Properties of Radiation

In the video below, nuclear physicist Dr Liam Gaffney from the University of Liverpool explains how we measure radioactivity and the effects that different types of radiation can have.  Find out about the banana equivalent scale and why radiation is around us all the time. 

As Liam explained in the video above, small amounts of radiation are around us all the time and are harmless. This is called background radiation, and it comes from both natural and artificial sources. 

Natural radiation is given out by rocks and soil, cosmic rays (coming from the Sun and stars), and all living things – even us! A more dangerous source is the radioactive gas, radon. You can check to see if this is a risk in your area on the UK Radon Map. 

Artificial sources of radiation also contribute to this background level. However, our highest dosage comes from medical uses - both imaging and treatments. We will learn more about this in Module 4. Other man-made sources include the fallout from nuclear weapons testing and nuclear accidents.

A person's radiation dose from this background radiation will vary depending on many factors, such as their job and where they live. Dosage is measured in sieverts (Sv). Bananas, which are very good for us, are a natural source of potassium – an isotope of which is radioactive. Eating one banana gives us a dose of 0.1µSv. We can use this as a way to measure radiation dose: it’s called the banana equivalent dose (BED). 

Check out some examples of the banana equivalent dose: 

Figure 1: The types of ionising radiation and their penetration power.

As well as conducting experiments, advanced software can simulate how different types of radiation (such as alpha, beta, and gamma) interact with different materials - everything from air, to lead and concrete, to body tissue and bones.  This allows accurate predictions to be made before technical equipment is built, or medical treatments are given, for example.  

There are three different outputs from the simulation.  Figure 4 (below) shows the 'Energy Deposition vs Depth' option. The radiation will deposit energy when it is absorbed into the material. This means that it does not travel any further. 

You will only need this graph option to answer the questions in Activity 2.3. However, you may also want to explore the two other outputs. The first of these shows the energy deposited (using colour coding) both in terms of depth into the material (as in the graph above), but also in terms of the distance from the beam (on the y-axis). The second shows the particle tracks, which are generated from the data each time the simulation is run.  

Try investigating different types of radiation, different energies, different materials, and different thicknesses of material.  What patterns do you notice?  Once you have experimented with this simulation, have a go at the Questions in Activity 2.3 (below).

Radiation is usually invisible to us. However, one way that we can actually see the paths of these particles is with a cloud chamber. Find out all about how these were invented and how they work in the video below, produced by post-graduate researcher Alexander Backis from the University of Glasgow.

Radioactive decay is a random process. In a sample of radioactive material, there are lots and lots of nuclei. We can't predict which nucleus will decay next, or when any particular nucleus will decay, and not all nuclei will decay at the same time. Instead, we know that a certain number of nuclei will decay in a certain time. The time taken for half the unstable nuclei in a sample to decay is called the half life, (t1/2). 

There are two important definitions of half life:

• The time it takes for the number of radioactive nuclei in a sample to decrease by 50%. 

• The time it takes for the activity/count rate of a radioactive source to decrease by 50%. 

We cannot affect the half life of an isotope - changing the temperature or pressure, for example, make no difference. Some isotopes have very short half lives of only a few seconds, whilst others can be thousands of years.