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From: "Terry Walker"
To: k2w at philbrickarchive dot org
Subject: serious radiation in K2 series plugins
Date: Mon, 13 Dec 2010 14:04:42 -0800
Hi Joe,
I got my CDV 700 geiger counter (not a '715') back from a friend today and checked the K2W and K2X modules I have on hand for radiation. I was looking for radiation related to the use of radium paint on the neon lamps. (refer to your articles on this).
WOW! Was that a shocker! I measured the radiation external to the module with the geiger probe held against the plastic housing. Maximum radiation occurred when against the side between pin 4 on V2 and pin 5 on the octal base. The K2W measured up to 2 mR/hour, one K2X measured 4 mR/hr, and the other K2X measured over 5 mR/hr. That is serious gamma radiation, since the housing would block all alpha and most beta radiation. So those things have a pretty good stripe of radium paint on the neons. As a calibration point, the minute pointer from a 1940's Big Ben mechanical alarm clock with radium dial might put out up to 20 mR/hr. (my friend has one). Keep in mind that normal room radiation background levels are less than 0.05 mR/hr.
I suggest that if you don't have a geiger counter, you should get one and mark all of your modules that have radiation with a red dot at the point of maximum output. You should also carefully check your small parts bins and work areas for contamination. A suitable unit would be something like the UNDX-1 from united nuclear at http://unitednuclear.com/index.php?main_page=product_info&cPath=2_78&products_id=484. (currently out of stock) There are other ones of a similar capability on the market as well.
The radium paint is a serious concern on units that have been opened and on parts, particularly if it has been flaking or powdering off of the surfaces. You need to observe proper decontamination care to make sure that radium is not haphazardly transferred around your work and storage areas, as it would be deleterious to you health to accidentally ingest or inhale the paint or dust. This can happen easily with small particules, as they get stuck to the skin and then transferred to other locations. As long as you don't keep these items on your person, they could be made safe by simply storing in ziplock bags to prevent loss of small particles into the environment, and then collecting them in a safe place if not in use for other purposes. The gamma radiation attenuates as 1/Rsquared, so it is in fact down to 0.1 mR/hr at a distance of 6 inches, and not detectible at a distance of more than a foot or so.
Unopened K2 series modules probably do not present much of a hazard, as the only way particles could escape is out the center of the tube sockets at the top. Those center holes could be plugged with a small amount of silicone glue. However, when a module is opened up, the paint could easily flake off of the neons, and any free particles would be liberated.
I don't want to be too alarmist, but simply to recommend that simple precautions are taken to minimize your exposure.
Incidentally I purchased a scintillator probe for use with my CDV 700 to give it greatly increased sensitivity compared to a geiger tube, and it helps in locating small radioactive particles. I got a Bicron type on Ebay for about $120 and it works fine.
Based on the radiation hazard, I have decided not to open up the K2X units to convert one to an improved opamp. I will simply build the new circuit in a different form factor with a small box. I found the octal plugs at a local surplus store for $1.25 each. (they are $2.95 to $15 on the internet, if you can find them).
[snip]
Best regards,
Terry
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Date: Wed, 15 Dec 2010 00:13:52 -0500
To: "Terry Walker"
From: Joe Sousa
Subject: Re: serious radiation in K2 series plugins
Hi Terry,
Thanks for the heads-up on the radiation counts.
As a pure coincidence, just recently I designed a little Geiger counter supply to drive the Russian pancake tube with mica window I got from Russian ebay. This is still on one of my benches in breadboard form. I attached a pdf with a photo of the breadboard and of the schematic. The pancake tube is of a fairly high grade with a wide mica window and it can detect Alpha beta and gamma. It is face down in the photo with a protective aluminum lid.
The funny thing is that I built this counter thinking that I would be looking at the radiation coming from the k2 modules, then forgot about them. My home lab has been busy with multiple projects.
I saw the same fast counts as you report on a random sampling of a few modules. The radium must be a point source because there was a strong proximity effect, and 1/r-squared applies.
I am not the least bit alarmed, but I remain informed. I go by the numbers more than by the fears.
[snip]
-Joe
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From: "Terry Walker"
To: "Joe Sousa"
Subject: Re: serious radiation in K2 series plugins
Date: Wed, 15 Dec 2010 10:22:53 -0800
Hi Joe,
I finally figured out that your circuit is basically a regulator, with variations in the error amplifier signal being used as the speaker signal. I would have expected to pick off the negative going signal at the anode of the geiger tube with a 100pF cap to a common emitter amplifier followed by a one shot to give quantized measurement results to a meter. It is surprising that the signal in the regulator is adequate for volume, considering the effective divide by 5 in the signal path (470K/2.2M etc).
Have you looked at the signal on the geiger tube anode?
[snip]
I'm glad you are setting up some type of radiation sensor device. The levels associated with the K2 modules are not too serious as long as the radium paint is undisturbed. My main concern I was expressing to you was to make sure that you do not have problems with paint particles causing unintended contamination of your work area, which would be a long term health hazard due to ingestion. On the localization, I think the paint is either dots or a swipe across the the neons (some HP instruments using neons have dots on them), so it is in a concentrated location.
Terry
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From: "Janis and Terry Walker"
To: "Joe Sousa"
Subject: further geiger counter comments
Date: Wed, 15 Dec 2010 21:46:32 -0800
Hi Joe,
Your pancake geiger counter tube looks interesting. I might be interested in getting one and making a counter with it. A few questions come to mind:
1) Can you give me more details on how you found it on Ebay and purchased it? Were there any problems or events different from a purchase from a seller in the USA?
2) Did it come with enough technical information to enable setting it up as a calibrated sensor without having to calibrate it in a radiation field? Specifically is there a known calibration factor of counts/minute for a known radiation field such as 1mR/hr?
This sensor looks interesting as pancake sensors are generally more sensitive for picking up radiation from areas when scanning for contamination. They also can give a larger count factor per mR/hr. Your HV power supply seems nice and simple, as well as low cost.
Terry
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Date: Thu, 16 Dec 2010 01:58:35 -0500
To: "Terry Walker"
From: Joe Sousa
Subject: Re: serious radiation in K2 series plugins
Cc: jlrmsousa@comcast.net
Hi Terry,
Some of my goal with the 400V regulator for the Geiger tube was to be as cute as possible, just for fun. I felt almost extravagant using 3 transistors instead of 2, but the third one is needed for margin in the current gain. I considered using a single Mosfet, but the Bipolars won.
Yes, I probed the anode, and it's voltage drops to about 100V under the 2Meg pull-up, so I have at least a 200V swing at the anode. This leaves plenty of stimulus even after the various attenuations. The 10000 current gain of the fist two transistors makes ~20mA current pulses at the 45 Ohm speaker. I measured the Geiger tube in operation before starting the design.
[snip]
I remain particularly warned about personal radioactive contamination, which is much more important than mere proximity.
Regards,
-Joe
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Date: Thu, 23 Dec 2010 01:41:17 -0500
To: "Sheingold, Dan" , Robert Pease
From: Joe Sousa
Cc: "Terry Walker"
[snip]
This evening, I finished constructing my geiger counter in a permanent form and surveyed nearly all my Philbrick modules. All the BROWN/BEIGE and BLACK K2-W and K2-X modules make the counter buzz when the zone under the output tube is brought near the tube. All GRAY K2-W, K2-X and K2-XA have no effect on the Geiger counter. My geiger tube is of the pancake variety with a mica window, about 2 inches in diameter. It came from Russia a few weeks ago. It is model Beta-2.
A couple of the K2-X beige modules arrived open and the white radioactive paint dabs on the neons was quite evident.
I surveyed all 50+ modules on the sage advice of Philbrick enthusiast Terry Walker, and put a red sticker on all that were hot. It appears that no Gray modules radiate, and all K2-W K2-X beige or black modules are hot.
At one point, after I brought one module near the Geiger tube, the buzz would not stop after removing the module. Looking at the mica window of the Geiger tube, it was clear that there was a grain-of-salt speck of radio active paint on it which later fell off, and the counter resumed normal operation. I checked around for other signs of stray radiation and found none, in particular on my hands.
Regards,
-Joe
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Date: Fri, 24 Dec 2010 01:38:42 -0500
To: Robert Pease
From: Joe Sousa
Subject: Re: "Let George Do It"
Cc: "Sheingold, Dan", "Terry Walker", Doug Coulter
Bob,
These photos show most of the modules that I tested last night. The green sticker indicates zero change from the background radiation of about 2-3Hz. While the modules with red stickers gave a pretty stiff buzz without opening them up. The red sticker also indicates the hot spot which is always under the output tube on the back. This check was all done by ear, while listening to the tics.
See the photos on pages 2 and 3 of the attached Geiger_counter_BETA-2.pdf for two drawers full of modules. There was 100% correlation of radiation with black or beige cases, and no radiation could be detected outside any of the grey modules.
Could it be that the change to gray plastic cases coincided with the elimination of radium paint from the neons?
The Geiger_counter_BETA-2.pdf attachment also shows photos and schematic for the actual home built radiation counter with the Beta-2 Geiger tube. The Pancake_geiger_data.pdf attachment shows the sensitive specs of the tube. Look for model Beta-2. It is specified to capture 65% of the beta radiation that hits it. Sensitivity to alpha is not mentioned.
Tonight I measured the actual frequencies for one of the K2-X modules that was already cracked open:
Background ~3Hz
K2-X beige module with closed case and back of module adjacent to Geiger tube ~57Hz (this is the buzz I heard on all the hot modules last night)
K2-X beige module with the CASE REMOVED ~1500Hz
This wicked increase from 57Hz to a 1500Hz, when the shell was removed, confirms Doug Coulter's assertion that most of the radiation is not gamma, because it is easily blocked by the plastic shell.
[snip]
Hope you are all enjoying the Holidays.
-Joe
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From: "Terry Walker"
To: "Joe Sousa"
Subject: radioactive K2-X modules
Date: Tue, 28 Dec 2010 14:37:05 -0800
Hi Joe,
Thanks for copying me on some recent emails.
It looks like you did a thorough job of investigating the radioactive problem of the Philbrick modules. Your geiger counter is nicely done. I'm glad to hear that you are properly apprised of the situation, and it is interesting that you did have an incident of a stray radium particle to point out the hazard. You wouldn't want to have accidentally ingested that particle.
Your photos of the interior of a K2-X unit which had radioactive neons was very instructive as to the source of the radiation and the general method and state of the construction. It is amazing that in those times past, the hazards of radium paint were not generally of much concern. I presume that you have heard of the case of the ladies in Japan who did radium dial painting. The internal construction did not appear particularly precise, but rather somewhat haphazard. Since they were making a lot of these, I would have expected that the construction would show more use of prejigged parts, with precisely bent leads etc.
In looking at your photo of the stock of K2-X units, I notice that some of the gray units have tape or a rubber band holding the shells together. It would be interesting if you would look in these units and verify if they still use neons, and if without the shell you can detect any radiation at all from the neons. As mentioned in the emails in the postings of http://philbrickarchive.org/radio-active_neon_bulb.htm, some neons may have slightly radioactive gas or metal elements inside them instead of using the external radium paint. Surely something had to be done to make sure that the neons would strike. Incidentally, this requirement probably could have been satisfied by putting an extra neon inside the case with a resistor so that it is across the entire 300 or 600 V supply until it strikes, to serve as a source of photons for keep-alive purposes. I have found that the common 1/25 W neons are quite sensitive to ambient light when they are energized with a sine wave peaking at a voltage just below their normal striking value.
[snip]
Sincerely,
Terry
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