Controlling 229Th isomeric state population in a VUV transparent crystal
T. Hiraki, Koichi Okai, Michael Bartokos, Kjeld Beeks, Hiroyuki Fujimoto, Yuta Fukunaga, Hiromitsu Haba, Y. Kasamatsu, Shinji Kitao, A. Leitner, Takahiko Masuda, Ming Guan, Nobumoto Nagasawa, Ryoichiro Ogake, Martin Pimon, Martin Pressler, N. Sasao, Fabian Schaden, Thorsten Schumm, Makoto Seto, Yudai Shigekawa, Kotaro Shimizu, Tomáš Šikorský, Kenji Tamasaku, Sayuri Takatori, Tsukasa Watanabe, Atsushi Yamaguchi, Yoshitaka Yoda, A. Yoshimi, K. Yoshimura
Abstract
Abstract The radioisotope thorium-229 ( 229 Th) is renowned for its extraordinarily low-energy, long-lived nuclear first-excited state. This isomeric state can be excited by vacuum ultraviolet (VUV) lasers and 229 Th has been proposed as a reference transition for ultra-precise nuclear clocks. To assess the feasibility and performance of the nuclear clock concept, time-controlled excitation and depopulation of the 229 Th isomer are imperative. Here we report the population of the 229 Th isomeric state through resonant X-ray pumping and detection of the radiative decay in a VUV transparent 229 Th-doped CaF 2 crystal. The decay half-life is measured to 447(25) s, with a transition wavelength of 148.18(42) nm and a radiative decay fraction consistent with unity. Furthermore, we report a new “X-ray quenching” effect which allows to de-populate the isomer on demand and effectively reduce the half-life. Such controlled quenching can be used to significantly speed up the interrogation cycle in future nuclear clock schemes.