- Data post-processing: Cygwin, sed, awk, OpenOffice-Calc, Gimp
The LND712 Geiger tube is housed into an aluminum case, placed indoors near a window on the 7th floor. It indicates the radiation levels of gamma rays only, expressed in μSv/h.
The radiation board that is normally stacked directly on top of the Arduino, in this case is detached, and relegated to a plastic case under the main one, in order to free up the other interface pins for additional functions of the system: SD card, keypad, alarm buzzer, LCD back-light (and in the near future real time clock chip). All this extra circuitry has been prototyped with 2 small breadboards. The intention is to reproduce exactly the functionality of System A above.
Calculation details: the measuring instrument returns the number of counts from the tube accumulated every 10 seconds. From this data I calculate the average rate in counts-per-minute (CPM) over one day. From this CPM value, and looking at the data sheet for the Geiger tube, it would be relatively accurate to convert it into milli Roentgen per hour (mR/h) which would give a precise indication of the exposure rate, even though expressed in “imperial” units (as opposed to “metric”). Maybe in the future I will revert to providing my graph in those units. For the time being, I would rather present my graph in micro Sieverts per hour (μSv/h) which give an indication of the dose equivalent rate, this time expressed in “metric” units, mainly because I got accustomed to those units from the news reports and the media. To do this conversion I assume (because I saw it used in another web site, and also because it agrees with the display on my instrument) that the following relationship holds:
1 mR = 8.77 μSv
which is the same as saying:
123 CPM = 1 μSv/h
This conversion factor is for me just a “magic number” and I think there is scope for different approaches, leading to different results, in the conversion from “exposure” to “dose equivalent”. On this regard I welcome your comments and insight, if you can provide any.