User:Jpazhaya
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3/1/06
In the last class, we learned how and what the scintillator does. This apparatus, protected from light in a rifle case and covered with foam, contains a photomultiplier tube and a plastic that detects when a particle hits it and sends a photon to the tube. There are two scintillators placed one on top of the other. This set up, connected to a logic unit and a counter, counts the number of cosmic rays that pass through by increasing one unit every time a particle hits both the top scintillator and bottom scintillator at the same time (there is a small difference in time but it can be adjusted so that this difference is neglected).
Using these devices, we found that there are cosmic rays coming from above and sideways. We also found that the set up does not detect many particles if the two scintillators are separated, the few that are detected could possibly result from two different particles hitting the scintillators at the same time.
We also explored the popping of corn in the microwave. We explored questions such as how long it takes for the first kernel to pop, how long it takes for it to stop popping, the distribution of pops from beginning to end, explanations for unpopped kernels, etc. We recorded the popping of the kernels and began to make a histogram of the number of pops (per 2 seconds). Interesting and challenging questions to consider while looking at the recording of the popping on the program Audacity, were ones such as what counts as a single pop, what waves with high amplitudes mean, how does one distinguish and count pops when many are occurring at the same time, etc.
Challenge moments/Questions: Why do we adjust so that the device detects a simultaneous hit on both scintillators? Is it easier? Couldn’t we get more data (speed, direction, etc) if the time difference were available? Is it possible to leave it so that the small time gap remains? If we turn it upside down with this setting, will the counter detect any cosmic rays (coming from below us)? Will the amount of hits change in a vacuum? In a magnetic field? How will it be affected by the field and why? Can we measure the strength of the particles somehow? Will the energy of the particles change if we shield it more (with boards, etc)?
3/7/06
Popcorn lab write-up: 
3/9/06
On Tuesday, we learned more about the oscilloscope and how it works. We also brainstormed for ideas for experiments. This brainstorming brought out many questions about cosmic rays themselves, their detection, etc, as well as what we can do with them in an experiment. My group came up with many ideas, such as, can certain materials/what materials can stop cosmic rays? We would use different materials such as water, a more viscous liquid, lead, iron, and other materials similar to what the earth is made of (since we know the earth does stop some or many cosmic rays). We also wanted to find the direction of cosmic rays (from above or below) and their rates by using a time difference. By separating the scintillators a far enough distance to have a measurable time difference, and then seeing which scintillator was hit first (top or bottom) we can tell the direction from which the cosmic rays came from. We also wanted to measure the rate of simultaneous coincidences.
Lightbulb moments/Challenge moments:
I learned that the photomultiplier tube detects all photons that occur at the same time and so if several particles were to hit the detector at the same time, it would be interpreted as one because it detects photons emitted, not how many. Photomultiplier tubes detect the light emitted as cosmic rays hit the molecules in the plastic detector in the scintillator. Cosmic rays knock out its electrons or cause its electrons to move to a higher energy, and as it electrons return to the atoms, and go back down to the ground state, light is emitted and the photmultiplier tube detects this light. The photomultiplier tube also amplifies the energy of the photons emitted using the voltage supplied into it. For this reason, we cannot measure the energies of the photons because we are not detecting these energies directly.
To detect simultaneous coincidences, we would have to separate the scintillators to see if any particles hit both at exactly the same time. Another method would be to have several pairs of scintillators (remove much of the noise from non-cosmic rays hitting the detector). Cosmic rays also arrive at the highest rates from above rather than from left or right or below because there is less interference from other materials such as the earth and there is also less distance from space directly above us to where we are, and therefore less to collide with.
How far apart would we have to separate the scintillators to see a measurable time difference? Assuming cosmic rays travel near the speed of light, using the equation v=d/t, we would have to separate the scintillators by .3 m to see a one nanosecond difference, 3 m for a 10 nanosecond, 30 m for a 100 nanosecond difference, etc. These are upper estimates. What is the smallest time difference that we can measure with our instruments?
March 14, 2006
On Thursday we began our first experiment. We wanted to find out how the rate of cosmic rays was affected by putting distance between the two scintillators. From this, we also hoped to find a time difference in when the cosmic ray hit the first scintillator to when it hit the second. From this time difference we hope to calculate a speed for the cosmic ray. The group broke up into two groups of three. One group (Rose, Zina, Liz), calculated the best time interval to count cosmic rays based on our control (not separating the scintillators). The best time interval turned out to be four minutes. Using this interval, they separated the boxes by small amounts, going as far apart as 120 cm, and recorded the cosmic ray coincidence rate at each distance. On the other side of the room, another group (Cher, Leah and myself) manually counted the cosmic ray coincidence rate of two scintillators placed 115 and 6/16 inches (294.005 cm ~ 3 meters) apart. We had to manually count because the counter was not working. This was not a difficult task as very few coincidences occurred. One cosmic ray coincidence was tallied for every time the oscilloscope refreshed to show us another set of waves (indicating the times of a cosmic ray hitting the first and second scintillators). So few cosmic rays were detected possibly because of the angles at which the rays are coming down. A cosmic ray might hit the first scintillator and not the second because of the angle at which the ray came down, and therefore not be counted. Another reason there were so few coincidences could be that the first scintillator was resting on top of an aluminum shelf. This may have stopped some of the rays from passing through. We also measured the time difference between these rays using the grid on the oscilloscope (one box= 5 nanoseconds). There were great variations in the amount of rays per four minute interval. This may be because a four minute interval is not the best interval for such a great distance. More trials may have minimized this problem, but unfortunately we only had time for three trials. The average cosmic ray coincidence count per four minute interval was 11 (2.75 per minute). Another thing that we noticed was the variation in the time difference between the arrival of signals from the scintillators. Nathan explained that a possible cause for this could be that the rays hit different parts of the plastic detector and so the signal would reach the photomultiplier tube at different times. Another possible cause is that the rays have different speeds and can be passing through the scintillators at slower and faster rates. A few times, the oscilloscope indicated that the signal from scintillator 2 arrived before the signal from scintillator 2. A possible cause for this is that it was two different rays that hit both scintillators, but hit in a close enough time span to be counted as a ray. Another possibility is that the ray was coming from below and not from above. Although this seems less likely, it seems that we cannot truly know which was the case.
Lightbulb moments: speculations on the causes of some of the data we were seeing.
Challenge moment: why were signals from scintillator 2 arriving before signals from scintillator 1? Why were signals from both coming at the same time? Shouldn’t there be some time difference caused by the separation?
3/16/06 On Tuesday, we conducted our second experiment. In this experiment we hoped to find out which materials, if any, can stop cosmic rays. My group conducted our experiment using lead bricks and concrete. We conducted our tests using 4 minute intervals. We also conducted a control experiment with just space between the scintillators (separated by 35.5 cm) for comparison. In both tests we found that the cosmic ray rate was not significantly different from the control rate. These tests would have been more conclusive if we had tried longer time intervals and more trials. However, we wanted to see if four minutes was a long enough interval. It turned out not to be the case, but by the time we could conclude that, we did not have time to redo the tests. Based on our results, it seems to be the case that neither lead nor concrete stops cosmic rays. More trials and longer intervals would have to be conducted to verify this idea, since I do not believe we conducted enough trials to be conclusive. Perhaps one of the materials stop cosmic rays to a very minimal degree (if so, most likely lead).
Lightbulb moment- we tested concrete thinking it may stop cosmic rays, but we know from past experience that it does not. The building we are in is made of concrete and rays still come down at a very rapid rate. Granted, concrete may still block a few/some rays and to test this, we could go to the roof and measure the rate of cosmic rays with no interference and compare.
Challenge moment- determining whether our time intervals were long enough for consistent measurements and whether the materials used had an effect on the cosmic ray rate based on these limited trials.
3/21/06 On Thursday we tried to find the direction from which cosmic rays came. This was done using a hexagonal “wheel’ into which the scintillators were inserted so that they remained facing each other as the angle was changed. The angles could be changed by moving the wheel or inserting a wedge. We measured the cosmic rate at 22.5 ° intervals ( 0°, 22.5°, 45°, 67.5°, 90°, 112.5°, etc, through 180°). These measurements showed us that the cosmic ray rate decreased as the angles became greater. The most cosmic rays were from directly above. The rate was similar for 90° and 180°, as well as the complementary angles. We also measured the cosmic ray rate as detected by Cosmic Chris, both on floor D and in the basement. The rate was significantly lower in the basement.
Lightbulb moment- it was confirmed that complementary angles (i.e. 45 and 135 degrees) had the same rate of cosmic rays. This means that angle, not direction (west, east, etc) matters when it comes to cosmic ray rate.
Challenge moment- keeping track of what position is 0° and which way to turn the wheel in order to get the angle we want.
3/23/06
On Friday we conducted our fourth experiment, which was done to determine the rate of simultaneous coincidences. This setup included 2 sets of 2 scintillators. There was one count for every time both scintillators detected a cosmic ray within 100 nanoseconds of each other. The rate was highest when the two sets of scintillators were right next to each other. The rates varied as they were placed 20, 40 and 60 cm apart, with 60 cm having the least number of simultaneous coincidences. Dr. Forman explained a lot about cosmic rays on Friday.
Lightbulb moments: What we detect with the scintillators are not the cosmic rays themselves, but mesons, secondary particles that were affected by cosmic rays. Mesons are nuclear particles. Cosmic rays come down and break up atoms, sending showers of nuclear and atomic particles down to the earth. These particles, now moving at high speeds, interact with other particles, causing them to do the same. We detect simultaneous coincidences when a particle moving at high speed hits another, breaking it up and causing the pieces to come down at the same time. Higher energy cosmic rays will cause simultaneous coincidences that are farther apart. These will be detected at the same time if both particles do not interact with anything else on the way down. This means that simultaneous coincidences are rare, especially those that are far apart (would require a very high energy initial ray).
Challenge moments: what does the rate of cosmic rays really tell us, since this rate seems to depend on how many interactions a cosmic ray and secondary particles had with the nuclei of atoms on the way down, which will not be equal for each particle. When you have cosmic ray detectors several km apart, and are looking for high energy cosmic rays, how can you be sure you have found the secondary particles resulting from one high energy cosmic ray and a random simultaneous coincidence?- by removing that error factor- but how can you be sure that even when the rate of random simultaneous coincidences hitting these detectors is taken out, that these rays result from one high energy cosmic ray? - measure the voltage? What are the chances of a high energy cosmic ray hitting a particle high in the atmosphere and resulting in high speed particles coming all the way down to the earth to hit two scintillators several km apart, without hitting anything else on the way down? Is this technique effective? What does it tell us?- the rate of cosmic rays hitting the earth above a certain energy?
Final Entry
On the last day of class, we discussed other experiments we would have tried if we had a few more weeks. We would want to repeat several of our experiments again, with more trials. We also wanted to create a cloud chamber to visually demonstrate the existence of cosmic rays. This session was a great experience because it made us think. We were pretty much on our own when it came to what we wanted to know and how we were going to find answers for our questions. I enjoyed trying to find out different things about cosmic rays and trying to explain what our data meant and why. This seems very similar to the situation we would be in when doing research, regardless of what area we were doing research in. Fortunately, we had a lot of assistance in getting the materials we needed to conduct our experiments, perfecting our procedures and in interpreting our data. There was a lot we did not know or could not do and our professors were there to help (thank you!). I think we definitely needed more time for each of our experiments. Our data could have been more conclusive if we had more time to do more trials at longer time intervals. There was a lot of work accompanying these labs but it was manageable and necessary. In all experiments it is important to record and properly explain what you did, why you did it and what you can or cannot conclude. I wrote the theory section of each of the labs our group did. It was interesting and challenging trying to explain what we were doing, why we were doing it and many of the ideas that we learned along the way. Often, this required the assistance of a diagram or picture. I believe they explain the ideas much better than an entire report could. I hope these diagrams were helpful and appropriate for a serious report. Using the Wiki was also a new experience for me and although I do not think I have mastered it yet, it was a good experience to be exposed to it and learn the basics of how to use it. Through our experiments we came to know a lot more about cosmic rays, I just hope that the conclusions we came to and the explanations for them were correct.
Some random discoveries from throughout the past couple of weeks: -Which direction are cosmic rays coming from?
Everywhere, but mainly from above.
-What materials stop cosmic rays?
Particular materials do not stop these high speed particles, but great quantities of matter do. The thicker the materials the cosmic rays have to go through, the more energy they lose.
-What we are detecting are not the cosmic rays coming from space themselves but the particles that got in the way of these rays and were broken up and sent speeding off into different directions. -What is the rate of simultaneous coincidences at different distances?
The rate generally decreases as the detectors are placed farther apart. This is because it is less likely that two particles will come down at the same time without hitting any other particles from a high distance (where they originated from a particle affected by a cosmic ray).
-Simultaneous cosmic rays can tell us more about the energy of the cosmic rays hitting the earth. -Cosmic ray rates detected change (decrease) as you separate the scintillators because rays coming in at fewer angles can be detected. This was useful to know in conducting experiment 3, in which we separated the scintillators to narrow the range of angles from which rays were detected so as to measure the rate from (or close to) a particular angle.
Still wondering... What can we do with this information we gather about cosmic rays? What do the detection of simultaneous cosmic rays at great distances apart tell us except that they’ve traveled without interfering with other particles? Or is this all we care to know from that data?
