Effect of Water on Muon Flux
Varying Depths of Water
07/28/2016
Abstract
The purpose of our experiment was to determine the relationship between depths of water and muon flux. We wanted to see if water could be effectively used to shield detectors from muons. To run the experiment, we set up detectors above and below coolers of water at different depths of water. The data was recorded for periods of over seven hours and each depth had only one trial due to time constraints. We recorded data from all four detectors with a coincidence level of 4, so each muon had to hit all four detectors. Therefore, they traveled relatively straight and passed through the water, making our results more accurate. After testing the various depths of water, we concluded that water does cause a statistically significant difference in muon flux. As a reult, it can be resonably assumed that water shields against low energy muons.
Introduction
Cosmic Rays are high energy particles (protons, electrons, and atomic nuclei) that travel at speeds close to the speed of light. When colliding with Earth's upper atmosphere, these particles create a rain of secondary particles consisting of muons and neutrinos. From these particles, muons are easier to detect and can be recorded through the use of cosmic ray detectors. These detectors consist of scintillators and photomultiplier tubes to record the passing of muons. While muons can pass through most materials fairly easily, it may be possible to shield against them using large quantites of materials of high density, such as water.
Building off an experiment run in 2012 by Sawan Dutta and Adam O' Donnell, we further investigated the question of whether water will affect muon flux. They concluded that water did result in an apparent decrease of muon flux, but error bars in their data resulted in inconclusive data. To improve upon their results, we increased the water levels tested in their experiment and ran the data for longer periods of time. We hypothesized that an increase in water between the detectors could effectively shield against muons.
Procedures
To set up our experiment, we stacked two of the four detectors on the ground, and the other two detectors 1.65 meters off the ground directly above the other detectors. Between the detectors, we stacked three large coolers on top of each other. We set the detectors at a 4-fold coincidence to ensure that only particles passing through the coolers would be recorded as an event. For the base trial, we left the coolers empty. Then, we we filled water 27.5 cm, 50 cm, 70 cm, and 85 cm high. After running data for more than 7 hours at each height, we measured the average flux for each water level for all four channels. For analysis, we set bin width to 1000 for all trials for consistency.
Results
As a result of our experiment, we determined that the muon flux significantly decreases when the water level increases. As you can see in our graphs, the average flux from a 0 cm depth to an 85 cm depth, in channel 1 for example, drops from 121.6 to 105.1. The results are similar in the other channels, which follow a consistent trend. Calculating the percent change for each channel from 0 cm to 85 cm results in C1 = -13.59%; C2 = -13.24; C3 = -13.71%; C4 = -14.18%. Furthermore, after running an ANOVA test on the variations with alpha set to .05, we determined the p-value to be 3.04E-18, making our data statistically significant.
Figures
Figure 1. Flux level 7/27/16 - 7/28/16 (channel 1)
Figure 2. Flux level 7/25/16 (channel 1)
Figure 3. Flux level 7/25/16 - 7/26/16 (channel 1)
Figure 4. Flux level 7/26/16 - 7/27/16 (channel 1)
Discussion and Conclusions
Our results lead us to conclude that if we put larger depths of water between the paddles, the flux would continue to decrease. For future study, run the experiment with greater water levels, and more trials at each depth. Also switch around the detectors to make sure the detectors are causing minimal error. To reduce errors due to varying levels of muon flux throughout the day, run all of the trials at the same time of day.
Bibliography