Beamtime

Hey everybody,

It seems that today is a major update date for the REU blog so far, and I figured I should make this day as big as possible. When we last left off, I was about to present my findings to everyone in the program. That all went ok. If there is anything I can handle, it is tongue and cheek public speaking events. 

After that began my weeklong struggle getting our actual experiment up and running. We tried to start setting up our stuff in the beam room, but we had to wait until another professor’s 100 hour beam experiment was over. This lead to me doing any sort of calculation that we would need. Cross section calculations to see what the probability of a photon–> pair production happens in air. What are the count rates we should expect to get for running the beam at such and such specifications. Basically, we wanted to know just how many electrons and positrons would happen in each pulse of the beam. Ideally, it wouldn’t be that much, so we could be sure that any time we get a hit in both detectors, we could then assume the electron and positron came from the same photon. 

The number we got was extremely large, so we had to add in a bunch of collimation to our beam line to get count rates low. Still, this wasn’t that much work to do, and we were basically just waiting to get the beam time. The downside of having your own linear accelerator at your school is that there is a lot of negotiating between professors on running the beam, since none of them have to pay to use it like an outside person would. The beginning of this week, we were set to go in the beam, but the other professor (who has a huge gov’t grant) was in a some sort of underground bunker talking to the military in D.C., so we couldn’t get a hold of him to ask if we could use the beam. There are some high school kids doing a sort of physics summer camp here, so I ended up helping them make more detectors because they were as lost as baby sheep with the circuit boards.

Finally, we had beam time (dedicated beam time so we could do whatever we want) on Friday. Yes, that means I had a miserably slow week as far as work goes. We were ready though. I had to move a lot of lead, aluminum and graphite bricks around to protect our detectors getting fried, but it was really worth it. I was so ready to do physics. Friday comes along, and everyone who is involved with he project comes down to the countroom to see the initial launch of the pair spectrometer everyone has worked so hard on. We set up a nice circuit to measure coincidences in our two detectors. 

The beam starts up and we start getting flashes of data. Or so we thought. It was just background cosmic rays. The beam didn’t started because they had a problem with the cooling system. 7 minutes later, they get it going, and we are seeing peaks on our oscilloscope. For about 20 seconds. “Something is wrong with the cooler still, I need to call the supervisor guy.” 30 minutes later. “We found the problem. A switch was stuck, and it needs to be replaced, but it will work for now.” The beam starts up and it is working. We see hits flying in…for 45 seconds. “Somethings wrong. We need to call a repair guy. It will be down until 1.” Ok, go to lunch and then come back ready to go.

The experiment is a pretty easy result. If we have pairs being made, we will see the majority of coincidences hitting the two detectors at roughly the same time. It won’t take long to know if we got it right, so losing the morning isn’t that bad. A hamburger, fries and ice cream cookie sandwich later, we’re back in the countroom. “Yeah, we fried a circuit board. The guy who is the electrical engineer for the beam is in Germany in Tuesday. We can’t run today.”

To sum it up, I am in a limbo of nothing to do. Joey, since you’re in Germany, if you can find an electrical engineer from ISU named Chad, could you send him back to the states for me? Thanks.

Sometimes, it sucks to be an experimentalist.

I’ll have the fun stuff I’ve been up to in my next post. I’ll probably have a ton of free time to blog this upcoming week.