? Community Altoids Scintillation Det. Project

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? Community Altoids Scintillation Det. Project

Postby lutzhoffman » Thu Jul 22, 2010 2:34 am

Hi Folks : )

I just had a crazy idea, what about a community project launch, to help celebrate this new site launch? It could be a symbol of true cooperation, and group effort, to test drive some of the new forum ideas: Like skills trading etc. and group buying power etc. If it is a worthy project it will live on for many years to come as more folks build it. Nearly everyone at one time or another has admired some neat and cool gadget inside of an Altoids can. For me it was a simple flea power cw ham rig that a club member built in the 1980's. This got me thinking about something more modern, which ties into physics, fusion, and even cosmology. The following idea came to mind:

What if we pool our skills and build an Altoids Scintillation detector project just for fun, if there is enough interest? Here is an outline of what I would like to propose:

1. CsI(Tl) scintillation crystal using an affordable Chinese 10-18mm packaged scintillator crystal. (A fast neutron one would be real cool!, but gamma is easy)
2. Hamamatsu S3590-08 Silicon PIN Photo Diode 10mm x 10mm active area.
3. Small IC amplifier compact electronics, with mini range selector switch. (full range unit)
4. 3V Li power cell to power it.
5. Either LED bar meters, or LCD mini meter display.

It could be a group design, where everyone gets equal credit, the design particulars are narrowed down by simple voting, the best idea wins plain and simple, an analytical process, with some minor aesthetic considerations, hey no harm in making it look cool, like with a carbon fiber radiolucent window, or face.

This is just my idea, I would be just as open to building some other form of community project if someone can think of something with a large group appeal. Thanks for your consideration.....Lutz : )
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Re: ? Community Altoids Scintillation Det. Project

Postby Jerry » Thu Jul 22, 2010 4:22 am

Like I mentioned over on fusor.net I think avalanche photo diodes would be the way to go. I have one out of a liquid particle detector. We would have to come up with a way to get a couple hundred volts for the diode. Maybe a modified CCFL inverter board.
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Re: ? Community Altoids Scintillation Det. Project

Postby Doug Coulter » Thu Jul 22, 2010 10:05 am

I'd agree with Jerry on the avalanche diode. Many years of signal processing have taught me to get as much S/N at the source as you can, and the signal out of a small scintillator crystal is only a few photons.
A detector with gain before any noise is a really good plan when you can have it.

Jerry, do you have a part number for a blue-sensitive APD I can go get specs on? virtually all the good scintillators are in the short-blue wavelength region. IR sensitivity (eg most diodes) is a real pain to have to handle as many things we think of as "opaque" let that stuff right on through -- and in our case there are few to zero good scintillators that make long wavelength light.

They can get away with less sensitivity at CERN even in calorimeters, where "tiny sub MeV energies" don't matter. I wouldn't mod a CCFL inverter for this, though. Too much quiescent current for the batteries that have to fit into it too.

The child-worn visio-tactile prosthetic "hearing aid" I designed had a 2 nimh cell to 5v regulated supply on it and another supply run from that which made 150 volt pulses to drive a piezo transducer on the kid's wrist. All SMD and all much less than a sq in. As we had a small uP available, I simply used its PWM output to make the HV in a flyback inductor/diode/cap boost design. We did have to hand-wind the small cup core for the HV, but it wasn't hard at all -- and that made more power than you'd need for this. Heck, I still have the board layout for it.

If you are not going to measure pulse height kinds of things for spectra, I'd go with the most QE you can get out of a scintillator, or one that might cover the whole box size (say under the board in there) for best sensitivity. I'd have to look in some of my instrumentation books for physics, but have had good luck here with cheap and easy BGO and plastic scintillators using phototubes, and "light is light". The point is, no need to pay more for something that gives good spectral resolution if you're not going to use the information, and simply count -- or at some point with lots of input, measure the run-together pulses as an average current. And of course something that doesn't need encapsulation to protect it from the atmosphere. No hygroscopic xtals for me. We got ahold of a bunch of 1/4" by 1/2" by 1" BGO xtals that would do well for this, I think, but a larger area of cheaper scint plastic might do better yet.

For readout, in another project going on here now (we call it MultiGeiger), we used a common LCD "glass" display and the uP to drive that interface so we had some choice of modes and what to show -- the whole interface on that one (menu driven!) is that display and a rotary encoder/pushbutton. In that one, we are using one of the hardware counters in the uP (actually, 5 channels of them) so the uP can be slow or busy doing other things and not drop counts. For the main geiger channel we used a 2 transistor preamp that also will drive a small speaker to get your clicks while the uP counts them. A photodiode might need a little more preamp (geiger tubes and photo tubes have a loud output, to say the least) -- I'd have to look at that. Most opamps are kind of on the slow side :? for phototube/diode pulses that may be only a few ns.
We'd have to fish around for a good display - the average LCD panel meter is far too large for an altoids tin all by itself -- too thick. In our case, the phototube inputs were just uP counter pins, as phottubes have a nicely "loud" output for that.

At any rate, I'd use a uP there, and there are ones so small they might as well be a SMD opamp in terms of board space and power consumption, but give all these other features that are nice to have and make it possible for a lot of other parts to go away -- they even make pics with opamps and comparators *inside* for things like this. And calibrated internal oscillators so you get accurate times as needed. In sizes similar to a pencil eraser and only drawing a couple of milliamps. And oh yeah, they're cheap as can be.

I'd prefer a real counter to just a numeric readout of average detector current or a bargraph, however, and with anything decently fast (almost any scintillator and diode) you could have resolved pulses to a level of radiation you'd not want to be around with this in your hand, and well above -- it would saturate in a reactor core, but I don't think we'd design for that one! 10-100k CPS is easy for example, and that's a bit above where I'd want to be. I have the shop geiger pull the power plug on my other gear if it sees 10k CPM -- 60 times less than the lower number above. I hit that number with a little U02 glued into the hole of a 3/8" washer sitting on the detector, a static master brush source, or many other things. If you were getting that much whole-body -- I dunno about you, but I'd run away!
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: ? Community Altoids Scintillation Det. Project

Postby Jerry » Thu Jul 22, 2010 8:22 pm

These would be the guys:
Http://www.perkinelmer.com/Product/Prod ... 0Gamma_245
Http://www.perkinelmer.com/Product/Prod ... 0Gamma_245
http://www.perkinelmer.com/Product/Prod ... 0Gamma_245

Not as nice but a maybe:

http://sales.hamamatsu.com/en/products/ ... 4-1010.php

Dont know how much, but I am willing to bet it costs more than the rest of the thing put together.

I have a 1mm x 10mm APD. I cant get specs as it was a custom part. :(

Really pretty to look at though!
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Re: ? Community Altoids Scintillation Det. Project

Postby lutzhoffman » Fri Jul 23, 2010 4:07 am

Hello:

Just for fun check this little $1200 gadget, the end result is quite impressive, this device is what gave me the idea to pack an "improved" version into an Altoids can. 1 uR/ Hr sensitivity is pretty good. Reference BGO: Yes it can work with silicon devices, but you end up with 25% (or less) of the total sensitivity, when compared to the longer 550nm wavelength of CsI(Tl), and especially when considering the much higher total scintillation efficiency of CsI(Tl), it just looks better. I started with the idea of using the Ebay BGO product, but after doing some research I was sold on CsI(TL) big time. CsI(Tl) scintillator is also not hygroscopic, and fragile like its NaI(Tl) cousin, and it is almost "plastic" in nature, with no fracture problems, real tuff stuff. Yes you have to keep it out of water, or direct condensation, but with our vacuum experience, sealing it would be simple for us, plus it already comes sealed in Al, or even Be with a glass or sapphire window, in a 1cm, and 1.8cm size from China. St. Gobain also uses it in their extreme condition probes, which are designed to go down hot bore holes on oil rigs, it is also the scintillator of choice in solid state surgical gamma probes.

The posted Perkin Elmer product link has my full attention for the time being.

Reverse engineering of a successful commercial product is sometimes a nice starting point, because it often saves you from having to re invent the wheel so to speak. Below are the specs for the unit which I thought represented a good starting point. I think the detector /scintillator setup in it is pretty good and reasonably well engineered, the improvement I think would be in making the readout more useful for folks like us, who enjoy the science portion a little more :D

[i]Gamma Radiation Detector & Dosimeter in One

* Overview
* Features
* Specs
* Applications
* Downloads

The GammaRAE II R is a gamma radiation detector and full-range dosimeter in a single instrument. Designed specifically to meet the needs of first responders, it has the rapid response of a detector and the accurate dose measurement of a dosimeter.

Key Features

* Sensitive CsI scintillator for excellent search capability and fast response
* Energy-compensated PIN diode sensor for high dose rate range and accurate dosimeter capabilities
* Prominent visible, audible and vibration alarms
* Alerts first responders to radioactive threats
* Accurately measures accumulated dose to the wearer
* Immersible in water for easy decontamination
* Top-mounted, invertable display
* Continuous digital readout in Rem/hour (μR/h & mR/h) or in Sievert/hour (μSv/h & mSv/h) and counts per second (cps)
* Two operation keys, simple intuitive programming
* Long calibration life
* Two AA Alkaline batteries last up to 600 hours
* Large, 30,000-point datalog capacity, downloaded via cable-free Bluetooth® connection

Sensor
Radiation Sensors 3cc CsI (TI) with Photodiode (Low channel) Energy-Compensated PIN Diode (High channel)
Energy Range 0.06 to 3.0 MeV
Dose Equivalent Rate (DER) Range for 137Cs 1 μR/h to 600 R/h (0.01 μSv/h to 6 Sv/h)
Accuracy of DER ±20%
Dosage Range 1 μR to 999.9 R (0.01 μSv to 9.9 Sv)
Background Reference Background level reference set automatically on start-up (Search Mode only), plus user-initiated as needed
Calibration None required. Periodic functional test recommended using 1 μCi and 16 μCi 137Cs check sources. Factory calibration available if needed.

Not bad ehhh.....Now a built in CdTe spectrometer, now that would make a cool addition as well. I did also find some interesting references to the new SiPMT technology, which is a silicon device operating in a high revers bias Geiger mode. In a nutshell I just have a feeling that there is some real interesting new stuff out there in the silicon world, but we do not see it as much because we are wearing our familiar PMT colored glasses. LaBr3 is real cool also with 2 x the resolution of NaI(Tl) for spectroscopy, sadly for good SS efficiency it would need to be shifted to something longer than 380nm, plus try to get some LaBR3? So what do you guys think, not interested? or worth at least talking about? No worries, my ego is not in this so if it does not generate any interest, then it was simply not meant to be. Take care......Lutz
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Re: ? Community Altoids Scintillation Det. Project

Postby Doug Coulter » Tue Jul 27, 2010 1:10 pm

I don't think I'm wearing phototube colored glasses, as much as we are all wearing "can I get these things" glasses, which is appropriate in all cases. I do know ways to get phototubes to run very low power input, and they are cheap and easy to get -- that's where I'm coming from on that. One example in an old RCA book is simply to make a CW multiplier at about 100v a stage, and drive all the dynodes off the taps of it -- gets rid of all the dynode resistors and their wasted power.

If we can do it with silicon, that's fine too. Kind of depends on some other things - I think we need to nail down a better spec before we talk too much about cramming it down into an altoids tin.
I will say this -- by far the most sensitive counter I've ever seen is a 2x3x1" block of scint plastic on a photomultiplier. It's a bit large to fit in a pocket, though (about the size of a brick). Nothing beats raw square inches for sensitivity. The plastic scint also sees fast neutrons easily. They knock H atoms out of the plastic which then generate light from their energy. Unless someone says otherwise, I don't think we're doing gamma spectroscopy with this thing so we have a much wider choice of possible scintillators?

But without a spec, we don't know what sensitivity we really need, either. Not hard to make a mini-geiger counter at all, sort of numb but good enough to see cosmic background and anything "hot" for example. That little pancake tube Geo used to sell in a nice little box -- it has room in the box for all the rest and would fit in a pocket, barely. Those give me a decent count rate on background cosmics, and are what I use to see activated silver and suchlike -- plenty sensitive for that sort of thing, and they even have a calibration curve for fairly low energy X rays (as in hospital X ray machine energies).

We should probably be doing this in the detection/metrology forum first -- I had meant this one to be things already put into a form you can easily put in a shirt or pants pocket. Or that's what I meant at the time, as I got the idea from Joe Sousa who I'm hoping will post some of the amazing things he's done. That last word is the key, unless we want to change the definition here --

Let's restart this up at
metrology

Then, when we've made some, the result goes here....
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: ? Community Altoids Scintillation Det. Project

Postby lutzhoffman » Fri Jul 30, 2010 4:11 am

Sounds good Doug, I get the drift of your meaning, you do have a valid point in the sense that there are many very small PMT's which would fit into only a slightly larger space. Combine this with the lower noise of the PMT, spectroscopy capability, and bingo a better idea I now agree. Upon further research I also found a similar size commercial micro PMT unit. The added bonus is an NaI scintillator, and this material is easy to find, reference you other valid point. If for some folks the physical properties of NaI were a problem, then CsI(Na) not (Tl) could always be used instead. For me personally I do not think that it is to hard too seal the NaI material. This new unit is made by Thermo-Scientific it is the: RadEye PRD-ER, here are the specs:

Specifications for RadEye PRD-ER
Application[s] Interdiction and response
Detector[s] NaI(Tl)-detector with high-quality microphotomultiplier
Measurement Ranges 1µrem/h to 10 rem/h (0.01µSv/h to 100 mSv/h)
Energy Range 60 keV to 1.3MeV, excellent detection from 30 keV
Count Rate For Cs-137 (662 kev): 1.5 cps per µR/h

For Am-241 (60 kev): 30 cps per µR/h

For Cs-137 (662 kev): 150 cps per µSv/h

For Am-241 (60 kev): 2000 cps per µSv/h
Overrange Threshold 10,000 rem/h (100 Sv/h)
Unit[s] cps, R/h, rem/h, Sv/h
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Re: ? Community Altoids Scintillation Det. Project

Postby Jerry » Sat Jul 31, 2010 1:47 am

I have mentioned this to Doug before, I have a couple of these little guys I have been wanting to make a detector with:

http://sales.hamamatsu.com/assets/pdf/p ... series.pdf

Came out of end point detectors from a plasma etch system. I need to see if they work first though. Bad thing about them is the small window.

I am mostly interested in alpha, beta, and x-rays. Thinking about getting some of the scintillating plastic from Geo over on the geiger yahoo group.
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Re: ? Community Altoids Scintillation Det. Project

Postby Doug Coulter » Sat Jul 31, 2010 7:29 pm

Guys -- take this to the thread in metrology linked in my previous message. This hasn't been built to put in an altoids tin -- it hasn't even been designed or built at all.

This forum is for *finished* projects.

Small windows aren't an issue with phototubes if you just do your optical design right. The ones you have though, are advertised to handle "high light levels" so they
weren't for single photon counting probably.
Posting as just me, not as the forum owner. Everything I say is "in my opinion" and YMMV -- which should go for everyone without saying.
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Re: ? Community Altoids Scintillation Det. Project

Postby Alex Funk » Mon Aug 22, 2011 10:58 am

[snip]
Moved to Physics/Metrology/Small radiation detector
[/snip]
Last edited by Alex Funk on Tue Aug 23, 2011 2:01 pm, edited 2 times in total.
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