Luca Lutterotti wrote:
> Sorry for the question, but I personally and philosophically don't think we
> can measure absolute values......
Hmmm, In that case, I guess you should persuade the USA to change the
name of my employer.
I disagree. There are such things as fundamental properties and they can
be measured. It takes careful work to plan an experiment so that
measurements are referred to primary constants, for example in this case
the fundamental length reference. I am glad I don't have to do this sort
of work myself, but have great respect for the folks that do.
It should be noted though that the certified lattice constant for a
standard reference material is something measured on a real specimen
(that must be available in ~100 kg quantities) under the sorts of
conditions likely to exist in the lab setting where the SRM will be
used. This is different from a fundamental constant, such as the lattice
parameter for one single crystal specimen of ultrapure Si, under a
highly controlled environment. Since the materials and conditions
differ, one would expect the lattice constants to differ too. Likewise,
since the SRM 640, 640a, & 640b, materials physically differ, both with
respect to impurities and with respect to processing, one would expect
their lattice constants to differ, too.
Brian
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Brian H. Toby, Ph.D. Leader, Crystallography Team
[EMAIL PROTECTED] NIST Center for Neutron Research, Stop 8562
voice: 301-975-4297 National Institute of Standards & Technology
FAX: 301-921-9847 Gaithersburg, MD 20899-8562
http://www.ncnr.nist.gov/xtal
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