Samples prepared at Johannes Gutenberg University Mainz facilitate direct measurement of the mass difference of Ho-163 and Dy-163 to solve the Q-Value puzzle for the neutrino mass determination

Using samples of 163Ho that were prepared at the Institute for Nuclear Chemistry at the Johannes Gutenberg University Mainz, the atomic mass difference of 163Ho and 163Dy has been directly measured with the Penning-trap mass spectrometer SHIPTRAP at GSI Darmstadt by applying the novel phase-imaging ion-cyclotron-resonance technique. Our measurement has solved the long-standing problem of large discrepancies in the Q value of the electron capture in 163Ho determined by different techniques. Our measured mass difference shifts the current Q value of 2555(16) eV evaluated in the Atomic Mass Evaluation 2012 by more than 7σ to 2833 (30stat) (15sys) eV/c2. With the new mass difference it will be possible, e.g., to reach in the first phase of the ECHo experiment a statistical sensitivity to the neutrino mass below 10 eV, which will reduce its present upper limit by more than an order of magnitude. The results were published in Physical Review Letters on August 05, 2015 (S. Eliseev et al., Physical Review Letters 115, 062501 (2015)).

163Ho was produced by intense neutron irradiation of 162Er at the high-flux reactor at the Institute Laue Langevin at Grenoble, France and subsequently purified by using radiochemical separation techniques similar to those also used in research on the heaviest elements.

More information:

ECHo Collaboration website
University of Mainz press release
Press release of the Max Planck Institute for Nuclear Physics in Heidelberg on idw
here on this website
on the GSI website

Holger Dorrer with produced and separated Ho-163 sample.
Holger Dorrer from Johannes Gutenberg University Mainz on the platform of the research reactor TRIGA Mainz that was used to verify the purity of the sample. He holds the produced and separated 163Ho.
Credit: H.-M. Schmidt / JGU Mainz
Q-values of Ho-163
Comparison of values reported for the Q-value of the 163Ho electron capture decay over time.
Credit: ECHo collaboration
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