High time resolution x-ray measurements with an avalanche photodiode detector

An avalanche photodiode (APD) detector has been developed for x-ray timing measurements with a subnanosecond time resolution. The performance of the APD detector was investigated with synchrotron x-ray beams in multi- and single-bunch runs at the Photon Factory (PF) ring. A time resolution of 0.28 ns (FWHM) and a peak-to-background ratio of more than 107 were obtained from the main peak of 14.4-keV x rays in a single-bunch time spectrum. The intrinsic efficiency and the counting-rate capability were also measured. As an application with a high time resolution, time spectra of quantum beats in nuclear resonance of 57Fe were observed with the APD detector at the undulator beam line BL-NE3 of the TRISTAN accumulation ring; the first peak of the beats was completely separated from the prompt peak of the non-nuclear components with a good time resolution and the beat structure was sharply seen to the range of ≳100 ns later with a very low background.