National 5 Radiation Flashcards
- State what is meant by an alpha particle.
An alpha particle is a Helium nucleus or two protons and two neutrons.
- State what is meant by a beta particle.
A beta particle is a fast moving electron.
- State what is meant by a gamma ray.
A gamma ray is an electromagnetic wave or pure energy.
- State for alpha particles
- the relative speed,
- the relative mass,
- the charge,
- the approximate range in air and
- what is the minimum needed to significantly absorb
Alpha particles
- are relatively slow moving
- are relatively heavy
- have +2 charge
- can only travel 2-3 cm in air
- are easily absorbed by something like a sheet of paper
- State for beta particles
- the relative speed,
- the relative mass,
- the charge,
- the approximate range in air and
- what is the minimum needed to significantly absorb
Beta particles
- are fast moving
- are relatively light
- have -1 charge
- can travel about 50 cm in air
- are absorbed by a few mm of aluminium
- State for gamma rays
- the relative speed,
- the relative mass,
- the charge,
- the approximate range in air and
- what is the minimum needed to significantly absorb
Gamma rays
- travel at the speed of light
- have no mass
- have no charge
- are not absorbed much by air
- are only absorbed by a few cm of lead or a few m of concrete
- Explain the term ionisation.
Ionisation occurs when radiation interacts with other atoms.
It is the removal of an electron from an atom to create a positively charged ion.
(There are other chemical processes that can result in an atom gaining an electron to create a negative ion.)
- State the relative density of ionization of alpha, beta and gamma radiation
- α particles: highly ionising
- β particles: ionising
- γ rays: very weakly ionising
Describe how a Geiger-Muller (GM) tube detects radiation.
The GM tube is a hollow cylinder filled with a gas at low pressure. The tube has a thin window made of mica at one end to enable radiation to enter easily. (See Image)
When nuclear radiation enters the tube it ionises the gas and the freed electrons are attracted to the positive rod, producing pulses of current which are counted. The greater the activity of a source, the more ionisation in the tube so the greater the rate of counts. These are usually measured in counts per minute (cpm).
Describe how a film badge detects radiation.
When radiation strikes photographic film it blackens or fogs the film. The more radiation, the more fogging. There are a series of absorbing materials in front of the film to help distinguish between different types of radiation because of their different penetrating properties.
Descrive how a scintillation counter detects radiation.
When radiation strikes certain materials they produce tiny flashes of light called scintillations. These flashes can be amplified then detected using either a light detector to give an overall reading or an image sensor to give a picture. When used with the image sensor this is known as a gamma camera.
- Define the Activity of a source and its unit of measurement.
Activity is the number of nuclei which decay each second.
1 Becquerel means 1 nucleus decays each second.
- What is meant by “An activity of 5 kBq”?
An activity of 5 kBq means that 5000 nuclei decay each second.
- A = N/t
(Define symbols and units)
A - Activity (Bq)
N - Number of Nuclei which decay (no units)
t - time (s)
- Example
A source has an activity of 20 MBq. How many nuclei will decay in 1 min?
A = 20 MBq = 20 x 10<sup>6</sup> Bq t = 1 min = 60 s N = ?
A = N/t
20 x 106 = N/60
N = 20 x 106 x 60
N = 1.2 x 108 nuclei will decay in one minute
- Explain the term background radiation and describe two of its sources.
Background radiation is radiation which is always present but which is not due to the deliberate introduction of radiation sources.
Sources of background radiation
Natural
Radon Gas emitted by rocks in the ground
Cosmic Rays that reach the Earth from outer space
Soil, Rocks and Building Materials
All animals (including ourselves) emit natural levels of radiation
Our food and drink can contain natural levels of radiation
Artificial
Medical uses of radiation such as scans and treatments.
- Describe the dangers of ionising radiation to living cells and the need to
measure exposure to radiation.
Since ionisation changes the chemical properties of materials, ionising radiation is dangerous to living cells which use chemical interactions to function. It can change their nature (e.g. make them cancerous) or kill them completely. Therefore, it is important that we can accurately measure exposure to radiation to minimise the risks.
- Define absorbed dose, radiation weighting factor and equivalent dose.
Absorbed dose, D, is defined as the energy absorbed per unit mass of the absorbing material.
Radiation Weighting Factor (wR) is a number which indicates the biological effect of a particular type of radiation.
Equivalent Dose, H, is a measure of the potential harm that could be caused by a particular exposure to radiation