Brunet, M.*; Podolyk, Zs.*; Berry, T. A.*; Brown, B. A.*; Carroll, R. J.*; Lica, R.*; Sotty, Ch.*; Andreyev, A. N.; Borge, M. J. G.*; Cubiss, J. G.*; et al.
Physical Review C, 103(5), p.054327_1 - 054327_13, 2021/05
The structure of Po populated through the EC/ decay of At is investigated using -ray spectroscopy at the ISOLDE Decay Station. The presented level scheme contains 27 new excited states and 43 new transitions, as well as a further 50 previously observed rays which have been (re)assigned a position. Through the analysis using the shell model calculations approximately half of the -decay strength of At is found to proceed via allowed decay and half via first-forbidden decay. The first-forbidden transitions predominantly populate core excited states at high excitation energies, which is qualitatively understood using shell model considerations.
Ghys, L.*; Andreyev, A. N.; Huyse, M.*; Van Duppen, P.*; Antalic, S.*; Barzakh, A.*; Capponi, L.*; Cocolios, T. E.*; Cubiss, J.*; Derkx, X.*; et al.
Physical Review C, 100(5), p.054310_1 - 054310_13, 2019/11
The aim of this work was to investigate the -decay properties of Fr and daughter products. Neutron-deficient francium nuclei are produced at ISOLDE-CERN bombarding a UCx target with 1.4 GeV protons. Due to the very high statistics and the high beam purity, improved decay data for Fr and its daughters were obtained. The observation of crossover transitions positioned the isomeric high-spin level of At at an excitation energy of 265(3) keV. Half-life values of 4.47(5) s and 1.28(10) s were extracted for the ground state and isomeric state of At and 52(3) ms for the ground-state decay of Fr.
Wrzosek-Lipska, K.*; Rezynkina, K.*; Bree, N.*; Zieliska, M.*; Gaffney, L. P.*; Petts, A.*; Andreyev, A. N.; Bastin, B.*; Bender, M.*; Blazhev, A.*; et al.
European Physical Journal A, 55(8), p.130_1 - 130_23, 2019/08
The neutron-deficient mercury isotopes serve as a classical example of shape coexistence, whereby at low energy near-degenerate nuclear states characterized by different shapes appear. The electromagnetic structure of even-mass Hg isotopes was studied using safe-energy Coulomb excitation of neutron-deficient mercury beams delivered by the REX-ISOLDE facility at CERN. The population of 0, 2, and 4 states was observed in all nuclei under study. Reduced matrix elements coupling populated yrast and non-yrast states were extracted, including their relative signs. These are a sensitive probe of shape coexistence and may be used to validate nuclear models. The experimental results are discussed in terms of mixing of two different configurations and are compared with three different model calculations: the Beyond Mean Field model, the Interacting Boson Model with configuration mixing and the General Bohr Hamiltonian. Partial agreement with experiment was observed, hinting to missing ingredients in the theoretical descriptions.
Berry, T. A.*; Podolyk, Zs.*; Carroll, R. J.*; Lic, R.*; Grawe, H.*; Timofeyuk, N. K.*; Alexander, T.*; Andreyev, A. N.; Ansari, S.*; Borge, M. J. G.*; et al.
Physics Letters B, 793, p.271 - 275, 2019/06
Gamow-Teller decay is forbidden if the number of nodes in the radial wave functions of the initial and final states is different. This = 0 requirement plays a major role in the decay of heavy neutron-rich nuclei, affecting the nucleosynthesis through the increased half-lives of nuclei on the astrophysical -process pathway below both = 50 (for 82) and = 82 (for 126). The level of forbiddenness of the = 1 10 transition has been investigated from the decay of the ground state of Hg into the single-proton-hole nucleus Tl in an experiment at the ISOLDE Decay Station. From statistical observational limits on possible -ray transitions depopulating the 0 state in Tl, an upper limit of 3.910 % was obtained for the probability of this decay, corresponding to log 8.8 within a 95% confidence limit. This is the most stringent test of the = 0 selection rule to date.
Barzakh, A. E.*; Cubiss, J. G.*; Andreyev, A. N.; Seliverstov, M. D.*; Andel, B.*; Antalic, S.*; Ascher, P.*; Atanasov, D.*; Beck, D.*; Biero, J.*; et al.
Physical Review C, 99(5), p.054317_1 - 054317_9, 2019/05
Hyperfine-structure parameters and isotope shifts for the 795-nm atomic transitions in 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 At has been found to be larger than the average.
Lic, R.*; Rotaru, F.*; Borge, M. J. G.*; Grvy, S.*; Negoita, F.*; Poves, A.*; Sorlin, O.*; Andreyev, A.; Borcea, R.*; Costache, C.*; et al.
Physical Review C, 95(2), p.021301_1 - 021301_6, 2017/02
The decay of Mg was used to study the Al nucleus through spectroscopy at the Isotope Separator On-Line facility of CERN. Previous studies identified two -decaying states in Al having spin-parity assignments =4 dominated by the normal configuration (d5/2) (f7/2) and = 1 by the intruder configuration (d5/2) (d3/2)(f7/2). Their unknown ordering and relative energy have been the subject of debate for the placement of Al inside or outside the = 20 "island of inversion". We report here that the 1 intruder lies only 46.6 keV above the 4 ground state. In addition, a new half-life of =44.9(4)ms, that is twice as long as thepreviously measured 20(10) ms, has been determined for Mg. Large-scale shell-model calculations with the recently developed SDPF-U-MIX interaction are compared with the new data and used to interpret the mechanisms at play at the very border of the = 20 island of inversion.
Barzakh, A.*; Andreyev, A.; Cocolios, T. E.*; de Groote, R. P.*; Fedorov, D. V.*; Fedosseev, V. N.*; Ferrer, R.*; Fink, D. A.*; Ghys, L.*; Huyse, M.*; et al.
Physical Review C, 95(1), p.014324_1 - 014324_12, 2017/01
Hyperfine structure and isotope shifts have been measured for the ground and isomeric states in the neutron deficient isotopes Tl 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 Tl have been determined as = 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 Tl from the trend of the heavier Tl nuclei is observed. The charge radii of the ground states of the isotopes Tl follow the trend for isotonic (spherical) lead nuclei. The noticeable difference in charge radii for ground and isomeric states of Tl 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 Tl has been found.
Lund, M. V.*; Andreyev, A.; Borge, M. J. G.*; Cederkll, J.*; De Witte, H.*; Fraile, L. M.*; Fynbo, H. O. U.*; Greenlees, P. T.*; Harkness-Brennan, L. J.*; Howard, A. M.*; et al.
European Physical Journal A, 52(10), p.304_1 - 304_14, 2016/10
Beta-delayed proton emission from Mg has been measured at ISOLDE, CERN, with the ISOLDE Decay Station setup including both charged-particle and -ray detection capabilities. A total of 27 delayed proton branches were measured including seven so far unobserved. An updated decay scheme, including three new resonances above the proton separation energy in Na and more precise resonance energies, is presented. Beta-decay feeding to two resonances above the Isobaric Analogue State in Na is observed. This may allow studies of the 4032.9(2.4) keV resonance in Ne through the beta decay of Mg, which is important for the astrophysically relevant reaction O(,)Ne. Beta-delayed protons were used to obtain a more precise value for the half-life of Mg, 91.4(1.0) ms.
Truesdale, V. L.*; Andreyev, A.; Ghys, L.*; Huyse, M.*; Van Duppen, P.*; Sels, S.*; Andel, B.*; Antalic, S.*; Barzakh, A.*; Capponi, L.*; et al.
Physical Review C, 94(3), p.034308_1 - 034308_11, 2016/09
A nuclear-decay spectroscopy study of the neutron-deficient isotope At is reported where an isotopically pure beam was produced using the selective Resonance Ionization Laser Ion Source and On-Line Isotope Mass Separator (CERN). The fine-structure decay of At allowed the low-energy excited states in the daughter nucleus Bi to be investigated. A -delayed fission study of At was also performed. A mixture of symmetric and asymmetric fission-fragment mass distributions of the daughter isotope Po (populated by decay of At) was deduced based on the measured fission-fragment energies. A DF probability (At) = 9(1)10 was determined.
Lic, R.*; Mach, H.*; Fraile, L. M.*; Gargano, A.*; Borge, M. J. G.*; Mrginean, N.*; Sotty, C. O.*; Vedia, V.*; Andreyev, A.; Benzoni, G.*; et al.
Physical Review C, 93(4), p.044303_1 - 044303_7, 2016/04
The levels in Sn populated from the decay of In isomers were investigated at the ISOLDE facility of CERN using the newly commissioned ISOLDE Decay Station. The lowest 1/2 state and the 3/2 ground state in Sn are expected to have configurations dominated by the neutron (=0) and (=2) single-particle states, respectively. Consequently, these states should be connected by a somewhat slow -forbidden transition. Using fast-timing spectroscopy we have measured the half-life of the 1/2 315.3-keV state, = 19(10) ps, which corresponds to a moderately fast transition. Shell-model calculations using the CD-Bonn effective interaction, with standard effective charges and factors, predict a 4-ns half-life for this level. We can reconcile the shell-model calculations to the measured value by the renormalization of the effective operator for neutron holes.
Van Beveren, C.*; Andreyev, A.; Barzakh, A. E.*; Cocolios, T. E.*; de Groote, R. P.*; Fedorov, D.*; Fedosseev, V. N.*; Ferrer, R.*; Ghys, L.*; Huyse, M.*; et al.
Journal of Physics G; Nuclear and Particle Physics, 43(2), p.025102_1 - 025102_22, 2016/02
-decay spectroscopy of Tl has been performed at the CERN isotope separator on-line (ISOLDE) facility. New fine-structure decays have been observed for both isotopes. -decay branching ratios of 0.089(19), 0.047(6) and 1.22(30) have been deduced for the (10), (7) and (2) states respectively in Tl and a lower limit of 0.49 for the -decay branching ratio of Tl. A new half-life of 9.5(2) s for the (2) state in Tl and 1.9(1) s for the low-spin state in Tl has been deduced. Using - coincidence analysis, multiple rays were observed de-exciting levels in Au fed by Tl decays. The transitions connecting these low-lying states in Au are essential to sort the data and possibly identify bands from inbeam studies in these isotopes. Owing to the complex fine-structure decays and limited knowledge about the structure of the daughter nuclei, only partial level schemes could be constructed for both gold isotopes in the present work. Reduced -decay widths have been calculated and are compared with values obtained in neighboring odd-A and even-A thallium isotopes. Except for the allowed decay of the Tl (10) state, the other fine-structure decays observed in this study are hindered. This points to strong structural changes between parent thallium and daughter gold isotopes.
Bottoni, S.*; Leoni, S.*; Fornal, B.*; Raabe, R.*; Rusek, K.*; Benzoni, G.*; Bracco, A.*; Crespi, F. C. L.*; Morales, A. I.*; Bednarczyk, P.*; et al.
Physical Review C, 92(2), p.024322_1 - 024322_8, 2015/08
An exploratory experiment was performed at REX-ISOLDE CERN to test the potential of cluster-transfer reactions at the Coulomb barrier as a mechanism to explore the structure of exotic neutron-rich nuclei. The transfer of triton and alpha particles in a reaction of a beam of Rb onto a Li target were studied through particle- coincidence measurements. The results indicate that such cluster transfer reactions can be an efficient method to investigate the structure of neutron-rich nuclei at medium-high excitation energies and spins.
Van Beveren, C.*; Andreyev, A.; Barzakh, A.*; Cocolios, T. E.*; Fedorov, D.*; Fedosseev, V. N.*; Ferrer, R.*; Huyse, M.*; Kster, U.*; Lane, J. F. W.*; et al.
Physical Review C, 92(1), p.014325_1 - 014325_8, 2015/07
Decay spectroscopy of Tl 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 -decay data of Bi populating levels in daughter nuclei Tl and supports the interpretation of the intruder character of the (10) state in Tl.
Fink, D. A.*; Cocolios, T. E.*; Andreyev, A.; Antalic, S.*; Barzakh, A. E.*; Bastin, B.*; Fedorov, D. V.*; Fedosseev, V. N.*; Flanagan, K. T.*; Ghys, L.*; et al.
Physical Review X, 5(1), p.011018_1 - 011018_15, 2015/01
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. 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 Po for the first time. Nuclear decay spectroscopy of Po is performed for the first time, revealing its half-life, -to--decay branching ratio, and -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.
Orlandi, R.; Mcher, D.*; Raabe, R.*; Jungclaus, A.*; Pain, S. D.*; Bildstein, V.*; Chapman, R.*; De Angelis, G.*; Johansen, J. G.*; Van Duppen, P.*; et al.
Physics Letters B, 740, p.298 - 302, 2015/01
Single-neutron states in Zn have been populated using the reaction Zn(d,p) at REX-Isolde, CERN. The analysis reveals that the lowest excited states in Zn lie at approximately 1 MeV, and involve neutron orbits above the N=50 shell gap. A 5/2 configuration was assigned to the 983-keV state. Comparison with large-scale shell model calculations supports a robust neutron N=50 shell closure for Ni. These data constitute an important step towards the understanding the magicity of Ni and the structure of nuclei in the region.
Rothe, S.*; Andreyev, A. N.*; Antalic, S.*; Borschevsky, A.*; Capponi, L.*; Cocolios, T. E.*; De Witte, H.*; Eliav, E.*; Fedorov, D. V.*; Fedosseev, V. N.*; et al.
Nature Communications (Internet), 4, p.1835_1 - 1835_6, 2013/05
The radioactive element astatine exists only in trace amounts in nature. Its properties can therefore only be explored by study of smallest quantities of artificially produced isotopes or by performing theoretical calculations. One of the most important properties influencing the chemical behaviour is the energy required to remove one electron from the valence shell, referred to as the ionization potential (IP). Here we use laser spectroscopy to probe the optical spectrum of astatine near the ionization threshold. The observed series of Rydberg states allowed the deduction of the IP of the astatine atom for the first time. New ab initio calculations were performed to support the experimental result. The measured value of IP(At) serves as a benchmark for quantum chemistry calculations of the properties of astatine as well as for the theoretical prediction of the ionization potential of super-heavy element 117, the heaviest homologue of astatine.
Orlandi, R.; Mcher, D.*; Raabe, R.*; Jungclaus, A.*; Pain, S. D.*; Bildstein, V.*; Chapman, R.*; De Angelis, G.*; Johansen, J. G.*; Van Duppen, P.*; et al.
no journal, ,
Single-neutron states in the = 49 isotope Zn were populated in the Zn(d,p)Zn transfer reaction at REX-ISOLDE, CERN. The combined detection of protons ejected in the reaction and of rays emitted by Zn permitted the identification of the lowest-lying 5/2 and 1/2 excited states. The analysis of proton angular distributions links these states to a significant amount of single-particle strength around 1 MeV, and specifically to the d and s neutron orbits, which lie above the = 50 neutron shell gap. Comparison with large-scale-shell-model calculations supports a robust = 50 shell-closure for Ni. These data constitute a considerable step towards the understanding of the magicity of Ni and of the structure of isotopes in the region.