GOSIA

**Coulomb Excitation Data Analysis Code **

T. Czosnyka, D. Cline, C.Y. Wu

The wealth of Coulomb excitation data collected using present day experimental technique allows model independent determination of almost all M1, E1, E2 and E3 matrix elements connecting low-lying collective nuclear levels populated by electromagnetic excitation. A semiclassical coupled-channel Coulomb excitation least-squares search code, GOSIA, has been developed to analyze the large sets of experimental data required to unambiguously determine the many electromagnetic matrix elements involved in heavy-ion induced Coulomb excitation. Up to 500 electromagnetic matrix elements, coupling up to 75 levels, can be fitted to reproduce simultaneously several thousand data from up to 50 independent experiments. Fast semi-analytic approximation of the coupled-channels system of differential equations describing electromagnetic excitation is used to achieve computational speed required for such a task. Evaluation of rotational invariants using the measured E2 matrix elements derived using GOSIA determines the intrinsic frame quadrupole shape parameters for low-lying states. The completeness and extent of such information on electromagnetic structure adds a new dimension to the study of collectivity in nuclei.

The suite of GOSIA codes were developed at the University of Rochester starting in 1980 and have been used extensively since that time. The codes are written in standard FORTRAN 77. During July/August 2007 Dr Nigel Warr upgraded the coding of the GOSIA suite to the latest FORTRAN standards making these codes easily transportable to different computers plus ensuring compatability with the newer FORTRAN compilers. Two versions of the Fortran source for the GOSIA code are given in the following links; the GOSIA06 link gives the final version of GOSIA as developed by Tomasz Czosnyka. The GOSIA07 link gives the March 2008 update of the 2007 version that includes major coding improvements by Nigel Warr. Only the more reliable 2007 versions of the GOSIA2 and PAWEL codes are given. The GOSIA Manual and GOSIA Manual Update list are applicable to all versions of the codes.

DOWNLOADS:

**GOSIA MANUAL**:

The GOSIA Manual applies to the complete set of GOSIA codes as of 28 March 2008.

**GOSIA UPDATES**:

The most recent updates to the GOSIA Manual and associated codes are listed in Gosia Manual Updates.

**GOSIA CODES:
**GOSIA07 is the Fortran source code for the Warr August 2007 version of the basic code including the March 2008 update.

GOSIA06 is the Fortran source code for the Czosnyka June 2006 version of the basic code.

A sample GOSIA Speed and Accuracy Benchmark Test is available to compare with the output and speed achieved using the Rochester EM64T system. The benchmark test package contains the GOSIA input, sample output, Ge detector file and a README file explaining the output. Unpack the the files on a Unix system using the command tar -xvf accuracy-speed-test.tar.

A set of sample files is provided for the GOSIA tutorial in chapter 11 of the GOSIA Manual. A new user can install GOSIA 2007 and execute a fit to the provided sample data.

GOSIA2 is the Fortran source code of a special version of GOSIA designed for use when analysing simultaneous Coulomb excitation with a common normalization.

This is useful for determining transition strengths in radioactive beams by normalization to a known transition strength in the target. The 2007 version will be released soon.

PAWEL is the Fortran source code for the August 2007 version of a special offspring of GOSIA designed to handle cases where a fraction of the nuclei have an excited isomeric state as the initial state.

ANNL is a special version of GOSIA, developed by Rich Ibbotson, that uses simulated annealing techniques to locate minima.

SIGMA is the 2006 Fortran source code for deducing the quadrupole invariants from the E2 matrix elements determined by GOSIA.

SELECT is the Fortran source code for the program SELECT that is used to select a subset of matrix elements used in the error calculation.

GREMLIN is the latest version of the gamma-ray detector efficiency code developed for use with GOSIA in 1987 by Alexander Kavka.