Replies

"But aside from that, suppose you need 1 pound. Start with 4 pounds and you have effectively tripled the half-life. Po-210 decay products can be separated from the remaining polonium through chemical and physical processes when such separation is desired. Since the half-life of polonium-210 is 138 days, the hypothetical 8x supply would last for a year and a half." - calenel

Not inside your weapon. What you are saying is correct for high school physics experiments, but it is incorrect for atomic physics packages due to purity issues. Put simply, you no longer have a pure source, and can't readily identify what is pure or impure (inside your weapon) after one half-life cycle has expired.

Your overall neutron emission rate will no longer be precise, as some neutrons will be absorbed or radiated at different times by the impurities that time introduces.

Plutonium 241 (commonly found in Pu-239) rapidly decays into Americium 241, for example...a problematic Gamma emitter.

Po-210, for instance, does an Alpha decay into lead...a neutron shield. So simply tripling your quantity of Po-210 can't triple your half-life (or effective weapon life) because you are introducing a lead shield into your fissionables in your physics package itself as Po-210 decays over 140 days!

The way around this natural time limit is *maintenance*. Lots and lots of highly advanced clean-room maintenance (by highly skilled personnel) who understand that Plutonium is pyrophoric, brittle, and oxidizes rapidly.

These are not things that are done out in the field. You don't distill plutonium out in the field. You don't machine it out in the field. Nor do you create meaningful supplies of Po-210 out in the field (you need a working nuclear reactor for that).

"Not inside your weapon. What you are saying is correct for high school physics experiments, but it is incorrect for atomic physics packages due to purity issues. Put simply, you no longer have a pure source, and can't readily identify what is pure or impure (inside your weapon) after one half-life cycle has expired."

Po-210 decays into an alpha and Pb-206 (stable lead isotope). Alpha particles would be stopped by any simple shielding making it easy to hide the Po-210. Having excess capacity would extend your time for constructing the weapon. Separation of the Po-210 from the Pb-206 can be accomplished chemically or physically just prior to use and the initiator constructed at that point. Not that I think it matters. Given that the purpose of the Po-210 is to provide alphas for the beryllium to "use" to generate neutrons, purity may not really matter all that much if you have excess capacity.

"Your overall neutron emission rate will no longer be precise, as some neutrons will be absorbed or radiated at different times by the impurities that time introduces."

Your neutron emission rate should (ideally) be zero until you mix the beryllium and polonium, at which point it can be determined by the relative concentrations of the two components. But it doesn't matter since the polonium gets purified in this scenario just prior to consumption.

"Plutonium 241 (commonly found in Pu-239) rapidly decays into Americium 241, for example...a problematic Gamma emitter."

What has this to do with anything? It isn't pertinent to the initiator, nor is it a factor for the plutonium.

"Po-210, for instance, does an Alpha decay into lead...a neutron shield. So simply tripling your quantity of Po-210 can't triple your half-life (or effective weapon life) because you are introducing a lead shield into your fissionables in your physics package itself as Po-210 decays over 140 days!"

As above - you separate just prior to use. Also, triple the amount would not triple the effective weapon life. You would need 4 times the amount to triple the time you would have at least the required amount.

"These are not things that are done out in the field. You don't distill plutonium out in the field. You don't machine it out in the field. Nor do you create meaningful supplies of Po-210 out in the field (you need a working nuclear reactor for that)."

You get the excess ahead of time from a working nuclear reactor, as I stated in an earlier post, or from a research lab or other source (Po-210). You don't do anything with the plutonium except transport it to where it will be used in a secure (air and water tight) container.