The original HYPERMET code was developed in FORTRAN language by Phillips and Marlow in the early seventies, at the Naval Research Laboratory, Washington D.C. for automatic and efficient analysis of multichannel pulse-height spectra using a high-speed mainframe computer. The authors' governing principle has been to require minimal input from the user in order to save manpower and to minimise human errors.
To achieve reliable results by automatic fitting, a carefully chosen semi-empirical parameterized function was adopted to represent the detector response of Ge(Li) and HPGe detectors, including all physical and statistical effects which contribute to a real spectrum. The peak shape function of HYPERMET is the linear sum of a Gaussian and an exponentially-modified Gaussian (EMG) on the left side. On the other hand, a step function folded with the same Gaussian and a similarly folded "tail" function, resembling a sharp Compton edge, are added to the usual first or second order polynomial background function.
The fit becomes nonlinear as far as parameters of the Gaussians and exponentials are allowed to vary. Fully automatic operation means that the parameters of peaks and background are found by a nonlinear fit for each separate region in the spectrum, starting from an initial guess.
Therefore, even very complicated multiplets can be successfully and automatically resolved with minimal user interaction. Note that multiplets may have curved, stepped or backstepped background, and peaks with different FWHM. The approximate widths and energy values of two distant peaks provided by the user are the only input needed.
At the time when HYPERMET was introduced only high-speed mainframe computers could be used efficiently due to the time-consuming nonlinear fitting involved. With some modifications the program became fast enough for use on personal computers. The progress of object-oriented programming languages in the '90s has motivated the development of an interactive version with a user-friendly graphics interface. In parallel, high-quality calibration routines and other innovative features were also introduced.
Thanks to these characteristics, Hypermet-PC has gained general acceptance and is applied with success in numerous PGAA, NAA, and other gamma-spectroscopy laboratories. Its remarkable peak evaluation performance was proven in the international intercomparisons.
Comments