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Manuscript Title: POSITRONFIT: a versatile program for analysing positron lifetime spectra.
Authors: P. Kirkegaard, M. Eldrup
Program title: POSITRONFIT
Catalogue identifier: AAGK_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 3(1972)240
Programming language: Fortran.
Computer: B67000.
Operating system: B6700 MCP MARK II.00.
RAM: 20K words
Word size: 48
Keywords: Atomic physics, Positron, Lifetime, Source correction, Least squares, Fitting, Convolution, Minimization, Sum-of-exponentials, Iterations, Marquardt, Constraints, Covariance matrix, Solid state physics, Experiment.
Classification: 2.3, 7.4.

Other versions:
Cat Id Title Reference
AAGX_v1_0 POSITRONFIT EXTENDED CPC 7(1974)401
AAGZ_v1_0 DBLCON CPC 13(1977)371
AAHI_v1_0 INTERACTIVE POSITRONFIT CPC 15(1978)97
AANN_v1_0 PATFIT CPC 23(1981)307
ACKX_v1_0 PFPOSFIT CPC 30(1983)359

Nature of problem:
In a condensed material positrons may annihilate at several different characteristic rates. A measured positron lifetime spectrum will therefore consist of a sum of decaying exponential functions with different decay rates, smeared somewhat owing to the finite time resolution of the measuring system and superimposed on a constant background.

Solution method:
Positron lifetime spectra are analysed by an iterative least-squares technique of the semi-linear Marquardt type. The mathematical model is a sum of decaying expotentials convoluted with a gaussian resolution function, and with a constant background added. Fixed values can be imposed on any number of lifetimes and relative intensities. Correction for the source annihilation is taken into account. A statistical analysis is made resulting in the covariance matrix of the estimated parameters.

Restrictions:
The program in its present version is restriced to include up to four lifetime components. The maximum number of channels in the multichannel analyser is 512, and of these max. 400 are used in the analysis.