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Prompt and delayed γ-ray spectroscopy of the neutron-deficient, semi-magic isotope $^{187}$Pb has been performed using the recoil-decay and isomer-decay tagging techniques at the Argonne Gas-Filled Analyzer. A new 5.15(15)-μs isomeric state at only 308 keV above the spherical 3/2$^{−}$ ground state is identified and classified as a shape isomer. A strongly-coupled band is observed on top of the isomer, which is nearly identical to the one built on the prolate 7/2$^{−}$[514] Nilsson state in the isotone $^{185}$Hg. Based on this similarity and on the result of the potential-energy surface calculations, the new isomer in $^{187}$Pb is proposed to originate from the same configuration. The retarded character of the 308-keV (7/2$^{−}$)→3/2gs− transition with a deduced B(E2)=5.6(2)×10−4 W.u. can be well explained by the significant difference between the prolate parent and spherical daughter configurations, leading to the shape isomerism. The excitation energy of the isomer is surprisingly low, being roughly half of the excitation energies of the known 0$^{+}$ intruder bandheads in the neighboring $^{186,188}$Pb isotopes. The combined results of the present work and the previous α-decay and laser spectroscopy studies present evidence for triple shape coexistence at low energy in the negative-parity configurations of $^{187}$Pb, which is well reproduced by the potential-energy surface calculations.

Physics letters / B 833, 137345 (2022). doi:10.1016/j.physletb.2022.137345, Published by North-Holland Publ., Amsterdam

The decay of the 13/2$^{+}$ isomeric state in $^{183}$Hg was observed for the first time following the α decay of the 13/2$^{+}$ isomer in $^{187}$Pb produced in the $^{142}$Nd($^{50}$Cr, 2p3n) reaction. Using α−γ delayed coincidence measurements, the half-life of this isomer was measured to be 290(30) μs. This isomer is proposed to deexcite by an unobserved low-energy M2 transition to the known 9/2$^{−}$ member of a strongly prolate-deformed 7/2$^{−}$[514] band, followed by a 105-keV M1 transition to the bandhead. A lower limit of B(M2) ≥ 0.018 W.u. was deduced for the unobserved transition. The presumed retardation is proposed to be due to the notable shape change between the initial, nearly spherical, and the final, strongly deformed, states. A similar scenario is also considered for the 13/2$^{+}$ isomer in $^{181}$Hg, suggesting both are cases of shape isomers. The B(M2) systematics of neutron transitions across the nuclear chart is discussed.

International audience; The neutron-deficient Bi188 and Po188 isotopes have been studied by γ-ray spectroscopy using the recoil-decay tagging technique with the Argonne Gas-Filled Analyzer. A new 0.25(5)-μs isomeric state and a prompt cascade formed by 319-, 366-, and 462-keV γ rays have been established on top of the (10−) α-decaying isomer in Bi188. The first excited (2+) state in Po188 was identified, its excitation energy of 242(2) keV continues the nearly constant trend for the first 2+ states in Po190,192,194. The state is most likely a member of a prolate rotational band built on the ground state, albeit mixing with other coexisting configurations cannot be excluded. The new results obtained in the present work provide new information to shape coexistence in bismuth and polonium isotopes near the neutron midshell at N=104. In this mass region, a reduction in the prompt γ-ray yield obtained with recoil decay tagging was observed for a few nuclides, and the possible reasons are presented.

International audience; The $\beta$ decay of the neutron-rich $^{134}$In and $^{135}$In was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number $Z=50$ above the $N=82$ shell. The $\beta$-delayed $\gamma$-ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-ionized and on-line mass separated. Three $\beta$-decay branches of $^{134}$In were established, two of which were observed for the first time. Population of neutron-unbound states decaying via $\gamma$ rays was identified in the two daughter nuclei of $^{134}$In, $^{134}$Sn and $^{133}$Sn, at excitation energies exceeding the neutron separation energy by 1 MeV. The $\beta$-delayed one- and two-neutron emission branching ratios of $^{134}$In were determined and compared with theoretical calculations. The $\beta$-delayed one-neutron decay was observed to be dominant $\beta$-decay branch of $^{134}$In even though the Gamow-Teller resonance is located substantially above the two-neutron separation energy of $^{134}$Sn. Transitions following the $\beta$ decay of $^{135}$In are reported for the first time, including $\gamma$ rays tentatively attributed to $^{135}$Sn. In total, six new levels were identified in $^{134}$Sn on the basis of the $\beta \gamma \gamma$ coincidences observed in the $^{134}$In and $^{135}$In $\beta$ decays. A transition that might be a candidate for deexciting the missing neutron single-particle $13/2^+$ state in $^{133}$Sn was observed in both $\beta$ decays and its assignment is discussed. Experimental level schemes of $^{134}$Sn and $^{135}$Sn are compared with shell-model predictions. Using the fast timing technique, half-lives of the $2^+$, $4^+$ and $6^+$ levels in $^{134}$Sn were determined.

International audience; A comprehensive study of the isotope $^{178}$Auhas been made at the CERN-ISOLDE facility, using resonance laser ionization. Two long-lived states in$^{178}$Auwere identified—a low-spin ground state and a high-spin isomer—each of which were produced as pure beams. Using the ISOLTRAP precision Penning trap, the excitation energy of the isomeric state in$^{178}$Auwas determined to be$E$$^{*}$=189(14)keV. Theα-decay fine structure patterns of the two states were studied using the Windmill decay station, providing information on the low-lying states in the daughter nucleus$^{174}$Ir. Nuclear spin assignments of$I$($^{178}$Au$^{g}$)=(2,3)and$I$($^{178}$Aum)=(7,8)are made based on the observed$\beta$-decay feeding and hyperfine structure intensity patterns. These spin assignments are used for fitting the hyperfine structures of the two states from which values for the magnetic dipole moments are extracted. The extracted moments are compared with calculations using additivity relations to establish the most probable configurations for$^{178}$Au$^{g,m}$.

International audience; Excited states in $^{133}Sn$ were investigated through the $\beta$ decay of $^{133}In$ at the ISOLDE facility. The ISOLDE Resonance Ionization Laser Ion Source (RILIS) provided isomer-selective ionization for $^{133}In$, allowing us to study separately, and in detail, the β-decay branch of $^{133}In$ J$^{\pi}$=(9/2$^+$) ground state and its J$^{\pi}$=(1/2$^−$) isomer. Thanks to the large spin difference of the two β-decaying states of $^{133}In$, it is possible to investigate separately the lower and higher spin states in the daughter, $^{133}Sn$, and thus to probe independently different single-particle and single-hole levels. We report here new $\gamma$ transitions observed in the decay of $^{133}In$, including those assigned to the deexcitation of the neutron-unbound states.

International audience; An α-decay study of At218 was performed at the CERN-ISOLDE facility. Laser-ionized beams of At218 were mass separated and implanted into an α-γ detection setup. Coincidence α-γ data were collected for the first time and a more precise half-life value of T1/2=1.27(6) s was measured. A new α-decay scheme was deduced based on the extracted reduced α-decay widths for fine-structure decays. The results from this work lead to a preferred spin and parity assignment of Jπ=(3−); however, Jπ=(2)− cannot be fully excluded.

10 pags., 8 figs., 1 tab.-- Open Access funded by Creative Commons Atribution Licence 4.0, Excited states in Sn133 were investigated through the ß decay of In133 at the ISOLDE facility. The ISOLDE Resonance Ionization Laser Ion Source (RILIS) provided isomer-selective ionization for In133, allowing us to study separately, and in detail, the ß-decay branch of In133J¿=(9/2+) ground state and its J¿=(1/2-) isomer. Thanks to the large spin difference of the two ß-decaying states of In133, it is possible to investigate separately the lower and higher spin states in the daughter, Sn133, and thus to probe independently different single-particle and single-hole levels. We report here new ¿ transitions observed in the decay of In133, including those assigned to the deexcitation of the neutron-unbound states., We acknowledge the support of the ISOLDE Collaboration and technical teams. This work was supported in part by the Polish National Science Center under Contract No. UMO-2015/18/E/ST2/00217 and under Contract No. UMO-2015/18/M/ST2/00523, by the Spanish MINECO via FPA2015-65035-P project, by the Portuguese FCT via CERN/FIS-NUC/0004/2015 and CERN-FIS-PAR-0005-2017 projects. The research leading to these results has received funding from the European Union’s Horizon 2020 research and innovation programme under Grant Agreement No. 654002.

International audience; Hyperfine-structure parameters and isotope shifts for the 795-nm atomic transitions in $^{217,218,219}$At have been measured at CERN-ISOLDE, using the in-source resonance-ionization spectroscopy technique. Magnetic dipole and electric quadrupole moments, and changes in the nuclear mean-square charge radii, have been deduced. A large inverse odd-even staggering in radii, which may be associated with the presence of octupole collectivity, has been observed. Namely, the radius of the odd-odd isotope $^{218}$At has been found to be larger than the average of its even-$N$ neighbors, $^{217,219}$At. The discrepancy between the additivity-rule prediction and experimental data for the magnetic moment of $^{218}$At also supports the possible presence of octupole collectivity in the considered nuclei.

The first accurate measurements of the α-decay branching ratio and half-life of the Iπ=1/2+ ground state in $^{181}$Tl have been made, along with the first determination of the magnetic moments and I=1/2 spin assignments of the ground states in $^{177,179}$Au. The results are discussed within the complementary systematics of the reduced α-decay widths and nuclear g factors of low-lying, Iπ=1/2+ states in the neutron-deficient lead region. The findings shed light on the unexpected hindrance of the 1/2+→1/2+, $^{181}$Tl→g177Au$^{g}$ α decay, which is explained by a mixing of π3s1/2 and π2d3/2 configurations in $^{177}$Au$^{g}$, whilst $^{181}$Tl$^{g}$ remains a near-pure π3s1/2. This conclusion is inferred from the g factor of $^{177}$Au$^{g}$ which has an intermediate value between those of π3s1/2 and π2d3/2 states. A similar mixed configuration is proposed for the Iπ=1/2+ ground state of $^{179}$Au. This mixing may provide evidence for triaxial shapes in the ground states in these nuclei.

Hyperfine structure and isotope shifts have been measured for the ground and isomeric states in the neutron-deficient isotopes 179–184Tl using the 276.9-nm transition. The experiment has been performed at the CERN-Isotope Separator On-Line facility using the in-source resonance-ionization laser spectroscopy technique. Spins for the ground states in 179,181,183Tl have been determined as I=1/2. Magnetic moments and changes in the nuclear mean-square charge radii have been deduced. By applying the additivity relation for magnetic moments of the odd-odd Tl nuclei the leading configuration assignments were confirmed. A deviation of magnetic moments for isomeric states in 182,184Tl from the trend of the heavier Tl nuclei is observed. The charge radii of the ground states of the isotopes 179–184Tl follow the trend for isotonic (spherical) lead nuclei. The noticeable difference in charge radii for ground and isomeric states of 183,184Tl has been observed, suggesting a larger deformation for the intruder-based 9/2− and 10− states compared to the ground states. An unexpected growth of the isomer shift for 183Tl has been found. ispartof: Physical Review C vol:95 issue:1 pages:1-12 status: published

D. A. Fink et al.; 15 págs.; 17 figs.; 3 tabs.; Open Access funded by Creative Commons Atribution Licence 3.0, A Laser Ion Source and Trap (LIST) for a thick-target, isotope-separation on-line facility has been implemented at CERN ISOLDE for the production of pure, laser-ionized, radioactive ion beams. It offers two modes of operation, either as an ion guide, which performs similarly to the standard ISOLDE resonance ionization laser ion source (RILIS), or as a more selective ion source, where surface-ionized ions from the hot ion-source cavity are repelled by an electrode, while laser ionization is done within a radiofrequency quadrupole ion guide. The first physics application of the LIST enables the suppression of francium contamination in ion beams of neutron-rich polonium isotopes at ISOLDE by more than 1000 with a reduction in laser-ionization efficiency of only 20. Resonance ionization spectroscopy is performed directly inside the LIST device, allowing the study of the hyperfine structure and isotope shift of 217Po for the first time. Nuclear decay spectroscopy of 219Po is performed for the first time, revealing its half-life, α- to-β-decay branching ratio, and α-particle energy. This experiment demonstrates the applicability of the LIST at radioactive ion-beam facilities for the production and study of pure beams of exotic isotopes. Published by the American Physical Society, This work was supported by the Bundesministerium für Bildung und Forschung (BMBF, Germany) within the Wolfgang- Gentner programme as well as through the consecutive project fundings of 06Mz9181I, 06Mz7177D, and 05P12UMCIA, by FWO-Vlaanderen (Belgium), by GOA/2010/010 (BOF-KULeuven), by the IUAP-Belgian State Belgian Science Policy (BRIX network P7/12), by the U.K. Science and Technology Facilities Council (STFC), by the European Union within FP7 (ENSAR No. 262010), by the Slovak Research and Development Agency (Contract No. APVV-0105-10), by the Slovak grant agency VEGA, and the Reimei Foundation of JAEA (Contract No. 1/0576/13). T. E. C. was supported by STFC Ernest Rutherford Grant No. ST/J004189/1.

This work presents a method for the ab initio calculation of isotope shift in atoms and ions with one valence electron above closed shells. As a zero approximation, we use relativistic Hartree-Fock and then calculate correlation corrections. The main motivation for developing the method comes from the need to analyze whether different isotope abundances in early universe can contribute to the observed anomalies in quasar absorption spectra. The current best explanation for these anomalies is the assumption that the fine-structure constant a was smaller at early epoch. We test the isotope-shift method by comparing the calculated and experimental isotope shift for the alkali-metal and alkali-metal-like atoms Na, Mg II, K, Ca II and Ba II. The agreement is found to be good. We then calculate the isotope shift for some astronomically relevant transitions in Si II and Si IV, Mg II, Zn II, and Ge II. ispartof: Physical Review C, Nuclear Physics vol:68 issue:3 pages:1-6 status: published

Production of on-line mass separator neutron rich isotopes using fission induced by 1 GeV protons on high density uranium carbide has been investigate and results compared with the low density targets yields.

Decay spectroscopy of Tl 184 has been performed at the CERN Isotope Separator On-Line (ISOLDE) facility. An excitation energy of 506.1(1) keV and a half-life of 47.1(7) ms of the intruder based (10 − ) state have been extracted. The internal decay characteristics of this state are determined and discussed, extending the systematics of such states in the even-mass thallium nuclei below neutron midshell at N=104 . The retardation factors of the isomeric M2 and E3 transitions are deduced and compared with retardation factors in neighboring odd-mass and even-mass thallium isotopes. The new information is combined with a review of hindered and unhindered α -decay data of Bi 187–192 populating levels in daughter nuclei Tl 183–188 and supports the interpretation of the intruder character of the (10 − ) state in Tl 184 .

The ionization efficiency is one of the most important parameters of an on-line used target-ion source system exploited for production of exotic radioactive beams. The ionization efficiency value determination as a characteristic of a target-ion source unit in the stage of its normalizing before on-line use is a very important step in the course of the preparation for an on-line experiment. At the IRIS facility (Petersburg Nuclear Physics Institute, Gatchina) a reliable and rather precise method of the target-ion source unit ionization efficiency measurement by the method of stable beam implantation has been developed. The method worked out exploits an off-line mass-separator for the implantation of the ion beams of selected stable isotopes of different elements into a tantalum foil placed inside the Faraday cup in the focal plane of the mass-separator. The amount of implanted ions has been measured with a high accuracy by the current integrator connected to the Faraday cup. After the implantation of needed amount of the investigated specie, tantalum foil has been implemented into the volume of the target-ion source unit prepared for the on-line utilization at the IRIS on-line separator. For the foil implementation the unit is equipped by a window, which is being closed by a plug after the inserting the tantalum foil with the defined amount of atoms of the measured specimen into the target volume. The first tests with the method used have supplied the ionization efficiency values (9020) % for Rb and (8520) % for Cs in the empty combined target-ion source unit, which was used as a reference one. For the combined target-ion source unit with UC target material inside prepared for on-line experiment the measured value of the ionization efficiency was (52 20) %, that likely can be explained by the carbonization of the inner surface of the target container that brings to the decrease of its work function.