Identification of the<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mrow><mml:msup><mml:mi>J</mml:mi><mml:mi>π</mml:mi></mml:msup><mml:mo>=</mml:mo><mml:msup><mml:mn>1</mml:mn><mml:mo>−</mml:mo></mml:msup></mml:mrow></mml:math>state in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Ra</mml:mi><mml:mprescripts/><mml:none/><mml:mn>218</mml:mn></mml:mmultiscripts></mml:math>populated via<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mi>α</mml:mi></mml:math>decay of<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML"><mml:mmultiscripts><mml:mi>Th</mml:mi><mml:mprescripts/><mml:none/><mml:mn>222</mml:mn></mml:mmultiscripts></mml:math>
E. ParrSchool of Engineering and Computing, University of the West of Scotland, Paisley PA1 2BE, United KingdomJ. F. SmithUniversity of JyväskyläP. T. GreenleesUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandM. SmoleńThe University of ManchesterP. PapadakisUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandK. AuranenUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandR. ChapmanThe University of ManchesterD. M. CullenSchuster Laboratory, University of Manchester, Manchester M13 9PL, United KingdomT. GrahnUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandL. GrocuttSchool of Engineering and Computing, University of the West of Scotland, Paisley PA1 2BE, United KingdomA. HerzáňUniversity of JyväskyläR.-D. HerzbergOliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE, United KingdomD. HodgeSchuster Laboratory, University of Manchester, Manchester M13 9PL, United KingdomU. JakobssonKTH – Royal Institute of TechnologyR. JulinIstituto Nazionale di Fisica Nucleare (INFN) Sezione di PadovaS. JuutinenUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandJ. KonkiUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandM. LeinoUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandC. McPeakeOliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE, United KingdomD. MengoniDipartimento di Fisica e Astronomia dell' Universit and INFN Sezione di Padova, Padova, ItalyA. MistryOliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE, United KingdomK. F. MulhollandSchool of Engineering and Computing, University of the West of Scotland, Paisley PA1 2BE, United KingdomG. O’NeillOliver Lodge Laboratory, University of Liverpool, Liverpool L69 7ZE, United KingdomJ. PakarinenUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandJ. PartanenUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandP. PeuraUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandP. RahkilaUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandP. RuotsalainenTRIUMF, Vancouver, British Columbia V6T 2A3, CanadaM. SandzeliusUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandJ. SarénM. ScheckSchool of Engineering and Computing, University of the West of Scotland, Paisley PA1 2BE, United KingdomC. ScholeyUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandJ. SorriUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandS. StolzeUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, FinlandM. J. TaylorSchuster Laboratory, University of Manchester, Manchester M13 9PL, United KingdomJ. UusitaloUniversity of Jyvaskyla, Department of Physics, P.O. Box 35, FI-40014 University of Jyvaskyla, Finland
ABI
Abstract
The $\ensuremath{\alpha}$ decay of $^{222}\mathrm{Th}$ populating the low-lying ${J}^{\ensuremath{\pi}}={3}^{\ensuremath{-}}$ state, and also a proposed ${1}^{\ensuremath{-}}$ state, in $^{218}\mathrm{Ra}$ has been observed. The observations suggest an excitation energy of 853 keV for the ${1}^{\ensuremath{-}}$ state, which is 60 keV above the ${3}^{\ensuremath{-}}$ state. The hindrance factors of these $\ensuremath{\alpha}$ decays give a possible boundary to the region of ground-state octupole deformation in the light-actinide nuclei. The relative positions of the ${J}^{\ensuremath{\pi}}={1}^{\ensuremath{-}}$ and ${3}^{\ensuremath{-}}$ states suggest they are produced by an octupole-vibrational mechanism, as opposed to $\ensuremath{\alpha}$ clustering or rotations of a reflection-asymmetric octupole-deformed shape.
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