Advances in constant-velocity Mössbauer instrumentation

A. VEIGA; N. MARTÍNEZ; P. MENDOZA ZÉLIS; G. A. PASQUEVICH; F. H. SÁNCHEZ

La Plata, Argentina

Workshop; Hyperfine Interactions International Workshop HFILP2005; 2005

A prototype of a programmable constant-velocity scaler is presented. Thismicrocontroller-based instrument allows the acquisition of partial Mössbauer spectra inselected energy regions using standard SCA, drivers and transducers. No additionalmultichannel scaler is required. It can be fully operated by a remote application, thus dataacquisition can be automated. The instrument consists of a programmable counter and aconstant-velocity reference. The reference waveform generator is amplitude modulatedwith 13 bit resolution, and is programmable in a wide range of frequencies andwaveforms in order to optimize the performance of the transducer. The counter iscompatible with most standard SCA, and is configured as a rate-meter that providescounts per selectable time slice at the programmed velocity.As a direct estimation of the performance, a partial Mössbauer spectrum of anatural iron foil was repeatedly taken. Positive energies were recorded in 512 channelsranging from 0 to 10 mm/s, accumulating 20 seconds per channel. A line width of 0.20mm/s was achieved in all cases, what is equivalent to the line width of the spectrum takenwith the same transducer, servo amplifier and SCA, using a constant-accelerationtechnique with a Nucleus MCS-II multi channel scaler. Long term stability proved to besatisfactory and overall efficiency reached 80%.This constant-velocity technique has been recently applied in differentexperiments. We show two non conventional applications of this technique: thedetermination of Fe hyperfine field temperature dependence in the FeSn2 compound, andthe study of the Iron magnetic moments