74
CROCKER, KAWAHARA, AND FREILING
Sedan was the well-known 100-kt cratering shot for the Plowshare
program. The device was buried 635 ft below the surface in alluvial
material in Area 10. NRDL collected samples at stations within 1 to
3.6 miles of ground zero. Analyses were performed on about 50 samples for the short list of nuclides previously given, and about one-third
of these were analyzed for the longlist.
TREATMENT OF THE DATA
The radiochemical analytical work was contracted out to three
commercial laboratories since NRDL does not have facilities for
handling a large volume of samples for routine analysis. The contractors were
also intended
quired nearly
the analyses.
selected on
to serve for
a year for
The results
the basis of qualification tests, which were
interlaboratory calibration purposes. It reall the contractors to complete and report
were reported to NRDL as disintegrations
per minute or equivalent ?U thermal-neutron fissions at shot time.
NRDL then converted the values to equivalent fissions of the device
at shot time, using mass-chain yield values supplied by the weapons
laboratories. At the same time the calibration factors derived from
the qualification-test analyses were applied.
As a reference nuclide *Zr was chosen for fractionation studies.
Some such choice seems unavoidable if fractionation is to be discussed. Zirconium-95 belongs to a class of nuclides (other members
are °°Mo, ‘“4Ce, and ‘4"Nd) that are generally present in debris in equal
quantities when expressed as equivalent fissions. Strontium-89, on the
other hand, shows wide variation when compared with any of these.
The ratio of equivalent fissions of ™Sr to equivalent fissions of Zr
is, in fact, a fairly good indicator of the degree to which a sample is
fractionated. The ratio will be 1 for an unfractionated sample, less
than 1 for a sample depleted in Sr, and greater than 1 for a sample
enriched in ®sr.
The behavior of other fractionating nuclides can be correlated
with that of "Sr by log—log plotting. The logof the ratio, r; 9., of
equivalent fissions of nuclide i to equivalent fissions of *°Zr is plotted
against the log of the similar ratio for “Sr and *Zr. The data so
treated can be fitted more or less satisfactorily to a straight line.
The slope of the line is then an indication of the extent of fractionation
of nuclidei.
RESULTS AND DISCUSSION
For the Johnie Boy and Small Boyshots, the local-fallout collections were sufficient to define the geographical extent of the close-in