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Scintillation Probe (Photomultiplier/NaI)

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Proud Mary

Thu Jun 09 2011, 05:07PM

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

Ash Small wrote ...

Proud Mary wrote ...

Nicko wrote ...

How did you end up with a bucket of goulash out in the wilds (of the South Downs?)

Goulash World's Miss Goulash Award for International Goulash Year, of course!

Did you really not know that I was Goulash Queen 2011, Nicko?

But it says here:

that the International Goulash Competition 2011 isn't until September....I'm confused now!

Impostors! Frauds! Mountebanks! How could anyone doubt that I was Miss Goulash 2011!

radhoo

Fri Jul 15 2011, 12:31PM

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

Here is the emission spectrum, computed using FFT on the sound card data . Software used PRA and INTUNE:
This can be used to identify the radioisotope emitting the particles detected by the probe like in the expensive dosimeters.

1310733064 1938 FT101817 1min Nothing 1min Cs137

The last graph is a energy/event frequency representation. There are two energy peaks. The isotope used was Cs137 (from an old spark gap tube).

Proud Mary

Fri Jul 15 2011, 02:15PM

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

radhoo wrote ...

The last graph is a energy/event frequency representation. There are two energy peaks. The isotope used was Cs137 (from an old spark gap tube).

So are you saying that the big peak is the 137mBa 661.6 keV gamma line, Radu?

You need to get some additional calibration standards sorted out before your relationship to this world becomes completely arbitary - often one of the first signs of serious mental disorder in my experience!

If you put an Al filter in front of the 241Am pellet from a smoke detector to block the alphas, then the 59.5 keV Î³ peak will be so very much larger than the other feeble Î³ emissions (if you can detect them at all) that you can be certain of its identity. With the alphas filtered out, you can consider it as a monochromatic 59.5 keV Î³ source for
most ordinary non-critical applications.

Afterthought added later: The 59.5 keV emission is not exactly bursting with meaty goodness, and I've seen pocket GM detectors using ZP1313 and similar miniature dosimetry tubes that couldn't detect it all. Just so you know....

radhoo

Sat Jul 16 2011, 01:26PM

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

I'm new to this field, and just joined a group where this kind of setups are somehow ordinary. Tens of different PMT tubes, scintillation crystals, all for one purpose and some impressive results.
So I'll do my homeworks quickly and hope to have a nice spectrometer soon.

It seems others managed to use a microcontroller for this purpose, something that didn't work for me, or at least not as expected. The key factor seems to be a module to "Sample and hold" the "over-discrete" (too short) scintillation events. Files attached. Not very complicated at all!

]gamma_grapher_v0_hand_drawings.pdf[/file]
]mca_rad_test.pdf[/file]

radhoo

Sat Jul 16 2011, 01:30PM

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

Some pictures for those too lazy to open the above PDF's:

1310822935 1938 FT101817 Schematics Sample And Hold

My scintillation probes are industrial and so they are the result of a professional design. I expect to get some excellent results once I manage to build a reliable counter, FFT processor and spectrum representation on LCD. For now they seem to respond well both to x-rays and Cs137 radiation (you can hear the clicks in the heatsets, when using an audio sound card). When using PRA and INTUNE I can do the graphs above. First is a signal representation, straight forward: without and then with a radiation source, the other is a FFT spectrum as computed by PRA based on the signal recorded. I don't know how to calibrate it yet.

Proud Mary

Wed Jul 20 2011, 11:58AM

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

A promising start, Radu!

Did you know that a few of the common Russian GM tubes were designed so that they could also operate in proportional mode, like a tail on the low voltage end of the Geiger region?

I've forgotten which type numbers they are, but if you are interested in gamma proportional spectroscopy, I'll see if I can find them again.

I was very lucky to buy the complete range of Svetlana Be-window proportional tubes covering 1.5 - 40 keV from a Bulgarian dealer a few years ago, but I've never seen them for sale anywhere since then.

radhoo

Wed Mar 07 2012, 02:37PM

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

I am looking for a larg NaI or plastic BGO scintillation crystal for a 9cm diameter PMT tube, posted here:

, the M12FS100 . Any ideas where to find some?

Proud Mary

Wed Mar 07 2012, 07:36PM

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

I bought BGO from this ebay dealer in America

a few years ago, and I see he still has some now.

You can always glue smaller pieces together with cyanoacrylate to make one larger sheet, with no loss that you will be able measure.

Take care if you buy NaI(Tl) scintillator second-hand, as it is hygroscopic, and old NaI(Tl) may disappoint.

Organic scintillators are often cheaper and easier to get - naphthalene (as used in moth balls) for example.

This ebay seller

will cut anthracene-based plastic scintillator to size, for very much less than you would pay for BGO.

radhoo

Thu Mar 08 2012, 09:35AM

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

Thank you, with the last one, Geo, I managed to get in contact on a group dedicated to this topic where he is a mod.

How can you tell that is anthracene-based plastic ?

Proud Mary

Thu Mar 08 2012, 10:26AM

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

radhoo wrote ...

How can you tell that is anthracene-based plastic ?

Sorry, Radu, I didn't make myself clear: it is the organic scintillator dissolved in the plastic that is anthracene, not the plastic itself. How do I know? Because it says so in the datasheet to which the ebay seller kindly gives a link!

In any case, anthracene is one of the most common active ingredients used in plastic scintillators.

PS: Don't forget that the natural mineral fluorite (CaF2) is a very fast scintillator, with about half the brightness of NaI(Tl) and little of the cost if you buy it on ebay in the rocks/fossils/minerals section

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