From: blue@nscl01.nscl.msu.edu
Subject: NTT, Yamaguchi, and $565,000 can't be wrong?
Reply-To: blue@nscl01.nscl.msu.edu
Organization: Sci.physics.fusion/Mail Gateway
Date: Wed, 16 Dec 1992 17:08:01 GMT

Jed, Rothwell keeps assuring us that corporate giants (in Japan) don't
make mistakes, but then we have an example laid before us that contradicts
that.  There are several things wrong with the Yamaguchi experiment.  It
really should be refined in some rather obvious and relatively inexpensive
ways.  And I take the fact that NTT has not recognized this fact as a clear
indication that their research establishment isn't as good as it really
ought to be.

First let me give a summary of the basic features of Yamaguchi's experiment.
Sample preparation starts with loading palladium foil with either hydrogen
or deuterium by exposure of a heated foil to the appropriate atmosphere.
The sample is then coated by a layer of gold on one side and a layer of
magnesium oxide on the other side.  Samples of this type are then installed
in a vacuum chamber pumped to 10^-8 Torr by a turbomolecular pump.  The
principle analytic instrument is a high resolution RGA set to scan for ions
in the mass 4 range.  A form of differential pumping is used that is
said to maintain a factor of 10 better pressure in the RGA than in the
sample chamber, but only the single turbo pump is employed.

With the sample in place and the chamber pumped down, the sample is heated
by applying a current by either electron or ion bombardment.  I haven't
sorted out which it is, but apparantly the power input is regulated.  The
temperature of the sample is monitored and the evolution of gas which
produces mass 4 ions is recorded in a series of scans.  Initially the
pressure rises rapidily to a peak, then falls to a plateau where it
remains for some time before it begins to return toward base pressure.
In Yamaguchi's interpretation, there are two correlated effects which
occur at the end of this pressure plateau.  The temperature of the
sample rises and the RGA scan shows the production of helium if the
gas loading was deuterium.  For hydrogen-loaded samples the temperature
rise appears to be the same, but there are no mass 4 ions in the RGA
scan.

What are the problems with this experiment as I see them?  Remember this
kit costs $565K so another $10 to $20K spent on improvements should be
no big deal for NTT.  First off the RGA should have its own turbo pump
so that operating pressure in the RGA could be better controlled.  As
the chamber pressure rises and falls in the transitions where the effect
is supposed to occur, partial pressures for light gasses relative to
other residuals can vary dramatically.  Both the turbo pump and the RGA
are operating outside the pressure ranges where than can be expected to
give their best performance.  For example the turbo pump may not be
pumping hydrogen and deuterium at all during the crucial parts of the
measurement.

It would seem that the sample temperature could also be dramatically
influence by the base pressure in the chamber (also the composition of
the residual gas).  Cooling by convection is probably significant until
the pressure starts to drop, and guess when the temperature rise is
observed?

As for the RGA scans, the mass 4 spectral region is dominated by
D2+ molecular ions and the peak width is strongly influenced by
pressure.  The scans that are supposed showing 4He are pretty ugly
so extracting the helium intensity is not straight forward.  It
must involve the subtraction of a D2+ peak shape as a function of
pressure, but there may be transient effects that are not duplicated
when the peak shapes are determined by the introduction of D2 gas
into the system.  I think the mass scans need to be made under more
stable and reproducible pressure conditions before they can be
given much credence.  As an alternative or suppliment I would recommend
some form of optical spectroscopy to provide a helium signal less
subject to confusion.  

The improvements I have suggested can be paid for many times over from
the profits on the sale of two of these kits.  Off the top of my head
I would say you could assemble the kit yourself for less than half the
asking price.

Dick Blue
NSCL @ MSU
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