How to safely handle radioactive sources

In a nutshell

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	$I=\frac k{x^2}$

Variable definitions

Quantity Name	Symbol	Derived Unit	SI BASE Units
$intensity$	$I$	$W\,m^{-2}$	$kg\,s^{-3}$
$constant \ of \ proportionality$	$k$	$W$	$kg\,m^2\,s^{-3}$
$distance$	$x$	$m$	$m$

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 $\alpha$	Paper or skin	Very small
Beta $\beta$	Thin aluminium	Large
Gamma $\gamma$	Thick lead	Very large

Physics; Nuclear physics; KS5 Year 12; How to safely handle radioactive sources

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.

Physics; Nuclear physics; KS5 Year 12; How to safely handle radioactive sources

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:

$I=\frac k{x^2}$

Example

A gamma source is set up along a workbench. The intensity is measured to be $360 \, Bq$ at a distance of $10 \, cm$ . What is the intensity at a distance of $55\,cm$ away?

Firstly, write down the known values:

$I_1=360\,Bq \newline \\[0.1in]x_1=10\,cm =0.1\,m\newline \\[0.1in]x_2=55\,cm=0.55\,m$

Next, write down the equations needed and rearrange if necessary:

$I=\frac k{x^2} \rightarrow I_1x_1^2=I_2x_2^2 \newline \\[0.1in]I_2=\frac {I_1x_1^2}{x_2^2}$

Then, substitute the values into the equation:

$I_2=\frac {360\times 0.1^2}{0.55^2} \newline \\[0.1in]I_2=11.900...\,Bq$

Make sure to round to the lowest number of significant figures of the values given by the question:

$intensity, \ I_2=12\, Bq$

The intensity of the gamma source at a distance of $55\, cm$ is $\underline{12\, Bq}.$

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.