FAQ - Activation Materials - Manganese

[Richard Hull]

Manganese is made up of a single naturally occuring isotope, Mn 55. Neutrons activate this to become Mn 56. This is basically a gamma emitter with a strong spectral line at 849kev.

The interesting thing is that the stuff is above 1 barn over a vast range up to and including fast neutrons. So even the odd fast neutron will activate the metal. Obviously, the more thermalized the neutrons are, the higher the cross section and the more activation per unit fluence.

The bummer is that this stuff never really rises to the kilobarn range at any point after thermalization

Even at thermal energy, you are only in the 20 barn range. Also, the half-life of its activation product, Mn 56, is about 2.5 hours! Ideally, you would like 10 hours exposure to maximize activation. This is just not possible with most fusors. Thus, less than optimum activation is obtained in most amateur hands. This means that only fusors kicking out lots of neutrons, (>600k n/s) can activate manganese for easy detection. It also means the amateur should have a gamma ray spectrometer.

Check out Carl Willis' supreb posting on this material for complete details.

viewtopic.php?f=13&t=5275&hilit=manganese#p33719

And

viewtopic.php?f=13&t=5313&hilit=manganese#p33757

All in all Manganese is a higher difficulty material for fusors and requires operation just under the mega neutron mark for easy detection with an activation run time of a minimum of 20 minutes.

I would think that the best arrangement is Carl's Manganous Sulfate procedure as the water medium is also the moderator. This allows for activating near that kilobarn peak seen in the cross section....Cool!

I made my own manganous sulfate solution by dissolving Mn chips in battery acid as I had both on hand and yet none of the chemical, itself. (note - Mn is rapidly soluable only in DILUTE acids.)

The usual ENDF 300K plot is attached.

Richard Hull