Increasing background anyone?

This is bound to get mixed up with things in Electronics, check both. Physics-specific stuff here, mostly.

Increasing background anyone?

Postby Doug Coulter » Mon May 23, 2011 10:20 am

I've been noticing increased background readings over the past few weeks here in my lab, which I'm having trouble explaining -- none of our sources have been "out loose" and this extends to more than one building we can carry our portable counters to. The increase is hard to quantify without better record-keeping than I've been doing, and inside the normal variation range, but for one thing - in the normal variation, we also see the odd low count (ten second periods) and those are gone entirely.

For example, in ten second counting interval, we'd see a range of about 60 to about 120 cpm. The extreme numbers would be more rare, but in a given day, you'd see some of both, with a lot in the middle. Now it seems I never see less than 100, and see 150+ a lot more often. Obviously this is somewhat disturbing. We did see a count increase on collected snow-melt just a few days after Fukishima, which went away quick, sadly before we got the gamma spec going to see if it was iodine -- it's gone now from our rain collection anyway (I think, next time we get rain, I'll check again).

So, we normally see a diurnal variation in cosmics - after dawn and before dusk it's hottest here. And of course, some we've traced back to solar weather.

Anybody else been running detectors and notice this, or am I perhaps looking at some local phenomenon? It's not just in the fusor lab, but all over my land - which is large and mostly forest and fields.

I'll try to get a sample and check it with the gamma spec to identify what it might be, but this is complicated by the fact that the bedrock around here is hotter than "normal", and to get low backgrounds in the lab I use the second floor for measuring to get away from that. This is one reason we look at rainwater - it didn't come from here, but surely does wind up in the soil.

Edit:
I just recalibrated the gamma spec and took a background upstairs, to compare with one from a couple weeks ago. They line up within the usual errors I think I have due to cal drift, but I'll now do it more carefully and try to get errors to nearly zero -- it's a real sensitive function of just how I do that, but I'm seeing nothing important different -- in gamma, which isn't what my pancake geiger is most sensitive to. The usual high end stuff from cosmics -- check. The usual mid band background which is pretty random (no peaks per se) check. There is some difference in the real low energy range, sub 100kv, which is going to require another calibration to really see -- but that stuff is below where a geiger sees well anyway.
No un-encapsulated sources have been anywhere near that pancake detector, so I really doubt something fell into it, but will try with another identical tube that's been in storage and see if I can track this down better.
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Re: Increasing background anyone?

Postby Doug Coulter » Mon May 23, 2011 4:39 pm

Here's some confusing follow-up.
Bkgndcomp1.jpg
600 second background compare on Harshaw 6" NaI

This is two 600 second spectra of background, with the newer one in white. I re-calibrated as close as I could, but I think we can ignore height on the low energy left most peak, it's a real sensitive function of noise just out of threshold. Ditto, any shift probably won't show up in that rightmost one, due to that being where the a/d in the MCA clips (which could be a different place re energy bins depending on tube cal and HV). Less! Yet I checked downstairs, and it's still high there.
Bkgndcomp1.jpg
600 second background compare on Harshaw 6" NaI

This one, taken separately against the same green reference, was let run 130 seconds more to get the basic shapes closer together so I could look at differences. As I said, the left most and right most peaks are noise and cosmics, respectively. It looks to me like the white trace is a little right-shifted to the green, but also that there are some things there that aren't in the green, and also something that is in the green but not here in white -- potassium?

Anybody with experience in these chime in - I'll do a subtraction and try to line match, and recheck the downstairs system which has been, up till now, really stable, and our recent runs weren't going to activate the lab -- nothing special at all.
Attachments
Bkgndcomp2.jpg
Second with longer exposure to get the white scaled with the green older data.
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Re: Increasing background anyone?

Postby chrismb » Mon May 23, 2011 4:51 pm

I have noticed my pager scintillator is reading very slightly higher these days [usually steady {occasional 8 to} 9 uR/hr, now 10uR/hr {occasional 11}]. I'd tend to put it down to statistical variation, but if it is a general increase then maybe it's not just USA. We are heading up in solar activity at the moment to a solar max anytime now 'til '13.
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Re: Increasing background anyone?

Postby Doug Coulter » Mon May 23, 2011 6:24 pm

10% increase is in line with what I see vs two weeks ago more or less, on the geiger. No clue why the NaI isn't seeing more (it's seeing less!) -- the tiny difference in apparent new lines in the longer capture doesn't blow my skirt up as an explanation, but I'll check against known things to see if I can figure what it might be -- might be something that affects geigers more than NaI, after all.

But 10% is a big number isn't it? So the clue train needs to see -- is it solar/cosmic, or...human-enabled, and if so, what is it.
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Re: Increasing background anyone?

Postby Alex Funk » Mon Aug 22, 2011 11:24 am

YouTube is alive with videos of higher readings which the posters are attributing to fallout from the melt-downs at Fukushima, which is an ongoing event, and will be for some time going forward.

You should be able to confirm/discount this fairly easily: let the rain off the roof drain into a rain gauge or other fairly deep container, wait a bit to let the heavy stuff settle to the bottom, pour off the top and check the residue.

Most of what is coming out of Fukushima is alpha -- you wouldn't expect to see much of anything with a standard CD rad monitor, so make sure you compare your new alpha readings with whatever alpha background you have come to expect.

Doug wrote: "Henny (a scintillator, also known as a TSA-470) is for example so sensitive it's almost useless for prospecting! We drove it around here in the truck and found some hot zones for example, but couldn't find the actual sources -- so much radon was coming out of the ground that it saw you couldn't localize anything, and rocks returned from those areas weren't hot anymore by the time they got here! They were just saturated in radon seeping from somewhere else in the about 100 yard square area Henny went nuts in. That's not so useful, it's like trying to use a saturated night vision device in bright sun -- you can't see with it."

Is it possible you were seeing low spots where rainwater had collected rather than radon? That might explain the rocks not being hot when brought into the shop.
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Re: Increasing background anyone?

Postby Doug Coulter » Mon Aug 22, 2011 12:13 pm

I've been seeing what I saw (now I should go take new readings) on things that see both alpha and beta. We're rich enough in detectors here that we don't use the crummy CD ones at all for geigers, only thin-window jobs for us, and the one I noticed this on originally is one such pancake geiger counter, sitting in the lab facing up (The one I use for personal safety and to count activations off the fusor). Most fission reactor byproducts are (primarily) beta active, FWIW, though some have enough gamma to compete well with their beta -- the original fuel is the main alpha generator in most decay chains. The beta is a consequence of fission products having too many neutrons to be stable that way so some flip to protons and emit an electron as the easiest way to reduce instability energy.

The get rainwater and "flock it for precipitates" method has had a good long standing in the biz. NRL used the method to blow away the Air Forces idea of flying big filters through the air on bombers. When the Russians started testing, the NRL samples were so much louder than the Air Forces, the latter weren't even used to confirm the NRL readings, which were of excellent quality and allowed the bomb material to be tracked to individual sources. I used the trick here, about 4 days after Fukishima to see a little I-128 - but so little its total output was about 1/1000th of the background inside a 3" thick lead castle -- using that big NaI detector. Since then, the odd rainwater test has shown zero, but I hear the west coast is now seeing some active sulfur, so I should do it again next time we get rain that started over there -- not much point in collecting from a system that started and ended in Floyd after all, which is the current weather pattern. If I can come across the cool Physics Today article that described that, I'll scan it and put it up here somewhere. I'm actually collecting rainwater anyway, we use it for everything but drinking here (and sometimes that if it tests good), and we get enough off my new clean roof to handle that. That's the one thing I can applaud the EPA for. When I first moved here, rainwater was on the toxic side due to emmisions from coal plants west of us. Those are largely cleaned up now, and rain tends to be ph neutral and our main "problem contaminant" is pollen in those seasons.

You'd think that if this were cosmic rays -- perhaps altered by solar activity affecting the earth's field, it would show up better on that huge NaI detector, which can time-resolve all the particles in a shower/burst, where a geiger counter cannot, it will just count once per original primary cosmic ray -- where the photo tube might count 100 or 1000 times on a shower due to the far faster time response (in this case limited by the NaI, other scints would show even more increase).

I just went down to the lab, and after carefully cleaning off the table top and blowing any dust off the 2" diameter thin mica window geiger tube, I got a bunch of readings that looked like "back to normal" to me, but honestly in just a few minutes it's hard to get a statistically reliable answer. What I saw was bouncing from 48 cpm to about 112 cpm (after cleaning off the table, which had a couple thorium doped TIG rods on it). When things are really normal, I sometimes see as little as 6 cpm, but the average tends to the high 70's, which is what I just saw. When it was bad I was seeing a floor in the 120 range.

Whatever it was it was time-variable. We'll just have to keep watching this. One big error the self-terrorizing media commits all the time (hey, scary bad news sells advertising!) is that they don't take a baseline to compare pre-event-du-jour with what was there anyway. I'd make a safe bet that seafood from the Pacific has been hot all along, from a couple ditched nuclear sub reactors that have been cranking and leaking on the ocean floor since the cold war, if nothing else. While I'm sure that some of Japan is now a rotten place to have to live, I don't think the hysteria about it is in line with reality -- how quickly they "forgot" the 10k+ people killed outright from natural causes tells you there's a "never let a crisis go to waste" agenda being pushed there. Which is kind of sick, IMO. Of course, they were po' folk living by the reactor, but killed by the wave -- NIMBY is everywhere and maybe worse there than here. So I guess they "don't count" to the anti nuke crowd. How hypocritical can you get? Dead is dead, and certain, and already happened. Some risk from rads is yeah, bad, but it ain't dead-already like those po' fishermen are.

But for awhile there, I was getting numbers like from the bad old days, when the fallout from the atmospheric nuclear testing had doubled the normal background count. I'm not seeing that today, FWIW.
Since this took awhile to compose, I went down and checked again, and saw normal mid-day readings again. We normally see a spike around dawn and dusk from cosmics here.
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Re: Increasing background anyone?

Postby chrismb » Mon Aug 22, 2011 12:32 pm

I'm back to normal readings for my scintillator-pager, here in UK, too.
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Re: Increasing background anyone?

Postby Doug Coulter » Mon Aug 22, 2011 1:02 pm

Thanks for another data point. I wish we had someone on the west coast to report their baseline and current readings too, but we seem not to have anyone there who's been watching awhile. I couldn't talk JonR over at fusor.net into looking for reactor byproducts on his super duper HPGE, sadly, either. I did give it a try -- it would be nice to know since the news media is having conniptions over it. Sadly, all the articles they've put out leave out enough info so as to be utterly useless for anything but fear mongering. No reference to baselines in them.

For example, one said the air over Fukishima showed emissions X times "normal". Would that be normal for air above other places, air over Fukishima, above the normal emissions for Fukishima (which would be almost zero compared to a coal plant), or what? At that point, the value of "X" means very little. And they are all like that, even ones paraphrased from real scientists to "dumb them down" for us stupids out here. They recently said they saw 10e15 atoms of radioactive sulfur in a collection off the west coast. Maybe bad, but what's normal? How much air or water did it take to get that many? And so forth. Just utter garbage for data, so anyone who buys into any of that is just using confirmation bias to push a long ago set agenda, or so I think.
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Re: Increasing background anyone?

Postby Alex Funk » Mon Aug 22, 2011 1:35 pm

Doug, I don't think you need to wait for rain. You know where the low spots from standing puddles are-- you probably have some in the driveway. Sticking your probe down flat on the low spot of a puddle location should be as good as any way to monitor for fallout. If that gives you background from your granite, just scoop some of the dirt up and take it to the top floor of the lab.
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Re: Increasing background anyone?

Postby Doug Coulter » Mon Aug 22, 2011 4:08 pm

We are sitting on what is maybe one of the largest uranium deposits on earth near here. It's in the soil - everywhere, though it's hottest in the lichens that concentrate it from the rocks. This is "radon alley" if you have a poorly ventilated basement (Mine has > 200 cfm forced through it continuously, BTW, and that keeps the ground floor noticeably quieter). Nothing that's touched the ground is usable for any conclusive measurement unless I'm putting it through the gamma spectrometer to see if there's something different in this dirt vs some other dirt, but all the dirt's been rained on so I can't get a baseline from it. We don't have puddles here in general, remember, Floyd ain't too flat anywhere -- all the water just goes down into the creek. So, I wait for rain when it comes to looking for stuff that came from say, Japan, and in that case, I wait for rain from systems that formed near there, and then moved here, like the one we got lucky on right after the event - it formed right in the airborne plume that Der Spiegel was showing in real time on the web for awhile. Not much point in measuring the rainwater from the afternoon thunderstorms that are formed from water evaporated right in Floyd, as far as I can tell, or from hurricanes on the Atlantic or Caribbean. Not that I haven't been measuring those too, just that I don't get anything at all from the most sensitive non-cryogenic sensor in existence (about 20 lbs of NaI:Tl on a 6" photomultiplier), except that one time, and all the I-128 has decayed by now. I was also looking for the longer half-life cesium-137, no score there at all.
I'd have seen that if there were any -- it has a very distinctive set of lines, and I use a bought sample of it to calibrate the thing so I'm pretty sure I know what I'm looking for there.

So far, all rainwater, including the stuff that did show positive for I-128 (and we're talking "just barely" here -- like ~100 counts on that line out of 100,000 total counts from background inside a thick lead "castle"), is much "cooler" than our soil, by factors in the range of 1000++, since the EPA cleaned up those coal plants up(jet)stream of us. Our TSA-470 portal monitor starts beeping as soon as you go outdoors, being overly sensitive to give the TSA more excuses to well, act like they act. We call it "Henny Penny" as it always thinks the sky is falling -- it's useful to scare antique shop owners out of things...It beeps on a radioactive glass or lamp mantle sample from >10 feet! That's not a rad level I'm going to let myself get worried about.

Too bad no one took baselines on the seafood before the event -- that's the sort of thing only the government can afford, and either they didn't bother or they are not talking. As we know, the food chain is really good at concentrating some things, especially heavy metals, and so it "should" have been somewhat hot to begin with, and now we can't tell if it's hotter, or how much. That is where I would expect to see signs of anything bad myself.

And, this is not Fukishima specific unless we can get a smoking gun tracing anything back to that, like maybe that hot I-128. That would NOT explain why for awhile I was getting hot readings indoors in the shop from the counter I got them from, well off the floor and facing up, and starting before that event. It would either have to be something cosmic-related, or some tectonic activity that released an unusual amount of radon, as far as I can tell from the actual evidence I've got. But that latter wouldn't explain seeing it in England or Texas, would it. It was only more recently we got the cool gamma spectrometer, which lets us see beneath the background that caught the Japanese event in the act.

But it's so sensitive you can't use it to look for cool minerals, because it's always showing something (400cps on background!). We have a shale outcropping that sets it off inside my truck, or on foot from about 100 yds either side. So, thinking I've got a score, I pick up some rocks from where it showed hottest and brought them home. By the time they got here, all the radon had come back out of them and they were stone cold -- Henny had just been reacting to airborne radon, I suppose, that cracks in the shale were letting get to the surface. We returned to the site with a regular survey meter that reads half-scale on cosmics, and couldn't find any specific hotter place to get samples from there.

So your results are pretty dependent on what sensor you use, how you use it, and what that sensor type is good for. This is one of the objections to the horribly inaccurate news and amateur sleuthing that's being reported. They don't have a clue how to do real science, and with their cognitive biases, always find what they are looking for whether it's there or not -- or is there but has been there for all time anyway and they don't know because they assume a baseline that isn't true.

Typical human herd behavior I use (the understanding of) daily to make money trading stocks, frankly. When it comes to fact, forget journalism, pro or blog, as far as I can discover.
(also true in stock trading, BTW)
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