Atomic physics and nuclear physics are essentially separated research fields; the energies required to excite electronic or nuclear transitions differ by many orders of magnitudes. This reflects in completely different experimental methods and tools used for their investigation, which for example employ laser excitation on one side and particle accelerators on the other side. 229Thorium is the only (radio) isotope with the possibility to manipulate a nuclear transition with a laser, bridging the gap between atomic and nuclear physics. This is due to an unnaturally low-energy isomeric nuclear state with a transition energy of 7.6 ± 0.5 eV (130 ¿ 200 nm) . The existence of this state is undisputed and experimentally evidenced by high-energy gamma spectroscopy of the higher excited states. The exact wavelength and the lifetime of the transition is yet unknown. The first aim of this project is to identify the exact transition wavelength and the lifetime of the low-energy isomeric state in 229Thorium. The expected narrow line width (< mHz) together with significant shielding by the electron shell will make this transition an excellent candidate for a new time standard with the potential of outperforming existing time standards by many orders of magnitudes. The complicated and bulky vacuum system currently required by atom or ion clocks could be replaced by a single crystal (e.g. LiCAF) at room temperature doped with 229Thorium atoms. The nuclear transition frequency is based on the strong interaction. Comparing with different time standards based on (electromagnetic) hyperfine transitions will allow to measure temporal variations of fundamental constants in tabletop experiments. Because of the large energy scales inherent to nuclear interactions, the sensitivity to such variations is enhanced by a factor of 1000. The second aim of this project is to implement a proof-of-principle ¿solid-state nuclear clock¿ in 229Thorium to search for variations of fundamental constants. We will employ UV spectroscopy (broadband lamp to UV frequency comb) with increasing accuracy to determine the exact wavelength and line width of the nuclear transition. Locking a UV frequency comb to the transition will allow a direct comparison to the in-house Rubidium standard or external frequency standards. The Atomic Institute in Vienna (ATI) is the ideal environment to apply atomic physics tools to radio isotopes, with few exceptions unique in the world: it combines the internationally accepted atomic physics group of Prof. Jörg Schmiedmayer and myself with a vast experience and infrastructure in radio chemistry. The extremely rare and delicate 229Thorium isotope can be derived in significant quantities from in-house stocks of 233Uranium or produced directly in the ATI TRIGA nuclear reactor.