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Author: Subject: Recommendations for Geiger Counter or Scintillation Detector
Texium (zts16)
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[*] posted on 16-7-2015 at 09:54
Recommendations for Geiger Counter or Scintillation Detector


I've been considering purchasing some kind of radiation detecting device for doing some future uranium ore hunting and radiochemistry. I went to Google and began looking at various Geiger counters and scintillation detectors, and was very overwhelmed by the sheer number of different ones and the wide range of prices. I honestly have no idea how to determine what kind I should buy. In fact, I don't even know whether a Geiger counter or a scintillation detector would be better for what I need. I was hoping that some of the resident radiochemistry enthusiasts would be able to help me out.



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[*] posted on 16-7-2015 at 11:46


Since Fukishima, there are several models made and sold in Japan.

I got one that says it measures micro sieverts/hour which is very portable, yet very unintersting.

I also got this kit :-
http://www.ebay.co.uk/itm/NEW-NetIO-Geiger-Counter-Embedded-...

which includes an SBM-20U tube.

Other tubes are supposedly supported, although i have no info as to the differences.




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[*] posted on 17-7-2015 at 03:41


In reality, you'd want both. Geiger tubes are sensitive primarily to beta (and alpha if the window is thin enough). The counting efficiency for gammas is very low. On the other hand, a typical [say, NaI(Tl)] scintillation detector is very sensitive for gammas and (for sealed probes) nothing else.

For prospecting I'd recommend a decent scaler (say, Ludlum 14C or Eberline 510; see Ebay) and a pancake probe (good for alpha/beta with a removable beta/gamma shields). The Ludlum scalers are also directly useful (and can be voltage tuned to whatever plateau you need) with a cheap, but sensitive scintillator such as a Bicron 1.12X1.12M3/1.2L (about $99 USD).

For spectroscopy, I use a Ludlum 44-10 2x2" NaI(Tl) with a Gamma Spectacular GS-1100-Pro soundcard MCA & variable PSU...but, that's another story.

O3




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neptunium
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[*] posted on 17-7-2015 at 05:19


if you doing some prospecting you might want the scintillation type they are more sensitive to gamma ray as Ozone pointed out, and most uranium and thorium ore have gamma emission .
this one is very simple yet rugged, perfect for carrying around ...


MINI_Instruments_Radiation_Monitor.JPG - 112kB
for radio chemistry and isotopes identification you`ll need a gamma spectrometer and a alpha spectrometer but thats a different range of prices..




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[*] posted on 17-7-2015 at 06:21


Suggestions are right - you want a sensitive gamma detector for survey work due to their range in air.

All natural ores of uranium and thorium will have accumulated decay chain products that put out strong gammas.

There are quite a variety of radiation detectors available in Japan now, thanks to Fukushima, many marketed to the mass public. The health monitor read-outs(microsieverts/hour., etc.) are less useful than raw click-counting devices.

For close up specimen work I have been looking at Geiger counter kits, of which there are several available from $75-$100 for the counter itself (w/o tube) but you need to assemble them.

A good tube to use is the LND712:
https://www.sparkfun.com/datasheets/Components/General/LND-7...
for $95. It has an alpha end window. With different screens (e.g. thicknesses of aluminum or what-have-you) you can generate some information on the emission profile of a specimen. You need to confirm that the voltage handled by any kit is compatible with that required by the tube you want to use.

It was not until 1928 that the Geiger counter was invented, and the electronic scintillation counter was not invented until 1944, so quite a lot of radiochemistry was done before fancy gamma ray spectometry was available. This is similar to the situation with GLC and HPLC chromatography which are considered essential for chemistry labs today, yet nearly two centuries of successful chemistry preceded them, and the modern hobbyist does quite a lot without.

[Edited on 17-7-2015 by careysub]

[Edited on 17-7-2015 by careysub]
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[*] posted on 17-7-2015 at 09:59


Thank you all for the suggestions! I've been looking over the different ones posted here, and the one that neptunium suggested seems to be the one that is most in my price range. I found a used one on eBay for a good price: http://www.ebay.com/itm/321368691563?_trksid=p2055119.m1438....

I just wanted to make sure though: that detector with that tube will work well for identifying uranium ore? And I don't really need anything fancy for lab work, I just wanted to be able to check for contamination in my lab and on my glassware with it. Sorry that I'm so illiterate when it comes to the specs of these things.




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Ozone
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[*] posted on 17-7-2015 at 15:29


A good scintillator (at proper voltage for the PMT) will detect (decent) Uranium ore easily 1-2 away. So...yes.

Background counts are higher, too, though, so you might want to make sure you can mute the audio output (it's cool at first, but gets old quickly).

edit: Ugh, I just noticed the one you are looking at is a GM...Regardless, it will be more than enough to get you started (presuming it works).

O3

[Edited on 17-7-2015 by Ozone]

Ludlum 14C and Bicron scintillator_01_small.jpg - 281kB calibration sources_01_smaller.jpg - 258kB

[Edited on 18-7-2015 by Ozone]




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[*] posted on 10-11-2015 at 07:08


Another cheap option is this:

http://petapixel.com/tag/scintillator/

someone tested this? Also is used for astrophoto, another very interesting use!!
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[*] posted on 26-11-2015 at 13:58
to Careysub


use 0.1uF for C and 100Kohm for R
runs at about 2000V DC

resistor chain.jpg - 17kB




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[*] posted on 26-11-2015 at 15:29


I will try to find the circuit diagram (from Hamamatsu application notes somewhere)
in which the multi-stage Cockroft-Walton type multiplier gives c100 v per stage (suitable for my photomultiplier, others may differ),
combining multiplier and divider in a low loss circuit.
It is such a useful circuit that it must be quite common.

Edit: found it, or similar, https://www.hamamatsu.com/resources/pdf/etd/PMT_handbook_v3a...
page 96
P.S. increasing capacitance value of the capacitors drawn in the diagram in the right hand 'column' decreases ripple voltages.
P.P.S. a worthwhile reference if you are considering using a photomultiplier.

[Edited on 26-11-2015 by Sulaiman]

[Edited on 26-11-2015 by Sulaiman]
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[*] posted on 26-11-2015 at 16:45
Scintillation Probes


Neptunium's post is in connection with a project I have started for building scintillation probes and systems.

Currently I am using a nice kit put together by "iradinc" on eBay, using a 3" Hamamatsu R10133 PMT Photomultiplier Tube, and a 3"x2.25" plastic scintillation block. it is intended for sweeping along the ground for field surveying, so it needs to be rugged. I would be using it with a Ludlum 2221 rate meter/scaler.

I already have a Ludlum 44-2 gamma detector scintillator, 2.5 D x 2.5 cm Nal crystal.

http://www.ludlums.com/component/virtuemart/area-monitoring-...

I am also interested in experimenting with gamma spectroscopy, and trying a cheap set-up seems the way to begin.
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[*] posted on 28-11-2015 at 16:54


What is the recommended procedure for coating the scintillation block/PM tube interface?

I have experience doing oil separated achromatic lenses - there you just put a drop of oil in the concave lens surface, place the second lens on top and wait a day or so for the film to migrate to the edge. If it does not, you can always separate them and try again (and it is easy to see).

With the thicker optical "grease" and the fact that you can't see how even the the coat is, thinks look a little trickier.

My plan was to make a ~quarter sized smear on the PM tube (as even as I can), heat the plastic block up to maybe 60 C, and place the tube on top with a bean bag weight, and wait for the stuff to migrate to the edge. I am not using this probe for spectroscopy, just pulse counting, so I imagine the requirements aren't as stringent.
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[*] posted on 8-12-2015 at 19:09


A few useful PDF's I have accumulated, size too great in total for one post.


Attachment: Photomultiplier_Handbook.pdf (4.2MB)
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Attachment: pmtinfo.pdf (19kB)
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Attachment: scintillation_probe.pdf (99kB)
This file has been downloaded 296 times

Attachment: ScintillatorsData.pdf (1.5MB)
This file has been downloaded 327 times




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[*] posted on 8-12-2015 at 19:41


I think the values in neptunium's circuit should be looked at. 0.1 uF is going to give a somewhat slow time constant, especially for NaI/Tl, and using 100K resistors gives rise to excessive current flow and therefore more noise than necessary.

Attachment: Scintillators.pdf (3.9MB)
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Attachment: dt590_to_nai.pdf (538kB)
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Attachment: Amperex_1958.pdf (743kB)
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Attachment: xp2102data.pdf (83kB)
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However the reason I am posting is to see if anyone can answer a question. I have found a couple places that can restore old NaI/Tl crystals that were yellowing/shrinking, yet charge too much for me to have it done. I doubt either one would provide their secret methods, I know slow careful heating is involved. I am wanting to save a project I put much effort into which ended up going nowhere due to a less than honest seller. Twice I purchased a great looking end on mica window tube for $80 each and both were useless. I used a case from a CDV700, built a board for the HV power supply and analog circuitry, a regulator so I had clean voltage sources to run a blue 16x2 LCD and Arduino Mega 2560, with four 18650 Li-ion batteries. Even added a regulator so I could just plug in a wall wort and recharge the 12 volt Li-ion battery pack. All in all a very great looking project. Problem is both tubes have lost their quench gas over the years through the mica windows so no matter how carefully adjusted and regulated by a very good circuit I designed the NOS tubes just go into avalanche when I get in the range for detection. Put simply the seller ripped me off for $160 total on these tubes leaving the entire project DOA. So I finally decided to use the PM tube - NaI/Tl assembly I salvaged from a 111B scintillator (the model that looks like a cool chrome ray gun). However the trouble there is dried out optical coupling and yellow crystal. I have the optical grease of the proper type so all I need to do is fix the crystal and remount it, and do a little redesign on the high voltage analog section. If I had received good GM tubes as advertised this project would have been a done deal almost 2 years ago. I had intended one to be a spare or possibly a whole new project. Appears the best low cost way to salvage my effort and money is to just build a scintillator out of this project. Assuming I can learn the proper way to restore my crystal without harming it. Anyone have useful information on the process?

Just remembered I had in the beginning posted some pics of this project before all the work was done and before the digital display + Mega had been added. You can see one of the two defective tubes the ebay seller sent me. Didn't work due to quench problems so hoping to get lucky on NOS I yet again risked $80 as only he had this type tube and I searched a long time. Had to take the risk to justify the effort building this project, I was finished with all work but the tube was a failure.

http://www.sciencemadness.org/talk/viewthread.php?tid=28985

Attachment: gamma.pdf (520kB)
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Attachment: NaI(Tl) Data Sheet.pdf (275kB)
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Attachment: Refurbishing an old but special large detector.pdf (2.6MB)
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This last file is useful for information but no way would I be sawing my NaI/Tl crystal. Having suffered from Tl poisoning decades ago I find creating a pile of the dust moronic at best unless one likes to lay in bed at night soaking in sweat for a very long time. Also the purpose of the optical grease is to aid light coupling and creating a surface looking like the craters of the moon on a microscopic scale is not a good idea. Not to mention polishing the surface is yet another source of Tl poisoning. The amount that can do serious long term harm is extremely low. Therefore I advise do not do what this person did even if it did seem to work for him.


[Edited on 12-9-2015 by IrC]




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[*] posted on 12-12-2015 at 04:30


On my comment about the PM circuit values posted previously, I suggest this image be studied.

feu-31-divider-pulse-amplifier-electrical-circuit.JPG - 71kB

Source:

http://www.rhelectronics.net/store/simple-homemade-diy-gamma...




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[*] posted on 5-2-2017 at 23:25


Quote: Originally posted by careysub  
What is the recommended procedure for coating the scintillation block/PM tube interface?

I have experience doing oil separated achromatic lenses - there you just put a drop of oil in the concave lens surface, place the second lens on top and wait a day or so for the film to migrate to the edge. If it does not, you can always separate them and try again (and it is easy to see).

With the thicker optical "grease" and the fact that you can't see how even the the coat is, thinks look a little trickier.

My plan was to make a ~quarter sized smear on the PM tube (as even as I can), heat the plastic block up to maybe 60 C, and place the tube on top with a bean bag weight, and wait for the stuff to migrate to the edge. I am not using this probe for spectroscopy, just pulse counting, so I imagine the requirements aren't as stringent.



Yes it is very tricky. I had a lot of trouble with that interface. EBay has this optical grease for sale pretty cheap but very difficult to get a clear coating between the crystal and the PM tube... I had good results with baby oil but it always evaporate after a while. You might be on to something with some form of wax...
It is vitaly important it is to have the best optical connection as possible for spectroscopy otherwise the spectrum looks like one big ugly smudge




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[*] posted on 16-3-2017 at 17:29


Model car diff heavy silicon grease can be used as optical grease
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[*] posted on 27-6-2017 at 00:28


Quote: Originally posted by zts16  
I've been considering purchasing some kind of radiation detecting device for doing some future uranium ore hunting and radiochemistry. I went to Google and began looking at various Geiger counters and scintillation detectors, and was very overwhelmed by the sheer number of different ones and the wide range of prices. I honestly have no idea how to determine what kind I should buy. In fact, I don't even know whether a Geiger counter or a scintillation detector would be better for what I need. I was hoping that some of the resident radiochemistry enthusiasts would be able to help me out.

For a nice, cheap Geiger counter use the GMC 300E +. For something more rugged, and with a probe try a Ludlum (expensive), or maybe get an old CD V-700.
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