Observation of the proton emitter 116La59

Wei Zhang*, Bo Cederwall, Özge Aktas, Xiaoyu Liu, Aysegül Ertoprak, Ayse Nyberg, Kalle Auranen, Betool Alayed, Hussam Badran, Helen Boston, Maria Doncel, Ulrika Forsberg, Tuomas Grahn, Paul T. Greenlees, Song Guo, Jacob Heery, Joshua Hilton, David Jenkins, Rauno Julin, Sakari JuutinenMinna Luoma, Olavi Neuvonen, Joonas Ojala, Robert D. Page, Janne Pakarinen, Jari Partanen, Edward S. Paul, Costel Petrache, Panu Rahkila, Panu Ruotsalainen, Mikael Sandzelius, Jan Sarén, Stuart Szwec, Holly Tann, Juha Uusitalo, Robert Wadsworth

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review


The quantum tunneling and emission of a single constituent nucleon provide a beautifully simple and unique window into the complex properties of atomic nuclei at the extreme edge of nuclear existence. In particular, for odd-odd proton emitting nuclides, the associated decay energy and partial half-life can be used to probe the correlations between the valence neutrons and protons which have been theoretically predicted to favour a new type of nuclear superfluidity, isoscalar neutron-proton pairing, for which the experimental “smoking gun" remains elusive. In the present work, proton emission from the lanthanum isotope 57116La59, 23 neutrons away from the only stable isotope 57139La82, is reported. 116La nuclei were synthesised in the fusion-evaporation reaction 58Ni(64Zn, p5n)116La and identified via their proton radioactivity using the mass spectrometer MARA (Mass Analysing Recoil Apparatus) and the silicon detectors placed at its focal plane. Comparisons of the measured proton energy (Ep = 718 ± 9 keV) and half-life (T1/2 = 50 ± 22 ms) with values calculated using the Universal Decay Law approach indicate that the proton is emitted with an orbital angular momentum l = 2 and that its emission probability is enhanced relative to its closest, less exotic, odd-even lanthanum isotope (57117La60) while the proton-emission Q-value is lower. We propose this to be a possible signature for the presence of strong neutron-proton pair correlations in this exotic, neutron deficient system. The observations of γ decays from isomeric states in 116La and 117La are also reported.

Original languageEnglish
Article number285
JournalCommunications Physics
Issue number1
Publication statusPublished - 14 Nov 2022

Bibliographical note

© The Author(s) 2022

Funding Information:
This work was supported by the Swedish Research Council under Grant No. 2019-04880; the United Kingdom Science and Technology Facilities Council (STFC) under Grants Nos. ST/P003885/1, ST/V001035/1, ST/P004598/1, and ST/V001027/1; the EU 7th Framework Programme, Integrating Activities Transnational Access, project No.262010 ENSAR; and the Academy of Finland under the Finnish Centre of Excellence Programme (Nuclear and Accelerator Based Physics Programme at JYFL). We thank the JYFL Accelerator laboratory staff for excellent operation of the K130 cyclotron and D. Delion, R. Liotta, N. Sandulescu, and C. Qi for fruitful discussions.

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© 2022, The Author(s).

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