NetNews Usenet Archive 1992 #18/NN_1992_18.iso/spool/sci/physics/fusion/2021

Internet Message Format | 1992-08-13 | 2.7 KB

Path: sparky!uunet!mcsun!Germany.EU.net!unido!sbsvax!mpii01036!dietz
From: [e-mail] (Paul Dietz)
Newsgroups: sci.physics.fusion
Subject: Re: Mr. Neutron gets divorced
Message-ID: <[e-mail]>
Date: 14 Aug 92 11:02:26 GMT
References: <[e-mail]>
Sender: [e-mail]
Lines: 51

In article <[e-mail]>, [e-mail] (John Logajan) writes:

 |> Comptom agitation makes the tunnel short.  Is there reason to
 |> doubt that 1-2 MeV kinetic deuterons can have nuclear relations
 |> with Pd's?  Even if the probability is low for any given
 |> approach, there is a heck of a lot of ricocheting going on.
 |> (I know, for instance, that air molecules at standard temp and
 |> pressure collide 10^9 times per second, and their kinetic
 |> energy is in eV rather than MeV!)


Wrong.  There is not a "heck of a lot of ricochetting" going
on.  The behavior of an energetic deuteron in solid materials
is to lose energy very rapidly to ionization.  The chance
the deuteron comes close to a Pd nucleus is quite small.

Also, the maximum energy a deuteron could get from elastic
scattering of a (say) 1 MeV gamma is only about 300 eV -- and
that only if the gamma is reflected 180 degrees.  Electrons get
much more energy, but then electrons are much less massive.

Please, use common sense: if "ricochetting" deuterons had some
massive effect, wouldn't that have been seen years ago when people
starting bombarding things with deuteron beams?


 |> And finally, as someone else pointed out, deuterons are oblong,
 |> and therefore at a minimum, 50% of the time, they will approach
 |> the Pd nucleus neutron first.  Add the repulsive force acting
 |> only on the proton, and you have a tendency for the deuteron to
 |> rotate neutron first toward the target Pd nucleus.

Yippy. You gain a whole 3 or 4 fermis (10^-5 angstroms) this way.
Utterly negligible.  The last 3 or 4 fermis is not the problem!

I also want to add a correction to another misconception: the fact
that a neutron would liberate energy upon reaching the palladium
nucleus does not make it (much) easier for the neutron to tunnel
into the palladium.  Go look at the equations -- the exponential
term depends mainly on the height of the barrier, not on the depth
of the "hole" at the end.  In the case of this supposed neutron tunneling,
the integrated barrier is (for all but gammas very close to
threshold) *higher* than the barrier for direct cold D-D fusion (which, as
we all know, is calculated to be negligible).

Finally: it hasn't been explained why we wouldn't see the capture
gammas.  There's no obvious reason why the proton should get the
energy liberated by the neutron capture.

    Paul F. Dietz
    [e-mail]