AS Physics - Matter and Radiation

Ok, today we will be having a quick lesson on particle physics, because while that shit might seem easy, it'll sneak up on you, and you don't want to be let down by one of the most fun parts of A level physics, do you? Aight then, lets do this thing.

First off, the basics you should know. This is only a refresher post, or at least it plans to be, before I inevitably start digging into really interesting but ultimately irrelevant articles. Anyway. Atoms: Really fucking small. Made up of even smaller things called nucleons. These are your garden variety neutrons, protons. They make up the nucleus. Nucleon, nucleus, you see what they did there? Fucking genius. And of course we can't forget electrons. No, those little bastards will come into nearly every aspect of physics ever, somehow.

Now, we all know that protons, neutrons and electrons have charges 1, 0, and -1 respectively, right? Wrong, motherfucker. Those are relative charges. Relative to what? Doesn't matter, because you're now going to forget them. Same goes for those masses of 1, 1, and negligible. In fact, you can super forget them, because they are just plain wrong. No, now we break out the metric, wherein the proton has a charge of +1.6e-19 C (e means x10 to the power of...), an electron has the same, only -ve, and a neutron, well, the neutron still has 0, being neutral and all. Masses are 1.67e-27, 1.67e-27, and 9.11e-31 kg.

Isotopes you should know, atomic symbols you should know...ah, here we go. Basically, after realising that the nucleus was made up of nucleons, physicists considered than maybe something existed that was holding these things together, overcoming the electrostatic force that should be pushing them apart. A force, that effects the nucleons, a nuclear force, if you will. They called this the Strong Nuclear Force, and I have another fun little analogy for you. See, the force only actually works within 3-4fm, and beyond 0.5fm. It's like when you see someone from a distance, and you think "Hey, she's pretty cute. Attractive even!" But then you get a little closer and BLAM. She wasn't nearly as attractive as she seemed from a distance. She is actually kinda repulsive. Got it? Aight. Next song.

Ok, I'm pretty sure we all did radiation in GCSE. Here the only real difference is a small, but important addition to β radiation. When it happens, you get your high speed electron, your atom with +1 proton number, but you also get a neutral antiparticle called an antineutrino, specifically an antiELECTRONneutrino. Because it came with an electron. get it? These were discovered when scientists worked out that in β radiation, energy was being lost. This meant that either Conservation of Energy was bullshit, or another particle was being released here. They went with the latter, since the former had been so good to them in the past, but this went unproven for a further 20 years, when in 1956 there was executed the Cowan-Reines neutrino experiment.

Cowan and Reines used a nuclear reactor, as a source of 5×10¹³ neutrinos per second per square centimeter.

The neutrinos then interacted with protons in a tank of water, creating neutrons and positrons. Each positron created a pair of gamma rays when it annihilated with an electron. The gamma rays were detected by placing a scintillator material in a tank of water. As mentioned in the Discovery of the Nucleus article, and scintillator is a doohickey that flashes, scintillates, when it is hit by something,  in this case gamma rays.

However, this experiment wasn't conclusive enough, so they came up with a second layer of certainty. They detected the neutrons by placing cadmium chloride into the tank. Cadmium is a bitchin' neutron absorber and gives off a gamma ray when it absorbs a neutron.

Most of this paragraph has been ripped from Wikipedia

The arrangement was such that the gamma ray from the cadmium would be detected 5 microseconds after the gamma ray from the positron, if it were truly produced by a neutrino.

Music break! Have one of the greatest pieces of soundtrack music ever composed.

To be honest, you don't need to know most of that shit. I just think it's interesting to know where our ideas come from. Point is we now know that neutrinos are everywhere, even more so than my claimed ability to play the guitar. Billions of them bombard us EVERY SECOND from our very own sun. These are grim days, friends, where our closest ally could also be our gravest threat. But I know that together we can be strong. We will prev--Oh, what, they're harmless? Well never mind then. Next!

Ok, most people know of photons as particles of light. However this is, well, not wrong, just inaccurate. Photons are actually the name given to bursts of electromagnetic waves, which, as you know, visible light is an example of. The idea was established by Einstein when he was working on photoelectricity, where electrons are emitted from metal when light is directed at it's surface, but that's something for another time. For now all you need to know is that LASERS are beams of photons with the same frequency. Note that the energy of a photon is given by hf, therefore is the number of photons passing a point per second is given by n, then the energy per second, i.e. the power of the laser of the specific frequency is given by the simple equation P=nhf.

Ok, here we go. I like this bit because it features a bit of Bristol talent. On 8 August 1902, one Paul Adrien Maurice Dirac was born in Bristol. 26 years later, two years ofter receiving his PhD from Cambridge, the same Bristolian predicted the existence of antimatter. 20 years earlier, Einstein had shown his whole fast particle=more mass thing, relating this with the infamous E=mc². He also said however, that when a particle is at rest, it's rest mass (m) corresponds with it's rest energy (mc²), and that this energy must be included in the conservation thereof. Using this, Dirac predicted that when a particle and it's antiparticle meet, they annihilate. Furthermore, he predicted the reverse, known as pair production, wherein a photon will split into a particle-antiparticle pair, both of which will then piss off from each other. The rest is just maths.

It's kinda difficult to come across image macros that relate to particle physics.

Ok, positrons. Let's do a little on their discovery. They are the antiparticles of electrons, and could just as easily be referred to as antielectrons. Similarly, I suppose, electrons could be referred to as negatrons, and funnily enough, that's what they used to be known as. In short though, a dude called Carl Anderson, one of the more boring names I've ever heard of, was firing beta particles into a cloud chamber. He was then surprised to find that  some trails were actually going in the opposite direction to that he has expected. Exciting stuff. Well, I suppose it was if you were there, but A Level seems to be specifically designed to reduce the most interesting stuff into grey sludge, which is a shame. Physics is such a beautiful subject, filled with elegance and wonderment, and this is lost on a majority of the population who just can't get past how god damn dull the initial learning of it is...Sorry, wrong meeting.

I'm going to leave it there folks. There is more about the weak nuclear force, and Feynmann diagrams, but that last bit kinda depressed me, so I'll leave that to you. Late'.

I was listening to the soundtrack through most of writing this.

(1902-08-08)