Jack said, "... you haven't explained why the nuclear physics is 'way
off'...neither radium, or any of its daughters, is a neutron emitter.
The story is HOIF (hokum on its face)."
Of course, I just didn't get that far.
But I didn't gather from the story that he was hoping to fission the
radium or thorium or any daughters of those. I gather that he first
wanted the americium or thorium, and then later wanted radium, for use
with beryllium to make a neutron source that could be used to create
fissionable material by bombarding 238U with neutrons to make 239Pu.
The reaction is 238U + n --> 239U, beta decay to 230Np, beta decay to
239Pu. So I think he wanted to make 239Pu from 238U, and that process
is correct nuclear physics, and he could have gotten that from any
nuclear book or have gotten it from the WWW.
Also, his use of an alpha source to bombard beryllium to get neutrons is
correct nuclear physics, except this is not usually done with Am or Ra
if you want just neutrons because the with Am and Ra you will also get
gamma emission and beta emission from the Am and Ra decays and/or
daughter decays. Rather, for a pure neutron source we use 210-polonium
and beryllium because 210Po alpha decays 100% to the ground state of
206Pb (stable). There are no betas, gammas, or further daughters. Just
alphas from the 210Po and then just neutrons when these hit the
beryllium.
But, of course, Am (smoke detectors), Ra (watch dials), Th (lantern
mantles), U (Fiestaware) would be the only readily available alpha
emitters without specifically buying an alpha source. So I don't find
fault with the idea of getting an alpha source, using it to bombard
beryllium to make neutrons, thermalizing the neutrons, using them to
bombard 238U to make 239Pu.
Of course, up to here there still isn't any "nuclear reactor." And
there won't be any reactor until enough 239Pu is made so there can be a
self-sustaining fission chain reaction, and the kid never got anywhere
remotely close to this. He did not build a reactor. Not even close.
So the basic nuclear physics (idea portion) of the story could be
obtained from textbooks or on-line. Where the story is "way off" is in
the described implementation, and in the described result (a reactor).
If he did anything beyond collect and dissassemble a few smoke
detecters, scrape a few watch dials, and get some lantern mantles I
would be surprised. Even if he could have pulled off recovery and
isolation and purification of Ra or Am or Th (which he could not do from
the methods he described, because he wasn't set up to do microscale
chemistry) he never approached having enough alpha material to get
sufficient neutron flux to get sufficient 239Pu to build a reactor.
That's where the nuclear physics is "way off." (Plus the story of the
geiger counter.) Indeed, the Harpers story never gets as far as
actually making any fissionable material and then trying to build a
reactor with it.
Michael D. Edmiston, Ph.D.
Professor of Physics and Chemistry
Bluffton University
Bluffton, OH 45817
(419)-358-3270
edmiston@bluffton.edu
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