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Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
______Version 3.3 Sept 02 - Oct 20, 2012__________________________________________________
________________ uRADMonitor is a network connected monitoring station, focused on continuous Environmental Radiation Surveillance. This capability is delivered by a digital dosimeter constructed around the highly sensitive Geiger Muller tube SBM-19. Additional sensors gather real time data on temperature , humidity and sky luminosity.
Construction details (this is version 3.3) and a few words on Geiger tubes and radiation detection can be found in the messages below or in this article.
Graphs built in real time with uRADMonitor data. Time is GMT+2 (Europe/Timisoara): Radiation (CPM): Temperature (Celsius): Humidity (RH): Luminosity (RL): Charts are built with the last 7 days data, integrated at a 2 hours interval. Size is xlarge (maximum). See how to change the parameters:
The hardware Several sensors, including a Geiger counter, are connected to a microcontroller (Atmega168). A network interface chip (enc28j60) provides an Ethernet interface. Data from sensors is collected on a one minute interval and exported online to the server (pocketmagic.net). Using PHP and SQL, the data is stored and post processed, so users connecting via a webbrowser can access various charts, in real time:
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
I see what you mean about the pancake detector. Generally, I would only expect the tube to light up like that with excessive anode voltage.
If this is the device with three elements, I suggest you connect the grid to a variable negative supply - say 0-100V - and increase the negative voltage until the continuous conduction is just extinguished, so light is only emitted at particle strikes.
This kind of continuous conduction is very damaging to GM tubes, so it would be best not to use it until you have the problem sorted out, or the tube may be ruined.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
radhoo wrote ...
Proud Mary wrote ...
I see what you mean about the pancake detector. Generally, I would only expect the tube to light up like that with excessive anode voltage.
If this is the device with three elements, I suggest you connect the grid to a variable negative supply - say 0-100V - and increase the negative voltage until the continuous conduction is just extinguished, so light is only emitted at particle strikes.
This kind of continuous conduction is very damaging to GM tubes, so it would be best not to use it until you have the problem sorted out, or the tube may be ruined.
Sorry for the confusion, please take only the video part showing the SI14G as a reference (recorded with lights on, 3:23 - 3:47). The last frames (beyond 3:47) are pictures added to the video, and they where recorded using very loooong exposures, to join all those tiny little neon discharges into the strong glow we see. So it's not as bad as it looks, but - at first the SI14G works as expected, and is very sensitive to any of my test source (including weak uranium glass) - then gradually, even with the test source removed, the number of counts rises, until it reaches an impossible level, a point where I shut down the HV, to prevent any further damaging - it appears this uncontrolled avalanche happens in a given region of the SI14g, where the electrodes also seem corroded by looking with the naked eye (probably over-voltage stress, or old tube)
Thanks for the advise with using the third electrode to temper down the uncontrolled discharges. It might help improving the tube's stability. I also tried lower voltages, bigger resistors, but didn't help.
I have seen a fault which was the exact opposite of what you describe, where a tube connection had failed, effectively placing the tube in series with a small capacitance. At first, when the 'capacitor' had no charge upon it, the tube would behave as normal, but in short time, the 'capacitor' would become fully charged, so the voltage across the anode and cathode of the tube fell below the threshold voltage of the tube, which would no longer work at all after a few seconds.
In your case, it is possible that the Br quenching gas has reacted with an electrode to produce the metallic corrosion you describe, and so is no longer available to quench. Thoughts added after lunch...
The circuit itself seems simple enough to build, that even I, with very little knowledge in circuits, could build it. But where in Orlando could I get a geiger tube? It's not like they are lying around or readily available at the electronics hobby store "Skycraft.." or are they? Can I pull one out of something? I mean... not that I could use a geiger counter for anything useful in orlando... I don't know where a nuclear one is near by that I could mess with the geiger counter. But then again, today in french class I was wondering how that water bottling company Evian is naive spelled backwards, and maybe we are easily being fooled to think that it is spring water while it is really water from the nuclear power plants there. Course I was joking up till when my teacher said 80% of their power is from nuclear and now I will never buy evian again. So I'd detect the amounts in it, and if it is more than jackfruit nuts or something, i'll never buy it again. How sensitive is that counter?
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
It's not good for what you need since it doesn't show an estimation on the quantity of radioactive material detected (uC) nor a radiation dose. You could still use it for relative comparisons (one rock is more radioactive than other, because the led blinks more, etc).
For me is just a test build to understand Geiger tubes better including testing various other tubes, and then move forward to more advanced detectors. I do not plan to use it for any other purpose.
But indeed, the project was simple and fun to make. Geiger tubes you can get online, Russian and Ukrainian sellers have some on ebay.
Registered Member #1938
Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701
Proud Mary wrote ...
In your case, it is possible that the Br quenching gas has reacted with an electrode to produce the metallic corrosion you describe, and so is no longer available to quench.
I do have a nice small G15H tube made by I.F.A. , unfortunately it is at the end of its life. These tubes where all painted black, so I can't see the electrodes. H in the end stands for Halogen, it might have provided a clue on how the electrodes look after a long use.
Do you perhaps have any resources available on the damage GM tubes suffer in time. They all seem to have a "Max number of clicks" life-time parameter in their specs.
This might work if the grid is placed between the anode and the cathode. I will try to visually inspect the geometry and put some drawings here. The datasheet shows the grid in a remote location, and my long-exposure pictures show only the center part of the tube being illuminated, showing that the third electrode/grid (unused in my setup) would be placed towards the exterior: (sorry for the blurry pic)
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uRADMonitor – Online remote radiation monitoring station
