It has already been established that, by using a resonant detector in Mossbauer spectroscopy, the minimum spectral linewidth is 1.46Gamma. Here Gamma is the linewidth of the Mossbauer excited-state nuclear level. It is well known that the minimum linewidth obtained in conventional Mossbauer experiments is 2Gamma. The quantum mechanical calculation using a nuclear-resonant detector, which predicts this result, is summarized. The fundamental equations describing the system are solved in the frequency domain and applied to the experimental results. The experimental results using the resonant-detector Mossbauer technique and an Sn-doped SiO2 sample are presented. The best fit to the data is obtained using the resonant-detector quantum mechanical theory.