Poster
Muon Attenuation by Building Materials Thickness
Effects of Varying Thickness of Concrete on Muon Detection
Combs, B., Fork, E., Grimes, B., Johnson, J., and Miller, B.
06/26/2013

Abstract

The purpose of this experiment was to investigate the effect of number of concrete layers of equal thickness between the detector and the atmosphere.  The experiment was performed in the Northwestern Parking Garage on Purdue University Campus on 25 June 2013 between 1:00 pm and 3:00 pm.


 

Introduction

Protons formed in space travel to Earth with extremely high energies.  As these protons reach the earth's upper atmosphere, they collide with air molecules and form secondary particles, including muons.  A cosmic ray detector counts the number of muons hitting each scintillating plate of the detector. 

The following question is the basis of this experiment:

Is the rate of muon detection attenuated as the number of concrete layers between the detector and the upper atmosphere increase?  

 

Procedures

The cosmic ray detector was made portable by connecting it to a 12 VDC car battery through a power inverter.  The detector was taken to the Northwestern Avenue Parking Garage on Purdue University Campus and data collected on each level of the garage.  This provided our forum for the varying layers of concrete of approximately equal thickness.  The plates were set to collect data for 2 minutes using a gate width of 100 ns, a pipeline delay of 20 ns and the same voltage sensitivity.  The coincidence rate was set to 4.

On each of level of the parking garage, two sets of data were collected.  One set was collected with the plates stacked vertically.  The second was collected with the plates set next to one another.  For each trial, all four rates and the coincidence rate were recorded in the graphs provided.

 

Results

The data indicates the count rates are attenuated as the thickness of concrete above the detector increases.  The count rate was lower on the rooftop than one level below the rooftop where they were the highest.  Three trials were conducted on the rooftop to validate this result.  The rate count then decreased with each level as the detector was moved down.  The values of each count rate for each channel are shown in the data figures provided.  Channel count rates were not affected signficnatly whether the plates were stacked or spread next to one another.  The coincidence rate also decreased as the detector was moved down each level when the detector plates were stacked, but was approximately 0.00 when they were spread next to one another.  Channel 4 count rates did not agree with Channels 1 through 3 on the rooftop and that data was disregarded.

 


Discussions & Conclusions

The data supports that the count rate is attenuated by the thickness of concrete above the detector while the detector is in the parking garage.  It was expected that the count rate would be highest on the rooftop when there was no obstrction between the sky and the detector; however, it was measured to be signficiantly lower than when it was one level below the rooftop.  It was suggested that the higher count rate might be a result of radioactive materials in the concrete.  This could be evaluated by measuring the count rate in the lab with and without a piece of the concrete from the Northwestern Ave Parking Garage on the detector plates.


 


Bibliography