“…In [1] and many papers since, it was supposed that this state would remain spatially unchanged in the course of decay; it is now evident, however, that significant change takes place [5,10,12,[14][15][16][17][18]20,25,26,[28][29][30]. This change can be explored by various methods, notably by finding the eigenmodes of the system [5,8-11,13,15,16,19,20,24-26, 28,29].…”