Stilbene Detector

Scintillation crystals, PMTs, voltage dividers etc...
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Steven Sesselmann
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Stilbene Detector

Post by Steven Sesselmann » 25 Nov 2018, 19:26

Some of you guys may be interested in this.

At the recent IEEE NSS exhibition, my neighbour was representing a company called InRad Optics (https://www.inradoptics.com/scintinel-stilbene) and on the last day I swapped a GS-1100 with him and got a 1" stilbene crystal in exchange. Thought it might come in handy for neutron detection.

Stilbene is an organic crystal grown from mostly carbon and hydrogen, it looks a bit like plastic and is not hydroscopic, it is a popular choice for neutron detection, as it exhibits a significantly longer pulse for neutrons than it does for gamma, and you apparently get good discrimination between gamma and neutrons.

1" Detectors is not a standard product for me so I don't have ready made housings, but fortunately I had a box full of old 1" Bicron NaI(Tl) detectors which have useless crystals (worse than 15% resolution), but the PMT's are fine.

Most of you guys may own some of these or at least you may heve seen them on eBay, the housings are sealed and the crystals inside are not encapsulated so they can be a bit of a nuisance to work with. Anyone intending to rescue PMT's from these ought to go about it carefully, so the crystal doesn't shatter and go everywhere.

Wearing some nitrate gloves, I carefully cut the end of the tube and removed the gain potentiometer and cables, I then measured how deep it was down to the crystal using a stick, and marked it on the outside.

Using a hacksaw I carefully cut through the housing where the PMT joins the crystal and removed the top part of the housing, thereby exposing the PMT. The PMT is glued to a square piece of glass which in turn is glued into the housing, so I used a heat gun to gently warm and soften the glue, this allowed me to remove the PMT along with the piece of glass, leaving the crystal surface exposed.

As NaI(Tl) should not be disposed of in the household waste, I quickly mixed up some Araldite epoxy and poured over the crystal, this sealed it completely in the tube and hopefully prevents moisture getting in. This way I can store the crystal until I have a few more and go to the chemical waste transfer station to dispose of it.

I cleaned up the PMT and fitted it to the Stilbene crystal and found some aluminium pipe in my scrap metal box, which made a nice housing for this cute looking detector.

I don't have a working neutron source right at the moment, so I just ran it overnight without any pulse shape discrimination (see attached). Post recording I used the advanced filter in PRA to filter the longer pulses from the shorter pulses, which revealed a couple of peaks. I can not be 100% confident that this kind of pulse shape filtering works, for that I will need to test it with a proper source.

One benefit of Stilbene is that it detects fast neutrons directly without first having to moderate them, which makes it great for D+D fusion neutrons.

I have no idea what this Stilbene stuff actually costs, but if it works, I might add a Stilbene detector to my range.

Steven
Attachments
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Making a Stilbene detector part 1
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Making a Stilbene detector part 2
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Making a Stilbene detector part 3
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Making a Stilbene detector part 4
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Making a Stilbene detector part 5
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Making a Stilbene detector part 6
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Making a Stilbene detector part 7
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Making a Stilbene detector part 8
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Making a Stilbene detector part 9
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Making a Stilbene detector part 10
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Making a Stilbene detector part 11
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Making a Stilbene detector part 12
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Making a Stilbene detector part 13
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Making a Stilbene detector part 14
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Making a Stilbene detector part 15
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Making a Stilbene detector part 16
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Steven Sesselmann | Sydney | Australia | gammaspectacular.com | groundpotential.org | rephopper.com | beejewel.com.au |

luuk
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Re: Stilbene Detector

Post by luuk » 25 Nov 2018, 21:34

Hi Steven,

I wonder if you can do psd( pulse shape discrimination) with Theremino software if that is possible that would be a very interesting option.
Unfortunately I don’t work or have any experience with software mca’s so maybe there is some one who knows if it is possible?
We use psd at work and it is the only good way to separate e.g. neutrons from gamma’s in plastic, Stilbene or liquid scintillators.
Psd is a complicated process and it is expensive if you have to buy the right equipment so if it is possible with free software that would be nice!
Stilbene is expensive but you can buy it now and then on eBay from Ukraine they sell 2x2” for a reasonable price.

Luuk

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Steven Sesselmann
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Re: Stilbene Detector

Post by Steven Sesselmann » 26 Nov 2018, 15:34

The jury is still out on weather sound card sampling can do PSD separation in plastic scintillators. Marek's thinks it is not possible, reckons pulses are too short for the sample rate, but I am thinking that the analogue 80-100 µs pulse coming from the GS preamplifier might be proportional to the input, so maybe it could work.

Found a paper on Stilbene here: http://iopscience.iop.org/article/10.10 ... P07023/pdf
Steven Sesselmann | Sydney | Australia | gammaspectacular.com | groundpotential.org | rephopper.com | beejewel.com.au |

luuk
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Re: Stilbene Detector

Post by luuk » 27 Nov 2018, 03:29

Hi Steven,

I checked our professional equipment for psd, the sample frequency is for one 250 and for the other 500Mhz.
So it would impossible that I can also work with a simple low(normal) frequency soundcard.

Luuk

stamasd
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Re: Stilbene Detector

Post by stamasd » 16 Jun 2019, 02:21

Very cool. Since I'm interested in neutron detection, I just found and purchased some stilbene crystals (from the Ukrainian source mentioned above) and will start experimenting with them. I do have a source of neutrons.
Real name: Silviu Tamasdan

stamasd
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Re: Stilbene Detector

Post by stamasd » 25 Jun 2019, 08:27

Quick update, the stilbene is still on the way but I got ahold of a suitable PMT tube with quartz window and increased response in UV since the stilbene appears to have maximum emission in that range. It may also be useful for experiments with Cherenkov emissions, hmm.
As for data acquisition, I have a MCA that can go up to 20MHz an can do some PSD. Not quite the range quoted above but we'll see how it fares in practice.
Real name: Silviu Tamasdan

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