JOANNA'S FINAL REPORT
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Xiaoshuai Yuan (Joanna)
WSE 187- Cosmic rays
April 29, 2008
Cosmic rays final report
Cosmic rays are high speed particles from outer space that can detect by a scintillation detector. Every second, the earth encounters a large amount of cosmic rays from all directions. From April 3, 2008 to April 29, 2008 (every Tuesday and Thursday), we performed the cosmic rays experiments. Our purpose of the lab was to, firstly, determine the efficiency of the scintillation detector, and secondly, test the factors which affect the determination of cosmic rays.
Firstly, we need to learn how to test the efficiency of the scintillation detector. We need to set up three scintillation detectors. In the very beginning, opened DAQ on the computer, and set up sixty seconds for time interval. In order to record correct data, we need to make sure each detector are connected the right spots by using cables, and set up certain voltage for the top and the bottom detectors. In this experiment, we controlled the voltage for the middle scintillation detector between 5.0V and 3.5V. We decreased the voltage 0.1V or 0.2V each sixty seconds when we ran the DAQ program. In the end, record the coincidence of the top and the bottom detectors and the coincidence of the all three detectors.
Data:
According to the above data, we drew the graph as following:
In order to calculate the efficiency of the middle detector, and the noise level, we need to use the following formulas:
Efficiency= ((coincidence of top and bottom)/ (coincidence of all three))*100%.
Noise level= (count of the middle detector)*10/time interval (sec.)
We could see the efficiency of the middle detector by taking the ratio of the coincidence of the top and the bottom detectors and the coincidence of the all three detectors. Through the graph we observed as the voltage increases, the efficiency also increased. After we added noise level to the graph, we could see the noise level (in Hz) rised as the voltage increased.
Secondly, we tested the factors which affect the determination of cosmic rays. Before we perform the actual experiment, we had an in class discussion about the factors affect the detection of cosmic rays. As we discussed, we could have the following factors:
1. Surface area. As we increase the surface area of the scintillation detector, more cosmic rays will be detected.
2. Relative position. If we increase the distance between each detector, the time interval between detected cosmic rays will expand.
3. Altitude. Changing the altitude of the detectors affects the cosmic rays detected because cosmic rays increase with altitude.
4. Orientation. We can test the direction of cosmic rays through changing in orientation.
5. Question about temperature and pressure which may also affect the detection of cosmic rays.
Group Experiments:
My experiment thesis is Rate vs. Compass, and my group member Veronica’s experiment thesis is Rate vs. Angle with respect to the ground. Because our experimental ideas were similar, therefore we formed a group.
Part 1:
We did Veronica’s experiment first. To begin the experiment, we need to use cables to connect the two detectors to the right spots of the coincidence box in order to get the coincidence of the detectors. And then turn on the power, set up voltage for the detectors, open the DAQ program on the computer, and set time interval for sixty seconds. Later, in order to improve the efficiency, we increased the time interval to one hundred and twenty seconds. We placed the two scintillation detectors parallel to the ground initially and set this direction as zero degree. Then, we ran the program. We tested at different angles by changing the orientation of the detector holder, and calculated the angles by measuring the base and the height.
Data:
We calculated the rate and statistical error by the following formulas:
Rate= (count)/ (time interval)
Statistical error= SQRT (count)/ (time interval)
From the graph, we could conclude that as angle increase, the rate decreases.
Part 2:
Then we did my experiment. We still need to run the DAQ program first. In first part of the experiment, we settled two parallel detectors with the short sides touched the ground. We set north direction to 0 degree. According to the date, we made the following graph. The top views as the following:
We had wheels underneath the detector holder, so we could turn the two parallel detectors around easily. Then we recorded the data.
Data:
From the above graph, we observed the lowest rate at 135 degrees, however the statistical error was big, and each time we detected cosmic rays came from two directions. Therefore, we decided to increase the time interval in order to decrease the statistical error, and to change the orientation of the detectors in order to detect the cosmic rays from only one direction.
In the second part of the experiment, we settled the long sides of the detectors parallel to the ground, and raised them 45 degrees with respect to the ground in order to detect most of the cosmic rays from one direction. We measured the counts at eight different angles, set north direction to 0 degree, and 45 degrees apart from each other.
Data:
From the above graph, we could see that the rate at 270 degrees (west direction) was the lowest clearly. We concluded the observation was due to the buildings on west side which blocked some cosmic rays. In order to improve my experiment, we should do my experiment in an open field, so we can avoid the effect due to buildings. We expect the magnetic fields of the earth will affect the rate of coincidence.
I never knew cosmic rays before I entered Mariachi Lab. This course opened a novel field to me, and enhanced my knowledge outside of my major.
