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.

Rainy Idaho=Raindaho

Hey everybody,

It has been pretty exciting to see everyone else’s REUs start up. We are in a lot of cool places, and I like the enthusiasm. I haven’t posted in a while, because my current project has been much of the same thing, and I wanted to at least wait until I was done with this part before I posted something. I guess I should put physics first and then move on to my cool, yet rainy adventures.

I have talked about how my work deals with a pair spectrometer and measuring things with a linear accelerator. Well, for the past week or so, I have had to calibrate (gain match) two photomultiplier tube detectors. What is the deal with gain matching? Well, no two photomultiplier tubes will be exactly the same, and a single PMT will have large difference in measurements depending on the voltage you have running into the detector and how high of a threshold you set for the detections. So, Dave(my partner) and I have had to do a lot of tests in the Laboratory for Detector Science. (Wait until Truman gets one of those)

A single “run” of tests would go like this: we hook up a PMT and setting a radioactive source(I need to wear a radiation badge thing) right next to the detector. Then we want to find out how many counts the detector registers from the source in a set time; we did it for two minutes. We set a threshold for how much energy the particles must have, and then we incrementally (25 volts at a time) decrease the detector’s voltage from 1400 until we don’t get any more hits. This takes about an hour. We had to do a run with three different thresholds, 2 radiation sources, and for both detectors. Factor in some faulty cables, scalar boxes and other stressful things, we were doing this for quite a while. As a side note, it is very interesting to live your life in 2 minute increments. You have 1 minute 50 seconds to do whatever you want, but then you have to get back to work. I’m happy Dave was there. The grad students also taught us a lot about their projects, so I’ve really learned a lot.

When we looked through the data sets for our 12 runs, we were able to figure out a lot more about what voltages to run the detectors so that they have similar count rates. We were also able to find the “plateau” where the count rates were least sensitive to voltage changes. Our Professor asked us to find the Compton Edge for the detectors. Compton edge is basically something in spectometry where gamma rays deposit some energy into the scintillator, the thing that picks up the radiation, even though they escape from the scintillator. The maximum energy of the particle allowed would be the particle that doesn’t escape, and that is the Compton edge.

This meant going back to the LDS and doing the same thing, except we had to collimate the sources by shooting them through a tiny hole in a lead brick and we kept the voltage constant and varied the threshold. This took a lot longer, but we only had to do two runs. Now, we will be presenting our data to all of the grad students and professors, about 15 people who know a lot more physics than me,  who are involved in the larger project in about 2 hours. I hope that goes well.

Now for the fun side of Idaho, or for this last week, Raindaho. It rained here for about a week. It wouldn’t rain during the day, just when we would be leaving dinner after work. A lot of the outdoor adventures have been postponed, like our tubing trip down the Portneuf River. This has left us with a lot of reading (Blood Meridian by Cormac McCarthy is fantastic so far), board games (a lot of late night Monopoly and Clue and Rummikub[Taner, if you read this, did anyone know Rummikub is just Castet?]) and most recently, someone brought a Wii from home (You all know how that ends up).

Before the rain, however, we were able to go hiking up Scout Mountain. I guess this is nothing compared to Nick’s elevation, but we ended up at 6,500 ft, which is about a 2,500 foot climb from ol’ Pokey(what locals call Pocatello). It took us about 7 hours of just constant incline. It started off as a 90 degree day, but remember, it is dry heat at least. Eventually, we hit the snow banks, one of which I fell through up to my hips. If that wasn’t interesting enough, on our way down through sage brush and Aspens, we were caught by rain(this was the beginning of Raindaho week) and eventually hail. This meant that last leg of the trip was through mud. One of the more tiring experiences I have had in a while, but it really was worth it. The views from high elevation are absolutely stunning. These pictures were taken by the professor who took us there and a Ukrainian grad student who had never made the hike before.  I’m going to leave you guys with these, because I can’t really say something that is more beautiful than this.

Until next time everybody (the rain has cleared up, so some good fun should be coming my way)

http://picasaweb.google.com/valeriias/ScoutMountain#

http://picasaweb.google.com/rshapova/ScoutMountain

Physics Adventures in Idaho

Hey everybody!

It seems like as good of a time as any to update everyone on my project here. In the very opposite of Joey’s REU, I have been pretty much entirely experimental here in Idaho so far. My project has many stages, and I mentioned that one of the ultimate goals for my project is to help determine a characteristic signature for different fissionable material when they are shot by a linear accelerator. This way, the government can scan more of the industrial shipping crates that come into our ports everyday, helping keep our country safer.

The first aspect of this research is building a pair spectrometer. What is this/what is it used for? Well, the linear accelerator is going to shoot a beam of photons at a converter, which will convert the photon into an electron/positron pair. This converter will be placed right up next to a magnet, so the two particles will move in opposite circular trajectories. After they leave the magnet, they will fly straight into scintillation detectors. Where do I come in?

Well, they have two magnets here. There is a variable B-field electromagnet and a permanent one. The plusses of the electromagnet? It is variable. The upside of the permanent magnet? It doesn’t have a leak in it. My first task was to see if we could use the permanent magnet, whether it would bend the electron/positron pair enough to  avoid each other and the beam. Since it is a permanent magnet, there is a return yoke. So, how much energy do we need to give the electron to clear the yoke. Balance the Lorentz and centripetal forces, use the relativistic energy equation and a ton of nasty trigonometry later, we worked out that the magnet was feasible.

From there, we had to make two scintillation detectors. The was a lot of finding the right parts. A scintillation detector is just a light guide connected to a photomultiplier tube connected to a voltage module. Light hits the light guide, which guides the light (shocker, I know) to the PMT, which sends an electric impulse to an oscilloscope or whatever so we can measure whatever radiation we need. We hooked these up to about 1000V and were able to measure cosmic rays, which I found pretty cool.

For us to gain any useful information from all of this, we need to make sure that our two detectors are collecting data from an electron/positron pair from the same photon. Right now, I am working on these coincidence measurements. We have the two detectors right next to a Sodium-22 source, so we are getting hits  on our detectors more often than the cosmic rays. We send the signals to a constant fraction discriminator, which helps put the two measurements into the same shape. We send both of these signals into another box. This box is a nice “and” or “or” circuit box. It is a lot simpler and nicer than what we had to do in Electronics Lab. We are able to adjust the threshold of each detector, so we are getting hits and not just background noise, and the width of the circuit. Basically, what it takes to generate a signal and then how much time between the two different signals we give it to register them both together and thus activate the and circuit. We are talking in the nanosecond range for these things.

The last part that we need to do for this setup is send the and circuit into a counter. That way we can plateau our detectors. Basically, find the optimum energies to run them at to get the best counts. That will all be done tomorrow. Then we can get into the particle lab and try out this part of the experiment before I move on to my next task. I think that all should make pretty good sense, but feel free to ask any questions.

In other news, I have been making myself feel like a complete wimp lately. I have been running around town and among the hills here lately, and hills can really take it out of you. It has been my goal to finish this 2.3 mile run that ends at the top of this hill. I haven’t made it all the way up the final stretch without stopping yet, but there is always tomorrow. Today, another REU student/my roommate Zac and I went to a local park to participate in their Tuesday/Thursday Open Climb. A very cool guy named Peter taught us how to do figure 8 knots and belay. We both made it up our first wall, but the second proved a little too hard for us, so we both got only halfway. I never knew how much finger strength it took! We tried a third wall, and while it should have been doable, my arms were hurting so much that we called it a day. Next Tuesday, though, I am showing it who is boss.

Later tater haters,

Ian

Idaho- Famous Potatoes…and awesome Physics

Hey everybody!

This is Ian Noble coming to you straight from the Gem State, Idaho. I am just starting my second week in the program. I am going into my final year at Truman and figured it would be a fantastic experience to spend a summer doing an REU. At the intersection of interesting physics, fun extras, and well paying (it is a 6-way stop apparently) is the REU program at Idaho State University.

This is their first year doing an REU program, so they decided to resolve any doubts by just trying to do more. I have one of the sweetest deals when it comes to money. $4,500 plus free room and board plus full travel reimbursement. The town here, Pocatello, is absolutely stunning. It is larger than Kirksville, but it is quite dead during the summer. Luckily for anyone who likes the great outdoors (like me) this is a perfect place to spend a summer.

I had to get used to the elevation here for the first day or so, because I am definitely not used to being 4,500 feet in the air. There are many large hills and mountains plainly in view from my room. Three of us hiked up a 1,500 foot “hill” on Saturday, and I was glad that I have adjusted to the elevation. We went with a professor’s family and their horses. We even had a neighborhood dog, Abdul, who wanted to tag along. It ended up being about 5 miles when it was all said and done with, but boy was there a view. The sky is so clear here that you feel like you can see forever. We were able to see the Portneuf river, which we will be inner tubing down on July 4th.

There is no end to the beauty of nature here. We are a short trip away from Yellowstone (which they are taking us to pretty soon), 40 miles from Lava Springs (which some of us are doing a bike trip to so we can relax there before heading back), white water rafting, and so many trails to take. I took a run today that ended at the top of the school’s big hill, and that proved to be interesting. I guess I should get more into the physics that I’m doing here though, shouldn’t I?

After touring the facilities, I believe that this school has to be one of the best for nuclear and particle physics research, especially for graduate work. They have 3 linear accelerators (call linacs in the business) ranging from a “pitiful” 20 meVs to 44meVs I believe. They work closely with the Idaho Accelerator Center, which is basically on campus, to do experiments. An hour of beam time here is $2,000/hour I believe they said. They also have a mini nuclear reactor that was especially designed for use in universities to teach students about nuclear physics. It is designed so that it is impossible to go Czernobyl. They are really dedicated to this stuff and giving their students the ability to work with these machines.

I will get into the big details of what I have been working on in my next post, which may happen tomorrow after a big research project meeting we’re having, but I can summarize the concept behind it now. My project’s title is “Linear Accelerator Techniques for Homeland Security and Nonproliferation.” I finally understood what we’re doing about last Wednesday.

There are thousands of shipping crates that are sent into the United States everyday. The big ones that fit on trains and such. Only 2% of them are subjected to random safety checks, so ISU received a grant from the government to investigate if they could work out a way to have a linear accelerator to beam particles into the crates to see if there is any fissionable material in them, increasing our ability to monitor the shipments. So, we need to see if we can find a unique “signature” for different fissionable materials.

I’ll get into my work tomorrow? but until then, enjoy your summers everybody.

Ian