Possible shears bands in At204 and Fr206, and identification of excited states in Fr205,207

Neutron-deficient astatine and francium nuclei were produced in the reaction 30Si+181Ta→211Fr* at 152 MeV. The evaporation residues from this very fissile system were selected with the HERCULES-II detector system and residue-gated γ rays were measured with Gammasphere. Excited states were observed for the first time in Fr205,207, as well as sequences of low-energy transitions between high-spin states in At204 and Fr206. These latter structures have properties similar to those associated with magnetic rotation (shears bands) in lead nuclei. Comparisons with established shears bands are presented and prospects for the magnetic-rotation phenomenon near the predicted N=120 "magic" number are explored

Structure of high-spin states in 91Sr and 92Sr

The nuclei 91Sr and 92Sr were produced at high spin as fission fragments following the fusion reaction 36S+ 159Tb at 165 MeV. γ rays were detected with the Gammasphere array. The level schemes of 91Sr and 92Sr were extended up to E≈6 MeV and E≈8 MeV, respectively. Level structures in 91Sr and 92Sr were interpreted in shell-model calculations performed in the configuration space (0f5/2, 1p3/2, 1p1/2, 0g9/2) for the protons and (1p1/2, 0g9/2, 1d5/2) for the neutrons. Negative-parity states in the yrast sequences are described in these calculations by coupling 3- proton excitations to the unpaired 1d5/2 neutrons. A possible reduction of the gap between the proton 1p3/2 and 1p1/2 orbitals in 92Sr is discussed

Multiple excitation modes in Hf 163

Excited states of Hf163 were populated using the Zr94(Ge74,5n) reaction and the decay γ rays were measured with the Gammasphere spectrometer. Two previously known bands were extended to higher spins, and nine new bands were identified. In addition to bands associated with three- and five-quasiparticle configurations, two γ-vibrational bands coupled to the i13/2 excitation were also observed. The lowest level of a newly identified, negative-parity band is proposed to be the ground state of the nucleus. A systematic delay of the high-spin proton crossing frequency with increasing quadrupole deformation from Hf162 to Hf172 was established. Extensive band searches failed to reveal a triaxial, strongly deformed structure in Hf163 similar to the one observed in several nuclei around A∼165

Reply to: Possible overestimation of isomer depletion due to contamination

We appreciate the interest of Guo et al., the points that they raise, and the opportunity that we have to provide additional details that are not included in ref. This allows us to strengthen our experimental case while, in parallel, recent developments are improving our theoretical understanding of nuclear excitation by electron capture (NEEC), such as the exploration of a substantial increase in predicted NEEC probability when considering capture by an ion in an excited state (S. Gargiulo et al., submitted) or the impact of the momentum distribution of target electrons (J.R. et al., submitted). In the accompanying Comment, Guo et al. focus on whether potential background contributions were underestimated in our analysis. As discussed below, these concerns are mostly unwarranted; aside from a small systematic uncertainty that could possibly slightly reduce our reported NEEC excitation probability of Pexc = 0.010(3), our original conclusions still stand

Yrast spectroscopy of 60128Nd68 and systematics of the νh11/2 crossing in A∼130 nuclei

High-spin states in 128Ca were populated with the 92Mo (40Ca, 2p2n) reaction at a beam energy of 184 MeV. The previously known ground-state band has been extended to Iπ=(34+) and four sidebands were observed. Configuration assignments for these sidebands are discussed based on their alignment behavior. A significant delay of the νh11/2 crossing frequency is observed in the A∼130 region, with the largest delays occurring consistently at N=70. Cranked shell model calculations were performed in order to investigate whether a variation of deformation and/or pairing parameters can account for this phenomenon

Rotational structures near 40ℏ in 123La

The neutron-deficient nucleus 123La was studied via the 92Mo(40Ca,2ap) reaction at a beam energy of 184 MeV. Previously known bands were extended to a much higher spin, and in two cases the structures are now observed near 40ℏ. In addition, three new sequences were identified and linked into previously known bands. The lowest (π,α)=(+,-1/2) structure displays characteristics similar to those of analogous bands in 127,129La, which have been proposed as examples of smooth band termination. Cranked Nilsson-Strutinsky calculations were compared with the experimental data in 123La to determine whether this band is approaching a terminating state as well

Isomer depletion as experimental evidence of nuclear excitation by electron capture

The atomic nucleus and its electrons are often thought of as independent systems that are held together in the atom by their mutual attraction. Their interaction, however, leads to other important effects, such as providing an additional decay mode for excited nuclear states, whereby the nucleus releases energy by ejecting an atomic electron instead of by emitting a 3-ray. This 'internal conversion' has been known for about a hundred years and can be used to study nuclei and their interaction with their electrons. In the inverse process - nuclear excitation by electron capture (NEEC) - a free electron is captured into an atomic vacancy and can excite the nucleus to a higher-energy state, provided that the kinetic energy of the free electron plus the magnitude of its binding energy once captured matches the nuclear energy difference between the two states. NEEC was predicted in 1976 and has not hitherto been observed. Here we report evidence of NEEC in molybdenum-93 and determine the probability and cross-section for the process in a beam-based experimental scenario. Our results provide a standard for the assessment of theoretical models relevant to NEEC, which predict cross-sections that span many orders of magnitude. The greatest practical effect of the NEEC process may be on the survival of nuclei in stellar environments, in which it could excite isomers (that is, long-lived nuclear states) to shorter-lived states. Such excitations may reduce the abundance of the isotope after its production. This is an example of 'isomer depletion', which has been investigated previously through other reactions, but is used here to obtain evidence for NEEC

Search for strongly deformed structures and observation of multiple nucleon alignments in W174

Highly excited states, up to spin 39, have been established in W174, using the Gammasphere array. Ultimate cranker calculations predict the appearance of triaxial, strongly deformed structures above spin 30 in W174. A new approach was developed for a comprehensive search of the data for such structures, similar to those observed in the Lu and Hf isotopes. No evidence was found for strongly deformed bands in the W isotopes populated in this experiment. Existing rotational structures have been considerably extended, allowing for the observation of both neutron and proton alignments in a number of bands. There is evidence for the i13/2 neutron and possibly both the h9/2 and h11/2 proton crossings. The observed neutron and proton crossing frequencies are in good agreement with predictions of Woods-Saxon cranking calculations using an empirical pair-gap energy, and they lead to an improved understanding of the underlying structure of the bands

Characterization of octupole-type structures in Th 221

A detailed level scheme for Th221 has been established in an experiment using the O18+207Pb reaction at 96 MeV. The evaporation residues from this fissile system were selected with the HERCULES detector array and residue-gated γ rays were measured with Gammasphere. Three band structures of interlinked, alternating-parity levels are observed, two of which are non-yrast. In addition, several high-lying excitations are found. The yrast band is seen up to spin-parity 37/2- and 39/2+, beyond which a high-spin feeding transition is observed. The non-yrast sequences are interpreted as parity-doublet structures, based on a configuration similar to that of the yrast band in Th223 (K=5/2). The key properties of even-odd nuclei in this mass region [B(E1)/B(E2) and B(M1)/B(E2) ratios, spin alignments, parity splittings] are reviewed

Triaxial strongly deformed bands in Tm160,161

High-spin states in Tm160,161 were populated using the Te128(Cl37, 5n and 4n) reactions at a beam energy of 170 MeV. Emitted γ rays were detected in the Gammasphere spectrometer. Two rotational bands with high moments of inertia were discovered, one assigned to Tm160, while the other tentatively assigned to Tm161. These sequences display features similar to bands observed in neighboring Er, Tm, Yb, and Lu nuclei which have been discussed in terms of triaxial strongly deformed structures. Cranked Nilsson Strutinsky calculations have been performed that predict well-deformed triaxial shapes at high spin in Tm160,161