After my first feeble attempts to find a source of radioactivity to test my Geiger Counter, I took one of Paul’s ideas and tested several old 35mm camera lenses. I tried a very old Asahi SLR (before Pentax) but I got no radiation. Then I tested 2 Canon EOS cheap lightweight plastic lenses, still nothing. I tested a Vivitar lens, but no radiation. I tested the telephoto lens of a Canon FT, still no clicks. I tested the wide angle lens, zero. I took the 50mm lens off the Canon camera, and when I held the back of the lens to the Geiger tube, the clicks went from 1 or 2 a minute to 1 to several a second. SUCCESS!!
Some camera lenses used thoriated glass. This was one of them. It says CANON LENS FL 50mm 1:1.8 on the front. This is not a lightweight plastic body, it’s the real thing. It’s heavy, so I think it’s made of brass. And the rear lens drives the counter crazy!
Next I tested the inside of a smoke detector. The openings around the metal can are like the blades of a squirrel cage fan: the fin is bent inward and lets the smoky air through, but each fin blocks the radiation source in the center so it can’t be seen, and the radiation can’t get out. My test of it gave no increase in the click rate. The smoke detector is unusable, so I may take the cover off the radiation source, but first I’m going to read up on it to find out how to avoid any unsafe conditions.
What I read said this is NOT a good idea. It is unsafe. The radioactive source can’t do harm if it stays in the detector. But if it gets damaged and particles come loose and enter the body through the air or digestive system, they can cause cancer. So for now, I think I’ll leave the detector alone.
I still have to take the Geiger counter down to the creek bed and test some of the rocks there, but a storm is supposed to hit hard here this afternoon, and it looks like I may not be able to walk in the creek bed for quite awhile until it dries up. No telling when that may be, since other rain may come soon after. After three years of drought, we really need all the precipitation we can get, especially snow in the mountains. And it’s saving me $$$ on my water bill because I don’t have to water the lawns.
Update Dec 12 – I cut off the end of a banana and held it close to the Geiger tube. It seemed like the count was higher, but that was just what I perceived, so I decided I would have to time the readings. I timed the background radiation and got 5 clicks in 2 minutes. Then I timed the banana and got 16 clicks over a 2 minute period. Definitely higher than the background radiation.
Yummy banana got eaten – my resistance yielded to temptation. So now I have (and always have had) radioactive potassium inside me, I decided to measure the count with my finger next to the Geiger tube. In one 2 minute session I got 7 counts, and in a second I got 10 counts. My finger seems to be higher than the background radiation, but the count really needs to be averaged over a much longer time to average out the randomness. But I don’t think I have the patience to hold my finger there for a half hour or more. So this confirms that bananas, or for that matter, any other living thing that has potassium, has a radiation count higher than the background count.
I have several rocks laying around that I should check for radiation. One problem I’ve found is that if the level is low, it may take a long time to find that it’s different than the background count.
I have a piece of galena on a shelf, so I tried that in front and on top of the Geiger tube for a few minutes. I heard nothing for quite a while. That makes sense since galena is mostly lead, and is so dense that it shields the tube from radiation. My guess is that a lot of the background radiation comes from above in the form of cosmic rays from space. A lot of these are blocked from above by the lead, so the background radiation count drops.
The galena crystal is about 13mm thick. That’s about 1/3 the thickness of the outer and inner stucco walls of my house. Apparently the lead is much more effective at blocking radiation than the walls or ceiling.
The banana was definitely higher than the background count. I have some potassium citrate capsules. They were dirt cheap, $2.50 for 120 capsules, from Swanson vitamins – about 2 cents apiece.
I put two of the capsules next to the Geiger tube, so far it doesn’t seem to be higher than the background count. It’s definitely less than the banana. For this reason, I think the banana is better, especially since the remainders serve an additional purpose (yum!).
Now this is true but odd. If you want something very subtle to test your GC with, try some Potassium salts in quantity. Like Thorium it’s a primordial nucleotide which is radioactive, but in thevgorm of LoSalt it’s one you are meant to eat! The rate is not much above background, but it is measurable with my setup. Of course for all the Potassium you eat you pee out the same amount and it’s all the same so you do not get fried really. Paul
The banana was definitely higher than the background count. I have some potassium citrate capsules that the dr. Rx’d for me, but then my other dr. switched my meds and now I’m not sure if I should be taking potassium. I have to check. They were dirt cheap, $2.50 for 120 capsules, from Swanson vitamins – about 2 cents apiece.
I put two of the capsules next to the Geiger tube, so far it doesn’t seem to be higher than the background count. It’s definitely less than the banana. For this reason, I think the banana is better, especially since the remainders serve an additional purpose (yum!).
I’m not sure I would have expected excitement from a lead ore. Most decay chains end up as a stable lead isotope.
On the subject of apparently erratic count rates, how many counts do you have to observe over time to be sure of their rate?
I’m not much of a statistician, but I would guess at least a hundred, or probably more like a thousand to narrow the whatever symbol it is, I forget. And then are we in the middle of a solar event? If so, then the count is probably way off.
Oh, I was thinking that since it was lead ore, out of the ground, it may have other contaminants, copper, silver, and even something that’s radioactive. But I suspected that even so, most of the radiation would be blocked by the lead.
Look for volcanic rocks or for old phosphorescent wristwatches.
I’ve been trying some rocks i got from the riprap along the creek levee. I think this is granite. But the Geiger counter has such a small tube that it has poor sensitivity, and it’s difficult to tell the difference between a rock with weak radiation and the background radiation. I ordered a G C kit with a larger tube, and once I receive it and assemble it, I hope the larger tube will be more sensitive and it will be easier to detect weakly radiating rocks. I think anything old with radioactive paint is extremely difficult to find because the dangerous radium paint has been banned for decades and anything that has it has been lost, destroyed or become valuable collectibles. Thanks for the advice.