Identification of a potential ultralow- Q -value electron-capture decay branch in Se 75 via a precise Penning trap measurement of the mass of As 75

M. Horana Gamage, R. Bhandari, G. Bollen, N. D. Gamage, A. Hamaker, D. Puentes, M. Redshaw, R. Ringle, S. Schwarz, C. S. Sumithrarachchi, I. Yandow

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Abstract

Background: Low-energy β and electron-capture (EC) decays are important systems in neutrino mass determination experiments. An isotope with an ultralow-Q-value β decay to an excited state in the daughter with Qes<1 keV could provide a promising alternative candidate for future experiments. Se75 EC decay and Ge75β decay represent such candidates, but a more precise determination of the mass of the common daughter, As75, is required to evaluate whether their potential decay branches are energetically allowed and ultralow. Purpose: Our purpose is to perform a precise atomic mass measurement of As75 and combine the result with the precisely known atomic masses of Se75 and Ge75, along with nuclear energy level data for As75 to evaluate potential ultralow-Q-value decay branches in the EC decay of Se75 and the β decay of Ge75. Method: The LEBIT Penning trap mass spectrometer at the Facility for Rare Isotope Beams was used to perform a high-precision measurement of the atomic mass of As75 via cyclotron frequency ratio measurements of As+75 to a C612 reference ion. Results: The As75 mass excess was determined to be ME(As75)=-73035.98(43) keV, from which the ground-state to ground-state Q values for Se75 EC decay and Ge75β decay were determined to be 866.50(44) and 1179.01(44) keV, respectively. These results were compared to energies of excited states in As75 at 865.4(5) and 1172.0(6) keV to determine Q values of 1.1(7) and 7.0(7) keV for the potential ultralow EC-decay and β-decay branches of Se75 and Ge75, respectively. Conclusion: The candidate ultralow-Q-value EC-decay and β-decay branches of Se75 and Ge75 to excited states in As75, identified by Gamage et al. [N. D. Gamage, R. Bhandari, M. H. Gamage, R. Sandler, and M. Redshaw, Hyperfine Interact. 240, 43 (2019)]0304-384310.1007/s10751-019-1588-5 are seen to be energetically allowed. The Se75 EC decay to the 865.4 -keV excited state in As75 is potentially ultralow with Qes≈1 keV. However, a more precise determination of the 865.4(5)-keV level in As75 is required to draw a more definite conclusion about the energy of this potential decay channel.

Original languageEnglish
Article number065503
JournalPhysical Review C
Volume106
Issue number6
DOIs
StatePublished - Dec 2022

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