were available for monitoring and rough estimation of samples.
The RCL 256 channel pulse height analyzer and shielded, tow-level 3-inch sodium
iodi
counter was used for checking the gamma energy spectrum results and for intercalibr ati ie
the 2%-inch, Nal, single-channel analyzer.
‘On of
5.6 RESULTS AND DISCUSSION
5.6.1 Airborne Activity, Table 5.1 presents the results of a portion of airborne Particulate
samples collected on aerosol Millipore filters. The sampling was begun at shot time and car.
ried on for 24 hours or longer.
An increase is shownin the air counts from 7 to 15 hours after
detonation, depending upon the position of the ship.
Horizon received dry particulate fallout.
Sixteen hours after Shot Zuni, the M/V
Following the fallout, the background of the ship was
found to be from 5 to 30 mr/hr, aS measured with a survey meter.
The gamma backgroundof
the lead-shielded scintillation counters rose to 108 counts/min, preventing any low-level count.
ing. After several days, the level had dropped to a point where beta counting was possible with
an instrument background of 250 to 500 counts/min.
The best record of airborne activity was
obtained from Shot Dakota, while the ship was moored at Site Elmer.
Figure 5,1 shows the
record of the airborne activity during a time when the instrument background had decayed to
about 1,500 counts/min gamma. Figure 5.2 gives the decay curves for three Dakota air Samples,
For each sample the radioactive decay constant K,
as described in Section 2.6.12, is indicated,
A peculiar abrupt change in slope occurs in each case.
ment error.
This could have been due to aninstru-
However, curve D-1 appears to have a smooth transition between the two slopes.
Figure 5.3 gives the decay curves for the particulate matter filtered through a Millipore
filter following Shot Tewa. The decay constant K is again indicated, but since both gamma and
beta activity are shown in this figure, the gamma decay is labelled yK and the beta, 8K.
The
decay curves are presented with those of the feathers of a live bird that had been singed by the
shot. Some fractionation had taken place.
Table 5.2 gives a comparison of the beta activity with particle size range for three filters
in series.
The particulate samples shown in Table 5.1 were insufficient for a complete chemical analysis.
A gamma spectrum of a series of air samples collected at Site Elmer from 10°to 20 hours after
Shot Dakota and analyzed 25 August 1956 showed the presence of 150 to 135 Mev photons of Ce’!
and Ce'4 420 dis/min Ru!3, 610 dis/min Zr® per 104 liters of air; no Ba!!? was detected.
An analysis of the singed feathers of a live water fowl caught 23 July 1956 at 11°53’N, 165°
12.8’ E and analyzed 23 June 1957 gave 0 dis/min Ce!110 dis/min Ru!*, 30 dis/min Zr,
45 dis/min Mn*4 and 400 dis/min Zn®5. The absence of the rare earths and the predominance
of Zn®* suggests that the activity may have been internal, rather than from airborne particulate
matter.
5.6.2 Water Analysis. Elemental iodine is readily adsorbed on polyethylene.
Sodium iodide
carrier was added to some of the water samples to reduce the oxidation and adsorption loss of
{31 Visible discoloration of the containers by free iodine was observed in most instances.
Mn* was identified in a number of samples of sea water. This isotope, probably existing as
Mn*’, appears to be reduced to insoluble MnO,on the organic surface of polyethylene storage
bottles. After one year storage, a 1-liter bottle containing 30 x 10° atoms of Mn** in sea water
had adsorbed 16 percent of the manganese as MnQ.
Shot Cherokee, 21 May 1956, produced insufficient oceanic contamination along the track of
the M/V Horizon for an accurate assay.
Shot Zuni, 28 May 1956, produced airborne activity detected at H+10 hours at 12°02’N, 165°
32’E. At H+15 hours fallout occurred aboard the M/V Horizon. The instrumental background
of the gamma scintillation counters and pulse height analyzer increased from 110 counts per
minute to over 10° counts per minute in spite of 2 inches of lead shielding. Water samples collected subsequent to Shot Zuni were processed, but were not assayed aboard ship.
114
Gross beta