Development of an advanced velocity modulator for a portable Mössbauer spectrometer

Mössbauer spectroscopy is a nuclear spectroscopic technique that measures changes in energy on an atomic scale. In a Mössbauer spectrometer, a velocity modulator oscillates a radioactive source to vary the energy of gamma rays. Conventional velocity modulators use wires primarily as motion guides; however, the tension state of these wires may change over time. Membrane springs are thus used as an alternative to wires; however, they also present certain challenges related to their design, manufacturing, and assembly. Instead of wires or membrane springs, this study used a linear bearing with preloaded compression springs. The advantage of this mechanism is that permanent deformation or changes in spring stiffness minimally occur during spring assembly and operation. The developed velocity modulator is compact and light, making it ideal for portable applications. A digital controller is used to easily modify and customize control parameters and the supporting algorithm, which is not easily achieved with conventional analog controllers. Moreover, by applying a switching amplifier, low-power operation is also achieved. Feedforward control values are calculated by an iterative learning method that is robust to the control of repeated motion. Using finite element method simulations and experiments, the performance of the developed prototype was evaluated. The velocity signal demonstrated linearity with a correlation with a straight line of approximately 0.996 for a triangular velocity profile (satisfactory performance).