An examination of the Mossbauer effect as the basis of a time/frequency standard

A variety of resonance phenomena are used as the basis for time and frequency standards. These include mechanical resonances in piezoelectric resonators, electromagnetic resonances in microwave cavities, and level transitions in atomic standards. Each type of resonance has its own set of advantages and disadvantages with respect to ultimate stability, sensitivity to environmental effects, and practical considerations in size, weight, power, cost, and complexity of the physical implementation. We are examining the potential for using the Mossbauer effect as the basis for a time and frequency standard. Whereas atomic standards are based on transitions between atomic (electron orbital) levels, the Mossbauer effect arises from transitions between nuclear (atomic nucleus) energy-levels. Our initial analysis of candidate resonances has identified four promising Mossbauer isotopes with relative linewidths on the order of 10^-14 to 10^-16: ⁵⁷Fe, ⁷³Ge, ¹⁸¹Ta, and ¹⁵⁷Gd. Other relevant characteristics, including state lifetimes, natural abundance, and environmental sensitivities, have also been determined. We discuss the basic form of a proposed Mossbauer effect time and frequency standard, the resonance parameters being examined, and the results of our analysis of some of the best candidate nuclear systems.