Dear Forum,(adsbygoogle = window.adsbygoogle || []).push({});

this is my forst time here, so forgive me if I don't conform to any etiquette or rules.

When I did nuclear physics in undergraduate school many years ago, I couldn't help noticing that little or no information was ever given on he issue of neutron multiplication and criticality of Uranium and Plutonium. At the time I thought that such information was still classified but I still was very curious about the basic physics involved. I vaguely suspected that diffusion was involved, but I never attempted to make any calculations.

Some years ago I read Richard Rhodes' book "The Making of the Atom Bomb". This is truly a fantastic source of information for physicists, not only about the Manhattan project but also on the scientific community involved in developing the first quantum theory and what would later become nuclear physics. In the book there is a reference to Robert Serber's "Primer", which was a series of lectures on the basics physics of the nuclear device and also to a paper by Rudolf Peierls. I downloaded a paper version of the "Primer" from a Los Alamos server about 4 years ago and have now also bought the edited version by Serber and Rhodes. I also have a copy of Peierls original paper, where gives a formula for the calculation of the critical mass.

I have tried to compile these two sources into a Mathematica (and html) document and tried to elaborate and compare the derivations of the critical mass in the "Primer" and in Peierls paper. It is curious that there is a typo in Peierl's paper, but with Mathematica it is easy to see the numerical values are the same. Here are the URL:s

http://hem.bredband.net/sormol/critrad/critrad.htm [Broken]

http://hem.bredband.net/sormol/critrad/criticalMass.nb [Broken]

The numerical values from the critical mass formula in the Primer and those derived from Peierls formula differ significantly. I would be very interested if anyone could comment on the URL:s above and also give some improvements. Please feel free to use the Mathematica (5.1) notebook as a start.

Best Regards,

Sören Molander

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# Critical mass formula: The Los Alamos Primer and Rudolf Peierls paper from 1939

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