June 2011 G485-Fields, Particles and Frontiers of Physics Watch

MarieLyon
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#481
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#481
meh either way MRI and Ultrsound came up because I was just lookign at both mark schemes
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MarieLyon
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#482
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#482
And the specimen paper is totally useless! They dont even give questions like that in the past papers.
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MarieLyon
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#483
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(Original post by johndory13)
You do not need the know the differences because they are completely different one uses X rays and the other gamma
And there are very few similarities

more likely to compare similar radiation
oh I know they wouldnt ask for similarites/differences in a question. I was just askig generally.
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M_I
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#484
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(Original post by Oh my Ms. Coffey)
Explain Compton Scattering and the Photoelectric effect.
Photoelectric effect - a photon with about 30keV of energy hits and electron in the tungsten atom, the electron is ejected, another electron fills the gap in the lower energy level shell, releasing a photon

Compton Scattering - a photon with about 0.5 - 5 MeV of energy hits an electron and knock it out, photon loses energy and is scattered.

Would I need to add any more info?

--------------------------------------------------------

How do radiographers try to produce a sharp image while minimising the radiation dose?
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TobeTheHero
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#485
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i ****in love this unit2 so many interesting concepts
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Nirgilis
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#486
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This may sound ridiculous, but what's the difference between potential difference and voltage?
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mrpope1000000
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#487
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Hey can someone please clarify if we need to know the moons of planets in the solar system?
The specification's a bit vague... it just says 'describe in terms of planetary satellites'.
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M_I
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(Original post by Kidms001)
This may sound ridiculous, but what's the difference between potential difference and voltage?
There's a difference?
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M_I
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#489
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#489
Can someone re-explain A-Scan and B-Scan?
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trapzbrah
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#490
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(Original post by TobeTheHero)
i ****in love this unit2 so many interesting concepts
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MarieLyon
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#491
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(Original post by M_I)
Can someone re-explain A-Scan and B-Scan?
Pulses of ultrasound are sent into the body, the signal is reflected. The time of delay is used to calculate the depth. The refraction of reflection is used to identify the tissue. A-scan is just one of these. B-scan is many of these producing a better image.
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scotzbhoy
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(Original post by MarieLyon)
I think we are going to get a long question on x-rays or the gamma camera because Jan 2011 asked for MRI and Jun 2010 asked for ultrsound.

Can someone give me any information on PET and CAT (like the differences between them).
X-rays came up in June '10
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mrpope1000000
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(Original post by M_I)
Can someone re-explain A-Scan and B-Scan?
A-scan (amplitude scan) shows reflections as vertical deflections on the CRO screen, like a wiggly horizontal line, indicating the time the echo took to return - so you can calculate distances.

B-scan (brightness scan) shows up as dots of varying brightness. Larger amplitude of reflected waves = brighter spot. You can build a 2-d image with this but not with A-scan.

Hope this helps
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MarieLyon
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(Original post by scotzbhoy)
X-rays came up in June '10
onlt the contrast media and intensifiers nothing to do with compton scattering... photoelctric effect and that positron one.
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M_I
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(Original post by MarieLyon)
Pulses of ultrasound are sent into the body, the signal is reflected. The time of delay is used to calculate the depth. The refraction of reflection is used to identify the tissue. A-scan is just one of these. B-scan is many of these producing a better image.
Oh ok, I think I'm seeing how it works now.

What do we need to know about the mass attenuation coeffecient?
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PhilliChilli
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(Original post by PpphelannN)
This goes into a big more detail than we need to know, but hey



I got it from this http://www.thestudentroom.co.uk/atta...8&d=1305275576
It's well sick

Also these might help



Hope this helps, the pdf is useful as well it highlights like keywords and stuff It's good cos our book (the pizza one) is useless for that kinda thing :/
Thank you ! (Jack...?) Ill definately be reading over this tonight! Good luck for tomorow!
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MarieLyon
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(Original post by M_I)
Oh ok, I think I'm seeing how it works now.

What do we need to know about the mass attenuation coeffecient?
there's an equation for it isn't there? And that isn't ultrasounds its x-rays. isn't it?
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jam.wa
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#498
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Hubble, with your stupid units for your stupid constant.

Why couldn't you always just leave it as s^-1?

Oh, you wanted loads of A-level candidates to waste time doing stupid 1 markers dividing km s^-1 by M Pc^-1?

Go AWAY.
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M_I
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(Original post by mrpope1000000)
A-scan (amplitude scan) shows reflections as vertical deflections on the CRO screen, like a wiggly horizontal line, indicating the time the echo took to return - so you can calculate distances.

B-scan (brightness scan) shows up as dots of varying brightness. Larger amplitude of reflected waves = brighter spot. You can build a 2-d image with this but not with A-scan.

Hope this helps
Making more sense everytime I read something about it.....i hate Ultrasound.
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susan23
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ok what answer do you get for this for the total capacitance...show ur working.
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