Crystal shape and size

Scintillation crystals, PMTs, voltage dividers etc...
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CareBear
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Crystal shape and size

Post by CareBear » 16 Jan 2020, 01:59

Hi again.

I’m about to buy my first gamma spectroscopy equipment and I wanted to get as much information about the technical side before I spent my money.

I’m going to buy a spectroscopy kit from gamma spectacular but can’t really decide on the detector size.
I already got in touch with Steven who helped me out a lot (thanks again), but I’m still not too sure what kit would be best for me.

I’m aware that the 2” NaI detector is going to give me best results, especially in the higher energy regions.
Since this is just a hobby of mine my budget is rather tight and I fear that I might not use the kit enough to justify the costs.

So I was wondering whether I could still achieve good results with the 1,5” x 2,5” crystal. The volume is smaller but I thought since the crystal is a bit longer than the 2” crystal the high energy resolution shouldn’t be too bad right?

Since I’m an absolute beginner in spectroscopy would I even be able to notice the performance benefits of the bigger crystals or could I compensate with increased measuring times etc.?

I’m looking forward to your input.
Marcel
Dortmund, Germany

luuk
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Re: Crystal shape and size

Post by luuk » 17 Jan 2020, 15:27

Hi Marcel,
The crystal size for most hobby use is in my opinion around 2”x2” but with a 1”x1” or even smaller you can have great results as well, if it fits the budget.
Also it is more easy and cheaper to make a simple (lead) shield for a smaller detector than for a large one.
If your interest field is up to ±2.5MeV like most, you will have less stopping power at the high region of the spectrum 1.9-2.5MeV but if you take a little more time to do your tests you can still get a great result, if you are more interested in lower energies ±20KeV-1MeV than a smaller crystal can be a good choice as well because you will have a much lower background that disturbs your signals, and you need les shielding.
The 2.5” long will give you a little advantage in the high energy region if used head-on, but like you said it is all a question of budget that decides what is still affordable.
If your budget is really tide than you could also think about to make your own assembly by buying a crystal/detector and a pmt and some other material from the internet and build(assembled) it yourself it is not too difficult and it is a great learning process while building it, and give much more satisfaction when it works.
There is lots of detector stuff on sale on eBay and prices are special for crystals not to high the Russians and Ukrainians are dumping lots of crystal detectors there for real interesting prices.
There are enough people on the forum that can give you advice and help with selecting the right materials and how making a detector out of it.
Luuk

CareBear
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Re: Crystal shape and size

Post by CareBear » 18 Jan 2020, 02:39

Thanks for answer luuk!

I hadn’t thought about the extra shielding needed with a bigger crystal. Since lead isn’t as cheap as I thought I guess I’ll have to use rather rudimentary shielding at first.
So for my purposes I think a 1,5” by 2,5” crystal will be a good choice and I can save/ spend the extra cash on other things.

I thought about building something myself but I get discouraged quite easily if stuff like that doesn’t work out.
So I wanted to buy something solid first to get into the subject and then build something in the future.

I’m quite interested in LYSO crystals because they’re used in PET-Scanners and I’m a huge fan of those things :)
I might try to make a detector out of those in the future.
Marcel
Dortmund, Germany

luuk
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Re: Crystal shape and size

Post by luuk » 20 Jan 2020, 06:01

Hi Marcel,
Building a detector is not so difficult as you may think, it is fun to do and building your own detector and will save you a lot of money.
You can get/find lots of information and support here on the forum to build your detector and I have always some materials for sale for real hobby prices if interested, and there are others like Tom(Iradinc) that has lots of materials for sale to completely build your own detector.
But buying is a save way to get a good working detector, so it is up to you what you going to do.
Luuk

James Luck
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Re: Crystal shape and size

Post by James Luck » 11 Jun 2020, 00:23

It's up to preference, and a lot of research into the type of crystals including what others had good results with.

I run spectroscopy with a 1x1 undopped CsI crystal. I get great spectrums, but without sheilding your spectrum will be lost in noise.
It's quite sensitive, hense the noise.

But I've seen many have luck with NaI( Ti) 1x1 to 3x3 crystals, most importantly is your sheilding from back ground and a even size crystal.

If you've aready chosen your kit hope its serving you well, if you havent run it yet hope it serves you well.
James luck
Chicago Ill, USA.
Hobbyist, primary meter: refurbished Eberline Esp-1.
Probe: 3 inch plastic scintillator kit from iradinc.

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Pavel M.
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Re: Crystal shape and size

Post by Pavel M. » 13 Jun 2020, 07:45

First of all, welcome to the world of gamma spectroscopy, Marcel!
It might seem counter-intuitive, but it's true that people with crystals like 1.5"x1,5" do sometimes get better results then people with bigger and more sensitive ones (2.5"x2.5"+), just because it's cheaper and easier to shield smaller probes.
Most widely used crystals are the ones with a "square cross-section" (like 1.5"x1.5", 2"x2" etc.). There is nothing wrong with using smaller crystals, just keep in mind that you won't get as much stopping power in the high energy region (you might not be able to see the 2.614MeV Thallium peak, for example).
Without any shielding, my current setup gets around 250+cps from the natural background, so you really have to shield it properly if you want to measure lower activity samples.
If you have high enough budget, you could go for the 2"x2", but if you want to save some money, the 1.5"x1.5" will probably serve you just as well, and you certainly won't be disappointed.

Just as luuk said (and he's the real expert here when it comes to crystals), even with a 1"x1" you can achieve some great things...
Good luck with your new spectrometer!
Location: Czech Republic
Equipment:
  • Spectrometer: Scintillix SCGS-01 v3.0
  • Probe: Scintillix 2.5" with 3" PMT

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