All methods (that they've told us about) for enriching uranium are slow and require many stages.  In this situation, given the U-235 fractions x[F] in the feed, x[P] in the enriched product, and x[W] in the depleted waste (or tails), the SWU is a measure of the amount of effort required to achieve that enrichment.  The customer would be charged so many $/SWU. There's lots of Google hits on Separative Work Unit.  I found this paper to be quite interesting. arxiv.org/pdf/0906.2505 The usually cited reference book, and one which explains the formula for calculating SWU, is Karl Cohen "The Theory of Isotope Separation", out of print and hard to find, but is in the collection at the King Library at San Jose State University. The gas diffusion and centrifuge methods are so slow because they depend on the mass difference.  Fortuitously, natural fluorine consists of the single mass-19 isotope, so UF6 molecules differ only in the uranium.  Laser isotope separation offers greater specificity by relying on isotopic differences in electronic spectra of uranium atoms or vibrational spectra in UF6 molecules.  So far, laser isotope separation hasn't displaced centrifuges as the preferred technology (at least as far as they're telling us). In principle, i.e. without violating any laws of physics, there could exist a membrane or barrier permeable to only one isotope.  This would allow instant single-stage separation. Diffusion of hydrogen through palladium foil is very effective since the D/H mass ratio is 2.  The obstacle to its use is the energy required to electrolyse huge amounts of water for the 1/5000 deuterium fraction.  If hydrogen sees use as a fuel, isotope separation can piggy-back on it.   --  Gene From: rwg <rwg@sdf.org> To: math-fun <math-fun@mailman.xmission.com> Sent: Sunday, March 22, 2015 8:02 PM Subject: Re: [math-fun] Computational effort On 2015-03-22 12:25, Eugene Salamin via math-fun wrote:

There already is a unit for isotope enrichment effort.  It is the Separative Work Unit, SWU.   --  Gene

Gene, are you saying there's a theoretical proof of no shortcut to enrichment?  That sounds like a dangerous assumption.

      From: Henry Baker <hbaker1@pipeline.com>   To: math-fun <math-fun@mailman.xmission.com>   Sent: Sunday, March 22, 2015 12:18 PM   Subject: Re: [math-fun] Computational effort

Separating U235 from U238 is a pretty decent "proof of work" system.

"Uraniumcoin" ?

"Isotopecoin" ?

"Hex[a]fluorocoin" ?

"Centricoin" ?

These "coins" put the "rich" into "enriched"...

https://en.wikipedia.org/wiki/Enriched_uranium

Of course, you may only want to use Oralloy certificates in commerce, exchangeable* for the real thing.  Who wants to carry around a lead wallet, with even heavier contents?

I've heard of deep pockets, but I can't picture one holding a critical mass of U235coins.  If that's a problem, enrich just short of finite critical mass.  Short of criticality, the lead would be superfluous. Bcc: Tehran mint --rwg

* (Except by certain not-so-friendly countries.)

At 07:16 AM 3/20/2015, James Propp wrote:

...

(b) the Manhattan Project,

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