25 Days of Particles: Day 1

Electron

Classification: lepton, fermion
Fundamental: yes
Family: First
Mass: 0.51 MeV = 9.11e-31 kg
Interactions: Electromagnetic (charge -1), Weak, Gravity
Spin: 1/2

Our Christmas tour of the world of particles starts with the electron. This is the negatively charged particle that zips around the perimeter of atoms, and is responsible for virtually all atomic and molecular interactions. Electricity is the flow of electrons through some material. Pretty much life and science as we know them are dependent on these little guys zipping around. It doesn't take a lot of energy to remove electrons from atoms, so they move around matter easily and interact with each other a lot. In particle physics, they can actually be a little annoying to work with. They readily interact with your detector, so you find them easily, but they readily interact with your detector, so they are going to make a mess splashing energy around as they plow into it and get stuck there.

Electrons are examples of leptons, those fundamental particles that can be separated from all other particles. They were the first sub-atomic particles to be discovered. During the nineteenth century, research into electricity and magnetism were cutting edge in physics, and several experiments had found that heating up metals caused them to spit out negatively charged bits of stuff. They even proved the stuff cast its own shadow. Early theories postulated that this strange material was negatively charged atoms or some previously unknown fourth state of matter. In 1896, J. J. Thomson and his colleagues began studying these 'cathode rays' and successfully measured their charge to mass ratio. They showed that these rays were intrinsically charged, and that you got the same rays regardless of what type of metal you heated up, and even that you got the same rays from non-metallic materials. They hypothesized that these rays were a type of matter found inside atoms, the first known sub-atomic particles, and dubbed them electrons. Contemporary experiments in radioactivity showed that these electrons were also emitted from radioactive materials without any interference from anyone, strengthening the proof that these electrons were parts of atoms. Thomson received the 1906 Nobel prize in physics for his work in discovering electrons.

Today, the electron is the most studied of the all the particles; physicists and chemists know it and the systems it appears in best. We use them for everything from making light bulbs glow to taking pictures of things too small for light to see to shooting them around giant particle accelerators. You can thank the mighty electron for both the lovely Christmas lights and for every time you get a static-electric shock when taking off your coat. It's all thanks to him.