Page 252 - Inorganic Mass Spectrometry - Fundamentals and Applications

238 Smith

of
0.1 % to 0.5% [49]. The same laboratory measured part per million (ppm) levels
iron in zirconium using isotope dilution [SO]; the study was aimed at elucidating
the defo~ation effects of iron contamination in alloys used in reactors. In both
for
these studies, mass spectrometers specifically designed the measurement of iso-
tope ratios were used, and thermal ionization was employed to generate the ion
beams.
to
In a different application not directly related nuclear matters but nonethe-
less addressing a similar problem, Beer and Heumann used isotope dilution to
quantify trace levels of U, Th, Cu, Lb, Cd, Cr, Ni, and Fe in titanium, a metal ex-
tensively used in the microelectronics industry, in which purity critical import-
of
is
ance [S l]. Detection limits ranged from 0.07 ngg for U and Th to 35 ndg for Fe.
An example of what one might call “double” isotope dilution was reported
by Smith et al. [52]. The specific problem addressed was the dete~nation of the
quantity of material (either by weight or volume) in holding tanks in the nuclear
fuel cycle. Safeguards require establishing material balance for these tanks, which
a
contain solutions of spent reactor fuel and, being highly radioactive, constitute a
hostile matrix. The method is a general one, however, and can be applied to any
situation in which the amount of solution is desired. The method involves adding
a known amount of natural lutetium to the tank; this was the first spike. Lutetium
was chosen because it was not present in the sample solutions and well behaved
is
under thermal ionization; other elements could of course be used. After addition
of
of the spike, the contents the tank were thoroughly mixed. An aliquot was with-
drawn and a lutetium spike of enriched 176L,u (the second spike) added. Isotope di-
lution analysis via thermal ionization mass spectrometry was carried out; knowl-
the
edge of the amount of natural lutetium added to tank and its conc~ntration made
calculation of the amount of solution in the tank simple. Precision and accuracy
of
about 0.5%, superior to those of other methods of tank calibration [53], were ob-
tained.

It is with considerable gratification to the author that preparation of this chapter
brought home the realization that in his professional lifetime isotope dilution has
by
moved from a recondite technique used only a few initiates into the mainstream
of analytical science, making valuable contributions a multitude of fields as dis-
in
parate as the nuclear fuel cycle and the workings of the human body.

1. Inghram, M. G.; Hayden, R. J. and book on Mass Spe~tros~o~~, Nuclear Series, Re-
port No. 14, NRC-USA, 1954.