Radioactivity

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

Stopped by:

• Human skin
• Paper
• 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

Stopped by:

• 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.

Stopped by:

• Thick piece of lead ( few centimetres)
• Several metres of concrete
• Unlimited range of air

Gamma rays are not deflected by electric or magnetic fields.

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.

Radiation plays a big part in industry - depending upon its half life and the type of radiation it gives outs.

Examples include:

• 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.