Radiation survey equipment, any exceptional values?

[cdev]

After reading about the remarkable screwup at Chernobyl, I have been thinking that I should add some kind of radiation monitor to my test equipment collection, mostly so I can scan our food for radiation in the event of a nuclear accident or whatever.

I cant spend the $600 that my friend spent on her radiation meter. What is available for less than that? In particular I want to be able to catch alpha emitters on food.

I cant trust governments to tell us the truth. For economic reasons, Japan didnt tell Japanese when locally grown food became unsafe after Fukushima.

[PartialDischarge]

I have a terra-p meter, very nice and sensitive.

[Louiebluey]

After reading about the remarkable screwup at Chernobyl, I have been thinking that I should add some kind of radiation monitor to my test equipment collection, mostly so I can scan our food for radiation in the event of a nuclear accident or whatever.

I cant spend the $600 that my friend spent on her radiation meter. What is available for less than that? In particular I want to be able to catch alpha emitters on food.

I cant trust governments to tell us the truth. For economic reasons, Japan didnt tell Japanese when locally grown food became unsafe after Fukushima.

It sounds like you probably want an assembled instrument, but here is a really interesting possible alternative project approach.  Thanks, I've been looking for a Si detector project, and just found this one while doing a bit of googling.  I just ordered some boards and parts to give a try!

DIY Particle Detector: https://scoollab.web.cern.ch/diy-particle-detector

alpha-spectrometer: https://kitspace.org/boards/github.com/ozel/diy_particle_detector/alpha-spectrometer/

[TurboTom]

Scanning food for contamination is a tricky job. Since the acceptable levels are quite low, depending on the amount and geometry of the food sample, and the stochastic nature of the radioactive decay, you need a lot of "events" to be able to quantify the amount of radioactivity in your food. If the food contains considerable amounts of potassium, the natural amount of radioactive ⁴⁰K may also affect your readings and deliver a positive reading that's not the result of contamination.

This means, if you want to be able to test food samples within a reasonably short time to be able to decide if it's edible or rather not, you need the highest possible sensitivity, and in order to identify the radioactive isotopes, you would want a gamma energy discrimination. In order to shield all this from external radioactivity, you'll want to house the whole sensor / sample setup within a substantial lead cabinet.

All this is pretty expensive if it's a professional system, but DIY solutions are possible. You'll be looking for a scintillator (e.g. Thallium-doped Sodium Jodide) in decent shape (this stuff is highly hygroscopic) coupled to a photo multiplier or a large surface, highly sensitive semiconductor detector (all this the bigger the better because you want the gammas to deposit all their energy inside the scintillator and not have them leave the crystal after partial deposition, and you want all the light generated in the scintillator to reach the photosensitive layer of your detector), amplifier with pulse shaper and a pulse amplitude analyzer to generate a histogram of the signal. The latter can be a PC soundcard with a freeware program, but there are other solutions with a Raspberry PI Pico or similar single board computers.

Btw, today's professional food contamination analysis systems use high-purity, cryostatically controlled germanium (bulk) detectors, providing a much better energy resolution than any scintillator, albeit at painful cost...

You can use highly sensitive geiger counters for some superficial food scans and you'll probably be able to identify "really dirty" samples, but it takes time and you hardly get any information on the isotopes that cause the contamination. But care has to be taken: There are isotopes that cannot be detected with a scintillator since their decay almost doesn't produce any gamma radiation (Polonium 210 is such an example). Yet if you're looking at the aftermath of a nuclear accident (power plant) or worse..., you are primarily looking for Iodine 131 in the first few weeks after the "event" and later on mainly for Cesium 137 and Strontium 90 which all emit some gamma radiation in their decay chain (some as bremsstrahlung as a result of their beta decay).

Small, personal Geiger Counters or Dosimeters are very useful for identifying general increased background radiation or for identifying radioactive houshold items (watches, alarm clocks, fiestaware) or minerals, but most of the inexpensive instruments cannot be considered useful for any kind of quantitative analysis since their detectors aren't energy compensated. Depending on the type of detector tube used, they can be useful for identifying the type of radiation though (alpha, beta or gamma).

It's advisable to define your requirements, do some reading and then decide what solution best suits your needs.

Good luck and all the best,
Tom

[Brumby]

It sounds like you probably want an assembled instrument, but here is a really interesting possible alternative project approach.  Thanks, I've been looking for a Si detector project, and just found this one while doing a bit of googling.  I just ordered some boards and parts to give a try!

DIY Particle Detector: https://scoollab.web.cern.ch/diy-particle-detector

alpha-spectrometer: https://kitspace.org/boards/github.com/ozel/diy_particle_detector/alpha-spectrometer/

I had a look at that - and while it does have some potential, there are a couple of things of which people should be aware....
* The main measurement process is designed to have a sample placed next to the detector inside a metal case.
* The metal case is required to act as a Faraday cage, as the circuit is very sensitive to RFI.
* The case also is required to block out all light, as the circuit is very sensitive to any extraneous light.

This limits the ability of the unit - especially the alpha detector version - from operating in an open environment.  The Faraday cage and light exclusion requirements make this truly problematic.  Mention is made of adding a "radiation window" - but that is covered with provisos and caveats.

[TurboTom]

Detecting or "spectrographing" alphas is a problem of its own. Since this type of radiation doesn't reach longer than several centimeters in the air, and their penetration capability of solids is virtually not present, one can do such spectroscopy using off-the-shelf large-area PIN photodiodes (obviously the types without encapsulation) as detectors -- the alpha particles will be completely absorbed within the junction, but, on the other hand, the sample will have to be placed in very close proximity to the sensor inside a "black box" to prevent any light from entering. Ideally, the enclosure should be evacuated for best spectral resolution since if the alphas have to travel even a small distance through air, they will lose some of their energy.

Alpha detectors (alpha-capable GM tubes) usually feature an ultra-thin window made of mica. This makes these tubes highly fragile. A few years ago, I designed and constructed an aßy-capable GM counter around a large-area tube equipped with a mica window of ~15µm. The tube isn't specified to be alpha-sensitive by the manufacturer since this window is already a little too thick(!) for this purpose. Consequentially, the alpha radiation of an Americium-241 "pill" out of a smoke alarm won't be detected unless I approach the detector tube window by 10mm or closer. I published some information on this contraption on a (geman language) "Radioactivity" forum.

The sensitivity of the windowed GM tubes cannot be over-estimated! The window must never be touched and it's not unheard of that even a substantial ambient atmospheric pressure change may crack it (i.e. air transport, fairly distant explosion). This should be considered when looking for such instruments if ruggedness is an issue.

[Louiebluey]

I only just started to read the documentation, including his academic paper (linked to the project site).  Here is a figure from the paper, where he has to break the glass on the windowed detector.  Hope I can do it more neatly without cracking the die. (note there are two different versions of the project, one with diodes (silicon PIN photodiode, Osram Opto, BPW 34 FA), the other with the windowed Si detector (silicon PIN photodiode, Osram Opto, BPX 61))

It may be little more than an advanced toy, but it's the first decent DIY project I've seen with a Si detector, been wanting to try one of these for some time.

[TurboTom]

I only just started to read the documentation, including his academic paper (linked to the project site).  Here is a figure from the paper, where he has to break the glass on the windowed detector.  Hope I can do it more neatly without cracking the die. (note there are two different versions of the project, one with diodes (silicon PIN photodiode, Osram Opto, BPW 34 FA), the other with the windowed Si detector (silicon PIN photodiode, Osram Opto, BPX 61))

It may be little more than an advanced toy, but it's the first decent DIY project I've seen with a Si detector, been wanting to try one of these for some time.

The Hamamatsu S8553 or the S3584-09 would be nice... No "metalwork" required and a huge active surface! 

[masterx81]

If you are in europe, i've bought this one:
http://arduino-geiger-pcb.blogspot.com/2017/09/enclosure-for-3d-printing-for-geiger.html
And seem quite nice. I think that is the best bang for buck. Works as it should, the SBT-11A isn't the best sensor, but for that moneys you can't get better. Tested it with thoriated TIG rods and all works.

[David Hess]

Look for a Geiger counter with an exposed window into the Geiger tube so that it can detect alpha particles.  In combination with air filtered through a medium like cheesecloth, it can be used to detect radon in your basement or atmospheric contamination from a distant nuclear accident.

Here is an example of what I would look for:

https://radiascan.com/products/dozimetr-radiascan-701a/

I don't know if it is even practical to scan for (α) because that's not often going to emit anything penetrating even a small layer of anything, right?

Geiger counters with an exposed window into the tube can detect alpha particles just fine.  The window in the Geiger tube is necessarily delicate so a screen is used to protect it from physical damage.

[Louiebluey]

Well, you got me chatting with Hamamatsu, but those two types are a bit pricey:
S8553, qty: 1-4 Price: $1102.00
S3584-09, qty: 1-4 Price: $1252.00

Interesting, they seem to have metal can models similar to the Osram BPX61, with taped on covers, specifically to allow users to remove the glass window.  I will post later if I get more information.

I could design a new front end for a larger detector (to avoid the ultra high gain of the CERN board), but $1k kind of kills it as a hobby project.

[Bud]

@OP and you will be walking in a grossery store pointing that thingy at things? How long it is going to be before security staff will approach you ?

[Louiebluey]

funny, I wonder anyone ever does a spot check anywhere in stores. 

I would think the risk would be higher in a home store from some metal products made from contaminated recycled scrap.

For food, I think TurboTom explained well that most testing has to be done over some relatively long period of time.  So, probably no instrument pointing, at least with an over the counter detector, is going to pick up anything meaningful.  Seems the really sensitive detectors, which probably include spectrometers, cost $10k or more.

[Louiebluey]

So cool the way the project site fills the shopping cart at DigiKey, and how they ship to experimenters the same way they ship parts to a national laboratory!  I have a lot of the parts, but wanted to try the full kit experience.  Pretty impressive.  Boards due in next week, but not sure when I will get to it.  I don't know about the design yet (the ultra high gain and shielding, etc.), but so far CERN certainly does a project with flare.