Lifetime measurements of low-lying excited states in the semimagic (N=50) nucleus Rh95 have been performed by means of the fast-timing technique. The experiment was carried out using γ-ray detector arrays consisting of LaBr3(Ce) scintillators and germanium detectors integrated into the DESPEC experimental setup commissioned for the Facility for Antiproton and Ion Research (fair) Phase-0, Darmstadt, Germany. The excited states in Rh95 were populated primarily via the β decays of Pd95 nuclei, produced in the projectile fragmentation of a 850 MeV/nucleon Xe124 beam impinging on a 4g/cm2Be9 target. The deduced electromagnetic E2 transition strengths for the γ-ray cascade within the multiplet structure depopulating from the isomeric Iπ=21/2+ state are found to exhibit strong deviations from predictions of standard shell model calculations which feature approximately conserved seniority symmetry. In particular, the observation of a strongly suppressed E2 strength for the 13/2+→9/2+ ground state transition cannot be explained by calculations employing standard interactions. This remarkable result may require revision of the nucleon-nucleon interactions employed in state-of-the-art theoretical model calculations, and might also point to the need for including three-body forces in the Hamiltonian.

A salient feature of quantum mechanics is the inherent property of collective quantum motion, when apparent independent quasiparticles move in highly correlated trajectories, resulting in strongly enhanced transition probabilities. To assess the extend of a collective quantity requires an appropriate definition of the uncorrelated average motion, often expressed by single particle units. A well known example in nuclear physics is the Weisskopf unit for electromagnetic transitions which reveals different aspects of collective motion. In this paper we define the corresponding single particle unit for alpha decay as induced by four uncorrelated/non-interacting protons and neutrons. Our definition facilitates an unified description of all alpha decay processes along the nuclear chart, revealing a simple mass dependence. The comparison of the uncorrelated decay rates with the experimentally observed ones, shows a significant enhancement of the decay rates pointing towards collective alpha like correlations in the nuclear ground state. As a limiting case, the formalism presented here is applied to proton decay revealing its single particle nature.

Lifetimes of low-lying excited states in the nu i(13/2+) bands of the neutron-deficient osmium isotopes 169,171,173Os have been measured for the first time using the recoil-distance Doppler shift and recoil-isomer tagging techniques. An unusually low value is observed for the ratio B(E2; 21/2(+) -> 17/2+)/B(E2; 17/2+ -> 13/2+) in 169Os, similar to the "anomalously" low values of the ratio B(E2; 4+1 -> 2+1 )/B(E2; 2(1)(+) -> 0(gs)(+)) previously observed in several transitional rare-earth nuclides with even numbers of neutrons and protons, including the neighbouring 168,170Os. Furthermore, the evolution of B(E2; 21/2(+) -> 17/2(+))/B(E2; 17/2(+) -> 13/2(+)) with increasing neutron number in the odd-mass isotopic chain 169,171,173Os is observed to follow the same trend as observed previously in the eveneven Os isotopes. These findings indicate that the possible quantum phase transition from a seniority conserving structure to a collective regime as a function of neutron number suggested for the even-even systems is maintained in these odd-mass osmium nuclei, with the odd valence neutron merely acting as a "spectator". As for the even-even nuclei, the phenomenon is highly unexpected for nuclei that are not situated near closed shells.

We analyze a recent study of the one-proton knockout reaction on N-19 in the framework of a time-dependent two-level model. Focusing on the specific case of C-18, we quantify the validity of the so-called "piston" mechanism in terms of the timescales involved in the process, namely, the reaction time, the period of oscillation between the mixed states, and the lifetime of the excited unbound state.

Excited states in the extremely neutron-deficient nucleus ¹⁷²Pt were populated via ⁹⁶Ru(⁷⁸Kr,2p) and ⁹²Mo(⁸³Kr,3n) reactions. The level scheme has been extended up to an excitation energy of  ~ 5 MeV and tentative spin-parity assignments up to I^π = 18⁺. Linear polarization and angular distribution measurements were used to determine the electromagnetic E1 character of the dipole transitions connecting the positive-parity ground-state band with an excited side-band, firmly establishing it as a negative-parity band. The lowest member of this negative-parity structure was firmly assigned spin-parity 3^-. In addition, we observed an E3 transition from this 3^- state to the ground state, providing direct evidence for octupole collectivity in ¹⁷²Pt. Large-scale shell model (LSSM) and total Routhian surface (TRS) calculations have been performed, supporting the interpretation of the 3^- state as a collective octupole-vibrational state.

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.

The Giant Pairing Vibration, a two-nucleon collective mode originating from the second shell above the Fermi surface, has long been predicted and expected to be strongly populated in two-nucleon transfer reactions with cross sections similar to those of the low-lying Pairing Vibration. Recent experiments have provided evidence for this mode in C-14,C- 15 but, despite sensitive studies, it has not been definitively identified in Sn or Pb nuclei where pairing correlations are known to play a crucial role near their ground states. In this paper we review the basic theoretical concepts of this "elusive" state and the status of experimental searches in heavy nuclei. We discuss the hindrance effects due to Q-value mismatch and the use of weakly-bound projectiles as a way to overcome the limitations of the (p,t) reactions. We also discuss the role of the continuum and conclude with some possible future developments.

The process leading to cluster emission from superheavy nuclei in the range 100 122 has been systematically investigated. This topic is of importance because it opens up the possibility of identifying superheavy elements through deposition of clusters in the detection system. In this paper we evaluate the cluster decay half lives by considering the cluster as a particle. The motion of this particle in the field induced by the daughter nucleus is determined by solving the corresponding Schrodinger equation imposing outgoing boundary conditions (Gamow state). The corresponding Wood-Saxon potential is fitted to obtain the energies provided by a mass formula that has been established recently to have a very high degree of precision. The resulting expression for the decay width is exact, i.e. no approximation besides the assumption of a preformed cluster is introduced. It is found that the heavy cluster emission probability in the superheavy region is much smaller than the corresponding a emission probability.

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 emissions of a particles and protons are the dominant decay channels in the neutron-deficient nuclei corresponding to the sdg major shell. The possibility of cluster emission is explored here. It is shown that the cluster decay mode has a small yet sizable branching ratio.