Programs in Physics & Physical Chemistry
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|Manuscript Title: A program for the extraction of radiative lifetimes from experimental beam-foil intensity decay data.|
|Authors: D.J.G. Irwin, A.E. Livingston|
|Program title: HOMER|
|Catalogue identifier: AAED_v1_0|
Distribution format: gz
|Journal reference: Comput. Phys. Commun. 7(1974)95|
|Programming language: Fortran.|
|Computer: IBM 360/67.|
|Operating system: MICHIGAN TERMINAL SYSTEM.|
|RAM: 16K words|
|Word size: 32|
|Keywords: Atomic physics, Ion, Life-time, Excited state, Beam-foil, Decay curve, Chi-square fit, Experiment.|
Nature of problem:
The problem is to analyse experimental beam-foil intensity decay data into a sum of exponential terms,each with an amplitude and lifetime parameter. The most apt number of parameters and the optimum value of each is to be determined, together with estimates of standard deviation. Method fo solution The minimum of chi-square is sought in an iterative procedure. Normal equations are obtained from a first order Taylor expansion of the multi-expotential fitting function, together with an auxiliary binomial expansion to first order. Non-convergence is impeded by two devices. A modified Marquardt method is built in as an option. Initial estimates may be computed from the data. Rejection of extra-statistical data points may be allowed.
The complexity of the fitting function is arbitrarily limited to, at most, a six-parameter fit in the form of a sum of three expotential terms. Provision is made for adjustment of the number of parameters during the computation so that a 6-,5-,4-,3- or 2- parameter best fit may be obtained.
Typical running time is about 2 s on the IBM 360/67 with the G compiler for 25 data points and a six-parameter fitting function. This estimate does not include compilation of the program. It is recommended that a compiled version of the program be used in the interests of economy.
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