54 research outputs found
Fast-timing study of the l-forbidden 1/2+→3/2+ M1 transition in Sn129
R. Lică et al. ; 7 págs.; 5 figs.; 3 tabs. ; Open Access funded by Creative Commons Atribution Licence 3.0The levels in Sn129 populated from the β- decay of In129 isomers were investigated at the ISOLDE facility of CERN using the newly commissioned ISOLDE Decay Station (IDS). The lowest 12+ state and the 32+ ground state in Sn129 are expected to have configurations dominated by the neutron s12 (l=0) and d32 (l=2) single-particle states, respectively. Consequently, these states should be connected by a somewhat slow l-forbidden M1 transition. Using fast-timing spectroscopy we have measured the half-life of the 12+ 315.3-keV state, T12= 19(10) ps, which corresponds to a moderately fast M1 transition. Shell-model calculations using the CD-Bonn effective interaction, with standard effective charges and g factors, predict a 4-ns half-life for this level. We can reconcile the shell-model calculations to the measured T12 value by the renormalization of the M1 effective operator for neutron holes.This work was partially supported by the Spanish MINECO through Projects
No. FPA2012-32443, No. FPA2013-41267-P, and CPAN
Consolider (Project No. CSD-2007-00042), and by Romanian
IFA Grant CERN/ISOLDE. It was also partly funded by
the NuPNET network FATIMA (PRI-PIMNUP-2011-1338),
by FWO-Vlaanderen (Belgium), by GOA/2010/010 (BOF
KU Leuven), and by the Interuniversity Attraction Poles
Programme initiated by the Belgian Science PolicyOffice
(BriX network P7/12). Support from Grupo de Física Nuclear
(GFN-UCM), Programmi di Ricerca Scientifica di Rilevante
Interesse Nazionale (PRIN) Grant No. 2001024324 01302,
German BMBF under Contracts No. 05P12PKFNE and No.
05P15PKCIA, the U.K. Science and Technology Facilities
Council, and the European Union Seventh Framework through
ENSAR (Contract No. 262010) is also acknowledged. Fasttiming
electronics were provided by the Fast Timing Collaboration,
the ISOLDE Decay Station collaboration, and MASTICON.Peer Reviewe
Beta-delayed neutron spectroscopy of In
The decay properties of In were studied in detail at the ISOLDE Decay
Station (IDS). The implementation of the Resonance Ionization Laser Ion Source
(RILIS) allowed separate measurements of its ground state (In)
and isomer (In). With the use of -delayed neutron and
spectroscopy, the decay strengths above the neutron separation energy
were quantified in this neutron-rich nucleus for the first time. The allowed
Gamow-Teller transition was located at 5.92 MeV in the
In decay with a logft = 4.7(1). In addition, several neutron-unbound
states were populated at lower excitation energies by the First-Forbidden
decays of In. We assigned spins and parities to those
neutron-unbound states based on the -decay selection rules, the logft
values, and systematics
133In: A Rosetta Stone for decays of r-process nuclei
The decays from both the ground state and a long-lived isomer of
In were studied at the ISOLDE Decay Station (IDS). With a hybrid
detection system sensitive to , , and neutron spectroscopy, the
comparative partial half-lives (logft) have been measured for all their
dominant -decay channels for the first time, including a low-energy
Gamow-Teller transition and several First-Forbidden (FF) transitions. Uniquely
for such a heavy neutron-rich nucleus, their decays selectively
populate only a few isolated neutron unbound states in Sn. Precise
energy and branching-ratio measurements of those resonances allow us to
benchmark -decay theories at an unprecedented level in this region of
the nuclear chart. The results show good agreement with the newly developed
large-scale shell model (LSSM) calculations. The experimental findings
establish an archetype for the decay of neutron-rich nuclei southeast
of Sn and will serve as a guide for future theoretical development
aiming to describe accurately the key decays in the rapid-neutron
capture (r-) process
Competition between Allowed and First-Forbidden beta Decay : The Case of Hg-208 -> Tl-2(0)8
The beta decay of Hg-208 into the one-proton hole, one neutron-particle Tl-208(81)127 nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the N > 126, Z 0(-)beta decay where the daughter state is core excited is unique, and can provide information on mesonic corrections of effective operators.Peer reviewe
Normal and intruder configurations in Si- 34 populated in the beta(-) decay of Mg-34 and Al-34
The structure of Si-34 was studied through gamma spectroscopy separately in the beta(-) decays of Mg-34 and Al-34 at the ISOLDE facility of CERN. Different configurations in Si-34 were populated independently from the two recently identified beta-decaying states in Al-34 having spin-parity assignments J(pi) = 4(-) dominated by the normal configuration pi(d(5/2))(-1) circle times nu(f(7/2)) and J(pi) = 1(+) by the intruder configuration pi(d(5/2))(-1) circle times nu(d(3/2))(-1) (f(7/2))(2). The paper reports on spectroscopic properties of Si-34 such as an extended level scheme, spin and parity assignments based on log(ft) values and gamma-ray branching ratios, absolute beta feeding intensities, and neutron emission probabilities. A total of 11 newly identified levels and 26 transitions were added to the previously known level scheme of Si-34. Large scale shell-model calculations using the SDPF-U-MIX interaction, able to treat higher order intruder configurations, are compared with the new results and conclusions are drawn concerning the predictive power of SDPF-U-MIX, the N = 20 shell gap, the level of mixing between normal and intruder configurations for the 0(1)(+), 0(2)(+), and 2(1)(+) states, and the absence of triaxial deformation in Si-3(4).Peer reviewe
Competition between Allowed and First-Forbidden β Decay: The Case of Hg 208 → Tl 208
6 pags., 4 figs., 1 tab.The β decay of Hg208 into the one-proton hole, one neutron-particle Tl81208127 nucleus was investigated at CERN-ISOLDE. Shell-model calculations describe well the level scheme deduced, validating the proton-neutron interactions used, with implications for the whole of the N>126, Z<82 quadrant of neutron-rich nuclei. While both negative and positive parity states with spin 0 and 1 are expected within the Qβ window, only three negative parity states are populated directly in the β decay. The data provide a unique test of the competition between allowed Gamow-Teller and Fermi, and first-forbidden β decays, essential for the understanding of the nucleosynthesis of heavy nuclei in the rapid neutron capture process. Furthermore, the observation of the parity changing 0+→0-β decay where the daughter state is core excited is unique, and can provide information on mesonic corrections of effective operators.This work was supported by the European Union
under Contracts No. 262010 (ENSAR) and No. 654002
(ENSAR2), the Science and Technology Facilities
Council (UK), the German BMBF under Contract
No. 05P18PKCIA and “Verbundprojekt 05P2018,” the
MINECO Projects No. FPA2015-65035-P, No. RTI2018-
098868-B-I00, No. FPA2015-64969-P, and No. FPA2017-
87568-P (Spain), FWO-Vlaanderen (Belgium), GOA/
2015/010 (BOF KU Leuven), the Excellence of Science
programme (EOS-FWO), the Interuniversity Attraction
Poles Programme initiated by the Belgian Science Policy
Office (BriX network P7/12), the Romanian IFA project
CERN-RO/ISOLDE and the Polish National Science
Centre under Contracts No. UMO-2015/18/M/ST2/00523
and No. UMO-2019/33/N/ST2/03023. P. H. R. and
S. M. J. acknowledge support from the UK Department
for Business, Energy and Industrial Strategy via the
National Measurement Office. Zs. P. acknowledges support
from the ExtreMe Matter Institute EMMI at the GSI
Helmholtzzentrum fr Schwerionenforschung, Darmstadt,
Germa
Evolution of deformation in neutron-rich Ba isotopes up to A=150
The occurrence of octupolar shapes in the Ba isotopic chain was recently established experimentally up to N = 90. To further extend the systematics, the evolution of shapes in the most neutron-rich members of the Z = 56 isotopic chain accessible at present, Ba-148,Ba-150, has been studied via beta decay at the ISOLDE Decay Station. This paper reports on the first measurement of the positive-and negative-parity low-spin excited states of 150Ba and presents an extension of the beta-decay scheme of Cs-148. Employing the fast timing technique, half-lives for the 2(1)(+) level in both nuclei have been determined, resulting in T-1/2 = 1.51(1) ns for Ba-148 and T-1/2 = 3.4(2) ns for Ba-150. The systematics of low-spin states, together with the experimental determination of the B(E2 : 2(+) -> 0(+)) transition probabilities, indicate an increasing collectivity in Ba148-150, towards prolate deformed shapes. The experimental data are compared to symmetry conserving configuration mixing (SCCM) calculations, confirming an evolution of increasingly quadrupole deformed shapes with a definite octupolar character.Peer reviewe
First -decay spectroscopy of and new -decay branches of
19 pags., 14 figs., 3 tabs.The decay of the neutron-rich and was investigated experimentally in order to provide new insights into the nuclear structure of the tin isotopes with magic proton number above the shell. The -delayed -ray spectroscopy measurement was performed at the ISOLDE facility at CERN, where indium isotopes were selectively laser-ionized and on-line mass separated. Three -decay branches of were established, two of which were observed for the first time. Population of neutron-unbound states decaying via rays was identified in the two daughter nuclei of and , at excitation energies exceeding the neutron separation energy by 1 MeV. The -delayed one- and two-neutron emission branching ratios of were determined and compared with theoretical calculations. The -delayed one-neutron decay was observed to be dominant -decay branch of even though the Gamow-Teller resonance is located substantially above the two-neutron separation energy of . Transitions following the decay of are reported for the first time, including rays tentatively attributed to . In total, six new levels were identified in on the basis of the coincidences observed in the and decays. A transition that might be a candidate for deexciting the missing neutron single-particle state in was observed in both decays and its assignment is discussed. Experimental level schemes of and are compared with shell-model predictions. Using the fast timing technique, half-lives of the , and levels in were determined. From the lifetime of the state measured for the first time, an unexpectedly large transition strength was deduced, which is not reproduced by the shell-model calculations.M.P.-S. acknowledges the funding support from the Polish National Science Center under Grants No.
2019/33/N/ST2/03023 and No. 2020/36/T/ST2/00547 (Doctoral scholarship ETIUDA). J.B. acknowledges
support from the Universidad Complutense de Madrid under the Predoctoral Grant No. CT27/16-
CT28/16. This work was partially funded by the Polish National Science Center under Grants No.
2020/39/B/ST2/02346, No. 2015/18/E/ST2/00217, and No. 2015/18/M/ST2/00523, by the Spanish
government via Projects No. FPA2017-87568-P, No. RTI2018-098868-B-I00, No. PID2019-104390GB-I00,
and No. PID2019-104714GB-C21, by the U.K. Science and Technology Facilities Council (STFC), the German BMBF
under Contract No. 05P18PKCIA, by the Portuguese FCT under the Projects No. CERN/FIS-PAR/0005/2017, and
No. CERN/FIS-TEC/0003/2019, and by the Romanian IFA Grant CERN/ISOLDE. 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. M.Str. acknowledges the funding from the European Union’s Horizon 2020 research
and innovation program under Grant Agreement No. 771036 (ERC CoG MAIDEN). J.P. acknowledges support from the
Academy of Finland (Finland) with Grant No. 307685. Work at the University of York was supported under STFC Grants
No. ST/L005727/1 and No. ST/P003885/1
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