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Science for Everybody: From the Atomic to the Nuclear Clock

Dr. Peter G. Thirolf. Photo: Thorsten Naeser

Wednesday, 07 March, 2018

Dr. Peter G. Thirolf (Ludwig-Maximilians-Universität München)

7 March 2018 at 7 PM (Tickets are available at the box office from 6 PM; Admission 3 €)

Venue: Ehrensaal des Deutschen Museums, Museumsinsel 1, München



Some 6000 years ago, the Sumerians in Mesopotamia were already using light to measure the passage of time. They used sundials, but nowadays we make use of laser light: The most precise determinations of time and oscillation frequencies now available are carried out with the aid of optical atomic clocks. The current record is held by an instrument with an accuracy of within 1 second in approximately 60 billion years. But even this level of accuracy could be surpassed by a nuclear clock. In atomic clocks, the rate of a defined transition between electron shells in the atoms of an element is used as the temporal yardstick. A nuclear clock, on the other hand, would make use of the frequency of a defined transition between two metastable states of an atomic nucleus. So far, only a single state that could potentially serve as the basis for such a nuclear clock has been identified. This is the theoretically predicted first excited state of the thorium-229 nucleus, an isomer referred to as 229mTh, which has an estimated lifetime of a few thousandths of a second. For over 40 years, nuclear physicists around the world have sought to detect and characterize this exotic nuclear transition experimentally. But until recently, the evidence for its existence was derived from indirect measurements. These results suggested that the excitation energy required to induce the transition is lower than that of any other nuclear state transition. The first direct detection of 229mTh was achieved by Dr. Peter Thirolf’s research group at Munich University, setting the stage for further investigation of the isomer’s properties. This experimental tour-de-force also opens the way to laser-based control of the transition, and represents an important step towards the long-sought goal of a highly stable nuclear frequency standard, the first nuclear clock. Such a clock could be used to address fascinating problems in both applied and fundamental physics, in contexts ranging from geodesy and seismology to the question of whether fundamental constants of nature vary with time. In his lecture, Peter Thirolf will describe the long search for the elusive thorium isomer and outline its potential applications.