Lifetime measurements of first excited states in ^{16,18}C (original) (raw)
Related papers
Decay of quadrupole-octupole1−states inCa40andCe140
Physical Review C
Background: Two-phonon excitations originating from the coupling of two collective one-phonon states are of great interest in nuclear structure physics. One possibility to generate low-lying E1 excitations is the coupling of quadrupole and octupole phonons. Purpose: In this work, the γ-decay behavior of candidates for the (2 + 1 ⊗ 3 − 1) 1 − state in the doublymagic nucleus 40 Ca and in the heavier and semi-magic nucleus 140 Ce is investigated. Methods: (γ, γ) experiments have been carried out at the High Intensity γ-ray Source (HIγS) facility in combination with the high-efficiency γ-ray spectroscopy setup γ 3 consisting of HPGe and LaBr3 detectors. The setup enables the acquisition of γ-γ coincidence data and, hence, the detection of direct decay paths. Results: In addition to the known ground-state decays, for 40 Ca the decay into the 3 − 1 state was observed, while for 140 Ce the direct decays into the 2 + 1 and the 0 + 2 state were detected. The experimentally deduced transition strengths and excitation energies are compared to theoretical calculations in the framework of EDF theory plus QPM approach and systematically analyzed for N = 82 isotones. In addition, negative parities for two J = 1 states in 44 Ca were deduced simultaneously. Conclusions: The experimental findings together with the theoretical calculations support the two-phonon character of the 1 − 1 excitation in the light-to-medium-mass nucleus 40 Ca as well as in the stable even-even N = 82 nuclei.
Anomalously Hindered E2 Strength B(E2;21+→0+) in C16
Physical Review Letters, 2004
The electric quadrupole transition from the first 2 + state to the ground 0 + state in 16 C is studied through measurement of the lifetime by a recoil shadow method applied to inelastically scattered radioactive 16 C nuclei. The measured lifetime is 75 ± 23 ps, corresponding to a B(E2; 2 + 1 → 0 + ) value of 0.63 ± 0.19 e 2 fm 4 , or 0.26 ± 0.08 Weisskopf units. The transition strength is found to be anomalously small compared to the empirically predicted value. PACS numbers: 23.20.Js, 21.10.Tg, 29.30.Kv Quadrupole strengths are fundamental quantities in probing the collective character of nuclei. The enhancement of the electric quadrupole (E2) transition strength with respect to that of single proton excitation may reflect large fluctuation or deformation of nuclear charge [1]. One of the important E2 transitions in an even-even nucleus is that from the first 2 + (2 + 1 ) state to the ground state (0 + g.s. ), the reduced transition probability B(E2) of which has long been a basic observable in the extraction of the magnitude of nuclear deformation or in probing anomalies in the nuclear structure. With recent advances in techniques for supplying intense beams of unstable nuclei, several exotic properties such as magicity loss have been discovered in neutron-rich nuclei through measurements of E2 strengths.
Physics Letters B, 2008
Lifetime measurements were performed on low-lying excited states of the neutron-rich isotope 17 C using the recoil shadow method. The γ-decay mean lifetimes were determined to be 583 ± 21(stat)±35(syst) ps for the first excited state at 212 keV and 18.9 ± 0.6(stat)±4.7(syst) ps for the second excited state at 333 keV. Based on a comparison with the empirical upper limits for the electromagnetic transition strengths, these decays are concluded to be predominantly M1 transitions. The reduced M1 transition probabilities to the ground state were deduced to be (1.0 ± 0.1) × 10 −2 µ 2 N and (8.2 +3.2 −1.8 ) × 10 −2 µ 2 N , respectively, for the first and second excited states. The strongly hindered M1 strength as well as the lowered excitation energy represents unique nature of the 212-keV state.
Scientific Reports
In this paper, we tried to get a new signature of regular nuclei based on their quadrupole transition rates. We have analyzed the experimental electric quadrupole transition probabilities of well-known "regular nuclei". The results indicate finding specific repetition patterns for E2 transition rates, similar to what has been reported for the energy levels of these nuclei. We also tested the existence of this observed repetition scheme for all known isotopes whose experimental transition rates are available and introduced several new candidates as regular nuclei. Then, the energy spectra (Experimental) of these new suggested "regular nuclei" are investigated in the framework of the Interacting Boson Model, in which the parameters of Hamiltonian confirm the placement of these nuclei in the "Alhassid-Whelan arc of regularity" region. In order to further study the statistical distribution of experimental energy levels related to the electromagnetic transit...
Excited-state transition-rate measurements in^{18} C
2012
Radioactive nuclides far from the valley of beta stability exhibit a variety of unique properties. For nuclei with large neutron-proton asymmetries, an extended and decoupled distribution of valence neutrons may occur [1, 2]. The emergence of neutron halo nuclei, with one or more weakly bound neutrons spatially detached from the nuclear core, lies at the extreme isospin limit of such decoupling [3]. Quantifying the changes in nuclear structure toward such exotic behavior at the drip line has been a major focus of nuclear physics in recent years.
Observation/confirmation of hindered E2 strength in 18C/16C
The European Physical Journal A, 2009
We have measured the lifetime of the first excited 2 + state in 18 C using an upgraded recoil shadow method to determine the electric quadrupole transition. The measured mean lifetime is 18.9 ± 0.9 (stat) ± 4.4 (syst) ps, corresponding to B(E2; 2 + 1 → 0 + gs ) = 4.3 ± 0.2 ± 1.0 e 2 fm 4 , or about 1.5 Weisskopf units. The mean lifetime of the first 2 + state in 16 C was remeasured to be 18.3 ± 1.4 ± 4.8 ps, about four times shorter than the value reported previously. The discrepancy is explained by incorporating the γ-ray angular distribution obtained in this work into the previous measurement. The observed transition strengths in 16,18 C are hindered compared to the empirical values, indicating that the anomalous E2 strength observed in 16 C persists in 18 C.
Decay of quadrupole-octupole 1 − states in 40 Ca and 140
2016
V. Derya,1,* N. Tsoneva,2,3,4 T. Aumann,5 M. Bhike,6 J. Endres,1 M. Gooden,6 A. Hennig,1 J. Isaak,2,7 H. Lenske,3 B. Löher,7 N. Pietralla,5 D. Savran,7 W. Tornow,6,8 V. Werner,5 and A. Zilges1 1Institut für Kernphysik, Universität zu Köln, 50937 Köln, Germany 2Frankfurt Institute for Advanced Studies (FIAS), 60438 Frankfurt am Main, Germany 3Institut für Theoretische Physik, Universität Gießen, 35392 Gießen, Germany 4Institute for Nuclear Research and Nuclear Energy, 1784 Sofia, Bulgaria 5Institut für Kernphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany 6Department of Physics, Duke University, Durham, North Carolina 27708, USA 7GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany 8Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA (Received 27 January 2016; published 10 March 2016)
Transition quadrupole moments of high-spin states in 170W
Nuclear Physics A, 1994
Lifetimes of states in 1720S have been measured by the Doppler-shift recoil-distance method. These states were populated by the reaction 144Nd(32S, 4n) 172Os at a bombarding energy of 162 MeV from the HHIRF tandem accelerator at ORNL. The data were collected in the 7y-coincidence mode in order to reduce the complexities of the y-ray spectra and to avoid some of the problems associated with side feeding to excited states. The experimental transition quadrupole moments, Qt, do not cluster about a constant value as a function of rotational frequency up through fi to = 0.27 MeV as predicted by cranked Hartree-Fock-Bogoliubov (I-IFB) calculations around N-96 for the yrast band. A striking feature in the experimental data for the yrast band is an abrupt increase of the Qt ValUeS for the 6 + and 8 + states where the first anomaly in the behavior of the moment of inertia occurs. A recent proposal of band-mixing between the yrast band and a quasi-is band to account for this anomaly in the moment of inertia also seems to provide a logical interpretation of the Qt values at low rotational frequencies. The large collectivity inferred for the quasi-fl band from our Qt ValUeS for the 6 + and 8 + states is an indirect, but plausible, argument that the quasi-IS band corresponds to the non-yrast band in the band-mixing model. The E1 transition probabilities for decay of states in the (it, a)-(-, 1) band to states in the ground-state band range between 1.4 × 10-5 to 3.1 × 10-4 W.u. The B(E1, I ~ I + 1) is an order of magnitude larger than the B(E1, I-, I-1). The origin of these effects can probably be understood in terms of a predominant admixture of the Coriofis-coupled octupole vibrational-state wave function in the (-, 1) band of 172Os at low spin.
Electric quadrupole moments of the21+states inCd100,102,104
Physical Review C, 2009
Using the REX-ISOLDE facility at CERN the Coulomb excitation cross sections for the 0 + gs → 2 + 1 transition in the β-unstable isotopes 100,102,104 Cd have been measured for the first time. Two different targets were used, which allows for the first extraction of the static electric quadrupole moments Q(2 + 1) in 102,104 Cd. In addition to the B(E2) values in 102,104 Cd, a first experimental limit for the B(E2) value in 100 Cd is presented. The data was analyzed using the maximum likelihood method. The provided probability distributions impose a test for theoretical predictions of the static and dynamic moments. The data are interpreted within the shell-model using realistic matrix elements obtained from a G-matrix renormalized CD-Bonn interaction. In view of recent results for the light Sn isotopes the data are discussed in the context of a renormalization of the neutron effective charge. This study is the first to use the reorientation effect for post-accelerated short-lived radioactive isotopes to simultaneously determine the B(E2) and the Q(2 + 1) values.