Radioactive sources need to be handled safely and correctly. Radioactive sources must never be touched or looked at directly. Different radiation has different properties and are absorbed by different materials. Gamma radiation follows an inverse square law.
Radiation is also used in medicine from diagnosis to treatment and also sterilisation of equipment.
Equations
Description
Equation
Inverse square law for gamma radiation
I=x2k
Variable definitions
Quantity Name
Symbol
Derived Unit
SI BASE Units
intensity
I
Wm−2
kgs−3
constantofproportionality
k
W
kgm2s−3
distance
x
m
m
Background radiation
Everyday you will be exposed to radiation that comes from your surroundings, also known as background radiation. This radiation can come from a number of different sources including rocks, food, medical equipment and procedures, the Sun and even buildings.
In rocks, there are several types of materials which emit radioactive material. Radon is a natural gas that emits alpha particles, and comes from sources of rock including buildings. However, in the UK background radiation levels are low enough to be at a safe level.
Safe handling of radioactive sources
Radioactive sources are dangerous in many ways, but perhaps the most dangerous property radioactive sources have are that you cannot see radiation or feel yourself being irradiated.
Therefore the precautions taken to safely handle radioactive sources must be strictly adhered to.
Whenever handling radioactive sources, long tongs must be used and sources must never be touched with bare hands. This is to stop contamination of persons or objects.
If an object or person were to become contaminated, this means that the radioactive material has been transferred onto the person. This is very dangerous as that person or object will now be emitting dangerous radioactivity, perhaps unknowingly.
Most radioactive sources used within schools are normally directional which means the radioactivity is only emitted in one direction. This direction must never be pointed towards other persons or living things.
Absorption methods for radioactivity
Alpha, beta and gamma all have different ranges and penetrative capabilities. These methods and materials are by no means exhaustive and should still be used with caution.
radioactivity
Absorbed by
range
Alpha α
Paper or skin
Very small
Beta β
Thin aluminium
Large
Gamma γ
Thick lead
Very large
1
Paper
2
Thin aluminium
3
Thick lead
Workers that work in high areas of radiation have to wear special badges which monitor their exposure to radiation. This is so the radiation incident on the workers can be tracked and kept under a safe level.
The badges contain a piece of photographic film behind three different filters to monitor the type and energy incident on the badge.
1
Photographic film
2
Different metal filters
3
Clear plastic window
4
Plastic filters
Inverse square law for gamma radiation
Gamma radiation is not absorbed by the air but its intensity decreases because it spreads out. The intensity is inversely proportional to the distance squared and is given by the equation:
I=x2k
Example
A gamma source is set up along a workbench. The intensity is measured to be 360Bq at a distance of 10cm. What is the intensity at a distance of 55cm away?
Firstly, write down the known values:
I1=360Bqx1=10cm=0.1mx2=55cm=0.55m
Next, write down the equations needed and rearrange if necessary:
I=x2k→I1x12=I2x22I2=x22I1x12
Then, substitute the values into the equation:
I2=0.552360×0.12I2=11.900...Bq
Make sure to round to the lowest number of significant figures of the values given by the question:
intensity,I2=12Bq
The intensity of the gamma source at a distance of 55cm is 12Bq.
Radiation in medicine
Radiation is used in lots of different aspects of medicine. Radiation can be used as a diagnostic measure but can also be used as treatment too.
Radiation can be used as a medical tracer which is given to the patient and the radiation is then observed from the outside of the body using a gamma camera or a PET scanner. This shows the function of the tissues and organs being observed.
Gamma rays can be used to treat cancerous tumours within the body. A high energy beam of gamma photons are directed towards a tumour which kills the cells within the tumour. This also kills the cells along the way so it is important that the optimal pathway is taken.
It is also important that the patient and medical professionals are both protected from any unintentional radiation exposure by wearing specialist clothing lined with lead or being behind protective shielding.
Gamma radiation can also be used to sterilise medical equipment. This is useful as the gamma radiation can penetrate through the equipment meaning that all sides of the equipment are sterilised without being rotated. It also means that it can sterilise equipment which are sealed therefore making them sterile until used.
Radiation in medicine obviously comes with risks, both to patients and the operators (doctors and medical physicists). However, it is important to remember that the benefits of life saving treatment will outweigh these risks.
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FAQs - Frequently Asked Questions
How do you handle radioactive sources?
Whenever handling radioactive sources, long tongs must be used and sources must never be touched with bare hands.
How is radiation used in medicine?
Radiation is used in lots of different aspects of medicine. Radiation can be used as a diagnostic measure but can also be used as treatment too.
What does it mean if something is contaminated?
If an object or person were to become contaminated, this means that the radioactive material has been transferred onto the person.