Philippos Papadakis

The magnetic dipole moments (μ) of 209 Tl g (N= 128) and 207 Tl m (N= 126) have been measured for the first time using the in-source laser resonance-ionization spectroscopy technique with the Laser Ion Source and Trap (LIST) at ISOLDE (CERN). The application of the LIST suppresses the usually overwhelming background of the isobaric francium isotopes and allows access to heavy thallium isotopes with A⩾ 207. The self-consistent theory of finite Fermi systems based on the energy density functional by Fayans et al. well describes the N dependence of μ for 1/2+ thallium ground states, as well as μ for the 11/2− isomeric states in europium, gold and thallium isotopes. The inclusion of particle-vibration coupling leads to a better agreement between the theory and experiment for μ (Tl g, I π= 1/2+). It is shown that beyond mean-field contributions to μ cannot be neglected at least for thallium isotopes with I π= 1/2+.

NUCLEAR REACTIONS 3 He (32 S, α) 31 S, E= 128 MeV; measured reaction products, Eγ, Iγ; deduced γ-ray energies, levels, T 1/2, resonances. Comparison with the shell-model code NuShellX calculations. Modern Markov chain Monte Carlo-based Bayesian statistical techniques. The Doppler Shift Lifetimes (DSL2) facility at the TRIUMF Isotope Separator and Accelerator (ISAC-II) facility.

Flerovium isotopes (element Z= 114) were produced in the fusion-evaporation reactions Ca 48+ Pu 242, 244 and studied with an upgraded TASISpec decay station placed in the focal plane of the gas-filled separator TASCA at the GSI Helmholtzzentrum für Schwerionenforschung in Darmstadt, Germany. Twenty-nine flerovium decay chains were identified by means of correlated implantation, α decay, and spontaneous fission events. Data analysis aspects and statistical assessments, primarily based on measured rates of various events, which laid the foundation for the comprehensive spectroscopic information on the flerovium decay chains, are presented in detail. Various decay scenarios of an excited state observed in Cn 282 are examined in depth with the help of Geant4 simulations and assessed by predictions of beyond mean-field calculations including triaxial shape degrees of freedom. Previous, revised …

Research Areas Beta decay Electromagnetic transitions Isomer decays Nuclear decay Nuclear shapes and moments 150≤ A≤ 189Background: The mercury isotopes around N= 104 are a well-known example of nuclei exhibiting shape coexistence. Mixing of configurations can be studied by measuring the monopole strength & ρ 2 (E0), however, currently the experimental information is scarce and lacks precision, especially for the I π→ I π (I≠ 0) transitions. Purpose: The goals of this study were to increase the precision of the known branching ratios and internal conversion coefficients, to increase the amount of available information regarding excited states in 182,184,186 Hg, and to interpret the results in the framework of shape coexistence using different models. Method: The low-energy structures in 182,184,186 Hg were populated in the & beta; decay of 182,184,186 Tl, produced at ISOLDE, CERN and purified by laser ionization and mass separation. The & γ-ray and internal conversion electron events were detected by five germanium clover detectors and a segmented silicon detector, respectively, and correlated in time to build decay schemes. Results: In total, 193, 178, and 156 transitions, including 144, 140, and 108 observed for the first time in a & beta;-decay experiment, were assigned to 182,184,186 Hg, respectively. Internal conversion coefficients were determined for 23 transitions, out of which 12 had an E0 component. Extracted branching ratios allowed the sign of the interference term in 182 Hg as well as & ρ 2 (E0; 0+ 2→ 0+ 1) and B (E 2; 0+ 2→ 2+ 1) in 184 Hg to be determined. By means of electron-electron coincidences, the …

The radioactivity of 76 160 Os 84 and 74 156 W 82 that lie at the two-proton drip line has been measured in an experiment performed at the Accelerator Laboratory of the University of Jyväskylä. The 160 Os nuclei were produced using fusion-evaporation reactions induced by a beam of 310 MeV 58 Ni ions bombarding a 106 Cd target. The 160 Os ions were separated in flight using the recoil separator MARA and implanted into a double-sided silicon strip detector, which was used to measure their decays. The α decays of the ground state of 160 Os (E α= 7092 (15) keV, t 1/2= 97− 32+ 97 μs) and its isomeric state (E α= 8890 (10) keV, t 1/2= 41− 9+ 15 μs) were measured, allowing the excitation energy of the isomer to be determined as 1844 (18) keV. These α-decay properties and the excitation energy of the isomer are compared with systematics. The α decays were correlated with subsequent decays to investigate …

We report on a study of the α-decay fine structure and the associated E α− E γ correlations in the decays of Os 171, 172 and Ir 171, 172, 174. In total, 13 new α-decay energy lines have been resolved, and three new γ-ray transitions have been observed following the new decay branches to Re 168 and W 167. The weak α-decay branch from the bandhead of the ν i 13/2 band in Os 171 observed in this work highlights an unusual competition between α, β, and electromagnetic decays from this isomeric state. The nucleus Os 171 is therefore one of few nuclei observed to exhibit three different decay modes from the same excited state. The nuclei of interest were produced in Mo 92 (Kr 83, x p y n) fusion-evaporation reactions at the Accelerator Laboratory of the University of Jyväskylä, Finland. The fusion products were selected using the gas-filled ion separator RITU and their decays were characterized using an array of …

Results of offline commissioning tests for a new dedicated gas cell for the Mass Analysing Recoil Apparatus (MARA) Low-Energy Branch are reported. Evacuation time, ion survival and transport efficiency in helium buffer gas were characterized with a radioactive 223 Ra α-recoil source. Suppression of the ion signal, originating from non-neutralized species in the gas cell, was explored with 219 Rn ions, the daughter recoil of 223 Ra, as a function of voltage applied to one of the ion-collector electrodes. Two-step laser resonance ionization of stable tin isotopes produced inside the gas cell from a heated bronze filament was demonstrated, and broadening of the atomic resonances in argon buffer gas was studied. These tests indicate the suitability of the new gas cell for future in-gas laser spectroscopy studies of exotic nuclei at the Accelerator Laboratory of the University of Jyväskylä.

The first experiment using radioactive beams post-accelerated by the HIE-ISOLDE facility has enabled to obtain a precise set of B (E 2) transition probabilities in neutron-rich Zn 74, 76 isotopes. The resulting B (E 2; 2 1+→ 0 1+) values are consistent with those determined in earlier REX-ISOLDE measurements. While the B (E 2; 4 1+→ 2 1+) transition probability in Zn 76 is also in agreement with earlier Coulomb-excitation results, the value obtained for Zn 74 is considerably lower. For the first time, a spectroscopic quadrupole moment of the 2 1+ state was measured for an exotic nucleus in this mass region. A detailed comparison is presented with large-scale shell-model and Monte Carlo shell-model calculations.

An experiment was performed at GSI with the objective of measuring theβ-intensity distribution in the decay of Hg, Au and Pt isotopes around N=126 using the total absorption gamma-ray spectroscopy technique. The aim is to benchmark theoretical models used to make predictions of half-life and neutron emission probabilities of exotic nuclei involved in the rapid neutron capture process, leading to the synthesis of very heavy elements. This paper presents some experimental details and the current status of the analysis.

A recoil-beta-tagging experiment has been performed to study the excited and states in the odd–odd nucleus Ag, populated via the Ca(Ni,1p3n)Ag reaction. The experiment was conducted using the MARA recoil separator and JUROGAM3 array at the Accelerator Laboratory of the University of Jyväskylä. Through correlating fast, high-energy beta decays at the MARA focal plane with prompt rays emitted at the reaction target, a number of transitions between excited states in Ag have been identified. The timing characteristics of these transitions confirm that they fall within decay sequences that feed the short-lived ground state of Ag. The transitions are proposed to proceed within and between the sets of states with and . Possible correspondence between some of these transitions from analog states in Pd has been discussed, and shell-model calculations including multipole and monopole electromagnetic effects have been presented, in order to enable predictions of the decay patterns between the and states and to allow a theoretical set of Coulomb energy differences to be calculated for the analog states.

The spectroscopic quadrupole moment of the first 2+ state of 12 C has been measured employing the Coulomb-excitation re-orientation technique. Our result of Q s (2 1+)=+ 9.3− 3.8+ 3.5 efm 2 suggests a larger oblate deformation than previously reported. Combining this with the consistently re-analyzed adopted value, we present the most precise value to date of Q s (2 1+)=+ 9.5 (18) efm 2, which is consistent with a geometrical rotor description. This simple outcome is compared to state-of-the-art shell-model, mean-field, ab initio calculations, cluster-based and geometrical-like theories, which show varying degrees of emergent quadrupole collectivity.

The first experiment using radioactive beams post-accelerated by the HIE-ISOLDE facility has enabled to obtain a precise set of B (E2) transition probabilities in neutron-rich Zn74, 76 isotopes. The resulting B (E2; 21+→ 01+) values are consistent with those determined in earlier REX-ISOLDE measurements. While the B (E2; 41+→ 21+) transition probability in Zn76 is also in agreement with earlier Coulomb-excitation results, the value obtained for Zn74 is considerably lower. For the first time, a spectroscopic quadrupole moment of the 21+ state was measured for an exotic nucleus in this mass region. A detailed comparison is presented with large-scale shell-model and Monte Carlo shell-model calculations.

A recoil-beta-tagging experiment has been performed to study the excited and states in the odd–odd nucleus Ag, populated via the Ca(Ni,1p3n)Ag reaction. The experiment was conducted using the MARA recoil separator and JUROGAM3 array at the Accelerator Laboratory of the University of Jyväskylä. Through correlating fast, high-energy beta decays at the MARA focal plane with prompt rays emitted at the reaction target, a number of transitions between excited states in Ag have been identified. The timing characteristics of these transitions confirm that they fall within decay sequences that feed the short-lived ground state of Ag. The transitions are proposed to proceed within and between the sets of states with and . Possible correspondence between some of these transitions from analog states in Pd has been discussed, and shell-model calculations including multipole and monopole …

The observation of a weak proton-emission branch in the decay of the 3174-keV 53mCo isomeric state marked the discovery of proton radioactivity in atomic nuclei in 1970. Here we show, based on the partial half-lives and the decay energies of the possible proton-emission branches, that the exceptionally high angular momentum barriers, and , play a key role in hindering the proton radioactivity from 53mCo, making them very challenging to observe and calculate. Indeed, experiments had to wait decades for significant advances in accelerator facilities and multi-faceted state-of-the-art decay stations to gain full access to all observables. Combining data taken with the TASISpec decay station at the Accelerator Laboratory of the University of Jyväskylä, Finland, and the ACTAR TPC device on LISE3 at GANIL, France, we measured their branching ratios as bp1 = 1.3(1)% and bp2 = 0.025(4)%. These …

A Low Energy Branch for the MARA separator, MARA-LEB, is under construction at the University of Jyväskylä, Finland. It will be used to purify and study exotic beams initially via nuclear decay and laser spectroscopy. Two experiments have been performed using the MARA separator to determine the acceptance of the gas cell and to assess the feasibility of future experiments at the new facility. Products of different reaction mechanisms have been produced and their transmission from the focal plane of MARA into the LEB gas cell has been estimated. In one experiment, medium-mass nuclei have been produced in fusion–evaporation reactions. In a second experiment, with the primary goal of studying the non-fusion reaction dynamics, heavy target-like fragments from multi-nucleon transfer reactions have been produced. Production cross sections have been measured and are presented in this work.

Fifteen correlated α-decay chains starting from the odd-A superheavy nucleus Fl 289 were observed following the fusion-evaporation reaction Ca 48+ Pu 244. The results call for at least two parallel α-decay sequences starting from at least two different states of Fl 289. This implies that close-lying levels in nuclei along these chains have quite different spin-parity assignments. Further, observed α-electron and α-photon coincidences, as well as the α-decay fine structure along the decay chains, suggest a change in the ground-state spin assignment between Cn 285 and Ds 281. Our experimental results, on the excited level structure of the heaviest odd-N nuclei to date, provide a direct testing ground for theory. This is illustrated by comparison with new nuclear structure calculations based on the symmetry-conserving configuration mixing theory.

Three three-quasiparticle isomers, one at an excitation energy of 2.3 MeV with T 1/2= 0.48 (4) μ s, and two shorter-lived with unknown half-lives at slightly lower energies have been identified in Nd 129 using the MARA+ JUROGAM 3 setup and the recoil tagging technique. All three isomers present decay patterns characteristic of high-K isomers. The known 6.7 s β-decaying isomer previously assigned to the 5/2+ level is now assigned to the new 7/2− ground state. A new low-spin 5/2+ isomeric state with a half-life of a few tens of nanoseconds has been identified, while a previously known 2.6 s β-decay activity was assigned to the band head of the ν 1/2+[411] band. The transitions depopulating the high-K isomers to low-lying states also establish the relative energies of three low-lying one-quasiparticle bands, leading to a new spin-parity assignment of 7/2− to the ground state of Nd 129. The partial half-lives of the …

The electromagnetic transition probabilities of the yrast states in the midshell Te isotopes, two protons above the closed shell at Sn, are of great importance for the understanding of nuclear collectivity in these isotopes and the role played by the neutron-proton interactions and cross-shell excitations. However, the large uncertainty of the experimental data for the midshell nucleus 118Te and the missing data for 116Te make it difficult to pin down the general trend of the evolution of transition probabilities as a function of the neutron number. In this work, the lifetime of the yrast state in 118Te was measured, with the aim of reducing the uncertainty of the previous measurement. The result is  ps. In addition, the lifetime of the state was measured to be  ps. The experimental transition rates are extracted from the measured lifetimes and compared with systematic large-scale shell-model calculations …

Four next-to-tribimaximal (NTBM) mixing patterns are widely considered as the feasible candidates for the observed leptonic mixing structure. With the recent measurements from T2K, as well as intensive global fits, the interval of sin δ C P> 0 for the Dirac C P-violating phase is persistently small in the normal ordering while sin δ C P< 0 is successively obtained up to 3 σ level in the inverted ordering. In this paper, we advocate the fitting results of Dirac C P-violating phase as a constraint, and show that it can basically rule out half of the regions allowed by the constraint from three mixing angles only. In addition, given the small sin δ C P> 0 interval, we find that a unique NTBM pattern can be selected out of the four candidates within 3 σ uncertainty of the latest n u fit 5.1, when the patterns are exposed to a Yukawa texture-independent leptogenesis for the baryon asymmetry of the Universe. For the surviving pattern, we …

The isoscalar single-pion production exhibits a broad bump in the energy dependence of the total cross section, which does not correspond to the usual opening of the N*(1440) production channel with subsequent pion decay. We reevaluate the current database and investigate whether the observed bump structure with a width of about 150 MeV points to the formation of dibaryon states with I (J P)= 0 (1+) and 0 (1−) near the N*(1440) N threshold. This situation would be similar to the situation at the Δ (1232) N threshold, where the signature of a number of dibaryonic resonances has been found.