Modern Software for Coulomb Excitation Analysis
- Adam Hayes, University of Rochester
Thursday, May 30, 10:00 AM - Special Seminar
NSCL Seminar Room
Coulomb excitation is a complex topic with a rich history of measurements stretching back more than 50 years. Successes range from early single-step excitation experiments using light-ion beams to measure B(E2) values and static moments, to contemporary multi-step heavy-ion experiments measuring shape evolution and band crossing at high spin.
Single-step Coulomb excitation data in its simplest form can be analyzed using perturbation theory, “on the back of an envelope”, whereas modern multi-step Coulex experiments require a semi-classical approach. The Gosia semi-classical Coulomb excitation code, developed at Rochester in 1980, can handle gamma-ray intensity data from very collective nuclei, where the excited states are coupled by as many as 1000 matrix elements. Mathematically, it can fit as many as 500 matrix elements, although, in practice, this would require an extremely over-determined data set.
However, Gosia has its limitations: It does not treat highly-adiabatic excitations in non-collective nuclei, because of numerical constraints. Data management and handling of matrix elements become intractable when hundreds of states are observed. If many states are excited, the analysis requires many hours of cpu time, interrupted frequently for long periods while the user sets up calculations.
I will describe the semi-classical approximation, with a focus on the numerical methods used by Gosia, accuracy and limitations. I will discuss past and current development of the Gosia suite and plans for future development, including extending the reach of the Gosia suite to match the capabilities of GRETA and FRIB.