Engineering Papers⌕ Search

SEARCH · Engineering Papers

Results for “COULOMB EXCITATION”

Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2021

Exploring the role of high- j configurations in collective observables through the Coulomb excitation of 106 Cd

In this work, the shape and collectivity of 106 Cd was investigated via a sub-barrier-energy Coulomb excitation experiment performed at the NSCL ReA3 facility using the JANUS setup. Transition matrix elements between low-lying states were found to agree with adopted values, and information on the shape and collectivity of higher-lying states was extracted for the first time. Locally-optimized large-scale shell-model calculations were found to describe well the B(E2) transition strengths but failed to reproduce the spectroscopic quadrupole moments Q s . An analysis of the E2 rotational invariants and the normalized quadrupole moment q s indicates that this may be due to a significant degree of triaxiality in 106 Cd which is not captured by the present shell-model calculations. Analogous calculations for the Fe isotopes (two protons below the Z = 28 magic number) reveal the critical role of high-j neutron configurations for the description of quadrupole moments in the heavy Fe and Cd isotopes (two protons below magic Z = 50), but this effect is insufficient to explain the shape of 106 Cd, posing a puzzle for the understanding of nuclear structure towards N = 50.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Magnetic moment and lifetime measurements of Coulomb-excited states in Cd 106

The Cd isotopes are well studied, but experimental data for the rare isotopes are sparse. At energies above the Coulomb barrier, higher states become accessible. Remeasure and supplement existing lifetimes and magnetic moments of low-lying states in 106 Cd. Methods: In an inverse kinematics reaction, a 106 Cd beam impinging on a 12 C target was used to Coulomb excite the projectiles. The high recoil velocities provide a unique opportunity to measure g factors with the transient-field technique and to determine lifetimes from lineshapes by using the Doppler-shift-attenuation method. Large-scale shell-model calculations were carried out for 106 Cd. As a result, the g factors of the 2 + 1 and 4 + 1 states in 106 Cd were measured to be g(2 + 1 ) = +0.398(22) and g(4 + 1 ) = +0.23(5). A lineshape analysis yielded lifetimes in disagreement with published values. The new results are τ( 106 Cd; 2 + 1 ) = 7.0(3) ps and τ( 106 Cd; 4 + 1 ) = 2.5(2) ps. The mean life τ( 106 Cd; 2 + 2 ) = 0.28(2) ps was determined from the fully-Doppler-shifted γ line. Mean lives of τ( 106 Cd; 4 + 3 ) = 1.1(1) ps and τ( 106 Cd; 3 – 1 ) = 0.16(1) ps were determined for the first time. In conclusion, the newly measured g(4 + 1 ) of 106 Cd is found to be only 59% of the g(2 + 1 ). This difference cannot be explained by either shell-model or collective-model calculations.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Relativistic Coulomb excitation within the time dependent superfluid local density approximation

Within the framework of the unrestricted time-dependent density functional theory, we present for the first time an analysis of the relativistic Coulomb excitation of the heavy deformed open shell nucleus 238 U. The approach is based on the superfluid local density approximation formulated on a spatial lattice that can take into account coupling to the continuum, enabling self-consistent studies of superfluid dynamics of any nuclear shape. We compute the energy deposited in the target nucleus as a function of the impact parameter, finding it to be significantly larger than the estimate using the Goldhaber-Teller model. The isovector giant dipole resonance, the dipole pygmy resonance, and giant quadrupole modes are excited during the process. As a result, the one-body dissipation of collective dipole modes is shown to lead a damping width Γ↓≈0.4 MeV and the number of preequilibrium neutrons emitted has been quantified.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2019

Electromagnetic properties of low-lying states in neutron-deficient Hg isotopes: Coulomb excitation of 182 Hg, 184 Hg, 186 Hg and 188 Hg

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 182-188 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 + 1,2 , 2 + 1,2 and 4 + 1 states was observed in all nuclei under study. Reduced E2 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.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2022

Coulomb excitation of the | T z | = 1 2 , A = 23 mirror pair

Background: Electric-quadrupole ( E 2 ) strengths relate to the underlying quadrupole deformation of a nucleus and present a challenge for many nuclear theories. Additionally, mirror nuclei in the vicinity of the line of N = Z represent a convenient laboratory for testing deficiencies in such models, making use of the isospin symmetry of the systems. Purpose: Uncertainties associated with literature E 2 strengths in Mg 23 are some of the largest in T z = | 1 2 | nuclei in the s d shell. The purpose of the present paper is to improve the precision with which these values are known, to enable better comparison with theoretical models. Methods: Coulomb-excitation measurements of Mg 23 and Na 23 were performed at the TRIUMF-ISAC facility using the TIGRESS spectrometer. They were used to determine the E 2 matrix elements of mixed E 2 / M 1 transitions. Results: Reduced E 2 transition strengths, B ( E 2 ) , were extracted for Mg 23 and Na 23 . Their precision was improved by factors of approximately 6 for both isotopes, while agreeing within uncertainties with previous measurements. Conclusions: A comparison was made with both shell-model and ab initio valence-space in-medium similarity renormalization group calculations. Valence-space in-medium similarity renormalization group calculations were found to underpredict the absolute E 2 strength, in agreement with previous studies.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2016

Nuclear Data Sheets for A = 70

Spectroscopic data for all nuclei with mass number A = 70 have been evaluated, and the corresponding level schemes from radioactive decay and reaction studies are presented. Since the previous evaluation, the half-life of {sup 70}Mn has been measured and excited states in {sup 70}Fe observed for the first time. Excited states in {sup 70}Ni have been more extensively studied while Coulomb excitation and collinear laser spectroscopy measurements in {sup 70}Cu have allowed for firm Jπ assignments. Despite new measurements, there remain some discrepancies in half-lives of low lying states in {sup 70}Zn. New measurements have extended the knowledge of high-spin band structures in {sup 70}Ge and {sup 70}As. This evaluation supersedes the prior A = 70 evaluation of 2004Tu09.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2015

Nuclear Structure Studies in the 132 Sn Region: Safe Coulex with Carbon Targets

The collective and single-particle structure of nuclei in the 132 Sn region was recently studied by Coulomb excitation and heavy-ion induced transfer reactions using carbon, beryllium, and titanium targets. In particular, Coulomb excitation was used determine a complete set of electromagnetic moments for the first 2 + states and one-neutron transfer was used to probe the purity and evolution of single-neutron states. These recent experiments were conducted at the Holifield Radioactive Ion Beam Facility at ORNL using a CsI-HPGe detector array (BareBall- CLARION) to detect scattered particles and emitted gamma rays from the in-beam reactions. A Bragg-curve detector was used to measure the energy loss of the various beams through the targets and to measure the radioactive beam compositions. A sample of the Coulomb excitation results is presented here with an emphasis placed on 116 Sn. In particular, the safe Coulex criterion for carbon targets will be analyzed and discussed.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2017

Reorientation-effect measurement of the first 2 + state in 12 C: Confirmation of oblate deformation

A Coulomb-excitation reorientation-effect measurement using the TIGRESS γ-ray spectrometer at the TRIUMF/ISAC II facility has permitted the determination of the $\langle$2$^+_1$ || $\hat{E2}$ || $2^+_1$$\rangle$ diagonal matrix element in 12 C from particle-γ coincidence data and state-of-the-art no-core shell model calculations of the nuclear polarizability. The nuclear polarizability for the ground and first-excited (2$^+_1$) states in 12 C have been calculated using chiral NN N 4 LO500 and NN+3NF350 interactions, which show convergence and agreement with photo-absorption cross-section data. Predictions show a change in the nuclear polarizability with a substantial increase between the ground state and first excited 2$^+_1$ state at 4.439 MeV. The polarizability of the 2$^+_1$ state is introduced into the current and previous Coulomb-excitation reorientation-effect analyses of 12 C. Spectroscopic quadrupole moments of $Q_S$(2$^+_1$) =+0.053(44) eb and $Q_S$(2$^+_1$) =+0.08(3) are determined, respectively, yielding a weighted average of $Q_S$(2$^+_1$)=+0.071(25) eb, in agreement with recent ab initio calculations. The present measurement confirms that the 2$^+_1$ state of 12 C is oblate and emphasizes the important role played by the nuclear polarizability in Coulomb-excitation studies of light nuclei.

73 NUCLEAR PHYSICS AND RADIATION PHYSICS↗
DOE OSTI2021

Twisted bilayer graphene. V. Exact analytic many-body excitations in Coulomb Hamiltonians: Charge gap, Goldstone modes, and absence of Cooper pairing

We find exact analytic expressions for the energies and wave functions of the charged and neutral excitations above the exact ground states (at rational filling per unit cell) of projected Coulomb Hamiltonians in twisted bilayer graphene. Our exact expressions are valid for any form of the Coulomb interaction and any form of A A and A B / B A tunneling. The single charge excitation energy is a convolution of the Coulomb potential with a quantum geometric tensor of the TBG bands. The neutral excitations are (high-symmetry group) magnons, and their dispersion is analytically calculated in terms of the form factors of the active bands in TBG. The two-charge excitation energy and wave functions are also obtained, and a sufficient condition on the graphene eigenstates for obtaining a Cooper pair from Coulomb interactions is obtained. For the actual TBG bands at the first magic angle, we can analytically show that the Cooper pair binding energy is zero in all such projected Coulomb models, implying that either phonons and/or nonzero kinetic energy are needed for superconductivity. Since Vafek and Kang [Phys. Rev. Lett. 125, 257602 (2020)] showed that the kinetic energy bounds on the superexchange energy are less 10 -3 in Coulomb units, the phonon mechanism becomes then very likely. If nonetheless the superconductivity is due to kinetic terms which render the bands nonflat, one prediction of our theory is that the highest T c would not occur at the highest DOS.

75 CONDENSED MATTER PHYSICS, SUPERCONDUCTIVITY AND↗