Automation of a pulsed FT NQR spectrometer with increased s/n ratio and resolution for zeeman studies of single crystals

Abstract

With a view to determine the parameters of the electric field gradient tensor from Zeeman measurements in a simple and precise way, we have adopted the system in which a Bruker pulse spectrometer is coupled to a NicoLet 1074 signal averager and a PDP 8/E mini-computer. The automation of the measurements and the precision of the experiment have been achieved by the development of a series of programs in the Assembler language and in FORTRAM and by the fruitful utilisation of the software instructions associated with the PDP-NICOLET INTERFACE, OS/8 Monitor system, and USR (User Service Routine) to replace the Keyboard Monitor. In most cases, the complete EFGT parameters can be derived from the rotation of the crystal around the r.f. axis alone, - for which the requirement of the goniometer is simple. In other cases, a second perpendicular rotation is needed to select the correct orientation of the Z-principal axis. For this, a two-circle goniometer has been constructed. Both these goniometers can be thermostatically stabilised at different preselected temperatures. The result of the experiment with a single crystal of CH 2ClCOOH is presented.