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Registered Member #3429
Joined: Sun Nov 21 2010, 02:04AM
Location: Minnesota, USA
Posts: 288
Patrick wrote ...
if you want to detect the presecnce of atomic nuclei in milk a GM may not be sensitive enough to make a health decision, i think you would need to consider a scintillator. I could be wrong, but i think the best way to detect radioactive elemental contamination is with traditional Mass-Spec-GC, but youll need to be an ace chemist to use one.
Most scintillators that I've seen use a Sodium-Iodide detector that's housed in a thick metal cylindrical body, which is only sensitive to gamma rays. In order to detect beta particles that many radionuclides emit, you would need an ionization chamber with a thin metalized mylar window. I happen to have such a detector (often referred to as a "pancake" detector. Not because it detects pancakes, but rather because of its disc-like shape.)
And the only way to know for certain what TYPE of radioactive isotope you are measuring is to view its spectrum on a Multichannel Analyzer (MCA). Unfortunately, most MCA's do produce a spectrum, but it's up to the user to determine what isotopes are being detected by deciphering the number and position (KeV) of the peaks within the spectrum. Some very sophisticated MCA's include software that can search the peaks and display the actual names of the isotopes. There are some really cool hand-held MCA's that the border patrol people use, but they are more expensive than the average citizen can afford.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Xray wrote ...
And the only way to know for certain what TYPE of radioactive isotope you are measuring is to view its spectrum on a Multichannel Analyzer (MCA). Unfortunately, most MCA's do produce a spectrum, but it's up to the user to determine what isotopes are being detected by deciphering the number and position (KeV) of the peaks within the spectrum. Some very sophisticated MCA's include software that can search the peaks and display the actual names of the isotopes. There are some really cool hand-held MCA's that the border patrol people use, but they are more expensive than the average citizen can afford.
Yes I was thinking of these devices too, but couldnt remember what they were called. Also I wonder what their lower detection limit is? I know that some MS-GC's can go to femtomoles.
I noticed in a demonstration, that the border guards were able to detect even granite kitchen counter tops, in their crates with isotopic composition being read out.
Also, I did not mean to imply that a scintillator could identify isotopes, I meant that he should be interested in overall emitted radiation above background, thus using a sensitve scintillator rather then the primative GM. Your point on Beta emission is well taken as well, didnt think that far out yet. I may have been drinking.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Patrick wrote ...
I did not mean to imply that a scintillator could identify isotopes.
What about Gamma Ray Scintillation Spectroscopy, with pulse amplitudes sorted by an MCA, a very common setup?
As for 'homeland security,' you can't beat the muon-based passive nuclear materials detectors as a means of spending large sums of public money. Energetic cosmic rays transit shipping containers, and entire ships, whizz through any lead shielding, as they like to do, and occasionally interact with any concealed uranium or plutonium creating a unique (and readily detectable) spectrum of characteristic photofission products.
Here is one paper of many: Tomographic Imaging with Cosmic Ray Muons
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Keep it on topic guys, enough of the political ranting. Yes, we know the government is crazy, but somehow there is still food in the stores and nobody shooting at us.
This is the worst possible time to buy a Geiger counter or other radiation detector, because the Fukushima scare has driven the prices up. You'll end up paying over the odds for a piece of junk.
I'm tempted by the Soviet DP-5A with its beautiful bakelite case and free cobalt-60 check source. If the apocalypse never comes, it'll still be a great conversation piece.
The point made about sunlight is true. UV is bona fide ionizing radiation that causes DNA damage. Probably a far higher risk of cancer than any radiation from Fukushima.
Registered Member #543
Joined: Tue Feb 20 2007, 04:26PM
Location: UK
Posts: 4992
Steve McConner wrote ...
This is the worst possible time to buy a Geiger counter or other radiation detector, because the Fukushima scare has driven the prices up. You'll end up paying over the odds for a piece of junk.
I'd been meaning to buy a Russian SOSNA twin tube GM beta/gamma dosimeter - probably the best pocket-sized GM instrument available anywhere, die-cast aluminium case, demountable beta shield and so on - and was shocked to see that the price had gone up from about £100 to £1000!
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
The original question was "is it time to buy a geiger counter yet? It is currently a bad time to buy a Geiger. There's a huge demand from nervous Nellies who don't realise that, as far as detecting contaminated food is concerned, Geigers are useless. This spike in demand has been matched by a rise in price. Wait a few months until those people realise they wasted their money and try to sell the counter on eBay and buy one then. It won't have had much use and it will be a lot cheaper.
Registered Member #1321
Joined: Sat Feb 16 2008, 03:22AM
Location:
Posts: 843
wrote ...
Keep it on topic guys, enough of the political ranting. Yes, we know the government is crazy,
That's much too generous. I prefer the phrase "criminally insane"; and I think even that's too mild. But to stay on topic, I'll end it at that.
wrote ...
but somehow there is still food in the stores and nobody shooting at us.
Wait.
wrote ...
This is the worst possible time to buy a Geiger counter or other radiation detector, because the Fukushima scare has driven the prices up. You'll end up paying over the odds for a piece of junk.
You're certainly right about that.
wrote ...
I'm tempted by the Soviet DP-5A with its beautiful bakelite case and free cobalt-60 check source. If the apocalypse never comes, it'll still be a great conversation piece.
LOL!
wrote ...
The point made about sunlight is true. UV is bona fide ionizing radiation that causes DNA damage. Probably a far higher risk of cancer than any radiation from Fukushima.
I just don't think it's a very good comparison. Don't forget human beings actually need some of that low energy ionizing radiation from the sun (vitamin D). And we've evolved natural defense mechanisms to protect us against getting too much, i.e., melanogenesis, (not to mention the natural photo-protective effects of a healthy diet). And lastly we know how to deal with the sun...we know where it is and isn't, and how to avoid it if we choose.
On the other hand, as far as I know, we have no use whatsoever for the high energy betas of the radiopoisons...strontium accumulating in our bones, iodine in our thyroids and cesium in muscle tissue or wherever it goes.
Registered Member #193
Joined: Fri Feb 17 2006, 07:04AM
Location: sheffield
Posts: 1022
"On the other hand, as far as I know, we have no use whatsoever for the high energy betas of the radiopoisons...strontium accumulating in our bones, iodine in our thyroids and cesium in muscle tissue or wherever it goes." True, but we still have repair mechanisms that let us cope with it. Whether you thank God or evolution for this is a matter of conjecture, but the fact is that we are quite tolerant. This may reflect the fact that we do need two beta emitters- potassium and carbon, and we have always had to put up with other radioisotopes in our environment. (BTW, we can eat things to get vit D)
Registered Member #30
Joined: Fri Feb 03 2006, 10:52AM
Location: Glasgow, Scotland
Posts: 6706
Yes, it is an interesting thought that one in however many carbon atoms in your DNA is carbon-14. They are going off and blowing tiny craters in your genes at the rate of several per second.
And somehow life goes on. Indeed, Isaac Asimov theorised that this is a major cause of mutations, a case of radiation rolling the dice for evolution. The effect may be horrible for some individual organism who happens to be born with major genetic defects, but it is probably beneficial for the species as a whole.
(Some radiogenic mutations must result in offspring who are extraordinarily brainy, or good-looking, or brilliant opera singers or whatever, but somehow radiation never gets the "blame" for those ones.)
Of course, I agree that hefty doses of radioactive iodine, caesium and strontium and so on are probably not that good for you. The major source of them worldwide is still fallout from the hydrogen bomb tests of the 50s and 60s: Chernobyl and Fukushima haven't matched that on a global scale yet, even if they caused major contamination locally.
Registered Member #2431
Joined: Tue Oct 13 2009, 09:47PM
Location: Chico, CA. USA
Posts: 5639
Steve McConner wrote ...
(Some radiogenic mutations must result in offspring who are extraordinarily brainy, or good-looking, or brilliant opera singers or whatever, but somehow radiation never gets the "blame" for those ones.)
I'd be careful making this (or the Hormesis) argument, the anti-nuclear mafia may come and get you in the night, like the NKVD, KGB, FSB, CIA, NSA, MIB's used to.
I tend to agree that some minimal mutation rate is needed for the advancement of a species and that natural radiation is a part of that process, I'd just rather it not be I who ends up on the "losing side" of a mutation. from my required biology class, I was told that: Of all a population--mutations are a rare occurance, of all mutations only rarely do they have a beneficial result. Or something like that.
If McConnor or I end up at the bottom of the Thames or Sacramento rivers, then you all know who did it.
EDIT: I find it hilariously cruel that an engineering student is required to take biology.
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Is it time to buy a Geiger counter yet?
