As I was a bit amazed at the small size of a burned in Base Camp 164 Pro mantle, I thought it may be interesting to see a selection of Tilley mantles before they are burned in. The numbers at each mantle are mr/hr taken from my geiger counter. The Base Camp mantles are thorium free. The most glaring observation is the huge size of the 164X mantle and the small size of the 164 Pro (about the size of the Tilley 190) The Pro may be small, but it is quite bright. Dan
Very interesting. My friend has a Geiger Counter and we have tested a variety of different mantles. He is an electronics enthusiast and has constructed his counter with an LND712 Geiger-Müller tube and a circuit of his own design. Our figures are counts per minute (cpm) which cannot be converted to milli Röntgen per hour (MR/HR) as far as I know. Anyway, I'd be happy to post our test results for the mantles we have available. The figures do give a idea of the relative radioactivity of the different mantles and thus an idea of the Thorium content. Is anyone interested in our results?
Millirem is 'old money' , at least in the UK , we now measure radiation (dose rate) in microsieverts (sieverts) per hour CPS (counts per second) measures contamination
Yes, I think it would be useful to have some idea of background radiation when people take their readings. Also some other figures to allow some sort of comparison e.g. a nice lump of granite or an old luminous watch. I presume we don't use radium or whatever it was in watches any longer...
Yes David, the background count is important and so it would only be meaningful to state the background count and then the absolute counts or to state the counts as corrected counts above background. Radium is not used in watches any more as you say. I have various lumps of granite collected from here and there including from glacier boulder fields in the Alps. They do register a bit above background but not much (uranium was mined in the Alps long before it was used for bombs or atomic energy, salts of uranium give a characteristic green colour to glass which is particularly impressive under UV light). Probably the most radioactive thing to be found in the house is the Americium-241 source found in some smoke detectors but uranium glass is fairly radioactive and even low-sodium table salt or bananas register above background (Potassium-40). Having said all that, the background count where I live in Surrey is about 30 counts per minute (cpm) but some mantles are over 1,000 cpm.
The meter I used was a 1961 Victoreen CDV-700, surplus from our old Civil Defense organization. The mantle readings were taken on the X10 scale. The meter shows mr/hr and counts/minute, so on this meter, 1.5 mr/hr is about 1000 C/M. This is an interesting write up here which contains among other things the readings of a an old Coleman mantle using this meter and shows 1.5K C/M & 2.5 mr/hr. Measuring a pair of old Silk-Lites in a package of two, I get 2.5 mr/hr. A single mantle measures about half that. A few more single mantle measurements.... Mantle------------------------mr/hr----C/M Peerless 2C-Hg ------------0.7------400 Peerless 24A ---------------0.5------300 Peerless 111 ----------------0.5------300 Coleman 21A Silk-Lite --1.25-----750 Coleman 1111 Silk-Lite --1.5-----1000 I don't know if there is a direct translation between how "hot" a thorium mantle is, vs. it's brightness. From my experience, old coarse weave 21A Silk-Lites are very bright, as good or better than Peerless, but YMMV. I usually use Peerless in my lanterns and Silk-Lites in my lamps for cost/availability/mantle survivability reasons. Dan
Thank you Dan. I am away at the moment so I can't post any measurements for comparison with your readings but I can say that, from memory, your readings tally closely with mine. The most radioactive mantle I have found so far was an old "Veritas" made in London and I think that was 1500+ cpm. The next most radioactive was a Silk Lite I think. That was somewhere around 1000 cpm. I have a scientific background but I am no expert in measuring radioactivity. I am a doctor so I have some limited experience in this field. I think in order to standardise readings it would be necessary to measure the count at a set distance from the mantle and from a set area of mantle. That would either mean destroying the mantle to take a measurement from a 1cm X 1cm piece at a distance of 1cm (for instance) or masking off the mantle with a shield of lead to expose only 1cm X 1cm or something like that. I will have to research how this is actually done.
I work in the nuclear industry and I'm more than happy to help out with your radiation measurements. Part of my job is to monitor radiation so I have access to calibrated insruments to accurately measure Alpha, Beta and gamma sources. Americium 241 is an alpha source we use to calibrate our full body monitors at work. Alpha sources are easily shielded by a sheet of paper, or even the outer layer of our skin. thorium is no risk on a radiation aspect, its far more of a risk inside our bodies as a contaminant through ingestion, injection or inhalation ( as in its powderised form) I.e A used mantle. Post them down to me if you like......
Yeah, that came in very useful when we shared a cottage at Ashover recently - we didn't need to put the lights on in the evenings...
Well I was handling peerless mantles yesterday and as far as I know I still only have 10 fingers, 10 toes and 2 eyes. Only things is all the forest animals keep following me.
Oh right, well i've had a couple of stiff drinks, so i'll go to the kitchen and cut two off. Thanks for letting me know.
