My first spectrum!

[sgt_bear]

This weekend i finished soldering my detector electronics.

I used a professional HV Supply fom ISEG, the Theremino Detection Circuit and added a PCM2912A (Texas Instruments) Ic to have a "one board" solution without needing the modification of a sound card. The Design fits in a small aluminium case.

The detector i have is a Nal(Ti) from Scionix (Model is 38B57&1.5M - E1). Sadly i have no datasheet. I've bought this detector from Ebay (seller:iradinc) and the detector works very well as spectrometer and as counter with my Ludlum Model3.

Im really just starting with theremino software, but i was excited to take some spectrum. It might be not very good, but as i said, i'm a beginner.

So here are my results.

1.) Americum
For the first Spectrum i used a "known" source. A Cerberus Smoke-Detector with 0.8uCi of Am-241. I did not open the smoke alarm completely, i just placed the metal can near the spectrometer. The Am-241 is very clearly visible

smokedetector.png (64.77 KiB) Viewed 10714 times

2.) LYSO Crystal
These LYSO Crystals came from the same seller that sold me the detector. The Lu-176 is visible, but it is a bit off the line of theremino. I have not found out why.

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3.) Vacuum Tube 6141
The 6464 Vacuum Tube is a Voltage Regulator made by Western Electric. According to "Cliffs Radioactive Tube List" it contains 4uCi of Kr-85 gas. Mine has a date code of 1957 - so now there should be 60nCi of Kr-85 left. The tube still tests very hot with a Geiger Counter

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4.) Uranium Glass
2 Glass disks of Uranium Glass - Source, compositon and age unknown

uraniumglass.png (61.31 KiB) Viewed 10714 times

5.) Wellness-Card
This "Wellness-Card" is a plastic disc that *removes all kind of bad effects from your body* and is quite hot. I picked this up on a flea-marked while searching for radium and uranium with a Geiger Counter
The blog of Carl Willis has a similar card, with a similar result. https://carlwillis.wordpress.com/page/5/

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6.) Lantern Mantle
This is a well known item for collectors of radioactive items. For better Spectrum i rolled the mantle around the detector.

lanternMantle.png (77.85 KiB) Viewed 10714 times

7.) Welding Rod
Thorium Welding Rod from a Surplus Marked. States "2% Thorium Oxid" (Thoriumoxide). Looks quite different from the Lantern Mantle. I also added a comparision from the Mantle and Rod.

weldingRod.png (80.76 KiB) Viewed 10714 times

comparision.png (86.79 KiB) Viewed 10714 times

So this is my first spectrum of items.
What do you think about it?
Any ideas to make it better?



Currently i don't own any more items to make a spectrum, but im currently working on a legal solution to get excempt isotopes to my country. Here in Switzerland you can own a rather large amount of isotope activity (eg. 20uCi of Cs-137 or 250uCi of Co-57) but i only can use short lived isotopes, because the limit for disposal is way less (0.2uCI for Cs-137) and disposal is very expensive.

[luuk]

Hello Jonathan,

Nice spectrums that you made, the noiseis is low and I cannot see he resolution but it looks good to me, I don’t se much to improve it.
You say that you don’t have a data-sheet from your Scionix detector, what kind of information are you looking for?
Maybe I can help you with that.

Luuk
Scionix test engineer

[lodovico]

Nice spectra,
in my opinion you have to work a little bit with equalizer in order to linearize the energy scale. You can also try the software compensation feature. Try to have a read to the manual also.

[brehwens]

The Kr-85 spectrum looks very much like a Ra-226 spectrum....

[sgt_bear]

Hi luuk,
Oh, very nice to hear you're from scionix! I was interestd in general specifications about this detector, and what voltages it can be run on, currently i run it at 800V, since my Ludlum Model 3 was on that Voltage. But i heard if you put up or put down the voltage for gamma spectroscopy it can change your spectrum. I would like to try around, but for this i would need a value for maximum working voltage or so.

Hi lodovico,
Yes i found this option now and it looks way better.

Hi brehwens,

Oh...i looked at Ra-226 spectrums and you seem to be right, so this tube contains maybe Ra-226 instead of Kr-85 so this means the list containing radioactive tubes is maybe wrong, or the made that tube in Kr-85 and Ra-226 too.

[iRad]

Hi Jonathan
Nice work so far. Luuk of course is the detector master , especially on Scionix detectors. I have found most of the 38B57&1.5M detectors I refurbished to work best between 650 to 850 volts. Cheers, Tom

[luuk]

Hi Jonathan,

The pmt used in this detector is a Hamamatsu R580 that can work up to maximum of ±1500V maybe a little higher(1750V).
But in my opinion try to work with any pmt on an as low as possible voltage just but always check if the detector is linear, if it works good on 600V why raise the hv to 900V? only if you need more signal out of the detector because the mca need more signal than is it useful to raise the hv.
A lower voltage will give you less noise and a smaller chance that there is a sparking problem and the pmt will last much longer.

Luuk

[Sesselmann]

Luuk,

I tend to agree that lower voltage yields better resolution, at least with the GS drivers.

When I test my drivers I use an electronic pulse generator which is adjusted to imitate the pulse height of Cs137, the test-pulser has a 10nF high voltage coupling capacitor and a BNC connector so I can connect it just like a real detector to the GS-1100-PRO.

With PRA pulse shape filter active the test-pulser gives me a resolution of 0.5% at 662keV when the bias is set to 500V, but the resolution becomes worse if I increase the bias to 1000V. I am not sure why higher tension in the cable makes a difference but it does. Might follow this up with an experiment when I get a moment to spare.