On the resonant neutrinoless double-electron-capture decay of 136Ce

The double-electron-capture Q value for the Ce-136 decay to Ba-136 has been determined at JYFLTRAP. The measured value 2378.53(27) keV excludes the energy degeneracy with the 0(+) excited state of the decay daughter Ba-136 at 2315.32(7) key in a resonant OvECEC decay by 11.67 key. The new Q value differs from the old adopted value 2419(13) key (Atomic Mass Evaluation 2003) by 40 key and is 50 times more precise. Our calculations show that the precise Q value renders the resonant OvECEC decay of Ce-136 undetectable by the future underground detectors. We measured also the double-beta decay Q value of Xe-136 to be 2457.86(48) key which agrees well with the value 2457.83(37) key measured at the Florida State University. (C) 2011 Elsevier B.V. All rights reserved.