Development of a measurement system enabling the reconstruction of γ-ray time spectra by simultaneous recording of energy and time information

Abstract

We developed a measurement system that enables the reconstruction of γ-ray time spectra in cascade decay schemes. As this system records all the time and energy information of γrays, reconstruction is possible after the measurement. Therefore, the energy regions for the γ-ray identification can be optimized in complicated cascade decay schemes. Moreover, in this system we can record data with time-dependent parameters of external perturbations, such as applied magnetic fields, and consequently we can investigate the correlations and responses of γ-rays to the perturbation. This property fulfills the demands required for quantum information research with γ-rays.The γ-rays emitted from radioactive isotopes (RI) have various useful properties. Because of the diverse characters of nuclides, various combinations of the energy E and the energy width ΔE of γ-rays are available. For example, Mössbauer spectroscopy, which is one of the most effective methods for condensed matter science, uses γ-rays with a high energy resolution that typically reaches ΔE/E~10 -13 , which can well resolve the hyperfine interaction in the nuclear levels through atomic electrons 1) . On the other hand, the fundamental processes and control of γ radiation have been extensively studied 2, 3) . Recently, γ-ray photons have attracted much attention in studies on quantum information and communication because γ-ray photons have the following advantageous properties compared with optical photons: high spatial resolution, high transparency in many materials, and in some cases ultra-high energy resolution. In recent research, coherent control of the waveforms of recoilless γ-ray photons using a cascade scheme of the decay of Mössbauer sources was reported 4) . In the cascade decay scheme using Mössbauer effects, a heralding γray photon is emitted when a nucleus decays from the higher excited state to the lower intermediate state, and a consequent γ-ray photon whose waveform is controlled is emitted