Neutron Activation of Manganese Using Am-241 and Beryllium

Neutron Activation of Manganese Using Am-241 and Beryllium 

Here's a quick little neutron oven I piled together.

Radioisotope AM-241 gives off alpha radiation.

Beryllium hit by alpha radiation gives off neutrons.

Neutrons hit Manganese which gets irradiated and changed--also giving off gamma radiation.

Gamma radiation serves as the indicator that activation has taken place.

Our victim: good of Manganese Dioxide. It's a black power. I put some in a zip lock baggie for the test. Underneath the bottle is some hdpe plastic. Not really needed, but it's important to note that some elements need slowed down thermal neutrons to be activated. Supposedly, Manganese can be irradiated by fast (unmoderated) neutrons--thus I don't really need the hdpe plastic to slow them down, but what the heck: I've got tons of moderators: hdpe, paraffin wax, wax with boron in it, etc.

Final cap containing additional AM-241.

Various Am-241 sources piled on top of a piece of beryllium. The beryllium came from a defunct x-ray machine.

Awesome old ionizing smoke detector. It has 80 micro curies of Am-241 in it, instead of less than 1 micro curie like modern smoke detectors.

The unused portions (for my work) of the smoke detector.

Here's the cap portion of the smoke detector. So many people overlook this part, there are two little rectangular foil ribbons on the inside that are also AM-241!

Here's the big-boy AM-241 source. Yes, there are three sources in many of these big old smoke detectors!

The radioactive part is under the little cap at the top of this photo.

See that screw in the center? That's the adjustment screw that you can use to adjust how much AM-241 is exposed from the third AM-241 source when the smoke detector is in use.

Pyr-A-Larm (Pyralarm) smoke detector. This one is an F 3/5A and was just loaded with Americium 241 radioistope sources. Three in all! This is the "before" photo before I started disassembly.

These are always on eBay for $120, but sometimes they pop up for much, much less. Just be patient.


From reading the works of Carl Willis I found that radioactive manganese has a half life of about 2.5 hours, so you should let it irradiate in the neutron fluence for double that.

I'm not sure my gamma probe will be able to detect this low amount of gamma, so I may have to let the sample sit for a half-life or two in my gamma spectrometer setup.


Results to follow later and will be posted here. Busy at work and I don't have time to babysit a 5 hour gamma spectrometer run :)

Update: here's a pic of my gamma spectrometer after only two minutes. Notice the huge peak at 823mev! Success!!

Neutron Gun

Neutron Gun

What's so neat about neutrons? Well, among other things they can have a direct impact on their environment. They can knock out atoms in a crystalline structure, it can eat away at metals-causing then to become brittle, or can knock enough atomic particles around to actually change one element into an entirely different one via a process called transmutation.

If you aim the neutrons at heavy water/deuterium ($10) can create tritium (for modern glow-in-the-dark watches and gun sights)...although it would take years and years to accomplish. By the way: tritium slowly decays into helium-3 which is what Geiger counter tubes (Geiger-Muller tubes actually) are filled with.

Back to the design I scribbled above:
Alpha particle hits the beryllium. The beryllium turns onto carbon+a neutron. The neutron hits the paraffin wax and does one of two things, it either: slows down and continues on its merry way, or it hits a nucleus of a hydrogen atom in the wax really good and that sends a proton zinging out.

A word about Beryllium safety...according the internet it's super-deadly. In real life it's used in golf clubs, spark-less hammers, copper-beryllium tools, non-sparking drill bits, DENTAL crowns and implants and all sorts of other common, everyday stuff. 

Hopefully some of this will cause my Geiger counter to click.  If that fails then hopefully a neutron will hit some of the boron sprinkled into the paraffin wax, which will zing out an alpha particle-which can't be seen by my current Geiger counter, but can be seen by my radioscope ($29).

Now, if I replaced the paraffin with more uranium the neutrons would change any U-235 into U-236 (fission!). The U-236 promptly explodes and send off THREE new neutrons which then do the same to more and more U-235 atoms until...well, until the U-235 runs out.

Now, any U-238 in the blob of uranium goes through a similar process and becomes U-239, which blasts of beta particles of all things (which are detectable by my Geiger counter) and it breaks down into neptunium (also number 239). The neptunium-239 zings off yet another beta and becomes plutonium (again, still number 239). The plutonium zings off, are ready for this: more stupid alpha particles! Just like the ones we started with like a billion sentences ago...of course, the whole plutonium end of this reaction is pretty rare: even in a nuclear reactor it would take days.

This is in contrast to the boron portion, which is easy; so easy that hitting boron's huge neutron capture cross-section had been likened to hitting a barn door (a barn is the unit of measurement for denoting the size of a capture cross-section). A single barn unit is about the same size as the cross section of a uranium nucleus...boron's neutron capture cross section is 3800 barns! That's for B-10, regular boring boron still manages 760 barns.

If I replaced the beryllium with aluminum foil the result should be the same. I could replace the uranium at the beginning of the process with any alpha emitter, alpha particles being identical to a helium atom nucleus (2 neutrons bound to 2 protons); although it's like helium-4, not the helium-3 mentioned earlier.

It's all a big circle: helium, uranium, plutonium, helium-3, neptunium, neutrons, neutrons, neutrons...and of course our friend boron.

That's enough boron talk for now. Meow!