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Manuscript Title: Program for fitting transition energies into a level scheme according to the combination principle.
Authors: I.R. Williams
Program title: RITZ COMBINATION PRINCIPLE
Catalogue identifier: ABKD_v1_0
Distribution format: gz
Journal reference: Comput. Phys. Commun. 1(1970)465
Programming language: Fortran.
Computer: IBM 360/91.
Operating system: S/360 0S(MVT).
RAM: 2K words
Word size: 32
Keywords: Atomic physics, Molecular physics, Spectra, Energy, Level scheme, Gamma ray, Photon, Quantum, Ritz combination Principle.
Classification: 2.2, 16.2.

Nature of problem:
In nuclear physics (but also in atomic and molecular physics) transition energies are often obtained from measurements of photon or internal electron conversion spectra. an attempt is then made to fit these energies into a level scheme (of which some levels may already be known) on the basis of the conservation of energy here termed the Ritz Combination Principle.

Solution method:
The essential input data are the measured photon energies and any level energies that are known. The program starts at a specified energy (E) and ascertains whether (a) an energy level (b) and energy level + a quantum (c) an energy level - a quantum or (d) a quantum + another quantum have that energy E within experimental error (also specified input data). The value of E is reduced a little and the program loops through the series of questions, again outputting the pertinent data if an answer is in the affirmative. This is repeated as long as desired; the output eventually having the semblance of an energy level diagram.

Restrictions:
This program takes no consideration of the fact that a transition between two levels may be forbidden because of an angular momentum and parity barrier. Also no intensity balance is accounted for in program RITZ so it is necessary to be on guard against accepting the program's assignment of a transition to a state in the decay scheme when this might be totally unreasonable from intensity considerations.

Running time:
The total CPU time for the test case is 2.9 seconds. The running time goes up rapidly with the number of gamma level energies taken as input.