substance drops from 20 counts per minute to 10 counts in 15 days. The half life therefore is 15 days.