Contamination & Irradiation (Edexcel IGCSE Physics (Modular))
Revision Note
Contamination & irradiation
Contamination
Contamination is defined as:
The accidental transfer of a radioactive substance onto or into a material
A substance is only radioactive if it contains a source of ionising radiation
Contamination occurs when a radioactive isotope gets onto a material where it should not be
It is almost always a mistake or an accident e.g. a radiation leak
As a result of this, the small amounts of the isotope in the contaminated areas will emit radiation and the material becomes radioactive
Irradiation
Irradiation is defined as:
The process of exposing a material to ionising radiation
Irradiating a substance does not make it radioactive
However, it can kill living cells
Irradiation is usually a deliberate process, such as in the sterilisation of food or medical equipment
Surgical equipment is irradiated before being used in order to kill any micro-organisms on it before surgery
Food can be irradiated to kill any micro-organisms within it to make it last longer
This sign is the international symbol indicating the presence of a radioactive material
Protection from irradiation and contamination
Radiation can mutate DNA in cells and cause cancer through both irradiation and contamination
Therefore, it is important to reduce the risk of exposure to radiation
Contamination is particularly dangerous if a radioactive source gets inside the human body
For example, through the inhalation of radioactive gas particles, or ingesting contaminated food
The internal organs will be irradiated as the source emits radiation as it moves through the body
To prevent irradiation, shielding can be used to absorb radiation
Lead-lined suits are used to reduce irradiation for people working with radioactive materials
The lead absorbs most of the radiation that would otherwise hit the person
To prevent contamination, an airtight suit is worn by people working in an area where a radioactive source may be present
This prevents radioactive atoms from getting on or into the person
Lead shielding is used when a person is getting an x-ray, as well as for people who work with radiation. Contamination carries much greater risks than irradiation
Differences between irradiation and contamination
The differences between irradiation and contamination are summarised in the table below:
Comparison of irradiation and contamination table
| Irradiation | Contamination |
|---|---|---|
description | when an object is exposed to a source of radiation but does not become radioactive | when an object becomes radioactive due to the presence of a source of radiation |
source | exposure to source of radiation outside the object | exposure to source on or within the object |
prevention | blocked by using shielding such as lead | radiation cannot be blocked once an object is contaminated, but can be prevented by handling the source safely |
causes | caused by the deliberate exposure to radiation | caused by the accidental transfer of radioactive material |
Worked Example
Summarise the difference in the risk posed by radioactive sources with very short and very long half-lives in regard to
(a) irradiation
(b) contamination.
Answer:
(a) Irradiation poses a greater risk in sources with...
Shorter half-lives
A short half-life means a source has a high activity
This means there is a high rate of radioactive emissions, compared to a source with a long half-life
(b) Contamination poses a greater risk in sources with...
Longer half-lives
Sources with long half-lives will remain radioactive for longer
They need to be controlled for longer, to prevent them spreading
Shielding and storage may be required
Exam Tip
Irradiation and contamination are very commonly confused.
Remember that something is radioactive only if it contains radioactive atoms. This can only occur from contamination, not from irradiation!
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