Efficient production of Th229m via nuclear excitation by electron capture

The nuclear isomeric state ²²⁹ᵐTh with an exceptionally low excitation energy makes the ²²⁹Th isotope a crucial candidate for nuclear clocks and many other applications. Efficient and controllable production of ²²⁹ᵐTh is essential and still remains a challenge. Here we report a novel approach for efficient production of ²²⁹ᵐTh by the excitation of ²²⁹Th to the above-lying excited state at 29.19 keV energy via the process of nuclear excitation by electron capture (NEEC). We show theoretically that the production rate of ²²⁹ᵐTh per nucleus with accessible conditions can be six orders of magnitude larger than the value experimentally demonstrated using 29-keV synchrotron radiation for this indirect excitation. With the efficient production of ²²⁹ᵐTh, our results identify scenarios, as well as the characteristic NEEC signature with which NEEC events could be unambiguously identified, for a clear experimental identification of the long-sought NEEC phenomenon.