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Tuesday, 17 November 2020

Indulging my doomsday fantasy

As a 'prepper lite' I had previously bought a selection of cheap (~$100) radiation detectors (0.05-99 uSv/hr), but although they seem quite precise (but not calibrated) for measuring normal background levels of gamma radiation and can indicate small increases in gamma radiation levels (e.g. if held close to an old thorium-enriched gas mantle or a piece of depression era 'uranium' glassware) they would not be of any use for civil defence (e.g. measuring significant radiation levels from a 'dirty bomb' terrorist attack, nuclear accident (not that Lucas Heights research reactor is capable of a serious nuclear incident), or if there was fallout from use of nuclear weapons).

So I finally bought myself some antique (cold war vintage) gamma radiation detection instruments that *might* be of some use (if ever needed). Without spending $395 to have them calibrated by ANSTO (and they'd probably laugh at anyone wanting these 'antiques' calibrated anyhow) they won't provide reliable measurements. But hopefully they would at least provide an indication that they was a problem (significant radiation levels) and let me know that evacuation or shelter-in-place was required (you don't have to know exactly how much radiation there is, as just knowing there is significant radiation tells you it's time to take action).

What I bought (on eBay) was a CD V-777-2  radiation detection 'kit' (well, at least that is what the vintage box says, but the actual items included were not the original set) that consisted of a CD V-715 model 1A survey meter, two 100R dosimeter pens (CD V-740) and a Bendix CD V-750 model 5b charger (plus some cool original instruction manuals etc.) for US$90 plus US$30.25 postage and US$17.03 import charges (GST). Total cost was A$189.57. A second purchase was for an IEH CD V-750 model 5b charger and three 200R dosimeter pens (CD V-742) that were supposedly "tested", for A$20.70 + A$39.76 postage and GST = A$59.46. Unfortunately only two of these three dosimeters will charge and zero properly (the third one can be charged and set to zero, but drifts towards FSD at a rate of several R every minute, so is totally useless. After recharging/zeroing many times over several days it was still no good, so I binned it. I've emailed the seller to try to get a replacement sent out for free, or get a few dollars refunded).

After charging and zeroing the four working dosimeters I've checked the readings daily for several days and there was no noticeable drift. I'll check the readings each week to chart their rate of drift. Then repeat the process several times to see if their rate of drift is consistent (if so, the raw dosimeter readings can be normalised to compensate for the know drift rate to get more accurate readings). All dosimeters will slowly lose charge and 'drift' towards FSD without any exposure to abnormal radiation levels (normal background radiation levels provide around 30 mR per year, so won't affect a 100R dosimenter).

The V-715 survey meter I bought would have been made in the early 1960s (the final model 1B was produced in 1964), and my one is not stamped with a "R" after the serial number, so it has not been through the refurbishment process that FEMA used on their V-715s in the 1980s to improve their reliability and maintain their calibration longer. So far I haven't even put batteries in the V-715 and done a circuit test, so it is really only a conversation piece/antique.

So, all up I've spent about A$250 to get some working (but uncalibrated) dosimeters and a survey meter that is of dubious functionality (but as a modern survey meter such as a Fluke 481_DESI costs over $7,000 and even a RadEye G series palm sized survey meter costs around A$2,000, I'm not going to spend much for something that will probably never be used). There is a miniscule probability that I'd even need them, but if I ever did they are not the sort of thing you can get at the corner store in the event of a crisis (that's why I also have a few packets of potassium iodide tablets in my first aid kit).

BTW I was also looking around on eBay for some vintage (original) fallout shelter signs that usually cost around $50-$100 each, and came across a batch of ten that I was able to purchase for 'only' A$255 (plus $100 for shipping from the US to Australia). I'll probably keep a couple of the signs and try reselling the remaining eight signs locally (so postage isn't too exhorbitant) on eBay. If I manage to sell them off I might make some money to cover the cost of the signs I keep and the radiation detectors I bought ;)

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