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  • MikeM124 commented on tanner_tech's instructable Simplest Geiger Counter2 months ago
    Simplest Geiger Counter

    Hmm, nice work and well done indeed :-)Your results however raise an interesting question re nucleonic interactions based upon these assumptions re smoke detectors, their radiation source purity, glass effect etc,1. Smoke detectors utilizing Americium (if very pure) only give off Alpha particles2. Alpha particles don't travel far in air before encountering air molecules which reduces their energy substantially - for a smoke detector something like 1-2 cm so beyond that there won't be a reading. I see when only close, this is a reading.3. Glass is effectively a brick wall for the energy range of Alpha expected from a typical (retail) Americium source however, Beta particles can pass through.Given these facts, then these questions arise:-a. Is it possible Americium isn't pure & can be...see more »Hmm, nice work and well done indeed :-)Your results however raise an interesting question re nucleonic interactions based upon these assumptions re smoke detectors, their radiation source purity, glass effect etc,1. Smoke detectors utilizing Americium (if very pure) only give off Alpha particles2. Alpha particles don't travel far in air before encountering air molecules which reduces their energy substantially - for a smoke detector something like 1-2 cm so beyond that there won't be a reading. I see when only close, this is a reading.3. Glass is effectively a brick wall for the energy range of Alpha expected from a typical (retail) Americium source however, Beta particles can pass through.Given these facts, then these questions arise:-a. Is it possible Americium isn't pure & can be contaminated with a Beta emitter ?b. If there's another radiation emitted Eg neutrons then they will pass through the glass but, on the way through encounter Boron which will absorb a neutron & emit an Alpha which is then detected. In so far as neutrons are not charged particles & wouldn't be ionize hence wouldn't be detected directly, it would be of interest to place a Alpha/Beta shield between the Americium & the glass which can allow neutrons through can you try this ?c. Although b. is unlikely, its more unlikely the Americium has a contaminant which is a very high energy Alpha emitter which allows the Alpha through the glass, this seems possible as the distance to the glass from the Americium needs to be short to get a reading, can you borrow an Alpha/Beta modern detector or take that Americium source for checking - maybe at a local unit - and hopefully with your setup so a graphical comparison can be made ?Possible regulatory issue arises as its not clear how well the Americium source you have has passed earlier inspection either at import or at time of fabrication and if indeed it has contaminants then you may have stumbled upon a lurking issue re the sources, Eg If they slipped inspection but, had other radiation sources contaminating then it would be worth pinning this down definitively for the safety of all concerned, good luck...Thanks for reading & again commendations on the work, well done :-)RegardsMike MassenPerth, Western Australia

    Hi,Further to my last comment, please don't panic, I realise you must have a far better quality geiger tube that most I've seen which either has a very thin glass or a composition which allows some Alpha particles through - this is sort of supported by the fact you need to be very close...Most geiger tubes I've encoountered years ago weren't so well built, it all depends of course, so please don't worry - though I am curious just how old that smoke detector Americium alpha source & if its passed manufacture/regulatory specs ?Cheers

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