[eliosfederico (OP)]

Hi everyone!

I like to experiment with old gieger counters that I buy online.
For test them I use a small source (smoke detector) of Americium 241. For the last year I kept it in a sealed plastic box covered in aluminium foil. When closed, I could measure around 0.150 uSv/h (on top of the background radiation) only when the pancake detector was directly on the box, raising it 10cm or more and it would detect only background. Also in the room where I keep the box there is no change in radiation levels. I did a 24 hours CPM count.

I read online that the alluminium foil isn't necessary; alpha particles are easily stopped by air or just plastic. I also read that the alpha radiation creates neutrons when striking alluminium and this got me worried. Did I get a dangerous dose of neutrons??
Can someone clear this up?

Thanks!

[alancalverd]

Unlikely to have done you any harm, but it might encourage you to learn about reaction cross-sections, radiation dosimetry, and radiation protection. There's a career out there!

[eliosfederico (OP)]

Hi,
Thank you for your answer!

I had the container in my attic, on top of an high closet (almost touching the low ceiling) and that was a bad idea because I use that room also as office, and the box was around 2 meters from me.

How far do the neutrons from Am-241 travel?

[alancalverd]

Neutron range is effectively infinite in dry air, but the neutron yield from pure Am241 is small. The real problem is the toxicity of inhaled or ingested alpha emitters, so beware of handling bare Am241 without a glovebox.

[eliosfederico (OP)]

Thanks for your tips!
In my container I had the button of Am-241 and on top of it I had adhesive putty (the one you use on walls to don't leave tape traces) and then a bunch of aluminum sheets bent together.
I guess the putty was 0,5cm thick and if I am correct most of the alpha were already blocked from the putty, so is it correct that then the neutrons production would have been even less than what I thought?

[alancalverd]

Not sure about the neutron cross section of BluTack, but what you were measuring is almost certainly the 50 keV gamma radiation from the Am241. Neutron detection and dosimetry is a black art as far as I am concerned!

[Bored chemist]

I would be somewhat impressed if any amateur scientist was able to either
Measure the neutrons generated from a typical 241Am smoke detector source (no matter what the"target" was- Be Al- whatever) or
Measure the increase above background radiation caused by a smoke detector at a range of more than a metre.