Poster
The Effects of Lead Shielding on Muon Counts
Nate Bramham, Jesse Honig, Maceo Hastings Porro
July 2011

Abstract

Our experiment was testing the shielding properties of lead (Pb) on charged particles coming through the atmosphere. We tested it by using differing layers of lead to shield the charged particles. The testing was all done indoors. Two detectors were placed under the lead and then we programmed the DAQ board to record coincidence only when both boards were triggered simultaneously. This allowed us to detect real particles coming through the atmosphere. The results were interesting. There was a decreasing trend that was linear initially, but when we had four layers of lead, the count went up. We tested it ten times, and the results were consistent. The error bars do not account for the change. We still do not know why this happened.


 

Introduction

For our project, we decided to investigate how placing lead bricks over our detectors affects the count rates that will be recorded. We chose to use lead because we knew that it is commonly used to shield radiation, so we assumed that it would work well to shield muons as well. This led us to the question of how many muons does lead actually block and how adding various amounts of lead shielding would affect the muon counts. 

 

Procedures

We started out by researching the energy loss of the muons when they pass through lead. We chose to use lead because of its ability to stop radiation. It has a stopping power of 1.122 MeV cm^2/g, and a density of 11.350 g/cm^3. Its high density is what provides the excellent stopping power. Unfortunately, lead's stopping power varies depending on the energy of the particle that is passing through it. Since there is a flux in the energy of muons that are passing through our setup, we did not expect our count rates to decrease in a linear fashion. This gave us an idea of what to expect when our experiment was performed. We set up our Cosmic Ray Detector under a small wooden frame. We performed sets of 5, fifteen minute tests for each layer of lead. We started testing with no lead above our detectors and then moved on to test one layer, two layers, three layers, and finally four layers This gave us clear results in which we could see the variation in rate of particle detection. We had to use Microsoft Excel to interpret the data because Quarknet would not interpret it the way we wanted. We used HyperTerminal to collect the data in hexadecimal. After every series of tests we added or removed lead respectively. When we found an unexpected data point, we re-tested for that amount of lead to make sure that the results were accurate.

 

Results

cm of lead   S0 Rate    S1 Rate     Coincidence

0117.529873.3166712.23244
5104.128262.14610.95222
598.0313362.1793310.80978
10103.161.6308910.61044
15100.677362.9042210.08711
20104.977862.1231110.53089
20101.519661.6262210.45622

These are the averages for our different layers of lead. Here we can see the decrease in average rates as the lead thickens up until 20cm of lead. We did expect to see a decreasing rate of muon counts as we added more lead above the detectors, so we were extremely surprised to see that from 15cm to 20cm of lead the count rate increased by 0.45 coincidences/second. As we said before, this data point was extremely unexpected. We had expected that the rate of decrease of the muon count rates would have slowed, but the last thing that we expected was for the count rates to actually increase after we added another layer of lead.

 


Discussions & Conclusions

Our results showed us that our predictions were partially correct. There was a general decreasing trend in the number of coincidences in the data. With no lead, there were about 12.23 coincidences per second. With1 layer (5 cm of lead) there were about 10.95 per second. At 2 layers (10 cm of lead) there were about 10.61 per second. At 3 layers (15 cm of lead) there were about 10.09 per second. Our data did take an unexpected and unexplained turn. At four layers (20 cm) of lead, there were about 10.53 coincidences per second. We expected the rate to be around 9.6 per second. We still do not know why this happened. To verify that this data was accurate and that it was not due to an error in our equipment, we ran another set of tests with 20cm of lead and also with 10cm, to make sure that the calibration of our detectors had not changed.


 


Bibliography

http://pdg.lbl.gov/2011/AtomicNuclearProperties/adndt.pdf

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/muonatm.html

http://scipp.ucsc.edu/outreach/internships/2007/references/Muon%20Absorption.pdf

http://en.wikipedia.org/wiki/Electron_rest_mass

http://www.ncsu.edu/labwrite/res/gt/gt-stat-home.html

Stuart Briber

Steven Ritz

Alex McKale Ph.D