Search

Across the physics disciplines, the 186Pb nucleus is the only known system, where the two first excited states, together with the ground state, form a triplet of zero-spin states assigned with prolate, oblate and spherical shapes. Here we report on a precision measurement where the properties of collective transitions in 186Pb were determined in a simultaneous in-beam γ-ray and electron spectroscopy experiment employing the recoil-decay tagging technique. The feeding of the 0+2 state and the interband 2+2→2+1 transition have been observed. We also present direct measurement of the energies of the electric monopole transitions from the excited 0+ states to the 0+ ground state. In contrast to the earlier understanding, the obtained reduced transition probability B(E2;2+1→0+2) value of 190(80) W.u., the transitional quadrupole moment |Qt(2+1→0+2)|=7.7(33) eb and intensity balance arguments provide evidence to reassign the 0+2 and 0+3 states with predominantly prolate and oblate shape, respectively. Our work demonstrates a step-up in experimental sensitivity and paves the way for systematic studies of electric monopole transitions in this region. These electric monopole transitions probe the nuclear volume in a unique manner and provide unexploited input for development of the next-generation energy density functional models. peerReviewed

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 11657La59, 23 neutrons away from the only stable isotope 13957La82, 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 (11757La60) 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. peerReviewed

A low-energy branch is under development for the MARA vacuum-mode recoil separator at the Accelerator Laboratory of the University of Jyväskylä. This development will allow for the study of proton-rich nuclei through laser ionisation spectroscopy and mass measurements. After stopping and extraction from a buffer gas cell, the ions of interest will be accelerated and transported to dedicated experimental setups by an ion transport system consisting of several focusing, accelerating and mass-separating elements. This article presents the current design and simulations for the ion transport. peerReviewed

Fine structure in the α decay of high-spin states in 156Lu and 158Ta has been identified by means of αγ - coincidence analysis. One new α decay from 156Lu and two from 158Ta were identified, one of which was found to populate a previously unknown state in 154Lu. The hindrance-factor systematics from all four odd-odd, N = 85 nuclei with known α-decaying, πh11/2 coupled states were reviewed and are discussed. These proved consistent with the previously assigned (πh11/2νh9/2 )10+ configuration of the α-decaying state in 156Lu, which differs from the (πh11/2ν f7/2 )9+ assignments in the other three nuclei. peerReviewed

A differential-plunger device was used to measure the lifetimes of the lowest states in the πg7/2 ⊗ νh11/2 rotational band in doubly odd 112I with the 58Ni(58Ni, 3pn) reaction. A differential decay curve method was performed using the fully shifted and degraded γ -ray intensity measurements as a function of target-to-degrader distance. The lifetimes of the lowest three states in the πg7/2 ⊗ νh11/2 band in 112I were measured to be 124(30), 130(25), and 6.5(5) ps, respectively. As the lifetimes of successive excited states in a rotational band are expected to decrease with increasing excitation energy, these measurements suggest that the order of the transitions in the established band in 112I may need revising and that the state tentatively assigned to be (7−) may not belong to the rotational band. peerReviewed

Excited states above the 17+ isomeric state in the proton-rich nucleus 152Tm were established by employing the recoil-isomer tagging technique. Data were collected using the JUROGAM gamma-ray array and the GREAT spectrometer together with the recoil ion transport unit (RITU) gas-filled recoil separator and analyzed to identify the prompt and delayed γ decays from the levels in 152Tm. Shell-model calculations, either in a large valence space or in a reduced model space with five protons in the π0h11/2 orbital and one neutron in the ν1f7/2 orbital, agree with the observed energies of the yrast levels up to angular momentum J = 21. The observation of near degeneracies in the energy spectrum can be attributed to specific components of the proton-neutron interaction. The isomeric decay of the 17+ level is not reproduced in the shell-model calculations as it arises from a delicate balance between hindrance due to seniority selection rules and enhancement due to configuration mixing peerReviewed

A multiparticle spin-trap isomeric state having a half-life of 179(4) ns and lying 2601 keV above the yrast 10 + state in 156 Lu has been discovered. The 156 Lu nuclei were produced by bombarding isotopically enriched 106 Cd targets with beams of 58 Ni ions, separated in flight using the gas-filled separator RITU and their decays were measured using the GREAT spectrometer. Analysis of the main decay path that populates yrast states observed previously suggests a spin-parity assignment of 19 − for the isomeric state, which is consistent with isomeric states identified in the N = 85 isotones. Comparison with other decay paths in 156 Lu indicates that the [ π h − 1 11 / 2 ⊗ ν h 9 / 2 ] 10 + state at the bottom of the yrast sequence is likely to be the α -decaying isomeric state, with the [ π h − 1 11 / 2 ⊗ ν f 7 / 2 ] 9 + state lying 62 keV above it. The relative ordering of the lowest-lying 9 + and 10 + states is inverted in 156 Lu compared with its odd-odd isotones. peerReviewed

Fine structure in the α decay of high-spin isomers in 155Lu(25/2−) and 156Hf (8+) has been studied for the first time using αγ -coincidence analysis. Three new α decays from 155Lu(25/2−) and two from 156Hf (8+) have been identified, populating seniority s > 1 states in the N = 82 nuclei 151Tm and 152Yb, respectively. The reduced hindrance factors of the α decays support the previous configuration assignments of the populated states. This is the first observation of states with excitation energy greater than 1.5 MeV being populated following α decay in nuclei outside of the 208Pb region. peerReviewed

Using fusion-evaporation reactions, a gas-filled recoil separator, recoil-gating technique and recoil-isomer decay tagging technique we have extended the level scheme of 203 At ( N = 118 ) significantly. We have observed an isomeric [ τ = 14.1 ( 3 ) μ s ] state with a spin and parity of 29 / 2 + . The isomeric state is suggested to originate from the π ( h 9 / 2 ) ⊗ ∣ ∣ 202 Po ; 11 − ⟩ coupling, and it is depopulated through 286 keV E 2 and 366 keV E 3 transitions. In addition, we have observed a cascade of magnetic-dipole transitions which is suggested to be generated by the shears mechanism. peerReviewed

The level structure of 136Nd has been investigated using the 100Mo(40Ar, 4n) reaction and the JUROGAM II+RITU+GREAT setup. The level scheme has been extended significantly. Many new bands have been identified both at low and high spin, among which are five nearly degenerate bands interpreted as chiral partners. Excitation energies, spins, and parities of the previously known bands are revised and firmly established, and some previously known bands have been revised. Configurations are assigned to the observed bands based on cranked Nilsson-Strutinsky calculations. The band structure of 136Nd is now clarified and the various types of single-particle and collective excitations are well understood. peerReviewed

The excited states of the proton emitter 151Lu were reinvestigated in a recoil-decay tagging experiment at the Accelerator Laboratory of the University of Jyväskylä (JYFL). The level scheme built on the ground state of 151Lu was updated with five new γ -ray transitions. Large-scale shell model calculations were carried out in the model space consisting of the neutron and proton orbitals 0g7/2, 1d5/2, 1d3/2, 2s1/2, and 0h11/2 with the optimized monopole interaction in order to interpret the experimental level scheme of 151Lu. It is found that the excitation energies of states above the 27/2− and 23/2+ isomeric levels in 151Lu can be sensitive to excitations from g7/2 and d5/2 to single-particle orbitals above N = Z = 64. peerReviewed

Lifetimes of excited states in the yrast band of the neutron-deficient nuclide 166W have been measured utilizing the DPUNS plunger device at the target position of the JUROGAM II γ -ray spectrometer in conjunction with the RITU gas-filled separator and the GREAT focal-plane spectrometer. Excited states in 166W were populated in the 92Mo(78Kr,4p) reaction at a bombarding energy of 380 MeV. The measurements reveal a low value for the ratio of reduced transitions probabilities for the lowest-lying transitions B(E2; 4+ → 2+)/B(E2; 2+ → 0+) = 0.33(5), compared with the expected ratio for an axially deformed rotor (B4/2 = 1.43). peerReviewed

The structure of the low- and medium-spin levels of the 211Po nucleus have been studied with in-beam γ-ray spectroscopy with the 208Pb(α,n)211Po fusion-evaporation reaction. The level scheme was further extended with levels of the configurations π(h9/2)22+−4+⊗νg9/2, π(h9/2)28+⊗νg9/2, π(h9/2)22+−4+⊗νi11/2, π(h9/2)22+−4+⊗νj15/2, π(h9/2f7/2)8+⊗νg9/2, and π(h9/2)20+⊗ν(g9/2)20+(s1/2)−1. The single-particle neutron states νd5/2 and νs1/2 were also identified. Furthermore, a number of states feeding the low-spin structures were added. peerReviewed

The evolution of collectivity with spin along the yrast line in the neutron-deficient nucleus 112Te has been studied by measuring the reduced transition probability of excited states in the yrast band. In particular, the lifetimes of the 4+ and 6+ excited states have been determined by using the recoil distance Doppler-shift method. The results are discussed using both large-scale shell-model and total Routhian surface calculations. peerReviewed

The neutron-deficient nucleus At199 has been studied through γ-ray and electron spectroscopy, using the recoil-decay tagging technique. Two experiments were conducted, using a gas-filled recoil separator with a focal-plane spectrometer alone and together with a germanium-detector array at the target position. The resulting level scheme for At199 includes a new isomer with a half-life of 0.80(5) μs and a spin and parity of (29/2+). The 13/2+ isomer, which de-excites via an M2 transition to the 9/2− ground state, was measured to have a half-life of 70(20) ns. Our earlier version of the level scheme for At197 has been updated as well. peerReviewed

In-beam γ-ray and γ-γ coincidence measurements have been made for the very neutron-deficient nucleus 176Hg using the recoil-decay tagging (RDT) technique. The irregular yrast sequence observed up to I=10ħ indicates that the prolate intruder band, seen in heavier Hg isotopes near the neutron midshell, crosses the nearly spherical ground-state band of 176Hg above I=6ħ. peerReviewed