2.4 PARTICLE WORK
Some investigation of particle characteristics was carried out for all the cloud and height
‘line samples from Shot Koa that were large enough to work with. Approximately a quarter of
each filter paper from the cloud samples and one section from the E-1 sampler were shipped
to UCRL by the first flyaway following the shot. On each sample, thefilter paper was removed
by burning off in a stream of atomic oxygen from a gas discharge generator.
The maximum
temperature reached during burnoff was around 200°C. The weight of material recovered
varied from 50 mg to about 4.5 gm.
At UCRL, some of the cloud samples were separated into coarse and fine fractions using a
Bahco centrifuge, and fall rate distribution curves were determined for the two fractions with
the micromerograph. Fall rate data was also obtained for all the height line samples, and in
several cases the specific activity-fall rate curves were determined for cloud and fallout samples. In operating the micromerograph, the weight could either be recorded continuously or in
16 increments by means of individual pans on a rotating turntable.
Two of the height line samples and three cloud samples, separated into coarse and fine frac-
tions with the Bahco, were transmitted from UCRL to NRDL for examination. The chemical
substances presentin these samples were identified with the polarizing microscope and by Xray diffraction, and the particle size distributions determined by microscopic observation.
A
binocular microscope fitted with ocular micrometers containing a linear scale was used for the
particle work. Each scale division of the micrometer represented 15 microns for the magnification used (100X). A portion of the sample was placed on a microscope slide and tapped gently
to disperse the particles. Traverses were made along the slide from one extreme edge of the
dispersion to the other and every particle within the micrometer scale was sized and typed.
Generally, several appropriately spaced traverses were taken.
The particles were sized tn
terms of maximum diameter and typed by the conventional classification of irregular, spherical,
or agglomerated.
Diameters were measured to the nearest half scale division, and particles
less than a half unit were ignored.
Particles adhering to each other were sized individually,
if possible, or otherwise not taken into account.
Particle characteristics and fall rate and size distribution curves are given in Appendix C.
No particle work was done on the samples from Oak and Walnut.
2.5 SAMPLE ANALYSIS AND RADIOCHEMICAL PROCEDURES
Radiochemical analyses were carried out on the gross particulate cloud samples from the
wing tank collectors, on size-separated cloud samples, on gas-particulate samples from the
coincident units, and on fallout samples.
The major part of the analytical work on the cloud
and fallout particle samples was done by NRDL (some by LASL), whereas the gas-particulate
samples for the determination of fission ratiog (Section 1.2.4) were analyzed at UCRL.
The gross particulate and fallout samples were shipped to NRDL onfilter papers as collected
{n the field. The size-separated samples were prepared at UCRL by the oxygen burnoff and
centrifuge technique described in Section 2.4, and were then transmitted to NRDL.
Two particle
groups were separated for the Koa and Oak samples and three for Walnut (Appendix B).
At NRDL the samples were prepared for analysis by wet ashing with fuming HNO, and HClO,
to destroy organic material, then fuming with HF to remove silica. The HF was expelled by
again fuming with HClQ,, and the resulting solution was transferred to a volumetric flask and
diluted to volume with 4NHC1.
Aliquots of the HCI solutions were taken for the analyses.
A
total of 1,040 radionuclide determinations and 41 elemental analyses (Section 1.3.5) were performed at NRDL using the following procedures:
1.
Elemental sodium and calcium were determined with the flame photometer using a matrix
very similar to the constituents of coral.
2. Mo! was determined by either of two methods, depending on the age of the sample. A
carrier-free anion exchange method (Reference 73) was used for fresh samples, whereas a
modified precipitation method (Reference 74) was used for older samples.
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