AQA A-Level Physics: Guide to Particles, Radiation, and Feynman Diagrams

Introduction to Feynman Diagrams

Feynman diagrams are like particle interaction maps that make complex physics much easier to understand. Think of them as comic strips showing what happens when particles bump into each other or change into different types.

These diagrams use simple rules: time flows from left to right, and space runs vertically. Straight lines represent particles like protons and electrons, whilst wavy lines show force-carrying particles like photons.

Quick Tip: The beauty of Feynman diagrams is that they turn complicated maths into simple pictures - perfect for visualising what's really happening in the particle world!

Basic Particle Collisions

When protons collide with protons, they don't actually touch - instead, they exchange a photon (represented by the wavy line γ). This electromagnetic interaction is what causes the particles to repel each other.

Electron-electron collisions work exactly the same way. Two electrons approach each other, exchange a photon, then fly apart due to their negative charges repelling.

The proton-antineutrino interaction is more complex because it involves the weak nuclear force. Here, a proton transforms into a neutron by emitting a W+ boson, which then interacts with an antineutrino to produce a positron $β+$.

Remember: Different forces use different exchange particles - photons for electromagnetic force, W and Z bosons for weak nuclear force!

Radioactive Decay Processes

Beta decay comes in two flavours, and Feynman diagrams show exactly what's happening inside the nucleus. In β- decay, a neutron transforms into a proton by emitting a W- boson, which then decays into an electron and an antineutrino.

β+ decay (positron emission) works in reverse. A proton becomes a neutron by emitting a W+ boson, which then creates a positron and a neutrino.

The neutron-neutrino interaction demonstrates how neutrinos can occasionally interact with matter, even though they're incredibly shy particles that usually pass straight through everything.

Key Point: These diagrams show that what we call "decay" is actually particles transforming through exchange of W bosons - nature's way of changing one type into another!

Advanced Interactions

Electron capture happens when a proton "swallows" an electron from the atom's inner shell. The diagram shows how the electron and proton combine via a W+ boson to produce a neutron and a neutrino.

Electron-proton collisions can result in similar outcomes, where the collision energy allows the particles to interact through the weak nuclear force rather than just electromagnetic repulsion.

These interactions are crucial for understanding how stars generate energy and how certain types of radioactive materials behave in medical applications.

Pro Tip: Notice how all these weak force interactions involve W bosons - they're like the universal translators that allow different particle types to interact and transform!