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When it underwent beta decay, one of the nuclear electrons escaped, resulting in a Calcium-40 nucleus with 40 protons and 20 electrons, and a net positive nuclear charge of 20. This gave it a net positive nuclear charge of 19. That is, it was believed that, for example, Potassium-40 had 40 protons and 21 electrons in its nucleus, in addition to the 19 electrons circling outside of the nucleus. At this time, it was believed that the electrons resided in the nucleus all along, and somehow escaped. The beta particles were later determined to be just electrons. īefore the structure of the nucleus was understood, this emission of negative particles was observed, and they were called "beta particles" or "beta rays". The most common radioactive decay involving the weak interaction is the transmutation of a neutron into a proton, with emission of an electron and an antineutrino. It is one of three major types of radioactivity (the other two being alpha decay and gamma decay), and the only one that involves the transmutation of a subatomic particle. The Feynman diagram for the beta decay of a neutron into a proton, electron, and electron antineutrino via an intermediate heavy W-bosonīeta decay is a type of radioactive decay involving the "weak force" and the transmutation of nucleons (ultimately, the transmutation of quarks) inside an atomic nucleus. Proton-antineutrino collision: p + ν̄ e → n + e +Įlectrons and protons are of course attracted by the electromagnetic interaction between them, but if they collide the weak interaction can make this interaction happen.Subject classification: this is a science resource. Neutron-neutrino collision: n + ν e → p + e –

There’s a very low probability of a neutrino interacting with matter, but here’s what happens when they do: You get an antineutrino in β – decay and a neutrino in β + decay so that lepton number is conserved. RULES FOR DRAWING FEYNMAN DIAGRAMSġ) Incoming particles start at the bottom of the diagram and move upwards.Ģ) The Baryons stay on one side of the diagram, and the leptons stay on the other side.ģ) The W bosons carry charge from one side of the diagram to the other – make sure charges balance.Ĥ) A W – particle going to the left has the same effect as a W + particle going to the right. You can draw Feynman diagrams for loads of interactions but you only need to learn the ones in this post for your exam. He worked out a really neat way of solving problems by drawing pictures rather than doing calculations.ġ) Gauge bosons are represented by wiggly lines (technical term).Ģ) Other particles are represented by straight lines. Richard Feynman was a brilliant physicist who was famous for explaining complicated ideas in a fun way that actually made sense. Creating a virtual W particle uses so much energy that it can only exist for a very short time and it can’t travel far.Ģ) On the other hand, the photon has zero mass, which gives you a force with infinite range.įeynman Diagrams Show What’s Going In and What’s Coming Out The Larger the Mass of the Gauge Boson, the Shorter the Range of the Forceġ) The W bosons have a mass of about 100 times that of a proton, which gives the weak force a very short range. The graviton may exist but there’s no evidence for it. Gravity only really matters when you’ve got big masses like stars and planets. Particle physicists never bother about gravity because it’s so incredibly feeble compared to other types of interaction. Each one has its own gauge boson and you have to learn their names: Type of Interaction Gauge bosons are virtual particles – they only exist for a very short time.Īll forces in nature are caused by four fundamental forces. The repusion between two protons is caused by the exchange of virtual photons, which are the gauge bosons of the electromagnetic force. These exchange particles are called gauge bosons. Particle exchange also explains attraction, but you need a bit more imagination.Ģ) Attraction – Each time the boomerang is thrown or caught the people get pushed together. It happens because the ball carries momentum. That’s the idea behind exchange particles.ġ) Repulsion – Each time the ball is thrown or caught the people get pushed apart. So, when two particles interact, something must happen to let one particle know that the other one’s there. You can’t have instant action at a distance (according to Einstein, anyway). To the casual observer, this might not seem entirely fair. Having learnt about hadrons (baryons and mesons) and leptons, antiparticles and quarks, you now have the esteemed privilege of learning about yet another weirdy thing called the gauge boson.