Victoreen 440 Survey Meter

[guest]

I just stumbled across a Victoreen 440 Ionization chamber survey meter while looking for something else altogether (isn't that how it always happens?). It looks more or less ok, except for corrosion in the battery chamber (nothing unusual there). Does anyone have a manual for this beast? It looks worth restoring.

[guest]

Late breaking news - By scraping the battery contacts, I have now rendered my Victoreen 440 at least partly functional. There appears to be some intermittent problems in the wire harness as well. Each wire goes to a push-on contact on the board edge, sort of like a poor man's edge connector. Of course, with this sort of setup, there are ample opportunities for intermittents due to wire breakage and contact oxidation. If all else fails, I can just solder the offending wire to the appropriate land on the printed circuit board. Some frustrated technician has aready done that with a couple of the wires...

[Jon Rosenstiel]

I just picked up a similar unit at a hamfest a couple of weeks back, it's a model 440RF/A. From what I can determine that particular model has been in production for quite some time. The last calibration done on the one I have was in 1989. I found some information here. http://www.surveymeters.com/products_440rfd.html
The unit I bought uses 4 "D" cells and one 22.5V, (Eveready #412), battery. The newest one uses 9V batteries.
I did get the unit to work after asking Richard Hull his opinion on the correct voltage for the "bias" battery, (It was 22.5V). The unit reads about 4mR/hr when a lantern mantle is held against the mylar window. I plan to test it further with my home-brew x-ray tube.

My unit doesn't have any push on contacts, (it could have been already modified as it appears to have been worked on quite a bit)!

[guest]

Mine is ancient history - no microprocessor, runs off 4 "D" cells. Serial number is in the hundreds, so it probably dates from the early to mid sixties, especially judging from the date codes on the caps. I'm rather divided as to whether the polarized caps are electrolytics or tantalums, but it's probably a good idea to swap them out whatever the case (when I get the time).

[Tom Dressel]

Just what is the story on radioactive lantern mantles. I vaguely remember hearing about this, but I cant remember the details

Tom

[guest]

At one time, lamp mantles incorporated some thoria as well as a few other metal oxides, so they were somewhat radioactive. Apparently, the thoria has been phased out of domestically made lamp mantles, but may still be in foreign-made product. I have some of these radioactive mantles, and they barely twitch the needle on my RO-3 survey meter.

[guest]

Hi Richard, I have a couple of pounds of cerium oxide for polishing glass, bought from a lapidary shop.I understand thorium is a contaminant in this material, just how dangerous is the stuff anyway?

[guest]

I'd tend to doubt there is enough thorium in the cerium oxide to amount to a real hazard, but the only way to really tell would be to use a survey meter of some sort. You'll need to get one anyway, sooner or later... You might also want to put a pile of the stuff on top of a piece of sheet film (say Tri-X or HP-5 + or some X-ray film)wrapped in light tight paper to see if it darkens it after a few hours of exposure.

[Richard Hull]

I have used and seen a lot of cerium oxide over the years, being an old ex-glass pusher (ATM). The stuff varies from lot to lot depending upon source and price. Expensive cerium oxide used in the pro-polishing industry is usually highly refined and the thorium has been removed along with other natural RE tramp contaminants. Older batches and some very cheap batches are usually just RE oxides directly reduced from Misch metal with is often 75% CexOx and can contain up to 3-5% thorium. This is just enough to indicate 2x-3X or more above background. I wouldn't sweat it though.
Ultra nice Cex0x which is hydrated and very pure is green-gray. De-hydrated Misch material with thorium is often a tan color. This later material is more often found used by rock hounds in tumblers and for rapid gem polishing.

Richard Hull

[guest]

Hi Richard Hester and Hull, I bought the cerium oxide to make a scope mirror with, it is the tan material...I wasn't aware there were any other kinds out there but I have slopped a lot of it all over the garage floor over the years. It'll be the first thing I look at when I obtain a detector of some kind. Two to three times background is ok i guess but it shows how easy it is to contaminate an area unwittingly.