Detectors and Free Pizza

Yesterday I went to the pizza seminar at lunchtime. JLab occasionally holds these seminars, chances for grad students to learn about things going on at JLab and as an extra bonus, get fed pizza :) Yesterday's talk was by Howard Fenker on detectors used in high energy physics.

I enjoyed the talk because I have so far been focused more on the computational (analytic) and theoretical side of things, rather than the "hands-on" stuff of messing about with the actual equipment. I know about the detectors, understand (more or less) how they work and all, but my relationship with them has up to now been rather impersonal.

Yestarday's talk brought it all into a new light, however, with slides such as "How to build a gas-filled wire chamber" for particle position tracking, and such. Thus it was with some excitement that I was able to get my hands on a photomultiplier tube that was being passed around. That's it on the left here, though it comes in a tube filled with gas.

For those of you who don't know much about photomultipliers, you can think of them as signal amplifiers. In high energy physics, we mostly try to detect single elementary particles at a time, such as electrons, muons etc. You can probably figure out that the "signal" given off by one of these little babies passing through a detector is pretty damn small, so in order for us to be able to pick it up on our computers, we need to amplify the signal.

Now, a common way to detect particles is to use the light they produce when going through some medium. For example, if we wanted to measure the speed of an electron, we use a Cerenkov counter. Now you all know that nothing can go faster than the speed of light, but did you know that this was only in a vacuum? Light slows down as it travels though other substances, such as gas. In such cases, an electron can actually travel faster than light speed in that medium, and light is emitted from the travelling particle. The number of photons emitted, and the angle at which they are emitted, tell us the speed of the electron.

This is where photomultipliers come in. As said before, for a single electron, even if it's going really fast, the number of photons it produces are still low. A photomultiplier takes one photon, and uses an "avalanche effect" to produce lots of them. They're rather useful little things :)

Anyway, that was yesterday. Today is a wonderfully bright sunny day - the first we've had since we've been here, it's been raining and I didn't bring a raincoat or umbrella. Mark and I went and did some food shopping at Wal-Mart this morning. I also bought an umbrella. What's the bet it won't rain again while we're here? LoL

This afternoon is the annual JLab Run-a-Round, a 1.5 mile race around JLab. I have decided to be fantastically lazy and am not going to participate in the race ;D but rather take lots of photos and be a cheerleader instead! Before the race, they are also unveiling this year's T-shirt, and I'm very eager to see if it's the one I voted for.

So I'd better get back to work now because this afternoon's going to be out. Now I wonder if anyone's got any pompoms....

Comments

[Karen]

Whew! Well, as the Mom person left behind in South Africa while my daughter is getting compulsively having travel dramas, I'm delighted to see you are finally there, Claire! JLab activities are fun - can't wait to see you in a fortnight, and put all the people and places you talk about into context.

[m. visaya]

i notice that that thing is big. theoretically, if one puts a D atom on track to hit a D atom target and they stick, giving off photons this "baby" could multiply this signal and a "nursery" could actually sustain a controlled fusion?

#10 LaBs