coulomb excitation data analysis codes; gosia 2007 - Physics and ...

11.2 LearningtoWriteGosiaInputsThe fastest way to learn to write GOSIA inputs is to begin with one of the sample inputs on the GOSIAwebsite and modify it in stages. The meaning of each line in the sample input can be understood bycomparing it with the manual entry for the relevant section (e.g. OP,YIEL or OP,INTG), while Chapter 5gives a listing of the options that are required for each of the functions of GOSIA. Each function is controlledby an “option” labeled in the input as “OP,XXXX”, where XXXX is a four-letter identifier. The subsectionsof each option are referred to in this manual as “sub-options,” and have a two- to four-letter identifier. Ingeneral, the physical problem is defined in several sections (“options”) of the code in the order that follows,with other sections being optional.OP,FILE Assigns file names to the input and output files. The OP,FILE entry is optional but recommended,because descriptive file names prevent confusion that can arise from the default names fort.1, fort.2,etc.OP,TITL The user’s choice of a description of the input.OP,GOSI This block defines, among other parameters, the nuclear system and a brief description of theexperimental situation. (OP,COUL can be used instead, if the user desires only to calculate gamma-rayyields, not to fit matrixelements.)LEVE This is the level scheme of the nucleus to be studied (either projectile or target).ME The starting values of the EM matrix elements are given here. The desired coupling of fit parametersand boundaries for the fit are entered if OP,GOSI was specified.EXPT This sub-option defines the experimental setup briefly, including particle detector geometry andspecifications for the point-approximations used to increase the speed of the fit. The mean beamenergy (as the beam traverses the target) is specified here, along with the projectile and target species.Up to 50 “experiments” may be specified, where each experiment may be defined as merely a range ofprojectile scattering angles, or as a truly distinct experiment with a different projectile, target, etc.CONT A number of accuracy controls are given here. Several other switches in this sub-option allow theuser to quickly fix or release matrix elements in the fit. The user may also choose output options inCONT.END, This entry marks the end of the CONT sub-option and should be followed by a single blank line.[Blank line]OP,YIEL This option defines internal conversion coefficents, gamma-ray detector types and angular coverages,normalization of the particle detectors (if necessary), normalization of calculated gamma-rayyields, detector sensitivity (for the calculation of chi-squared). Optionally, a set of lifetime, matrix element,gamma-ray branching ratio and mixing ratio datacanbeenteredandincludedinthechi-squaredfit.OP,INTG This option defines the particle scattering angle ranges over which the yields are to be integratedfor each experiment. This consists of defining the particle detector shape (if necessary), angular limitsand meshpoints for the integration. Stopping powers and beam energy ranges effectively define thetarget thickness here.The input is generally run several times to perform the fit, with minor changes to the input at each stage,as demonstrated in the tutorials in this chapter. It is recommended that the user begin analysis of real databy running an integration (OP,INTG) based on one of the inputs used in the tutorials. When the physicalsystem is satisfactorily defined (beam, target, level scheme, initial guesses at the matrix elements, beamenergies and scattering angles), the integrated yields can be compared to the data. A fit toexperimentaldata can then be accomplished by following the steps that are described in the fitting tutorials.155