I'm wondering how do we detect protons, and wat sort of detectors are used for this?
hi again, i need an idea for this quite urgently, i am thinking protons could be detected using a mass spectrometer i.e we can use the known mass and charge, and apply specific E and B fields, and thus measure the radius f deflection to see if it corresponds to the expected calculated value. Is this an acceptable detection method?
Yes. Apply a B-field.
Thanks. So the proton mass is not too small to be used in a mass-spectrometer?
What sort of experiment is this for? What range of energies do you expect the protons to have? Do you know the energy in advance (say by producing them with a specific energy), or do you have to measure the energy, too?
Note that measuring the deflection in a magnetic field, all by itself, gives you only the momentum. To get the mass, you need to know or measure the velocity. A mass spectrometer uses a "velocity selector" to ensure that the particles have a known velocity.
Response to the original poster:
Not if you design your spectrometer correctly. You can even detect electrons.
Modern particle detectors are considered souped-up spectrometers.
I just need a general method for detecting proton's. With the mass spectrometer method, mass,E and B, and velocity are assumed known, so using these we can determine the radius of deflection. If the measured radius is equal to the calculated, then we have detected a proton.
Are there any better methods of detecting protons?
Right - or you can use other information like dE/dx (energy loss in matter) to determine the nature of the particle.
I must be missing something... Why aren't people finding it "strange" that putting this in a magnetic field would be a valid "detection"? All you're doing is causing the proton's path to be bent... how would this be a sign of "detection"? You are forgetting that you STILL need the proton to LAND somewhere and leave an imprint!
The most primitive means of detecting a proton is not that trivial IF you are in a situation where there are other charged particles around. This means you have to somehow discriminate between all the other garbage and the proton you have in mind. This isn't mentioned in the original question, so it is difficult to know if one is answering for such a scenario, or if one simply has a stream of protons and one just one to "detect" that such a stream is turned on. This latter scenario is easier IF one doesn't care about energy spectrum of the beam, etc. (i.e. just use the fact that protons can cause a large secondary electron emission when it hits a semiconductor surface, etc.)
Right, that's why I asked what kind of experiment this is. My very first thoughts when I saw the original question were of the bubble-chamber experiment I worked on as a grad student. In the absence of other information, the usual way to decide whether a particular track was a proton, pion, muon, etc., was to measure the curvature (in a B field) at various points along the track, and see which "mass hypothesis" fit the data best, taking dE/dx into account.
This is true... Unfortunately, doing this also doesn't discriminate between a very fast proton and a slow but heavy charged particle. Till this person explains a little bit more (actually A LOT more), there's nothing any of us can do.
Hey, sorry guys my question was very ambiguous, but the assignment question was just as vague. Basically we were all given a different particle, i was assigned proton, and we were told to outline the principles of operation of a detector of that particular particle.
It might be a good idea to talk to your teacher or prof and get more details.
(1) What is the source of the protons? If you know the source, you will probably know whether you know the energies or not.
(2) What is the background? In other words, what other particles might you detect and have to discriminate from?
If you can't get more details, then I would say that a generalized concept of a spectrometer should do the job if you have no background and know the energy of the protons. Something like a bubble chamber or drift chamber with a uniform magnetic field running through it. (Then again, if it's ONLY protons, you don't even need the magnetic field).
There's a section on wire chambers here:
and look at particle detectors.
I was assuming it was a school assignment that was looking for a crude answer.
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