Breaking Down The Atom OR Inside the Atom.

by Katie O'Flaherty


Everything we see around is made up of atoms. From the screen you’re reading this on now, to the food you eat, and the water you drink, it’s all made up of tiny structures called atoms, all bonded together to form the materials you see in front of you, with the properties you know so well.

Until the 18th century, there was no concrete evidence for the existence of atoms, with Joseph Dalton using comparisons between reactions to prove every substance is made up of lots of smaller ‘parts’, called atoms. J.J Thompson’s discovery of electrons in 1897 further deepened our understanding, Ernest Rutherford’s famous ‘Rutherford Scattering’ refined our understanding of the structure of atoms in 1909, with the discovery of the neutron in 1932 by James Chadwick finally completing the picture.

Yet, there were still unexplained properties. A number of anomalies in observed effects, such as the Zeeman Effect, could not be explained with the models we had. In 1927 Paul Dirac suggested that electrons could have both a positive and a negative charge, thus introducing the idea of the positron. The first two subatomic particles, the positron and the electron (both types of lepton), were now known. Over the next century, over 200 more subatomic particles were to be found, with the ‘Quark Model’ being put forward by Gell-Mann and Zweig in 1964. This proposed that hadrons (particles such as protons and neutrons) were not elementary particles, but rather could be broken down even further into quarks and antiquarks. Their model was the first step down a long road of discovery.

Use of the Standford Linear Accelerator Centre in 1968 proved the existence of quarks, even though a significant proportion of the science community refused to accept their existence for many years. It showed that the proton contained much smaller, point like objects, thus was not an elementary particle. Simply put, the accelerator uses electric fields to accelerate an electron (or other lepton) to exceptionally high speeds, then collide it with a target hadron (subatomic particle made of two or more quarks), in an attempt to ‘knock’ a quark out of it. This is called deep inelastic scattering. The displaced quarks are then detected due to the process of hadronisation (the formation of hadrons from 2 or more quarks combining), which produces different, observable particles.

The understanding today is that protons are made up of two ‘up’ (u) quarks, and one ‘down’ (d) quark, and a neutron udd (up, down, down). In every interaction between subatomic particles, the mass, charge, baryon (type of hadron) number, and lepton number is conserved, which enables us to calculate what would be produced in various interactions, and whether a particular interaction is feasible.

Still our understanding of subatomic particles is not complete, with the Large Hadron Collider (LHC) at CERN being one of the most famous international collaborations to date. The LHC has a massive circumference of 16.6 miles, and has been responsible for a number of leaps forward in our understanding. The 2012 observation of the Higg’s Boson, which was first proposed in 1964, produced massive waves in the world of science, being nicknamed the ‘God Particle’ in the media. It helps to explain how particles obtain mass, which is a fundamental property of all matter.

Higg’s theory proposes that a so-called Higg’s energy field exists everywhere in the universe, and as particles move around the field, they interact with and attract Higg’s Bosons, which can cluster around the particles. Certain particles will attract more Higg’s Bosons, thus will be given a higher mass. Particles that interact with the field will become slower as they pass through it, and it is this result of the particle ‘gaining’ mass from the field which prevents it from travelling at the speed of light (as the particle moves faster, it gains more mass, thus is slowed down more). Giving mass to an object is called the Higg’s Effect, and is fundamental to explaining the ‘Standard Model’ - the theory of elementary particles, which explains three of the four fundamental forces of nature.

CERN’s plan to open the Future Circular Collider (FCC) to replace the LHC in 2040 will cost £20bn to build, have a circumference of over 62 miles, and will enable us to understand further the tiny fragments that make up our world around us. Not only this, but the Chinese are planning on building the Chinese Circular Electron Positron Collider (CEPC) with a similar circumference, which is planned to be a “Higg’s Boson Factory”. When they are completed, the work of scientists in both of these projects will enable us to accelerate subatomic particles to ever greater speeds, and analyse the results with ever more precision, thus enabling us to greater understand the world around us.