The components of each sample were dried to constant
weight in the laboratory at Seattle
(Table 1).
The entire
diet for each individual was then homogenized with added
water in a high-speed blender,
to a fine powder.
fat,
protein,
dried at 98°C and pulverized
Subsamples of the powder were taken for
carbohydrate and radiochemical analyses.
Forty to 250-gm portions were wet ashed with HNO3 and H202
and the ash dried in 250-ml beakers for gamma ray spectroscopy.
The gamma-counting equipment consisted of a three-inch
thallium-activated sodium iodide crystal used in conjunction
with a 256~-channel analyzer with a digital print-out.
total counts
per minute under the photopeak
The
were calculated
by summing counts per minute of all channels included in the
peak and subtracting the background counts.
The
counting
efficiency for the gamma energy measured was determined by
calibrating the instrument with standards with an error of f
10 per cent.
Counts per minute were converted to disintegra-
tions per minute by a factor derived from the counting efficiency and the fraction of disintegrations giving rise to the
gamma radiation counted.
zinc-65,
te factors used for cobalt-60,
manganese-54 and cesium-barium-137 were 27.4,
18.8 and 16.5 respectively.
54,
The correction factor used for
sample size as compared to a point source,
determined