Hello world!

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3 Responses to “Hello world!”

  1. Mr WordPress Says:

    Hi, this is a comment.
    To delete a comment, just log in, and view the posts’ comments, there you will have the option to edit or delete them.

  2. John Baez Says:

    Hi, this is another comment.

  3. grlcowan Says:

    Hello. I started this when I thought I was going to get around to a nice visualization of spent fuel radioactivity reduction over time.

    Spent fuel radioactivity has two components: beta decay of fission fragments, and alpha decay of fuel that hasn’t really been spent, just converted from the naturally occurring, slowly alpha-decaying forms 235-U, 238-U, and — so far just experimentally — 232-Th, to forms that alpha-decay more quickly.

    At different times, different sets of beta-decayers dominate the beta-ray output, but their total, as a fraction of the fission power that made them, is always fairly close to this, the Untermeyer and Weill approximation:

    (t+10)^(-0.2) – (t+10+T_0)^(-0.2)
    – 0.87*
    (t+20000000)^(-0.2) – (t+20000000+T_0)^(-0.2)


    Time since fission ceased, in seconds, is ‘t’. Time it continued before then, also in seconds, is ‘T_0’.

    “Fairly close” meaning almost always within a half-order of magnitude, usually within a third of one, while beta-decay power output is declining by many Os of M. This regularity is because, for beta decays,

    … there is a proportionality between the disintegration constant and the fifth power of the disintegration energy …

    Alpha decays also have a well-defined variation of energy versus lifetime, and I got a spreadsheet to show it, but it’s iterative, with lots of cosine- and log-taking at each iteration. Fortunately it converges quickly. So in principle one could, and I may yet get around to, fit a sum of the U&W business and a similar thing for alpha decay to the raw data.

    But the raw data are hard to get! ORIGEN provides a pretty good version of them, if you have the willingness to beat it into submission, and spend US$791 to first get your copy. I definitely don’t have the latter.

    Fortunately Ted Sorensen has done both, and provided a nice shrinking-circle visualization on his thorium-energy website, available only if you register.

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