More thought on DYI food monitoring with single channel spectrometry

Submitted by Anonymous on Tue, 2011-07-12 16:00

Berkeley Radiological Air and Water Monitoring Forum

Posted by by BC 7/12

I posted about this last week and dchivers was kind enough to post some good info on how this could be done. But this morning I got to thinking that maybe full range spectrometry is unnecessary for our purposes here. It would be adequate to just test for Cs-137, right? Basically, at this point the Cs-134 and Cs-137 activities have been roughly similar, so I think we can imply Cs-134 activity from Cs-137 activity.

So a quick google, and this video:

http://www.youtube.com/watch?v=kO0fdvoUmKU

Could this approach work for food testing? Essentially, a detector is connected to a rate meter and then dialed in to optimize detection of a known substance (in this case, Cs-137).

If this were coupled with a "lead cave" (I am thinking 1" plywood framework, surrounded by lead shot on all sides), a miranelli beaker, and a computer to take a count, could you make a reasonably accurate measurement? Also, is the cave even necessary if we are just looking for Cs-137(or would "background/legacy" cesium screw that up)?

I have read so much about people trying to make measurements with geiger counters, and hell, I've done it myself, but it's a joke for the levels we are dealing with. I mean, CPM measurements are in no way qualitative and that is what we need here - we are not looking for radiation , we are looking for radiation from Fukushima.

Thoughts? Ideas?

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A couple of comments: The

Submitted by tjaucott on Tue, 2011-07-12 16:51.

A couple of comments:

The detector used in that video is a scintillator, not a Geiger counter. The difference is key, because a scintillator has sufficient energy resolution to identify isotopes, while a Geiger counter does not. We mentioned that we use germanium detectors -- weighing in at at least $10k -- but scintillators are (somewhat) more affordable at a few thousand dollars. Perhaps this gentleman found a cheaper one on ebay!

The difficulty is not whether or not you're looking at the whole spectrum, it's what detector you're using. The guy in that video could've used the same detector but with a computer and multi-channel analyzer, and he'd see the whole spectrum without much additional effort.

The lead cave is still critical. The reason is not because there's a bunch of Cs-137 in the background, but because the background radiation (from uranium, potassium, etc.) will still create some counts in the detector in the Cs-137 energy window. If we were to try this experiment, we could take some measurements with and without the lead, and we'd see the rate go down tremendously with the lead, even though we're only focused on Cs-137.

Tim [BRAWM Team Member]

Thanks Tim. I see some

Submitted by BC (not verified) on Thu, 2011-07-14 11:12.

Thanks Tim.

I see some scintillators on ebay for reasonable prices. So a guy would need a scintillator, a multichannel analyzer, computer, software, cables etc, and a lead cave (which I am envisioning made out of 1" plywood and lead shot). Also, some arrangement to keep the scintillator in the middle of the sample. I know the team is using marinelli beakers, but would a doubled up ziploc

Am I looking at something very difficult to do here? I mean, other than getting the parts and slapping it together? Is there ready to go software for an appliaction like this? And what would you anticipate in terms of resolution (I would think that one would want an MDA no greater than 1bq/kg with a 3 or 4 day count time)?

And hey, for all the rest of you guys, does someone else want to jump in on this? Everyone's clamoring for more testing. I think that it could be done, and would be happy to participate with time and or/money.

Tim- Thanks. And my bad, it

Submitted by BC (not verified) on Tue, 2011-07-12 16:58.

Tim-

Thanks.

And my bad, it was you, not dchivers, who posted on the other DYI thread.

Another question - have you ever seen a home testing set-up? I realize that Fukushima is a recent "development" but it strikes me that there must be guys out there making and using testing set-ups in their home workshops.

Well, dchivers responded as

Submitted by tjaucott on Wed, 2011-07-13 21:13.

Well, dchivers responded as well!

Interesting question; I dunno how many people out there would just happen to have a scintillator lying around (although apparently that guy did!). When you add in the required electronics, it's a pretty unique hobby for the lay person to have.

As a further thought, if you did get a hold of a scintillator, you'd definitely want to get a multichannel analyzer and look at the whole spectrum. This is because the mediocre resolution will hurt your detection limits otherwise. In a sense, the high-purity germanium detectors are "easier" to use, in that the isotopes are so much simpler to identify. With a scintillator, there's more detailed analysis required to get a good result.

Let us know if you get a hold of a detector!