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uRADMonitor â€“ Online remote radiation monitoring station

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Proud Mary

Thu Oct 25 2012, 02:55PM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

Radhu, here is another paper full of useful detail on background measurement:

Background as a Residual Radioactivity Criterion for Decommissioning

radhoo

Fri Oct 26 2012, 02:13PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

thank you!

radhoo

Sat Oct 27 2012, 08:48AM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

It looks like rain, today! Let's see how good is that case. I don't expect any issues, though.

Maybe some interesting data related to this phenomenon?

A friend working in this field, indicated that the level of radiation detected by the device should stay almost constant. He indicated I should use a ion chamber to better track the Radon variations.

So we'll probably see a new "sensor" added to the device, soon.

Stella, what is your experience with those giga-ohmic resistors that you've purchased earlier? Are they any good? I was looking for something similar, and I found a 1000GOhm glass resistor I'm tempted to purchase.

I also got the DHT-22 sensor, and now I'm thinking about replacing the DHT-11 currently in use. If only the two humidity scales would match ...

Proud Mary

Sat Oct 27 2012, 11:21AM

Registered Member #543 Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992

radhoo wrote ...

A friend working in this field, indicated that the level of radiation detected by the device should stay almost constant. He indicated I should use a ion chamber to better track the Radon variations.

So we'll probably see a new "sensor" added to the device, soon.

"almost constant" I have been able to track small but distinct diurnal variations over 24 hour periods - a sine wave - which has been known since the early day of cosmic ray research. Google: "On the Interpretation of the Diurnal Variation of Cosmic Rays" which is a pdf I couldn't link to. It is an old one, but nice and clear for all that!

If you look through the skyshine and 'Background as a Residual Radioactivity Criterion' papers, you'll see that it is these small changes in background that contain almost all the interesting information, and what makes long term observation worthwhile. Once you have a base-line figure from months of obeservation, you'll be able to detect these smaller changes and trends, all of which have a reason behind them which it is our business to understand.

Now as for Rn-222, its daughters, and their alpha emissions, clearly these cannot be detected with a non-window GM tube, and would be much better detected with an ionisation chamber (if there are enough of them) or a scintillation device and MCA. BUT, alpha ranges are but a few cms, as we know, so alpha detection in the open air is a specialised business (as far as I understand it). Most concern about Rn is in the domestic indoors, especially in cellars, where the gas can seep up from rocks below, and accumulate to hazardous levels due to want of ventilation. In Britain, long term alpha dosimetry in high radon areas like Cornwall has been done with photochemical film badges, and more recently Track Etch Detectors, which the householder sends off to a government laboratory every three months or so. I do not think you will get any results worth having if you fix an ionisation chamber to the outisde of your house.

radhoo wrote ...

Stella, what is your experience with those giga-ohmic resistors that you've purchased earlier? Are they any good? I was looking for something similar, and I found a 1000GOhm glass resistor I'm tempted to purchase.

I think the Russian glass envelope high GÎ© resistors are very good so long as we always think of the glass as a resistance in parallel with the desired resistance, and take every precaution to make sure the outside is chemically clean and dry. Deposits from finger prints WILL increase surface leakage, in a temerperature and humidity sensitive way, so the amount of leakage will not be constant, causing false readings. This applies to everyting else in the high Z part of the circuit too, especially PCB boards. Once constructed, the circuit should be placed in a sealed box with a dessicator like silica gel. I have found it very difficult to set up an ionisation chamber that is both highly sensitive and highly stable over time with good re-set accuracy - but this doesn't mean that other people won't be able to do much better!

radhoo

Sat Oct 27 2012, 11:07PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

I've completed a short film for this project:

Ash Small

Sun Oct 28 2012, 12:02AM

Registered Member #3414 Joined: Sun Nov 14 2010, 05:05PM
Location: UK
Posts: 4245

This is quite an impressive project, Radhoo.

I've been following it with considerable interest.

mikeselectricstuff

Sun Oct 28 2012, 11:07AM

Registered Member #311 Joined: Sun Mar 12 2006, 08:28PM
Location:
Posts: 253

Does having a full-wave rectifier make much difference vs. half-wave? With a single-ended drive like this you get most of the output on one polarity, so you may find you can lose 3 of the diodes with minimal performance loss. Obviously you do then need to make sure the windings are the right way round.

wrote ...
Saturation alarm: if the tube becomes paralyzed by high dose rate as in an X-ray beam.

I noticed this when sending a counter through my baggage x-ray (150kVp) - counts increase as it approaches the beam but it then goes silent til it comes out the other side.

radhoo

Sun Oct 28 2012, 03:27PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

@Ash Small, thanks mate.

@Mike,
While not essentially important for the tube itself, you will want to minimize the ripple effect to its maximum extent, to make sure the detector runs undisturbed by various interference factors. Especially the detector/counter part. Let's take a look at the following two photos:

1.The first, shows my version 3.2 inverter output, that uses a NPN oscillating transistor in an Armstrong oscillator, and a feedback mechanism constructed with zenner diodes set for 400V, that triggers an oscillator-blocking second transistor. See the trace for CH1 - yellow, set for 400V

2. The second shows the output in 3.3, fully rectified and produced by a a precisely calculated PWM signal. See the CH2, cyan trace, set for 350V

I have plenty of diodes and do not feel the need to spare any of them, given the nice improvement in the results. But yes, it is possible to only use a single diode to rectify the inverter's output. I just don't see any reason for doing that.

Steve Conner

Sun Oct 28 2012, 06:41PM

Registered Member #30 Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706

I don't understand how these scope traces show an improvement in the results. They are traces of two different things. The first one shows the high voltage AC output before the rectifier and smoothing capacitors, the second one shows the smoothed DC.

radhoo

Sun Oct 28 2012, 08:46PM

Registered Member #1938 Joined: Sun Jan 25 2009, 12:44PM
Location: Romania
Posts: 701

Steve Conner wrote ...

I don't understand how these scope traces show an improvement in the results. They are traces of two different things. The first one shows the high voltage AC output before the rectifier and smoothing capacitors, the second one shows the smoothed DC.

Steve, they both show "DC" , in the same place, right before the 10M resistor connected to the tube's anode.

Remember that for the first trace, there is an oscillator blocker transistor, controlled by the zenners for voltage regularization. This is why we see those huge variations, but also a frequency value is being computed by the scope. Circuit diagram here:

. Scope connected before R2.

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