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1)
Message boards :
Science :
Beta versus Gamma attenuation
(Message 2001)
Posted 3880 days ago by Craig Daniels Thank you, "exsafs". Your explanation, has helped me understand what's going on when the beta count unexpectedly falls off to nothing. |
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2)
Message boards :
Science :
Additionnal preference in the project ?
(Message 1996)
Posted 3882 days ago by Craig Daniels Otax's concerns are also mine, since I have differential red-green color blindness (which sometimes results in "retinal rivalry", making the border between adjacent colors vibrate). Suggestions: * Rendering the map's continents in gray scale would help everyone. * It would also be easier for everyone to discern colors (or shades of gray) with slightly larger station icons/circles. * I'm guessing that the 3 station colors are red, yellow and green. Since the normal background for a given station can vary considerably with local geology, construction materials (Chinese drywall!) and altitude, why not have the 3 colors (or shades) designate "near normal", "over 1.7x", and "over 3x normal" --instead of fixed ranges? (You could get fancy --calculating 2x and 3x the "standard deviation" for each station, but such factors serve Radiation Network well enough.) * How about a legend for the station graphs? Am I supposed to read the red line or the more jagged blue line? Why are they different? What are all those little triangles about? * Why (at the moment I'm looking at it, screen capture upon request) does station #8373's 24 hour average list at 0.11 uSv/hr in the box, while his graph clearly shows an average more like 0.17 uSv/hr? (A graph legend might make that clear, even to obtuse folks like myself.) * Is "Add a sensor" where I begin joining the network, or is that for adding 2nd and 3rd sensors to an existing station/account (as I now suspect)? I don't see much by way of explanations there --or anywhere, and the Q&A search utility has so far found nothing that I've asked for --even when using single, mono-sylabic words. * I think you/we need a section which "takes people by the hand", saying things like: "here's what equipment you need", "these are the brands and models of Geiger counters that we provide data cables and drivers for" (so I don't have to learn how to solder for the first time in my life), "these are our standards for placing and maintaining a Geiger counter", and "here are the steps --in order-- that you have to take in order to join and register your new station". (Actually, I've been a soldering electronics technician for 60 years, which is why I'm apprehensive about those who'd be soldering for the first time.) Craig (in Oregon, USA) |
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3)
Message boards :
Science :
Beta versus Gamma attenuation
(Message 1993)
Posted 3884 days ago by Craig Daniels * I think I'm good on gamma --it's like light (photons). If I shine light through a 0.3d (50%) neutral density filter --there are half as many photons on the other side, but the color (energy) doesn't change. By extension, a "half value layer" of lead or concrete will reduce my Geiger CPMs by half, but I could still recognize the source's energy signature with gamma spectrometry --right? (Aside from a bit of line spreading --and that G-M tubes miss 98% of the gammas.) * So okay: can someone tell me about a beam of beta --plowing through a half value layer (thickness) of aluminum (and aside from the bremsstrahlung/fluorescence effects). Specific question: do I simply lose half the beta density, or does approximately the same beta population per square centimeter now have half the original KeV energy? Thanks, Craig |
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4)
Message boards :
Science :
Is it essential where the detector is placed?
(Message 1992)
Posted 3884 days ago by Craig Daniels As to placement of an SBM-20 tube device, I can only speak from my experience with a Radex-RD1503, since March of 2011. (I'm new here, but am a member of Radiation Network, patched in with a Medcom "Inspector" GC. I post separately at: > http://webpages.charter.net/123goto/map.htm ~ At 85cm above the ground, I seldom see a difference from inside readings with the 1503. I see greater (but not significant) variations with sensor orientation and placements. Furthermore, blocking the G-M tube side of the 1503's "view" of the ground with aluminum made no difference. ~ In general, I find it very hard to significantly attenuate the gamma count, not that it matters (in my opinion), since we're interested in each station being compared to its own baseline. The important thing (IMO) is to locate your GC where it doesn't have to be moved, the weather can't effect it, and where the geometry of other things in its immediate vicinity will not change. ~ The 1503's SBM-20 tube does have beta sensitivity at high enough energies, which you can prove to yourself by blocking the beta from a sealed^ packet of potassium chloride (ie: "salt substitute") with a 3mm or so thickness of aluminum. ^ KCl readily migrates into the air --perhaps partly driven by ionization, but via the air's moisture content for sure, so don't let it foul/contaminate your Geiger counter. Bag that fine white powder. ~ My understanding of the understanding in Germany --of their 1800 station system (all uniformly isolated, meter high, outside sensor placements) is that they're monitoring the ground plus any gamma from fallout which might settle in the vicinity of a monitoring station --per: > http://odlinfo.bfs.de/ They frequently see a little bump with rainfall, which might be about hard beta. ~ If we wanted to have a separate network/reportage doing outside air monitoring, I believe it could be done with a setup like: > http://www.blackcatsystems.com/GM/acc4.html --and a bagged-with-desiccant GMC-200 (rated -50 +60 ะก) (I'm retired and have zero affiliation with GQ-Electronics or any other business interest.) Craig |
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5)
Message boards :
Science :
Is it essential where the detector is placed?
(Message 1991)
Posted 3884 days ago by Craig Daniels * The max USB cable length is 15 feet --unless you get something special (with built in powered repeaters?). * However, if you have something like a GMC-200 or an "Inspector" (best block beta and alpha on that one for network use) --with a typical mini-jack pulse output, then you can use it with the intended "data cable" (comes with a driver and it has a powered chip in the USB end) and extend the pulse/audio end out at least 40 feet (about a 1% response roll-off at higher CPMs when I tested an Inspector). I suspect that the GMC-200 and its data cable could be extended much further, since it works at lower impedance. * Pulses for data do have limitations. The Inspector's square wave is about a millisecond wide, so Poisson distributions on the high side of average will start "piling up" and overlapping some of the pulses above 5000cpm (--which levels we'll hopefully never see). |
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6)
Message boards :
Science :
Additionnal preference in the project ?
(Message 1989)
Posted 3884 days ago by Craig Daniels This web page: > http://colorfilter.wickline.org/ --should be helpful. Craig |