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Scintillation Probe (Photomultiplier/NaI)

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radhoo

Mon Dec 13 2010, 05:16PM

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

Yes .
I also need to make a counter or some kind of data logger for the probe.
For the first tests I'll use the mVmeter, but I'll be needing a uC + LCD soon.

Proud Mary

Mon Dec 13 2010, 05:20PM

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

radhoo wrote ...

Yes .
I also need to make a counter or some kind of data logger for them.
For the first tests I'll use the mVmeter, but I'll be needing a uC + LCD soon.

It should be pulse amplitude spectral analysis, rather than event counting, if you are to make the most of your scintillation probes.

radhoo

Mon Dec 13 2010, 06:27PM

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

Proud Mary wrote ...

It should be pulse amplitude spectral analysis, rather than event counting, if you are to make the most of your scintillation probes.

Indeed. And that would be another reason to use a uC: recording the amplitude on a time axis would be easy.

Too bad I have no clue on how tick the NaI aluminum casing is. I feels like 0.2 - 0.3 mm, but I can't say for sure.

Proud Mary

Mon Dec 13 2010, 06:52PM

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

radhoo wrote ...

Too bad I have no clue on how tick the NaI aluminum casing is. I feels like 0.2 - 0.3 mm, but I can't say for sure.

If you have a look at my never-ending Geigermania thread in the Projects section, in my entry for Sun Jun 06 2010, 08:28PM I found that only about a quarter of background gamma counts where blocked by 20mm Pb shielding over a 24 hour counting period.

So this thin skin of aluminium will have no effect on gamma counting that you can measure, and not much with X-rays either until you start going below 20keV.

radhoo

Mon Dec 13 2010, 11:19PM

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

Thanks, however at this step I'm much more confused:

The probe requires a bipolar power source -12 0 +12V . So I quickly put together a small rectifier with L7812/L7912, all good, the inverter inside the probe started to oscillate with the well known ultrasonic ferrite core sound.

Then I connected the multimeter to the signal pin.

Probe shows -0.948Volts.

The next step was to bring some sources close to the NaI capsule:
I have an Americium pill from a fire alarm, some Uranium Glass marbles (twice the background level), and a DU check source on my CDV 700 case (quite strong).
None of these produced any variation on the amplitute/voltage level displayed by my multimeter.

There is a small possibility that the photon events are so quick and short, that the multimeter doesn't have the time-slot sensibility to record them, but then again the DU check source should have produced an avalanche of events, resulting in an average level visible even on the laziest multimeter.

EDIT: The probe is actually very responsive to X-rays, I've tested with 50KeV x-rays and they produced lots of dtection events.

Proud Mary

Mon Dec 13 2010, 11:38PM

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

You have to have some method of examining the output signal - an oscilloscope for, example.

The next best thing might be to connect the outpin pin via capacitor of say, 1nF, to an AF amplifier of medium to high impedance input, and see if you can hear any clicks, or other indication.

But without a full circuit diagram - what Americans call "a schematic" - these voltage values appearing at a terminal of an unkwown
circuit really tell us very little, I am afraid.

radhoo

Fri Jun 03 2011, 08:03PM

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

Slow progress, but project alive: I managed to finish the bipolar supply needed for my probe (+12V,0V,-12V), and a basic board with a microcontroller , a UART Bluetooth Module set to 9600bps doubled by a MAX 232 serial connection as a backup.

Using bluetooth I can now establish wireless connections to the microcontroller, to read the scintillation probe data, and to send commands such as Start/Stop the High Voltage supply connected to the X-ray tube.

Pictures (not much to see yet) in the first thread.

radhoo

Mon Jun 06 2011, 10:39PM

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

it works!

(pics and vids tom)

radhoo

Tue Jun 07 2011, 12:59PM

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

video added to first post.

Proud Mary

Tue Jun 07 2011, 07:18PM

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

Good good, Radhu.

All you have to do now is build a fast, linear, small signal conditioner-amplifier, and you'll be able to sort out your pulses with a software Multi-Channel Analyser, which will do very well until you decide you want one of these:

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