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# Physics A2 nuclear physics watch

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1. I'm taking physics A2 (OCR) in the next few weeks, but I'm pretty much clueless on everything to do with nuclear and particle physics. Especially those weird nuclear equations. The fact that I have to take it as my option module doesn't help either.

PLEASE can anyone help me, point me to any useful websites or anything like that, in particular anything on nuclear equations. I mean, are we meant to memorise them or is there some way to logically calculate it a la chemical reaction equation? Hopefully some of you can put me out of my misery, or shoot me so I don't have to fail the exam.
2. you dont memorise nuclear equations. You just need to remember this:

6 quarks: up down charm strange top bottom
and that proton = uud (up up down) and neutron = udd

up has charge +2/3 e, down has -1/3 e. Thus proton total charge = +1, neutron charge = 0;

charm have charge +2/3 e, strange have -1/3 e
top and bottom you dont need to know (in fact you dont need to know about charm...just that it exists)

All things made of quarks are called hadrons. All hadrons must have an integer (or 0) total charge. You can get this from groups of 3 quarks (like the proton and neutron, which you have to know) and the from pairs of quarks, occuring as quark anti-quark pairs.

Anti-quarks are identical to their quark companion apart from opposite charge....an anti-up quark has charge -2/3 e

so that's all you need to know about strong interactions (interactions involving quarks). Stable pairs can be u-anti-up for example, and is called a meson (that one is called a pi-0 meson - the 0 stands for it's charge)

Weak interactions involve things called leptons. There are 6 leptons (as well as their anti-lepton equivilent):

Electron: charge -e
muon: charge -e
Tau: charge -e

To go with those 3 are their neutrinos:

Electron Neutrino, Muon neutrino, Tau Neutrino - all neutral.

Leptons get made in weak interactions.

Lepton number is always conserved. Baryon Number is always conserved.

What's a Baryon? 3 quarks together (so you have Baryons and Mesons that make up hadrons)

A quark therefore has a baryon number of 1/3 (so one baryon, eg a proton, has total baryon number of 1). A lepton has lepton number =1

Any anti-particles have opposite lepton/baryon number (so anti-up has -1/3 baryon number, anti-electron neutrino has -1 lepton number).

Valid reactions must conserve:

1. Charge
2. Baryon Number
3. Lepton Number

From all the above you can figure everything out...

e.g. Beta Decay: neutron turns into a proton:

n -> p + e + anti-electron neutrino

Baryon number on left: 1
On right: 1
Lepton on left: 0
Lepton on right: 0 (e = 1, anti electron neutrino = -1)

Charge on left: 0
charge on right: 0 (proton = 1, electron = -1, neutrinos are always neutral)

that's a starter - and summarises most of what you need to know
3. nice summary there willa, but there are a few things i dont get.

in the OCR book theres no mention of lepton numbers (seems logical that they exist but we probably dont need to know about them).

Also the weak interaction (or force) is stated as being the interaction responsible for quarks changing flavour.
4. conservation of strangeness rather than lepton number for this module i tihnk
5. i too am doing this **** module

yes its ****

have to know things in detail because there isnt much content, and you have to know all of module D for it really as well.
6. (Original post by friday13th)
i too am doing this **** module

yes its ****

have to know things in detail because there isnt much content, and you have to know all of module D for it really as well.
yeah i was revising today for it, hope it willb ok tho

last ****ing exam
7. what i wanna know is why they chose a strange particle to have -1 strangeness.....Why not choose +1 and make everything simple!!!
8. i need liek 100%, not going to happen!

also they put a unifying concepts question on there, how sad!
9. (Original post by friday13th)
i need liek 100%, not going to happen!

also they put a unifying concepts question on there, how sad!
yeah i know but in a way it can be seen as a good thing
10. (Original post by Willa)
you dont memorise nuclear equations. You just need to remember this:

bla

yes, that summarises a lot of particle physics, but there's a lot more in nuclear physics, as well as the stuff about particle accelerators...

You might also need to know how some graphs look. I've been looking at them and trying to visualise them as other things - r = r0A^(1/3) looks a bit like a train

and nuclear fishing needs a controlled rod. lol.

Reading through the syllabus helps, if you have it. Or if you have the OCR textbook just look at the learning outcomes. Just tick them off or something when you think you can do it.

wikipedia.org might or might not help, if you look up something you don't understand it might contain some more useful information, or it might be confusing... I haven't really used it much myself.

If you just go through the textbook reading and takiung some notes, you might find you understand more. You'll probably need to know how fission and fusion work, and probably the different types of particle accelerator. I found that in the end the textbook was more useful than the teaching. It might pay to remember those overall equations for the different cycles in fusion... Not sure tho.

That was some pretty random waffle I just made up there...

edit: oh, and an anti-strange quark does have +1 strangeness, I think
11. yes, but why should the anti-strange quark be +1 strangeness, why not make that one -1, and strange quark be plus 1.....GRRR!
And i'm dreading the synoptic question, i havent revised any other stuff, i'm just gonna rely on my ability to figure things out!
12. (Original post by Willa)
yes, but why should the anti-strange quark be +1 strangeness, why not make that one -1, and strange quark be plus 1.....GRRR!
And i'm dreading the synoptic question, i havent revised any other stuff, i'm just gonna rely on my ability to figure things out!
true. What can I say, physicists are strange, a bit like quarks.

And the synoptic questions are a bit odd...

Also the seem to ask for the wavelength of gamma rays alot..., this is quantum physics stuff? Does this mean I'm gonna have to break out the AS textbook?
13. anybody got an answer to this:
"suggest why the gamma photon leaves no track in the cloud chamber"

So why do some particles/photons create a coloured track in a bubble chamber and others dont?
14. cloud chambers detect charged particles only - gamma particles are not charged, neither are neutrinos. They leave no track. As regards to colours, i always thought they were all the same colour (you sure they havent added the colours on after to make it clearer)
15. (Original post by Willa)
cloud chambers detect charged particles only - gamma particles are not charged, neither are neutrinos. They leave no track. As regards to colours, i always thought they were all the same colour (you sure they havent added the colours on after to make it clearer)
They may have done, but why do they leave colour at all?
16. Mentioned this on another thread, but "SURE Higher Physics" software from Counting Thoughts might be useful - covers much the same syllabus...
17. Okay! The bubble/cloud chamber works by ionization events. As a charged particle moves through the chamber it encounters other particles, such as atoms. Usually the charged particles are moving with lots of kinetic energy. This means that when it interacts with the atoms it will usually only ionize them. This slows down the charged particle, but also causes a small flash of light at this point. As the charged particle moves about it leaves a trail of ionization events, which show up as paths of light.

However, in gamma rays more of the energy can go directly into the receiving particle, this is simply due to the conservation of momentum. So usually it just generates a high energy electron as opposed to generating many ionization events.

As for neutrenos, they don't interact with matter very often. This is because the only method of interaction is the weak nuclear force, which is very short ranged (as opposed to the electric force which has a much longer range). Although once again when it does interact, with its low rest energy and very high KE it produces some new particles, which can be tracked.

Colour. Me thinks yu guys must be talking about QCD. First I will not pretend to know much about the subject. But it was formulated to explain why certain reactions occur and others don't. Essentially we have 3 extra properties for quarks and the mediators of the strong nuclear force that acts on quarks, gluons. These properties were to be known as Redness, Greeness and Blueness. Of course each property could take negative values etc etc etc. Each interaction had to obey conservation of colour as well as all the other conservations, like strangeness, charmness, charge and energy. Also when quarks exchanged gluons, these gluons needed to have colour, hence the quark that produces them change colour. Since gluons also had colour gluons also act upon gluons. This means that when you try to seperate two quarks energy increases until you have enough energy to generate more quarks.
Also gluons are rather massive, having large rest masses so for a quark to generate gluons tends to use energy it does not have. However the uncertainty principle allows this if the time that this energy debt exists is shorter than t < h/(4piE). This is what is meant by virtual particles. Also in a hadron the overall colour is always white (the colours cancel).

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