Description:

Abstract:

Among thousands of nuclei, the isotope Thorium-229 (229Th) is the only nucleus having an extremely low-lying excitation level of only a few electron volts. This low-energy state, known as an isomer, has been attracting much attention as it could be excited by a laser.  One promising application is the “nuclear clock”, which could potentially outperform the atomic clock and be utilized in many fields, including fundamental physics and various practical applications.

In order to achieve laser excitation, detailed information about the isomer, such as energy and lifetime, is needed. Numerous studies over the years have gradually revealed this information.　We have developed a new method using nuclear resonant scattering with synchrotron radiation X-ray. This "active X-ray pumping" method allows us to produce controllable isomer states from the ground state 229Th. By applying this method to 229Th-doped CaF2 crystals, we have successfully observed the deexcitation vacuum ultraviolet (VUV) radiation from the isomer. This result leads to a detailed understanding of the isomer in CaF2 crystals toward the realization of nuclear clocks. In this talk, I will discuss our observations of VUV radiation and its potential for future laser excitation.

Speaker: Koji Yoshimura, Okayama University