One fine day, my friend Doyle emailed me about a $150 geiger counter for the PC. Being unemployed at the time, I resisted the temptation to get one of the coolest unpredictable random number sources a geek could have, but on the third day I just couldn't take it anymore. Shortly thereafter, a Black Cat Systems GM-10 serial #592 arrived.
Oct 11 - I let it run for about 15 minutes to see what the background radiation in my office is like, then I put a smoke detector right up against the front of the GM tube for about 15 minutes. The smoke detector contained .9 microcuries of americium 241. Moving the smoke detector a few inches away from the GM tube made it almost impossible to detect.
Oct 12 - I ran the monitor for two hours, and then I put a little chunk of rock with traces of what looked like yellow pumice surrounded by tiny translucent crystals and bits of black rock in front of the detector tube for a little while. My mom found this rock, probably a piece of carnotite, on the ground near Uravan Colorado in 1995. I got about 100 times background radiation with the rock right next to the detector, but from more than about a foot away, the readings dropped off to almost nothing.
Relative readings are useful in terms of knowing whether I'm detecting any radiation in addition to background radiation. I can now tell that I can safely store this chunk of uranium ore and it's not going to radiate anyone, but what I really want to know about geiger counters is what the clicking means in terms of when it's time to start hollering and waving my arms around and getting the hell outta there. For all us average dolts, that's mostly all geiger counters are good for anyway. Well, of course that and gettin' the chicks.
I interpret the 712's sensitivity graph, to mean that getting 10 counts per second, or 600 counts per minute from the GM-10 while holding it about the same distance from the radiation source as my chest would be roughly equal to my chest receiving .0004 R/Hr or .004 mGy/Hr of radiation from Cobalt 60, which emits radiation at a particular energy level. The dosages would be different for different atomic sources, but this gives me a starting point to understanding how many clicks per minute are "a lot", and how many are just "more". To fill out the rest of the picture, I need to know what an R/Hr and mGy/Hr are.
Fortunately for me, my sweetie was just reading that to me out of a Mercke manual the other day. Who said romance is dead? Anyway, 1 Gy equals 100 rems, so 1 rem equals 10 mGy. The Mercke manual talks about limited data being available for "very low doses" less than about 100 mGy. I appear to be reading less than one ten thousandth of that, .001 R/Hr or .01 mGy/Hr when right up against the rock. If I held the rock in my hand for 1000 hours, then my hand would have received 1 rem, which is the whole body exposure limit per year proposed in the U.S. Code of Federal Regulations.
From this, I surmise that the danger of having radioactive minerals around comes not from direct exposure to them, but from storing them in such a way that constant exposure to radon gas or to pieces that break off can result. Keeping them in a plastic box, labelling them so a third party would know what they are, and storing them out in the drafty garage sounds like a plan.
About 2 mGy is perhaps what I might receive in one year from background radiation, X-rays, smoke detectors, and all the nuke testing they did in Nevada up until the early 90s, so if I hear the geiger counter going off at a rate that means about that much in an hour, I'm going to call that my personal Scream And Run Out Of The Room limit. If 10 CPS is .004 mGy/Hr, then 5000 CPS is 2.0 mGy/Hr on my little GM-10. Okay, I'd probably have run out of the room before then anyway. This is good to know.
Now I want to build a little mobile battery power and CPS readout display for the GM-10 so I can wander through thrift stores looking for fiestaware.
Serial Port Connections Computer (DTE) GM-10 DB-25 DE-9 Signal Direction DB-25 2 3 Tx Data -> 2 (used as a ground!?!) 3 2 Rx Data <- 3 (17 us pulses) 20 4 Data Terminal Ready -> 20 (used as power)
Uranium-238 is a radioactive isotope. It's not as hot as Uranium-235, but it does hang out for four billion years and exposure to it can kill you. Five years from now, we're going to have a large population of Iraq war vets with radiation poisoning, who like the "Desert Storm" vets, breathed too much vaporized U238 in the form of uranium hexaflouride dust. Anyone who is anywhere near an area where U238 was vaporized is breathing radioactive dust. The ancient city of Baghdad is now an open nuclear waste dump, and a significant portion of the people there will get sick or die just as a result of being there. A trillion dollars in war reparations wouldn't be enough money to clean up that mess.
The U.S. continues to develop and use weapons that disperse dangerous levels of radioactivity, and has demonstrated to the world that it is not only willing, but that it will contaminate and render uninhabitable swaths of land in sovereign countries as a matter of course during a military engagement. The behaviour of the U.S. has become a global problem of such severity that it seems that it's only a matter of time before action is taken by some other country to correct it.
The medical horrors from the Iraq invasion have begun.