Gamma Spectrometry Forum

Hi everybody,
beeing busy with too many hobbies, but radiation is one I never forgot. Educated in medical radiation assistant, working in NucMed a short time, handling hot stuff, get rid of the fascinating measurements but working now within a medical X-ray company were the radiation is switchable - now for 18 years. Recently got the chance to pick up an unknown Scintillation probe and a Harshaw 12S8-x, so from now on dealing again with my dream to operate my own gamma analysis. But I still need help to get everything working. So I will read - and hope to get some help after.
Located in Hamburg/ Germany - with own working bench in my garage, several geigercounters and a fascinating movable lead box - nearly a cubic meter surrounded by 20mm of lead. This will be the place were I want to do my analysis... Calibration source available, but no electrical HV, driver or counter so far, looking to get one from Australia first and hope my Harshaw 12S8 is able to work with Stevens box...
The - I call it preamplifier- and connectors to the tube with 14 pins are available but both probes do have HV input and signal output. Stevens Box just provide one conector, so this will be the first I need to find out.
On the unknown probe is a handwritten +HV max 1500V and I suggest it´s a 1,5" crystal. NaI(Tl) ?
The Harshaw is much bigger. 8cm in diameter (inclusive aluminum case)
Both capsuled in aluminum and sealed.
So yes, I will spend time to them now to get them work.
see you, Kolja

Hi Kolja,

Welcome to the forum.

Those detectors look interesting and hopefully the crystals are dry and undamaged, so it should not be too hard to get them working.

It is difficult to see what electronics are attached to your detectors, but all you will need to operate these detectors is a divider and coupling on the PMT, any powered preamplifier. can be discarded or at least bypassed.

Steven

PS: You can change your username to Kolja, as I am pretty sure there are no other Kolja on the forum ;)

Hi Steven, Kolja,
I am still looking at the electronics too, because in my Canberra 802-3 with 2007P socket and Bicron 3M3/3P with P-14X socket preamps are inclusive.
As Steve advised me recently, I can discard the preamps and connect the PMT anode signal directly (via a capacitor) to the GS1100.
In the schematics for the Canberra 2007 I see that there are two signal outputs: one from the PMT anode and one from the last dynode.
See:
http://www.canberra.com/products/radioc ... SP0071.pdf

From Gilmore (Practical gamma ray spectrometry, pg 217, Wiley ed) I read that he advises to take last dynode signal for energy spectrometry purposes and the anode signal for timing purposes.
My question to Steven is: what is your opinion about these considerations, while looking at the electronics of the GS1100 ?

Willem

Steven Sesselmann wrote:Those detectors look interesting and hopefully the crystals are dry and undamaged, so it should not be too hard to get them working.

Well I hope so, as they were lying years in an office of our radiation officer who recently retired and presented me the probes I believe she was handling them with respect and took care of them quite well.

Is there a link available I need to read to understand the electronics of the 14pin connector?
And am I right that I will need the 2000series from you to run my probe stating 1500V, as the 1000 series just provide 1100V ?
regards, Kolja

Kolja,

The main reason for choosing the GS-2000-PRO would be because it has the SHV connector. A BNC connector is very likely to fail at 1500V, it is only rated for 500V, but in dry conditions it is fine up to 1100V. My main reason for using it on the GS-1100A and 1100-PRO is to save a bit on cost for the average amateur who usually runs a detector at max 750V.

It is not just the cost of the SHV connector on the GS, but also the cost of cables, however if your probe needs 1500V then you don't have much choice.

Steven

Hi Kolja,
Looking at the picture from your detectors the small unknown detector with the black coating looks to me also a Harshaw detector, if the black coating is not smooth but more ripple than it is a Harshaw detector for sure.
The voltage dividers or amplifiers on top of both detectors are have never seen so I expect that they are made by the customer not by Harshaw.
Regards,
Luuk

Got it Steven, I fully understand.
have a look to the BNC which is build in... a massive ceramic insulator...
Thanks a lot.


Luuk, that is a fantastic news for me. Yes, its a litte rippled, the attached voltage divider comes definately from Philips.
Do you know the type of the small one, as I think I need to search for documentation to know what is inside and to build up the correct electronic for it.

Not sure if interesting, but some pictures from other views.
BTW: the large one has a matching amplifier (translated from german) and a discriminator and comes as well with BNC.

So far I´m not interested in both attached electronics, as both provide separate HV and Signal output, If I go for Stevens box I need to buid it up from scratch I believe...
Thanks and best regards, Kolja

Kolja,

I suggest you bypass that whole board at the top, and run a HV insulated wire straight from the BNC connector to Pin 11 on the blue socket.

Once you have it working perfectly you can remove the other board, but to test it this would be straight forward.

Steven

PS: Check the resistors on the divider what are the values?

Hi Steven,
the resistors are mostly 169k
I tried this evening to copy it down...
I also attached the first circuit where the HV enters.
The "signal circuit" contains 3 transistors, three electrolyte caps and lots of resistors... but I will bypass that one.

attached the circuits...

I still dont know which kind of PhotoMultiplyerTube is inside, so that will complicated to find out right? I didnt found that much about Harshaw NaI(Tl)´s

This post is just about the "unknown small detector" which Luuk stated is also a Harshaw.
interesting that the small one is much ligher than the large one.
regards Kolja

Kolja,

This divider is going to be a problem, because the total resistance is only in the order of 1.6M and I recommend at least 10M ohm dividers for the GS.

The GS voltage read out is calibrated to infinite impedance (well at least 1G Ohm which is what I use to adjust it) and it uses a 1M load resistor inline with the detector essentially forming part of the divider circuit. If we take the extreme case where the PMT divider has a total resistance of 1M and the load resistor is 1M then the voltage on the display will read exactly half of what it really is across the PMT.

For my own dividers I use 1M resistors and there are 12 of them, so the total resistance is 12M + 1M so the error on the voltmeter is then only 1/13.

The other reason such low resistance is not suitable is the limitation of the USB port to supply max 2W power.

If it's not too awkward I would rebuild the voltage divider with new 1M or 1.2M quality metal film resistors.

Steven