NetNews Usenet Archive 1992 #26/NN_1992_26.iso/spool/sci/physics/18503

Internet Message Format | 1992-11-09 | 4.0 KB

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From: [e-mail] (Jim Carr)
Newsgroups: sci.physics
Subject: Re: heavy doubly magic nuclei
Message-ID: <[e-mail]>
Date: 6 Nov 92 22:52:32 GMT
References: <[e-mail]>
Sender: [e-mail]
Reply-To: [e-mail] (Jim Carr)
Organization: SCRI, Florida State University
Lines: 63

In article <[e-mail]> [e-mail] (Douglas R Fils) writes:
>
>    While reviewing my 300 level quantum bokk I came upon a
>section that hadn't impressed me as much as it does now.  It's
>in reference to possibility of doubly magic nuclei at Z=114
>and N=184 (Shell model) or perhaps more accurately, Z=110
>and N=184 (Collective model prediction) with decay on the order
>of 10^8 years via alpha or spontaneoius fission.
>
>    Has anyone got any good references or heard anything about
>this subject?

You bet.  After all, FSU is the home of the original experiments on
primordial superheavy nuclei, experiments that appeared to have located
such nuclei in halos that surround certain inclusions found in mica
from places like Madagascar.  The halos are produced by damage in the
mica produced by alpha decay of the stuff in the inclusion.  The extra
large halos in some samples suggested a high decay energy and, indirectly,
an origin in previously unknown superheavy nuclei.  One of the persons
involved, Gentry, thought this was evidence for a young earth.

Anyway, they did PIXE (proton induced X-ray emission) with a microbeam
that allowed them to scan the inclusion, looking for K x-rays from a
high Z nucleus.  They thought they saw some, ran some tests, fought
with all kinds of leaks (two funding agencies were involved so there
was a turf battle over who might get the credit for funding it), and
published in PRL 37,11 (1976).  It turned out (PRL 37,629) that there
was a previously unsuspected gamma ray that caused the peak they saw.
What was left is insignificant.  Suspicions abound surrounding the
fact that the test runs of that set of targets (they ran a test on
every natural isotope) had been made by one of the proponents.  The
FSU group is quite proud that they caught the mistake -- unfortunately,
the pressure from Washington DC to publish kept them from doing another
test that would have warned that something was wrong.  Science in the
fast lane....

The big advance that came out of this was in the theory.  The Z they
thought had been found was not in the region where some calculations
had predicted.  It turns out (see PRL 37,558) that these predictions
used the wrong spin-orbit force for heavy nuclei, but since all that
work had been done within a small group talking only to each other,
no one had noticed that they got increasingly more accurate answers
with input that was not consistent with other data.  What else is
new, right?  Same old story....

Up to then, most searches had been done by looking at radioactivity
produced in the beam dump at the Bevalac or in other experiments done
by splattering a real heavy projectile like Cf-251 into a real heavy
target like U-238 and hoping they would get lucky.  They did not,
mainly because the fused combination was so "hot" that it blew apart
into lots of tiny pieces.  More recently, experiments pioneered in
Germany used projectile-target combinations where fusion leaves the
final nucleus with very little excitation energy.  They have seen
nuclei up to Z=109 in this way.  Only time will tell if an island
of stabilty will be found.  If it is, it will be a wonderful place
to study many questions about the nature of the nuclear force and
what happens in places like neutron stars.

--
J. A. Carr                                    |  "The New Frontier of which I
[e-mail]                           |  speak is not a set of promises
Florida State University  B-186               |  -- it is a set of challenges."
Supercomputer Computations Research Institute |   John F. Kennedy (15 July 60)