Efficient production of ^229mTh 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.