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Manuscript Title: Programs in C for parameterizing measured 5" x 5" NaI gamma response functions and unfolding of continuous gamma spectra.
Authors: H.V. Nguyen, J.M. Campbell, G.P. Couchell, S. Li, D.J. Pullen, W.A. Schier, E.H. Seabury, S.V. Tipnis
Catalogue identifier: ADCE_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 93(1996)289
Programming language: C.
Computer: VAX station 40000 60.
Operating system: VMS, DOS.
RAM: 23K words
Word size: 32
Peripherals: disc.
Keywords: Nuclear physics, General experiment, Nai(tl) spectrometer, Gamma-ray spectrum, Response function, Energy distribution.
Classification: 17.4.

Nature of problem:
The program NGRC was written to implement a gamma response function interpolation scheme for a 5" x 5" NaI(Tl) spectrometer. The program takes a library of response functions that were measured at specified energies and constructs response functions at any intermediate energy. These response functions are used in the unfolding of continuous gamma spectra measured by the same spectrometer. The number of response functions to be constructed is input by the user and NGRC places their centroids so that their separation is a constant times the full width at half maximum. The unfolding is performed by program CRSUP. It assumes the measured spectrum consists of a superposition of the response functions produced by NGRC. The program then computes the superposition weighting factor in a least-squares fashion. Two utility programs are also included. RES-FIT is useful in constructing response function peak features and SPEC-FIT allows one to test a response function on a discrete, known spectrum.

Solution method:
The procedure for constructing response functions at any arbitrary energy assumes that their shape can be characterized by a set of parameters which are smooth functions of energy. Features considered are the shape of the tail, the tail-to-peak-area ratio R, the energy of the Compton edge, the full widths at half maximum (FWHM) of the full energy peak, the 0.511-MeV annihilation peak and the single- and double- escape peaks. The construction of a response function at a particular energy consists of obtaining the shape of each feature at the desired energy, and appropriately recombining them to form the interpolated response function.

In the problem of unfolding measured spectra, the uncertainty in the measured response functions has not been taken into account. The number of response functions used to model the measured spectrum should be such that their separation is no less than 0.6*FWHM.

Running time:
The running times listed here for both programs are for 100 response functions. Construction of the response matrix using NGRC required 6 hours. The unfolding of each measured spectrum with CRSUP required 5 minutes.