Need feedback on my setup

@g346342, Ahh, then please accept my apology. From your wording I assumed you were sort of trolling me. After re-reading I can see what you wrote could be taken either way. Sorry pal, my bad

I had no idea the Americium is plated with gold or an alloy there of. It was my understanding that the AM-241 was plated (I assumed maybe by molecular plating method) onto the metal disc and that was all. I have had a quick search about and found different pages that state both; that it is plated onto a disc and that an AM-241 alloy is made and then plated with gold, albeit only a few microns thick. I'm starting to wonder if there are or have been different manufacturing methods and maybe it changed some time in the past. It is possible they changed the manufacturing process to make them safer? My AM-241 samples are from smoke alarms that were about 20 years old and as yours in brand new it is possible they were manufactured differently. Mine don't look gold in colour at all. I would have expected that even a 2 micron gold plate would have a very slight yellow colour, but mine are simply grey. I have attached photos of mine at the bottom of this post. The quality isn't great as just took quick close ups with my phone.

My main concern with the AM-241 from smoke detectors, which would certainly be less if an alloy of and plated with gold, would be from touching it and inadvertently ingesting it. You know, touch it by accident, don't realize or forget then go eat a sandwich, or packet of crisps, smoke a cigarette, you get where I'm coming from. Americium is soluble in acid and there is a small chance the acid/moisture/grease on your fingers could cause a small amount to come off onto the finger. I'm not too concerned about inhaling AM-241. I'm not going to be going about poking it with a sharp thing or buffing it up with a wire brush so the AM-241 should stay where it is. The same goes for the radiation it emits. The alpha is really no worry at all and the gamma is low energy so kept out of the way of ones self or others is probably enough. I keep mine in a little lead lined box. I have had a couple of accidents in the past involving chemicals so I tend to be a little more cautious these days. Handled correctly and with knowledge and forethought it should never cause harm but I do fear that some people without knowledge could handle it wrongly.

Keeping your sample simply in some kind of enclosure would suffice for storing it.

I find your results ever so slightly confusing. I try and use CPM in most cases for background monitoring as it is hard to get that wrong compared to using conversion factors. The conversion factor for a tube is usually only for one specific radionuclide so say the tube should be calibrated with Cobalt-60 and the conversion factor is given, it is just for that radionuclide which could skew the results for different radionuclides. I'll let you know when I get my J305 kit and we can work out some way of comparing them. Maybe I load your sketch onto an arduino of mine or something similar so we are both looking at the same output. I'll also have a play about with the voltage and see how their method of setting the voltage compares to my own. I made a 1000:1 voltage divider using a 1 gigaohm 1% resistor and calibrated using a few resistors in series for the other side of the voltage divider and seems very accurate. I have used that a few times for setting voltages in counters and appears to work very well with a 20M ohm meter.


The first image is a better representation of the colours of the metal but the 2nd image looks like the AM-241 disc in the center is oxidizing. I suspect that wouldn't happen if it were either an alloy or gold plated. Mine are a plastic disc, not ceramic with the large metal piece that would be one connection to the smoke alarm PCB, then the little holder and finally the AM-241 disc in the center.


 

 

FSM19 wrote:

we need to follow the advice of experts like the NRPB https://www.gov.uk/government/collections/national-radiological-protection-board-nrpb-report-series.

The only issue I have with your statement FSM19, is......... I don't trust my government. Because of that I find it very hard to digest anything on any government website. If I trusted them I probably wouldn't need a background radiation monitor, which I do because I don't trust anyone else with the task of letting me know there is an issue in a prompt manner. That same logic applies to many other things with me.

Aside my tinfoil hat laden skepticism, we do need to heed the knowledge of experts, you are very right.

g346342 wrote:

Let me know when you get your j305 kit so we can compare the measurements.

I got my counter with tube a couple of days ago. I have been playing about with it a little and it seems to work as described. At some point I'm going to do a bit of a write up/comparison of 4 cheap digital PCB type counters (NetIO CG10, BroHogan's 'Radmon', Banggood's counter and the RH Electronics 'Arduino IDE' counter' (just ordered and about a 2 week ship to me) so I'm not going to go into Banggood's counter here, that's for another day.

It has been running for about 48 hours now solid and no issues as such. Using the conversion factor of 0.00812 the counter gives me about the same uSv/hr as my SBM-20 on a GC10; between 0.1 uSv/hr - 0.2 uSv/hr (100 nSv/hr - 200 nSv'hr) so I would say about the same as yours. The same background is seen also with my Gamma Scout so seems OK for background. With a few short tests using various radioactive sources I'm seeing it not quite as sensitive as the SBM-20, but not far off. Researching the tube I find the cathode is a Tin Oxide coating on the outside of the glass with a wire at one end bonded to the outer glass tube. Looking at the tube under a magnifying glass It appears to not be consistent throughout the whole tube and appears to have a varying density. My conclusion for this is when light is shone at an angle the Tin Oxide coating gives off different colours depending on the angle, but the colour fades on one side and end of the tube to just glass so I don't think it is a complete uniform coating. Another 'feature' of this tube is that it is sensitive to UV light. I have proved this by shining a 365nm UV torch at it and the counter goes a little nuts. I have read that it is suggested to cover the tube with black electrical tape to block the light but my fear in doing that is the adhesive could react with the thin Tin Oxide coating or even pull it off, or parts of the coating if the tape was removed. I think a better method would be to use some dense black paper and roll it round the tube and either glue or tape to keep it wrapped around. It is not a tube I would use in an outdoors counter where there was potential of daylight to hit the tube. The construction of the tube is super cheap, built to a price I think, but the cheapest I have found the tube itself was on Aliexpress at £15-16 each, which is about the same price I'm paying for an SBM-20 shipped from Ukraine, so I don't quite understand the price point of the J305 as I would expect the cost of production for the J305 to be no more than £3-£4.

It works though, seems to do the job but it does appear to be the cheapest Geiger counter including tube I have seen so far that is comparable with an SBM-20 performance. I'll do some more tests and comparisons soon when I get all my ducks lined up.