Gamma ionizing radiation detection with Raspberry

[root]

I also tested the SBM-20 tube on this device.

Conversion factor for SBM-20 tube.

Russian SBM-20
60Co 1/150 = 0.00664
226Ra 1/198 = 0.00504

Please note that conversion factor varies depending on the tube sensitivity at different isotopes, Cobalt60 and Radium226

Nevertheless, based on my testing compared to the local university lab readings, and based on what Libellum (the company that manufacture the kit) declares here:
http://www.libelium.com/wireless_sensor ... _counters/
the most appropriate value for SBM-20 tube whit this circuit seems to be 0.00277

[root]

A very interesting declassified document from U.S. Army Ballistic Research Laboratory about how to perform radiological monitoring in case of incidents involving the release of radioactive materials:

https://apps.dtic.mil/dtic/tr/fulltext/u2/a207901.pdf

[root]

After some extensive testing it seems to me that the chinese tube J305B, supplied with this device, is totally unreliable, the CPM reading varies from 3 to 15 without any apparent reason.
If I use the SBM-20 tube everything works well.

In my opinion this chinese tube is a sort of piece of junk, like many low cost chinese products

[root]

If you want to use the SBM-20 geiger tube instead of the junky J305By default tube, you need to do a little modification on the radiation board:
the C2 capacitor of 1 uF (see image below) should be increased at about 2 uF to higher the H.T. from 370V to 400V to better supply the SBM-20 tube.
Actually the SBM-20 works even at 370V, but obviously 400V is better.

It's enough to solder in parallel to the existing C2 cap another electrolytic cap of 1 uF, be careful with the polarity, on SMD capacitor the line is the + (positive), in the ciclindrical standard capacitor the line is the - (negative).



In case you would need 500V for another kind of tube, the capacitor should be increased up to 10 uF.

[root]

Sometime it may happen that the "measure" process involved in the CPM measurements could die, in that case you will notice "0" CPM readings for long time.
To avoid that I wrote the following two scripts that continuously check if the "measure" process is running and if not they can restart it.

geiger-check.sh

Codice: Seleziona tutto

#!/bin/bash

# Check if "measure" process is running, if not launch a script
# -x flag only match processes whose name (or command line if -f is
# specified) exactly match the pattern.
while [ 1 ]
do
if pgrep -x "measure" > /dev/null
then
    echo "Running" > /dev/null
else
    echo "Stopped" > /dev/null
    /bin/sh /root/restart-geiger.sh
fi
/bin/sleep 30
done

restart-geiger.sh

Codice: Seleziona tutto

#!/bin/bash
#
# kill measure process if running.
/bin/kill $(ps aux | grep 'printout-html.sh' | /usr/bin/awk '{print $2}')
/bin/sleep 1
# restart CPM reading processes
/bin/sh /root/print_rad2csv.sh &