Lake Michigan environmental survey : final report / [edited] by John C. Ayers.

A copy of this program was obtained from Dr. Trombka and substantially revised
to fit the needs of this Department. The program is called NASA after its
original sponsor.
The NASA program is designed to receive a library of standard spectra.
The standard spectra are linear arrays of numbers with dimensions of "cps/
channel." The activity which produced each of the library spectra must be
known. The program can then receive a sample spectrum and determine how much
of each of the library standards is present in the sample spectrum.
In routine operation a set of library reference spectra are transferred
by the computer from punched paper tape to the beginning of a reel of magnetic
tape. Each spectrum occupies a specific location, called a record, on the
magnetic tape. As sample spectra are taken they are transferred to the magnetic tape occupying successively higher record numbers. Any spectrum on the
magnetic tape can be recalled and printed or graphed if desired.
The NASA program constructs a spectrum from the library reference spectra
to match the sample spectrum. The final results given by the NASA program for
each sample are a graph of the spectrum (the net spectrum if background subtraction is requested by the user) and one data sheet which contains the activities of each of the library references that are present in the sample spectrum. The graph of the spectrum is used to detect the presence of any radioisotopes for which the NASA program is not programmed.
The data sheet also includes two error values for the sample spectrum
analysed. The chi square value is a measure of how well the entire calculated
spectrum matched the entire sample spectrum. The amount of each radioisotope
predicted to be in the sample spectrum has associated with it a standard deviation expressed as a percent of the predicted amount. The two error values together with the graph of the spectrum are used to decide the validity of the
predicted activities for the given sample spectrum.
Calibration of a Gamma Spectrometer - Part 2
Method for Determining Minimum Detectable Activities and Levels.
1. Arrange numerically all samples on planchets by increasing percent
standard deviation of their radioactivity content.
2. Create a frequency distribution such as that given in Table A-16.
Activities which are considered significant have a standard deviation

A-35