Univ Liverpool, Oliver Lodge Lab, Dept Phys, Liverpool L69 7ZE, Merseyside, England..
Univ Jyvaskyla, Epartment Phys, POB 35, FI-40014 Jyvaskyla, Finland..
Univ Manchester, Sch Phys & Astron, Schuster Bldg, Manchester M13 9PL, Lancs, England..
Univ Jyvaskyla, Epartment Phys, POB 35, FI-40014 Jyvaskyla, Finland.;Lund Univ, Dept Phys, S-22100 Lund, Sweden..
Osaka Univ, Res Ctr Nucl Phys, JP-5670047 Osaka, Japan..
CEA, GANIL, DSMa, CNRS,IN2P3, F-14076 Caen 5, France..
KTH. KTH Royal Inst Technol, S-10691 Stockholm, Sweden..
Univ Oslo, Dept Phys, NO-0316 Oslo, Norway..
Univ Liverpool, Oliver Lodge Lab, Dept Phys, Liverpool L69 7ZE, Merseyside, England.;Univ Jyvaskyla, Epartment Phys, POB 35, FI-40014 Jyvaskyla, Finland..
Univ Paris Saclay, Ctr Sci Nucl & Sci Mat, CNRS, IN2P3, F-91405 Orsay, France..
Univ Jyvaskyla, Epartment Phys, POB 35, FI-40014 Jyvaskyla, Finland.;Ist Nazl Fis Nucl, Lab Nazl Legnaro, I-35020 Legnaro, Italy.;Sodankyla Geophys Observ, FI-99600 Sodankyla, Finland..
Univ Manchester, Sch Med Sci, Div Canc Sci, Manchester M13 9PL, Lancs, England..
Lifetimes of the first excited 2(+) and 4(+) states in the extremely neutron -deficient nuclide Pt-172 have been measured for the first time using the recoil-distance Doppler shift and recoil-decay tagging techniques. An unusually low value of the ratio B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) = 0.55(19) was found, similar to a handful of other such anomalous cases observed in the entire Segre chart. The observation adds to a cluster of a few extremely neutron -deficient nuclides of the heavy transition metals with neutron numbers N approximate to 90-94 featuring the effect. No theoretical model calculations reported to date have been able to explain the anomalously low B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) ratios observed in these cases. Such low values cannot, e.g., be explained within the framework of the geometrical collective model or by algebraic approaches within the interacting boson model framework. It is proposed that the group of B(E2: 4(1)(+) -> 2(1)(+)/B(E2: 2(1)(+) -> 0(gs)(+)) ratios in the extremely neutron-deficient even-even W, Os, and Pt nuclei around neutron numbers N approximate to 90-94 reveal a quantum phase transition from a seniority-conserving structure to a collective regime as a function of neutron number. Although a system governed by seniority symmetry is the only theoretical framework for which such an effect may naturally occur, the phenomenon is highly unexpected for these nuclei that are not situated near closed shells.
The advent and intensive use of new detector technologies as well as radioactive ion beam facilities have opened up possibilities to investigate alpha, proton and cluster decays of highly unstable nuclei. This article provides a review of the current status of our understanding of clustering and the corresponding radioactive particle decay process in atomic nuclei. We put alpha decay in the context of charged-particle emissions which also include one- and two-proton emissions as well as heavy cluster decay. The experimental as well as the theoretical advances achieved recently in these fields are presented. Emphasis is given to the recent discoveries of charged-particle decays from proton-rich nuclei around the proton drip line. Those decay measurements have shown to provide an important probe for studying the structure of the nuclei involved. Developments on the theoretical side in nuclear many-body theories and supercomputing facilities have also made substantial progress, enabling one to study the nuclear clusterization and decays within a microscopic and consistent framework. We report on properties induced by the nuclear interaction acting in the nuclear medium, like the pairing interaction, which have been uncovered by studying the microscopic structure of clusters. The competition between cluster formations as compared to the corresponding alpha-particle formation are included. In the review we also describe the search for super-heavy nuclei connected by chains of alpha and other radioactive particle decays.