Searching for electric monopole transitions with electron positron pairs

by Prof. Tibor Kibedi (Australian National University)


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The emission of electron positron pairs is a third order electromagnetic process and only allowed for nuclear transitions with energies above 1 MeV. This process competes with gamma-ray and conversion electron emission. The probability depends on the atomic number, the transition energy and multipolarity. For light nuclei, where transition energies are in the MeV range, the observation of electron positron pairs is particularly important. Single photon emission between spin zero states is strictly forbidden. In these cases, electron conversion or electron positron pair conversion are the only open decay channels for atomic nuclei.
In this talk we will describe the 2.1 tesla superconducting pair spectrometer, Super-e, constructed and operated at the Heavy Ion Facility at the Australian National University. The spectrometer can be used to measure conversion electrons as well as electron positron pairs up to an energy of 8 MeV in a range of nuclei, including the decay of the Hoyle state in 12C [1,2], the direct observation of the E0 transition from superdeformed state in 24Mg [3] and searching for E0 transitions and shape coexistence in Cr-Fe-Ni nuclei [4,5].

[1]    T.K. Eriksen, et al., Physical Review C: Nuclear Physics 102, (2020) 024320
[2]    T. Kibédi et al., Physical Review Letters 125 (2020) 044319
[3]    J.T.H. Dowie, et al., Physics Lett. B 811 (2020) 135855
[4]    J.T.H. Dowie, et al., EPJ Web of Conferences 232 (2020) 1-4
[5]    L. Evitts, et al., Physics Lett. B 779 (2018) 396.

Organized by

Marchi Tommaso, Gianni Carugno