A comparison of time-of-flight (TOF) and three axis spectrometer (TAS) techniques for the study of excitations in single crystals

Abstract

Arguments on advantages and disadvantages of TOF against TAS are quite old and the situation for single crystals seemed clear for many years. But the advent of spallation sources restimulates this discussion. The difficulties in determining dispersion curves in complex crystal structures are therefore explained in detail, followed by a presentation of the TOF technique for single crystal studies in general and of the sophisticated PRISMA technique in particular. The example of Cr₂O₃, with 30 dispersion branches is discussed in detail because the same sample was examined at PRISMA/ISIS and on TAS-1/JAERI. The conclusion is that complex systems such as Cr₂O₃ cannot successfully be studied on PRISMA. More generally, when many different Brillouin zones have to be examined in a given region of q and W, then the TAS technique is superior to the TOF.