CHAPTER 2
EXPERIMENTAL PROCEDURE
2.1
RECORDING OF SPECTRA
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The shots at Greenhouse, Buster-Jangle, and Tumbler-Snapper, as well as the King shot
(1.0 to 1.1 sec exposure) at Ivy, were studied with a Baird 2-meter, concave grating spectrograph. The first-order spectrum, at a dispersion of 8.3 A/mm, was photographed in each case
in the 3000 to 5000 A wavelength region. The slit width was always 0.030 mm, and the average
aperture of the spectrograph was {/24, which in most cases included a large enough solid angle
of space to see all of the fireball.
A Jarrell-Ash, 21-ft Wadsworth-mount, grating spectrograph was used for the Mike and
King shots at Operation Ivy. This instrument had two gratings, one directly above the other,
each having 15,000 lines/in. The grating in the upper deck illuminated one set of plates and
was used in the first order to cover wavelengths from about 4000 to 7000 A with a dispersion
of 5A/mm. The second-order spectrum was photographed in the lower deck on a second set of
plates so as to cover the 3000 to 4200 A region at a dispersion of 2.5 A/mm. Eastman II-0
spectroscopic plates were used for the second order, and Eastman U-F and I-N plates were
used in the first order. Each deck of the spectrograph had an average aperture of about £/40
and was pointed somewhat above shot center in order to include as much of the fireball as
possible.
No lens or mirror was used between the slit and the bomb in any of the described cases
except in Tumbler-Snapper 6 and 7 and with the Baird spectrograph at King shot. Step wedges
were used in all cases except Tumbler-Snapper 6 and 7 in order to obtain proper exposure.
These were not always the proper ones to obtain a good plate characteristic curve; therefore
an approximate H and D curve was used. This seemed justifiable for comparison of intensities
between different plates and also on the sameplate.
2.2
REDUCTION OF DATA
A Mann comparator was used for measuring wavelengths, and two sets of readings were
made on each plate. The wavelength determinations were accurate to about 0.1 A except in the
cases of the Mike and the King plates, where a shift of the iron comparison spectrum occurred,
and the case of Tumbler-Snapper 7, where the iron calibration lines did not touch the absorption spectrum. In these cases the accuracy was about 0.2 A. Density traces were taken on 2
JACO recording microphotometer using a slit width of 0.015 mm. This was narrow enough to
record all the structure observable on the plates.
The total strength of any spectral line in emission is directly related to the area under the
curve in a plot of intensity vs frequency. In absorption the strength, or intensity, is given by
measuring the area under the whole absorption peak, provided the optical density due to the
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