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Manuscript Title: INTERACTIVE POSITRONFIT: a new version of a program for analysing positron lifetime spectra.
Authors: C.J. Virtue, R.J. Douglas, B.T.A. McKee
Catalogue identifier: AAHI_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 15(1978)97
Programming language: Fortran.
Computer: PDP 11.
Operating system: RT-11 (VERSION 2-C).
Program overlaid: yes
RAM: 24K words
Word size: 16
Peripherals: disc.
Keywords: Atomic physics, Positron, Lifetime, Fitting, Least squares, Interactive, Convolution, Resolution function, Minimization, Sum-of-exponential, Marquardt, Constraint, Convariance matrix, Solid state physics, Experiment.
Classification: 2.3, 7.4.

Other versions:
Cat Id Title Reference
AAGK_v1_0 POSITRONFIT CPC 3(1972)240
AAGZ_v1_0 DBLCON CPC 13(1977)371
AANN_v1_0 PATFIT CPC 23(1981)307
ACKX_v1_0 PFPOSFIT CPC 30(1983)359

Nature of problem:
Positrons annihilate in condensed matter from different states (e.g., from defect traps in metals) so that a measured lifetime spectrum consists of a sum of exponential decay components smeared with the instrumental resolution function and superimposed on a constant background. Experimenters want to extract the lifetimes and intensities of the annihilation from different states.

Solution method:
Positron lifetime spectra are analysed by a weighted least-squares fitting to a model: a sum of expotentials, convoluted with a resolution function which is a sum of gaussians. Component lifetimes, relative intensities and time zero can be left free or constrained as in Comp. Phys. Commun. 7(1974)401. In addition, the gaussian widths of the resolution function and the total intensity can be free or constrainted. Interactive recycling of the program, permitting a convenient change of data or fitting range, constraints, etc. is included.

Our memory size limit requires the following restrictions: four lifetime components, two gaussian functions in the resolution function, 150 channels in the spectrum, 120 channels analysed. These restrictions may be severe for some applications of this program (e.g. positronium studies), and can be lifted by increasing the length of various arrays.

Unusual features:
(1) The program is interactive and will run on a mini-computer (any minimum PDP-11 with 24 K of memory, supporting RT-11 and FORTRAN).
(2) An auxillary program is included to generate a test file from the test deck.