Cook Plant preoperational studies 1970 / John C. Ayers ... [et al.].

The effective area over which the detector can measure
gamma radiation was determined by coiling Tygon tubing to form
a flat plane on the surface of the sand with the detector
mounted inside the rubber tire above the Tygon tubing. A
solution of cesium-137 was pumped through the Tygon tubing and
the activity of the cesium-137 was recorded. The diameter of
the coiled Tygon tubing was increased until the activity
measured did not increase with an increase in coil diameter.
It was determined that a coil diameter greater than 70 cm contributed no additional counts from the cesium-137. Thus, 70
cm was taken to be the diameter of the effective area over
which the detector is sensitive.
The coiled Tygon tubing was used to obtain standard
reference spectra by pumping known activities of various radionuclides through the tubing. Reference spectra were obtained
for Cs-137, Zn-65, Mn-54, Co-58, Co-60, K-40, and Ra-226. The
library of reference spectra are used to analyze quantitatively
gamma ray spectra obtained in the field.
A spectrum analysis computer program which uses the least
squares method has been developed by J.I. Trombka of the Goddard
Space Flight Center (4). The computer program was revised
substantially for counting environmental samples and named NASA
after its original sponsor.
The NASA program constructs a spectrum from the library
reference spectra to match a spectrum taken in the field. The
final results given by the NASA program for each sample consists
of c. raph of the field spectrm an d on(? ~ta shept which con