Introduction to Nuclear Physics
Nuclear physics is an area of science that studies the nuclei of atoms. It’s about far more than just nuclear power. Researchers study everything from the shapes of nuclei, to cancer treatments and medical imaging; from exotic nuclei (highly unstable nuclei that only exist for fractions of a second), to nuclear detectors used for national security; from how stars produce different chemical elements, to how we can use the processes happening inside stars to generate electricity here on Earth.
The post-16 course assumes GCSE-level knowledge of Nuclear Physics. Refresh your knowledge with the information below and check out BBC Bitesize.
The Structure of the Atom
Atoms are made of protons (positively charged particles), neutrons (neutral particles) and electrons (negatively charged particles). The protons and neutrons are at the centre of the atom in the nucleus, and the electrons surround the nucleus. Elements are defined by the number of protons in this nucleus. For example, anything with one proton is hydrogen, anything with two protons is helium, anything with three protons is lithium. All of these elements are listed in the periodic table. If an atom was the size of a football pitch, the nucleus would be the size of an ant!
Isotopes
If two atoms have the same number of protons but different numbers of neutrons, we say that they are different isotopes. The full chart of all the isotopes is called the Nuclide Chart (more about this later!).
To distinguish between isotopes, scientists use the following notation where the total number of particles in the nucleus is also referred to as the mass number (A) and the number of protons is also referred to at the atomic number (Z).
Nuclear Stability
Some isotopes are stable and last for millions of years. Most are unstable and may last for less than a second. Isotopes that are unstable will always become more stable over time by changing the properties of their nucleus. A proton might change into a neutron, or a neutron into a proton, or the nucleus may even split into two different smaller nuclei. When they do this, we say that the nucleus has decayed.
Unstable isotopes are radioactive - when they decay, they give out radiation, often in the form of fast-moving particles that carry lots of energy.
Types of Radiation
At GCSE level, we talk about three types of radiation - alpha (⍺), beta (ꞵ) and gamma (𝛾) - as well as fission.
Alpha particles are helium nuclei composed of two protons and two neutrons (24⍺). They are easily absorbed.
Beta particles are high energy electrons (-10ꞵ). They are created when a neutron turns into a proton.
Gamma radiation is a type of electromagnetic wave (00𝛾). It passes easily through most materials.
Image credit - Wikimedia Commons/Alpha beta gamma radiation svg
Fission is when a large nucleus splits into two or more smaller nuclei. This can be spontaneous or can be triggered (for example, by firing a neutron into the large nucleus).
We can write nuclear equations to show what happens in a decay or a fission reaction. Remember that the sum of the mass numbers must be equal on both sides of the equation, as must the sum of the atomic numbers. Worked examples are shown in the Isaac Physics decay notes and the Isaac Physics fission notes.
There are more types of decay that we’ll be talking about in the Nuclear Masterclass. You can see these here:
More on these later!
Half Lives
Radioactive decay is a random process. This means that we cannot predict how long it will take an individual nucleus to decay. Instead, we talk about the half-life of an element. This is the average time taken for half of the radioactive nuclei to decay (or the time taken for the count-rate to half). Again, have a look at the Isaac Physics notes for some worked examples.
Is Nuclear Physics Safe?
Small amounts of radiation are around us all the time. Radiation is given out by rocks and soil, cosmic rays (coming from the Sun and stars), and all living things – even us! This is called background radiation. The amount of radiation received is called the dosage and is measured in sieverts. Bananas, which are very good for us, are a natural source of potassium – a radioactive isotope. Eating one banana gives us a dose of 0.0000001 sieverts. We can use this as a way to measure radiation dose: it’s called the banana equivalent dose (BED).
Having an X-ray of your arm gives you a radiation dose equivalent to eating 10 bananas.
A transatlantic flight is the same as eating 800 bananas.
The typical annual dose of a person living in the UK is equivalent to 27,000 bananas (eaten over a year – that’s 74 a day!).
A chest CT scan would be the equivalent of eating 66,000 bananas.
A six-month trip to the International Space Station is equivalent to 800,000 bananas.
Very high doses of radiation can cause burns, cancer, radiation poisoning, and even death. A fatal dose of radiation is 4 Sv or 40,000,000 bananas.
Have a look at the fascinating XKCD Radiation Dose Chart. Christian Diget, a nuclear physicist at the University of York, calculated that he received a higher dose of radiation on his flight to Vancouver than during the nuclear experiment he went there to conduct!
Optional Activity
Nuclear Masterclass: Practice Questions
Log in to Isaac Physics and answer the questions:
Essential GCSE Physics 51.1, 51.2, 54.2, 54.3, 53.1, 53.2, 53.2
Essential Pre-Uni Physics J1.1, J1.2, J1.4
Don't forget to log in to Isaac Physics!