States In 40Ca Research Articles

Multiphonon structure of high-spin states in 40Ca, 90Zr and 208Pb

The method of description of the high-spin states, which was previously developed and applied for the states of this type in [Formula: see text]Pb, is generalized for the case of the states having more complex multiphonon structure. In this method, the harmonic approximation with the renormalized phonons is used in which the phonons themselves are determined within the nonlinear version of the model based on the random-phase approximation (RPA) and including both the RPA correlations and the beyond-RPA ones. The mean field and the residual interaction are derived within the framework of the self-consistent RPA from the energy-density functional of the Skyrme type. The method is applied for the analysis of the available experimental data in doubly magic [Formula: see text]Pb and [Formula: see text]Ca and in semi-magic [Formula: see text]Zr.

40Ca+ optical frequency standards with high accuracy

With the development of the technologies in the lasers and the manipulation of cold atoms, the high precision optical frequency standards have been extensively studied and built in recent years. These high precision frequency standards may play an important role in establishing the new time reference, promoting the researches in the fundamental fields, fulfilling the national strategic needs, etc. In this paper, the research progress of high accuracy 40Ca+ optical frequency standard in Wuhan Institute of Physics and Mathematics (WIPM) of Chinese Academy of Sciences is presented. A new ULE super cavity is adopted for stabilizing the frequency of 729 nm clock laser, and the stability of the laser is improved now to 2×10-15 in a duration of 1-100 s. By controlling the external fields and other environmental influences, especially suppressing the micromotion effects of the trapped ion, the uncertainty of the optical frequency standard based on a single 40Ca+ is reduced to 5.5×10-17. The stability of 5×10-17 in a duration of 20000 s is achieved via the comparison between two 40Ca+ optical frequency standards. Several precision measurement experiments are performed, based on the high precision 40Ca+ optical frequency standard. The absolute value of the clock transition frequency of the 40Ca+ optical frequency standard is measured second time, using an optical comb referenced to a hydrogen maser which is calibrated via GPS referenced to UTC (NIM)) using the precise point positioning data-processing technique. The frequency offset of UTC (NIM) relative to the SI second can be evaluated through BIPM circular-T reports, and the newly measured value of m 4s 2S1/2-3m d 2D5/2 transition is adopted by CCTF-20, thus updating the recommended value of 40Ca+ optical clock transition. Besides the absolute frequency measurement, the magic wavelengths of 40Ca+ optical clock transition are measured precisely, and this work is a milestone for establishing all-optical trapped-ion clocks. The lifetime of the m 3 d 2D3/2 and m 3 d 2D5/2 state in 40Ca+ are precisely measured, too. The work mentioned above contributes to the researches of the precision measurements based on cold atomic systems.

Examining the role of transfer coupling in sub-barrier fusion ofTi46,50+Sn124

In this study, the presence of neutron transfer channels with positive Q values can enhance sub-barrier fusion cross sections. Recent measurements of the fusion excitation functions for 58Ni+132,124Sn found that the fusion enhancement due to the influence of neutron transfer is smaller than that in 40Ca +132,124Sn although the Q values for multineutron transfer are comparable. The purpose of this study is to investigate the differences observed between the fusion of Sn + Ni and Sn + Ca. Methods: Fusion excitation functions for 46,50Ti +124Sn have been measured at energies near the Coulomb barrier. As a result, a comparison of the barrier distributions for 46Ti+124Sn and 40Ca+124Sn shows that the 40Ca+124Sn system has a barrier strength resulting from the coupling to the very collective octupole state in 40Ca at an energy significantly lower than the uncoupled barrier. In conclusion, the large sub-barrier fusion enhancement in 40Ca induced reactions is attributed to both couplings to neutron transfer and inelastic excitation, with the octupole vibration of 40Ca playing a major role.

Precision Measurement Method for Branching Fractions of ExcitedP1/2States Applied toCa+40

We present a method for measuring branching fractions for the decay of J=1/2 atomic energy levels to lower-lying states based on time-resolved recording of the atom's fluorescence during a series of population transfers. We apply this method to measure the branching fractions for the decay of the 4²P(1/2) state of 40Ca+ to the 4²S(1/2) and 3²D(3/2) states to be 0.935 65(7) and 0.064 35(7), respectively. The measurement scheme requires that at least one of the lower-lying states be long lived. The method is insensitive to fluctuations in laser light intensity and magnetic field and is readily applicable to various atomic species due to its simplicity. Our result distinguishes well among existing state-of-the-art theoretical models of Ca+.

2+ level densities in 40Ca extracted from high energy-resolution (p,p′) experiments

Level densities of 2+ states in 40Ca have been extracted from the high energy-resolution (p,p′) experimental data by means of a fluctuation analysis. Two different methods of background determination have been considered, namely, Quasi-free calculations and Discrete Wavelet Transform (DWT) technique. The results are then compared to theoretical models based on phenomenological and microscopic approaches.

Computational Aspects of Nuclear Coupled-Cluster Theory

We discuss computational aspects of the spherical coupled-cluster method specific to the nuclear many-body problem. Using chiral nucleon-nucleon interaction at next-to-next-to-next-to leading order (N3LO) with cutoff Lambda = 500MeV, we present coupled-cluster results for the ground state of 40Ca. Scaling and performance studies are presented together with challenges we meet with when extending the coupled-cluster effort to nuclei mass hundred and beyond.

Realization of Fast Rabi Oscillations in Radio Frequency Magnetic Resonance of Ground Zeeman States of40Ca+

Realization of Fast Rabi Oscillations in Radio Frequency Magnetic Resonance of Ground Zeeman States of⁴⁰Ca⁺

Measurement of the coherence time of the ground-state Zeeman states in 40Ca+

The transition between the two Zeeman sublevels of 2S1/2 in a single trapped 40Ca+ ion is directly excited by a radio-frequency magnetic field. A coherence time of 29.4±2.5 ms is measured by Ramsey interferometry. The ratio of the maximum Rabi frequency of the Zeeman transition (∼250 kHz) to the inverse of the coherence time is 7.3×103, which is considered to be a figure of merit for Zeeman states when they are used as a quantum bit. Several applications of the Zeeman qubit to quantum information processing are also discussed.

Nuclear energy functional with a surface-peaked effective mass: global properties

A correction to the nuclear functional is proposed in order to improve the density of states around the Fermi surface. The induced effect of this correction is to produce a surface-peaked effective mass, whose mean value can be tuned to get closer to 1 for the states close to the Fermi energy. In this work we study the effect of the correction term on the global properties of nuclei such as the density of states in 40Ca and 208Pb, pairing and specific heat at low temperature in 120Sn. In the latter application, an explicit temperature-dependent form of the correction term is employed and it is shown that the critical temperature is reduced by 40–60 keV.

Phase-locked light sources with low-phase noise for manipulating terahertz-separated metastable states in 40Ca+

We report the development of phase-locked light sources for manipulating terahertz-separated metastable states in 40Ca+. Two Ti:sapphire lasers with frequencies separated by 1.82 THz are phase-locked using an optical comb generator. The obtained phase noise is 49.8 mrad when the phase-locked loop is closed. Using the developed light sources, we excite Rabi oscillations between the terahertz-separated 32D3/2 and 32D5/2 states in 40Ca+. We discuss the phase noises of the light sources and their effect on excitation of Rabi oscillations.

Rotational Frequency Dependence of Octupole Vibrations on Superdeformed States in 40Ca

By means of the random phase approximation (RPA) calculation based on cranked deformed Woods-Saxon potential, we investigate how rotational motion affects the properties of octupole vibrations built on superdeformed states in 40 Ca. A major structure change of the superdeformed yrast states toward a reflection-asymmetric shape is suggested to take place in the region of angular momentum a little higher than the observed maximum value 16~, owing to a cooperative effect of octupole vibrational correlation and the rotation-aligned particle-hole excitations from the f7/2 to the g9/2 shell. Subject Index: 213

Precision spectroscopy with two correlated atoms

We discuss techniques that allow for long coherence times in laser spectroscopy experiments with two trapped ions. We show that for this purpose not only entangled ions prepared in decoherence-free subspaces can be used but also a pair of ions that are not entangled but subject to the same kind of phase noise. We apply this technique to a measurement of the electric quadrupole moment of the 3d D5/2 state of 40Ca+ and to a measurement of the linewidth of an ultrastable laser exciting a pair of 40Ca+ ions.

Decay of 1, 2 and 3-phonon states in 40Ca

Inelastic scattering of 40 Ca on 40 Ca at 50 A.MeV has been measured in coincidence with protons at the GANIL facility using a very performant set-up. The SPEG spectrometer was associated with 240 CsI(Tl) scintillators of the INDRA 4 π array, allowing for the measurement of complete decay events. The missing energy method was applied to these events to study the particle decay of collective states. For events with excitation energy between 42 and 55 MeV, a direct decay branch by three protons towards the low energy states of 37 Cl gives the first evidence for a 3-phonon giant resonance state. A significant direct decay branch by alpha-particles of the GQR is also measured for the first time.

Mixed representation RPA calculation for octupole excitations on superdeformed states in the 40Ca and neutron-rich sulfur regions

By means of the mixed representation RPA based on the Skyrme–Hartree–Fock mean field, we investigate low-frequency octupole excitations built on the superdeformed (SD) states in the N = Z nuclei around 40Ca and the neutron-rich sulfur isotopes. The RPA calculation is carried out fully self-consistently on the three-dimensional Cartesian mesh in a box, and yields a number of low-frequency octupole vibrations built on the SD states in 32S, 36Ar, 40Ca and 44Ti. In particular, a strongly collective K π = 1 − octupole vibration is suggested to appear on top of the SD state in 40Ca. For 48,50S close to the neutron drip line, we find that the low-lying state created by the excitation of a single neutron from a loosely bound low Ω level to a high Ω resonance level acquires an extremely strong octupole transition strength due to the spatially very extended structure of the particle–hole wave functions.

Soft octupole vibrations on superdeformed states in nuclei around 40Ca suggested by Skyrme-HF and self-consistent RPA calculations

We present the results of fully self-consistent RPA calculation for low-frequency negative-parity modes built on superdeformed states in the 40Ca region. The RPA calculation was carried out using the mixed representation on the three-dimensional Cartesian mesh in a box. The SD shell structure provides a very favorable situation for octupole shape fluctuations, and we show that the coherent excitation of protons and neutrons play an important role in the emergence of strongly collective octupole vibrations buit on the SD states in the N = Z nuclei, 32S, 36Ar, 40Ca and 44Ti. In particular, the calculation suggests that a low-frequency, strongly collective K Δ = 1− octupole vibration appears on the SD state in 40Ca.

Comparative Study of Octupole Excitations on Superdeformed States in 32S, 36S, 40Ca and 50S

By means of an RPA calculation based on the deformed Woods-Saxon potential in the coordinate-mesh representation, we make a comparative study of octupole excitations built on superdeformed states in the 40 Ca region and those in 50 S. For the N = Z stable nuclei, 32 Sa nd 40 Ca, enhancement of octupole transition strengths results from the coherence of the proton and neutron excitations. Contrastingly, for 50 S close to the neutron drip line, we find that the low-lying state created by the excitation of a single neutron from a loosely bound low Ω state to ah ighΩ resonance state acquires an extremely large transition strength. A similar enhancement of the octupole strength is also found in oblately deformed 40 Mg close to the neutron drip line.

Parameters of the proton shell structure of the 40,42,44,46,48Ca nuclei and their analysis within the dispersive optical model

By matching data on proton-stripping and proton-pickup reactions occurring on the same nuclear species, new experimental results for single-particle energies, occupation numbers, and fragmentation widths of proton states in the vicinity of the Fermi energy are obtained for the even-even isotopes 40,42,44,46,48Ca These results, along with the experimental values determined in the relevant (p, 2p) reaction for the single-particle energies of deep hole states in 40Ca, are analyzed on the basis of the dispersive-optical-model version proposed in the present study. The results of this analysis are compared with the predictions of various nuclear models, including the relativistic mean-field model.

Strong enhancement of two-proton transfer in the 40Ca(37Cl,39K)38Ar - reaction

Measurements of one- and two-proton transfer in the system 37Cl + 40Ca at energies close to the Coulomb barrier have been performed. The two-proton transfer to ground states attains cross sections which are comparable to the one-proton transfer. The strong enhancement of the proton-pair transfer is interpretedinterms of a combined actionofstatic and dynamic proton-proton correlations, for example in the 2+ state of 38Ar andin the 0+ ground state of40Ca which are introducedbymixing of shell model configurations across two major shells with hω = 2 and 3 of different parities (s1/2, d3/2 and f7/2, p3/2). This effect, which is called hybridization, induces a strong spatial polarization of the nucleons in the two-proton wave-function and enhances the two-proton transfer cross section. Coupled reaction channel calculations reproduce consistently the one and two proton transfer using spectroscopic information from light ion reactions.

Decay of the giant quadrupole resonance and higher excitation states in 40CA 1

Light charged particles have been measured in coincidence with inelastically scattered fragments from the 40Ca + 40Ca reaction at 50 MeV/N. Such a measurement allows to unravel the different reaction mechanisms contributing to the inelastic spectrum: pick-up break-up reactions, knock out and inelastic excitations. The giant quadrupole resonance in 40 Ca is shown to present a 30% non statistical decay branch. A prominent structure at 34 MeV is attributed to target excitation, the decay of this structure is studied.

Comparison of the Nilsson and Skyrme Hartree-Fock results for the properties of highly deformed states in nuclei

A Comparison of the Nilsson model and the Skyrme Hartree-Fock model for studying highly deformed states in nuclei is made. The states constructed are the 4-particle, 4-hole and 8-particle, 8-hole states in 40Ca and the linear alpha chain states in 12C and 16O. The deformations obtained in the two approaches are remarkably similar. The change in the radius of the np-nh state in 40Ca relative to the ground state is smaller in the Skyrme Hartree-Fock model than in the Nilsson model, indicating monopole shrinkage in the former approach, hence volume non-conservation. Whereas the energies of the 4 p−4 h states are nearly the same in the two approaches, the 8 p−8 h is at too high an energy in the Nilsson model. For the linear chain states in 12C and 16O, the Skyrme 3 Hartree-Fock approach gets the energies of the projected J π = 0 + states a factor of two too high while the results of the Nilsson model are in surprisingly good agreement with experiments. The quadrupole moment in momentum space ( Q p ) for the ground state and the metastable highly deformed states is discussed.