This project is a continuously operating gamma radiation monitor to measure environmental background radiation.  It is very effective at detecting the spikes that occur during rain and snow due to the effect known as radon washout.  

Radon, a naturally occurring radioactive gas, is part of the uranium-238 decay chain.  As a noble gas it is chemically unreactive.  It slowly percolates out of the ground and gets into the atmosphere.  As it decays, it produces radioactive daughter products that are strong gamma emitters.  Some of the radon and/or daughters dissolve in raindrops as they form.  Falling to the ground, these emitters increase the radiation at ground level for a short time as they decay.  The two most prominent emitters are Pb-214 and Bi-214, which have a half life of 20-30 minutes.  (This half-life is obscured in the plots below due to the filter corner frequency).

The radiation monitor consists of:

• NaI(Tl) scintillation probe and PMT powered by the Theremino PMT driver.

• USB audio dongle to capture the amplified PMT signal.

• Beaglebone Black running a simple program to read audio samples and count pulses that exceed a threshold.

A planned future enhancement is to perform spectroscopy by measuring the pulse heights and generating a histogram to show the spectrum.  The characteristic peaks of Pb-214 and Bi-214 should then be visible.

Data is collected continuously and plots are uploaded to a website.  The software is posted on github.

Click here for the latest daily and weekly plots.