P1bL7 Radiation
Key Words
Alpha particle - a helium nucleus ejected from the decaying nucleus.
Background radiation - nuclear radiation coming from all sorts of natural sources in the environment.
Beta Particle - a high speed electron ejected from the nucleus.
Cosmic rays - very energetic EM waves coming from Space.
Gamma ray - very short wavelength EM radiation.
Ionise - knock electrons off atoms
Nuclear radiation - energy coming from the nucleus in the form of particles or electromagnetic waves.
Radon - a radioactive gas
Grade E
The three kinds of radiation are shown in this table:
| Radiation | What it is | Range | Stopped by |
| Alpha (a) | Helium nucleus (NOT atom) | 1 cm in air | Skin, sheet of paper |
| Beta (b) | High speed electron | 50 cm in air | 3 mm aluminium sheet |
| Gamma (g) | Electromagnetic radiation | Infinite | Several cm lead |
Radiation can be detected by a Geiger-Müller Tube connected to a counter. If you turn one of these on in the lab, it will count even though there is no source out in the room. This is because there is always background radiation, coming from soil, rocks, space, and even living things. Some is man-made, but the rate is so low that it does no harm.
Alpha particles, beta particles, and gamma rays are NOT
radioactive themselves.
Grade C
Ionising radiations knock electrons off atoms, making them positive ions.
The ionising radiations above are shown in more detail in the next table:
| Radiation | Mass | Charge | Ionisation | Use |
| Alpha (a) | 4 times mass of a proton | +2e ( 2 × charge of an electron) | Intensely ionising | Smoke detectors |
| Beta (b) | Mass of electron (1/1800 mass of a proton) | -1e | Moderately ionising | Thickness detectors |
| Gamma (g) | Zero (it's a wave) | Zero | Weakly ionising | Killing cancer cells |
Alpha particles will not penetrate skin, but if placed near living cells, will kill them. That is why it is highly dangerous to ingest an alpha emitter. Gamma emitters are used for medical tracing.
Background radiation is particularly strong where there are a lot of granite rocks. The rocks give off radon, a radioactive gas which can leak through the ground into peoples' houses to cause illness. Houses are now ventilated to reduce the background radiation. Areas at particular risk are South West England and North East Scotland.
Pilots of high-flying aeroplanes are at risk from cosmic rays, as the atmosphere is very thin. Radiographers and other people working with radiation may receive a higher dose of background radiation. They wear film badges which show the amount of radiation to which they are exposed. If they are exposed to too much they are withdrawn from working with radiation for a period of time.
Grade A
The charged radiations (a and b) interact with magnetic fields and electric fields. Gamma rays do not. This can be summed up in the pictures below:
In an electric field:
The alpha particles, being positively charged, are attracted towards the negative plate. Beta particles are negative and are attracted to the positive plate.
For a magnetic field:
The charged particles are deflected by the magnetic field.
Gamma rays, not being charged, are not affected by either an electric or a magnetic field.
When we are doing counts, we need to take the background count into account. This we do by timing the count for a period of time, then doing an average, to give an average count per second.
average count per second = total count in the time period ÷ time period
If we measure over 60 seconds, we would divide by 60.
Also radioactive decay is an entirely random event. Sometimes there are a lot of counts a second, then only a few. So again we need to time over a period and do an average.
Therefore:
average activity count per second = total average count per second - average background per second
The activity of a source is measured in becquerels (Bq) where 1 Bq = 1 count per second.