Final Report

From MariachiWiki

The Kelly Steph & Sophie Project

Introduction:

So, what exactly are cosmic rays? They are tiny charged particles that are constantly bombarding the earth. Although they are constantly going through us, most people are oblivious to them and their effects on us. Although they do not have an enormous effect on us, they do contain radiation that we get as they hit us. Surprisingly I came across the exact percent of radiation we get from cosmic rays in my new WISE rotation. The actual amount is 9 percent radiation, which is not a lot when it is compared to the 68 percent you get from smoking. Although it is a small amount of radiation, cosmic ray research will help us understand and protect against radiation produced diseases and other problematic effects of cosmic rays.

The Experiment:
Our experiment focuses on the effect location has on the rate of cosmic rays hitting the earth per second. To count the number of cosmic rays we used Cosmic Chris. This is Cosmic Chris:

Cosmic Chris is made of two scintillators, a type of cosmic ray detector that can actually count the number of cosmic rays passing through the detector. Cosmic Chris counts the number of cosmic rays that passes through both counters. This is called the coincidence. For our experiment, we wheeled Cosmic Chris around (and outside) the Physics Building to determine what effect shielding (i.e. the building) had on the rate of cosmic rays hitting the Earth. We expected to see different rates of cosmic rays in different locations of the building. Each different location had a different amount of sheilding or stuff between the atmosphere and Cosmic Chris that would result in different rates of cosmic rays.(See Figure 3)
This is what the physics building looks like:

We took Cosmic Chris to these locations:

For each location, we took five trials of one minute each. Cosmic Chris was standing up for all of the trials. We chose to take trials of him standing up because when Cosmic Chris was laying down it was much harder to record the number of cosmic rays(the number was much larger and it was hard to record large numbers because there are only three digits on the Geiger counter. We used trials of one minute each to achieve a fairly precise measurement and averaged the results to further increase the precision.

Results:

Figure 3

Illustration of the direction from which cosmic rays are hitting the scintillator

Discussion The central concern for our experiment with Cosmic Chris was to see if the rates of cosmic rays increased as we became closer to the atmosphere, or rather the source of cosmic rays. The data that we collected over the course of the experiment shows a general increase in the rates from the S Level, which is underground, to the D Level, which is the top floor of the building. This increase seems support our hypothesis that more rays will reach the floor closest to the atmosphere. However, during our experiment we discovered several factors that can have an influence on the number of cosmic rays that hit the scintillator in the span of one minute. The three trials that were run on the S Level were all lower than the trails conducted on the P Level; however, there was a significant range between these trials. The lowest rate was seen near the elevator, where the area had the entire building above it and was underground. This made it more difficult for the rays to get to the counter because they had to go through several levels of concrete and plaster. They also could only hit the counter from above since the ground is too massive and dense for the rays to travel through for long distances. A higher rate of cosmic rays on the S Level was seen in the particle accelerator room. This room was not under the building but rater next to it. However, four feet of thick concrete separated it from the atmosphere and because it was underground, the number of rays that could reach the counter was limited. The four feet of concrete did not shield the rays as much as the tens of feet of building that separated the other trial from the atmosphere. The NSL was also on the S Level but it showed a higher rate of cosmic rays than both the other trials. Like the particle accelerator room, the NSL is separate from the building but unlike it, there is only a little concrete above it. Thus, the rays have less material to fight through to reach the counter. Yet it's still underground so it makes sense that the rate would still be less than the P B and D levels.

Differences in the rates of cosmic rays hitting the counter were also observed on the P Level, which is at ground level. We saw a drastic increase in the rates when we brought our scintillator outside. This was expected because there are no barriers to block the scintillator from the atmosphere. When Cosmic Chris was first brought outside, we ran our experiment directly next to the building. This means the cosmic rays had to travel through the building on one side but needed only travel through open air on the other (Figure 2). Our next trial, we moved Chris out away from the building, in the open. This means that cosmic rays could easily come into contact with Chris from all directions. The lack of barriers would explain why the rates of the trials outdoors would be larger than the trials indoors.

Floor B has a higher rate of cosmic rays than the P and S Level indoors because it is higher up in the building, which results in less barriers between it and the atmosphere. There is still enough material though, to show a lower cosmic ray rate than the measurements that were taken outside the building. Floor D is the highest floor so it makes sense that these rates would be larger than any of the other floors inside the building. Since the walls of Level D are not tremendously thick, it is also logical that the rates measured inside the building were higher than the rates directly outside the building. Figure 2 illustrates how the cosmic rays have to travel through most of the building on the left hand side before they can reach Cosmic Chris. On the other hand, the D Level has only its walls and not an entire building between it and the atmosphere. This also provides insight to why the rate of the outdoor measurement is so close to the measurement of the D Level measurement. We would have hypothesized that the outdoor rate in the open would have been a little higher than the D Level simply because it had no barriers. On the other hand, the D Level is much higher up than the outdoor measurement so that might explain why they balanced out. It is still unclear why there is such a drastic difference between the B Level and the D level. While it's true that Level C separates the two, it is also true that there is Level A separates P and B Levels and the graph does not show a drastic change between those.

Other factors that could affect the rates of cosmic rays that were either discussed or analyzed in this experiment include weather, whether the scintillator is lying down or standing upright, whether Cosmic Chris's right or left hand was facing the window, the effects of doing counts next to the window or next to the concrete wall and several other factors. We ran a trial where Cosmic Chris is lying down verses standing upright. We found that there was a distinct difference between the two. When standing upright, the rate turned out to be 16.7 counts/sec whereas when Chris was laid down, the rate turned was 31.7counts/sec. This is probably closely related to surface area. More of the scintillator is facing upward towards the source of cosmic rays when it is lying down. Unfortunately due to time constraints, we were unable to test most of the other possible factors so we leave that in the hands of able scientists, or possibly future WISE students.

Whenever one conducts a scientific research project, one of the most important aspects is to insure that the data collected is reliable and creditable. One way to represent the accuracy of the information is to include error bars in the graph that represents the data. Our error bars were surprisingly small, suggesting our accuracy. Overall, it seems the data we collected was quite reliable and could be used and expanded upon in future research projects.

What We Would Change: Now that we have completed our experiment, we can look back and see some things that we would change to improve the accuracy and validity of our experiment. First off, we would use a stop watch instead of a second hand watch to increase the accuracy. Also to make the experiment more accurate, we would like to have a switch that would stop the counts without resetting the counter so that we could clearly discern what number it is on. Another change that we would make is to place Cosmic Chris lying down instead of standing up when taking the counts. This would increase the number of cosmic rays that he gets and ,therefore, make the results more representitive. Although we thought about this during our experiment, we did not want to chance breaking him with all the movement. We possibly could have taken more data points; however, our error bars were small enough that we did not feel the need to. The final change that we would make is to decrease the number of variables. Throughout the experiment we ran into questions like "Will this matter or effect the counts?" Now that we realize how many things really do affect the results, we would create a research experiment that is more focused and reduces the effects of the variables.