# Radioactivity and radioisotopes

We can detect radiation using a Geiger Müller tube, and we can di erentiate which type it is either by checking how penetrating it is, or by using a magnetic eld to de ect it to see which way (if any) it de ects.

2.5.1 Background radiation
Radiation isn’t something only found in nuclear facilities, it is found everywhere. We call this radiation that is not generated intentionally experimentally background radiation. The largest source of background radiation is from naturally occurring radon gas. Other natural sources (from Earth, these are the largest contributors to background radiation) include our food and drink and buildings and the ground, which all contribute from radioactive isotopes such as potassium-40, carbon-14, uranium and thorium. Other sources include cosmic

rays which arise from high-energy particles arriving from space and the remainder of background radiation is man-made. Man-made radiation is mostly from X-ray imaging, but a tiny percentage is from nuclear power and weapon testing (although of course this varies by location). A normal background count is around half a count per second.
2.5.2 Calculating radioactivity
Radioactivity can be calculated probabilistically, because while each individual decay is entirely random, the over decay is entirely predictable. Note: If you are wondering what di erence between random and predictable, look up stochastic. Stochastic is something random that is not predictable. So if we know the activity, i.e. number of decays (disintegrations) per second, we know that this is proportional to the number of nuclei (A ∝ N) and hence:

2.5.3 Uses of radioisotopes
A radioisotope is simply an isotope (same number of protons, di erent number of neutrons) of an element which is radioactive. There are many uses for them but you only need to know two di erent applications, for example:
1. You can use a gamma emitter such as cobalt-60 to sterilise medical equipment or food. Gamma is useful because it isn’t very ionising so it is relatively safe for humans but it kills all germs, bacteria and viruses.
2. You can use a beta emitter such as strontium-90 to check the thickness of paper as it rolls o of a paper mill. By using a source and a detector with the paper in between you can use the count rate to measure the thickness and change the adjust the rollers accordingly.