T have endeavoured in these few pages to discuss in a simple, but not oversimplified, straightforward but not unbending, way those names physicists usually associate as adjectives with models: shell, collective and optical. The courage to try this came in the Norwegian mountains, at the joint Nordic-Dutch meeting on nuclear reactions, when I felt that by giving really ‘basic’ lectures, I would necessarily come first on the program, at 8.30 a.m., and would then have the rest of the day free to ski on slopes unencumbered by physicists, all inside absorbing the necessarily less basic material which must follow. And what was, at this time, the basic of basics, the modest excuse for existence of theoretical nuclear physicists, but nuclear models, which I disposed of one by one each morning. Whether the exhilaration associated with this rapid disposal came primarily from success in this or from the Norwegian mountains, I cannot say, but I approached the task outlined in this short book in the same light-headed manner. In any case, if the reader receives half the enjoyment out of reading this book that I did out of skiing in Gola, I shall consider my task successfully completed. Of course, since the Nordic-Dutch Skiing School, I have expanded the lectures greatly, in giving them at the Massachusetts Institute of Technology and the University of Minnesota. As befitted these august institutions, the treatment became more and more extensive and less and less understandable. Iam, none the less, very much in debt to many people for criticism and to others for much secretarial assistance in both of these places, which offered excellent conditions for putting these notes together. In case reviewers of this book take time to read this preface before putting their gratis copy up on their bookshelves and broadcasting nasty comments, let me say that I treat each problem the way that I enjoy treating it. Nature and I have achieved a reasonable modus vivendi in the past, and I have every reason to believe in the realization of further enjoyment in the future. If, on the other hand, the reviewers wish to see their pet treatment which is buried somewhere in the extensive archives of physics, then they are welcome to make a xerox copy and paste it over the relevant pages. One or two have been left blank for this purpose. In the process of writing, I have often been reminded of my debt to David Thouless, whose work has clarified so many connections, and whose laconic comments have caused me so much mental struggle. Criticism and help of many people at Copenhagen, especially of Brian Easlea and Sven Wahlborn, have prevented the text from being catastrophically bad. Chief overseer of the preparation of notes from my Copenhagen lectures, Mrs. Ebba Larsen, suggested innumerable cor- rections and improvements. I am also indebted to J. Bro-Jorgensen, K. Gjotterud and E. Sanderson for help and comments. Finally, if it appears that not sufficient people have been helping me, let me add that Harvey Picker has gone through the entire manuscript and pointed out almost countless errors. I refused, however, to accept his suggestions on styling, wishing to retain a certain amount of colloquial illiteracy.

Brown, G. E.. Unified theory of nuclear models / G. E. Brown. – Amsterdam : North-Holland, 1964. - Bibliogr.: p. 173-175.