Zdzisław Szymański had a unique position in the international community of nuclear structure physicists. Not only was he an outstanding scientist working in theoretical nuclear physics, but also a teacher and friend of the many students that were attracted to his rostrum. As an experimental physicist I was always very impressed by Zdzisław's humble approach to nuclear models and hypotheses and his patience when instructing and leading the experimentalist through the ins and outs of nuclear theories. I have been fortunate enough to have had Zdzisław Szymański as a coauthor on a couple of papers, but in many more I have had the pleasure of acknowledging his help in the interpretation of our experimental data.

Meeting at Physics 34 at Caltech in Pasadena

My first interaction with Zdzisław Szymański happened at California Institute of Technology in 1964 when we shared an office at the Norman Bridge Laboratory as members of Felix Boehm's group. With a fresh Ph.D. this was my first encounter with the international family of nuclear physicists and I had the fortunate privilege of having a first rate teacher as room mate. It was here that I learned most of what I know about nuclear structure theory from the discussions with Zdzisław, but also how to understand the lectures of Feynman and Gell-Mann, which were being given at that time. Furthermore, we also enjoyed a rich social life under the Californian sun with excursions in the western part of the USA. It was a special joyful time when Wiesia and their son Pawel could join Zdzisław towards the end of his stay in California. Zdzisław and Wiesia were always positive, welcoming and generous and shared some funny little culture shocks with us.

Among the many projects we were involved in during the Caltech years I should like especially to mention the study of the rotational bands on two-particle configurations in odd-odd nuclei with K_n = K_p = 1/2. There are very few occasions in the periodic table where neutron and proton orbitals, both having K=1/2, are coming close together. The only case, where the two K=1/2 orbitals appear in the ground state seems to be ¹⁷⁰Tm. The results of Coulomb excitation with heavy ions on ¹⁷⁰Tm and ¹⁶⁹Tm(d,p)¹⁷⁰Tm reaction experiments were interpreted within a coupling scheme for the two K= | K_n ± K_p | bands. The Coriolis coupling induces an effective interaction between the two K=0 and K=1 bands. The splitting between the two bands was found to be predominantly due to the neutron-proton residual force. It was very stimulating to have Zdzisław Szymański working also with the experimental data.

Visit to Berkeley, California

In connection with the investigation of the structure of ¹⁷⁰Tm Zdzisław and I were invited in the spring of 1965 by John Rasmussen to the Lawrence Radiation Laboratory in Berkeley, as it was called at that time. John Rasmussen and colleagues were interested in the same problem and Zdzisław was asked to give a talk about his calculations. An aspect of the political situation in the mid 60's can be illustrated by an incident on this visit, where Zdzisław was found to be in the category of those not permitted to enter the laboratory grounds. To John Rasmussens' great embarrassment, the lecture had to be shifted to a lecture hall at the Physics Department outside the perimeter. In spite of this slight "hiccup" the lecture was excellent and the visit very useful for the project.

Excitements in Stockholm

A systematic study of rotational bands in Rare Earth nuclei had started at the end of 1960's with the use of the newly extracted beam of 43 MeV alpha particles from the 225-cm Stockholm cyclotron. In particular, we found the ground state rotational bands in doubly-even, well deformed nuclei up to reasonably high spins by the use of coincident gamma-rays emitted in (a,xn) reactions. We found an unexpected irregularity in some of the rotational bands studied, which led us to the discovery of back-bending.

It was most fortunate that both Zdzisław Szymański and Ray Sorensen happened to be spending several months at the Research Institute for Physics in Stockholm during the years 1970-71. For us experimentalists in the group undertaking these studies it was extremely valuable to have these theorists in the "house", for discussions concerning the interpretation of the back-bending observations. The sudden jump in the value of the moment-of-inertia as the rotation of the nucleus increased was at first interpreted as a sign of a phase-transition in nuclear matter, from a super-fluid state to a "normal" state. It was a very exciting time and Zdzisław and Ray took a great deal of trouble in patiently explaining their ideas of the possible underlying nuclear processes. Later, the suggestion of Frank Stephens of the breaking and aligning of a pair of nucleons was accepted as the most likely mechanism.

Lund and Copenhagen

Zdzisław Szymański had, of course, always a very close contact with Aage Bohr and Ben Mottelson at the Niels Bohr Institute in Copenhagen and therefore also with Sven Gösta Nilsson in Lund. Zdzisław kept his contact with the physicists in Lund even after Sven Gösta's sudden and untimely death in 1979, and his stimulating presence was always appreciated by theorists as well as experimentalists.