Two-hole Excitations Research Articles

Nuclear many-body effects on particle emission following muon capture on Si28 and Ca40

Background: Muon captures on nuclei have provided us with plenty of knowledge of nuclear properties. Recently, this reaction attracts attention in electronics, because charged particle emissions following muon capture on silicon become to trigger non-negligible soft errors in memory devices.Purpose: To date, there is no theoretical framework based on the nuclear structure that describes a muon capture reaction followed by particle emissions comprehensively. The purpose of this work is to develop a new method that considers the nuclear many-body correlation for the accurate understanding of the soft errors in memory devices.Method: We combined the second Tamm-Dancoff approximation that is used to estimate muon capture rates with the two-component exciton model, the model describing particle emission from the pre-equilibrium state. For particle evaporation from the compound state, the Hauser-Feshbach statistical models were applied. We chose $^{28}\mathrm{Si}$ and $^{40}\mathrm{Ca}$ to check the performance of the framework.Result: We paid attention to the muon capture rates, the particle emission spectra, and the multiplicities that have a close interrelation with each other. We found that the nuclear many-body correlations including two-particle two-hole excitations is a key to explaining them simultaneously.Conclusion: The present study showed that the combination of the microscopic approach of muon capture and the two-component exciton model of particle emission is an effective tool to describe particle emission following the muon captures, giving the nuclear structure information additionally. For a finer understanding of particle emission following muon capture and a validation of the present framework, further experimental studies on particle emission spectra are highly expected.

Finite particle number description of neutron matter using the unitary correlation operator and high-momentum pair methods * *Supported by the National Natural Science Foundation of China (11822503, 11575082, 11947220), by the Fundamental Research Funds for the Central Universities (Nanjing University), by JSPS KAKENHI (JP18K03660, JP16K05351), and by a Project funded by China Postdoctoral Science Foundation (2019M661785). The author N. W.

Using bare Argonne V4' (AV4'), V6' (AV6'), and V8' (AV8') nucleon–nucleon (NN) interactions, the nuclear equations of state (EOSs) for neutron matter are calculated with the unitary correlation operator and high-momentum pair methods. Neutron matter is described using a finite particle number approach with magic number under a periodic boundary condition. The central short-range correlation originating from the short-range repulsion in the interaction is treated by the unitary correlation operator method (UCOM), and the tensor correlation and spin-orbit effects are described by the two-particle two-hole (2p2h) excitations of nucleon pairs, where the two nucleons with a large relative momentum are regarded as a high-momentum (HM) pair. With increasing 2p2h configurations, the total energy per particle of the neutron matter is well-converged under this UCOM+HM framework. Comparing the results calculated with AV4', AV6', and AV8' interactions, we demonstrate the effects of the short-range correlation, tensor correlation, and spin-orbit coupling on the density dependence of the total energy per particle of neutron matter. Moreover, the contribution of each Hamiltonian component to the total energy per particle is discussed. The EOSs of neutron matter calculated within the present UCOM+HM framework agree with the calculations of six microscopic many-body theories, especially the auxiliary field-diffusion Monte Carlo calculations.

Variational calculation of nuclear matter in a finite particle number approach using the unitary correlation operator and high-momentum pair methods

We propose a new variational method for describing nuclear matter from nucleon-nucleon interaction. We use the unitary correlation operator method (UCOM) for central correlation to treat the short-range repulsion and further include the two-particle two-hole (2p2h) excitations of nucleon pair involving a large relative momentum, which is called 'high-momentum pair'(HM). We describe nuclear matter in finite size with finite particle number on periodic boundary condition and increase the 2p2h configurations until we get the convergence of the total energy per particle. We demonstrate the validity of this 'UCOM+HM' framework by applying it to the symmetric nuclear and neutron matters with the Argonne V4$^\prime$ potential having short-range repulsion. The nuclear equations of state obtained in UCOM+HM are fairly consistent to those of other calculations such as Brueckner-Hartree-Fock and auxiliary field diffusion Monte Carlo in the overall density region.

Determination of the neutrino mass in 163Ho

KATRIN plans to determine the electron anti-neutrino mass in the Tritium decay. Electron capture in 163Ho can measure the electron neutrino mass supported by the small decay energy The decay energy of 2.8 keV is used to emit a neutrino and to excite the Dy atom. The neutrino mass is then given by the difference between the Q value and the upper end of the Dy deexcitation spectrum. The Dirac-Hartree-Fock approach is used for the bound and the continuum states in Holmium and in Dysprosium. The present background must be reduced by at least two orders to extract the neutrino mass from the spectrum. The present work discuses the one- and the two-hole excitations in Dy. The two-hole states are excited by shake-up of an electron into a free bound state and the shake-off into the continuum. The shake-off contribution can practically be neglected. It seems not to influence the neutrino mass determination.

Electron scattering of 14N based on two-hole excitations

The nuclear structure of 14N is studied in the framework of the hole-hole Tamm-Dancoff Approximation (hhTDA) and hole-hole Random Phase Approximation (hh RPA). The Hamiltonian is diagonalized within a model space with particle orbits {1d5/2, 1d3/2, 2s1/2 and 1f7/2}and the hole orbits {1s1/2, 1p3/2 and 1p1/2} using Warburton and Brown interaction WBP. The TDA and RPA amplitudes are used to calculate the longitudinal and transverse electron scattering form factors. The results for JfπTfExMeV= 1+0(0.0), 0+1(2.313), 1+(3.945), 2−0(5.106) and 3−0(5.834) states are interpreted in terms of the harmonic-oscillator (HO) wave functions of size parameter b and compared with the available experimental data. Configurations outside the model space are included approximately, in terms of polarization effective charges and g-factors.

Improved description of one- and two-hole excitations after electron capture inHo163and the determination of the neutrino mass

The atomic pair 163 Holmium and 163 Dysprosium seems due to the small Q value of about 2.3 to 2.8 keV the best case to determine the neutrino mass by electron capture. The bolometer spectrum measures the full deexcitation energy of Dysprosium by X rays, by Auger electrons and by the recoil of Holmium. The spectrum has an upper energy limit given by the Q value minus the neutrino mass. Till now this spectrum has been calculated allowing in Dysprosium excitations with 3s1/2, 3p1/2, 4s1/2, 4p1/2, 5s1/2, 5p1/2 one-holes only. Robertson calculated recently also the spectrum with two electron hole excitations in Dy. He took the probability for the excitation for the second electron hole from work of Carlson and Nestor for Z=54 Xenon. He claims, that the bolometer spectrum with two holes is "not well enough understood to permit a sensitive determination of the neutrino mass in this way." The purpose of the present work is to determine the theoretical bolometer spectrum with two hole excitations more reliably directly in holmium and dysprosium. In addition it will be shown, that the two-hole excitations do not complicate more the determination of the neutrino mass compared to the situation with one-hole states only. At the Q value the highest one-hole resonance is dominant. Under the assumption of a Lorentzian line shape one has to fit after inclusion of the experimental spectral function of the detector four quantities to the data: (1) The neutrino mass, (2) the energy distance of the dominant resonance to the Q value, (3) the line witdth and (4) the strength of the resonance. Compared to Robertson this work includes major improvements and it shows, that a determination of the neutrino mass is difficult but not impossible.

Possible excited deformed rotational bands in82Ge

Excited states of neutron-rich nucleus ${}^{82}$Ge were studied from the spontaneous fission of ${}^{252}$Cf. Eleven new transitions and seven new levels in ${}^{82}$Ge were identified by using $X$(Dy)-$\ensuremath{\gamma}$-$\ensuremath{\gamma}$ and $\ensuremath{\gamma}$-$\ensuremath{\gamma}$-$\ensuremath{\gamma}$ triple coincidences. Possible excited deformed rotational bands are observed, for the first time, in this nuclear region. Coexistence of the spherical ground and deformed excited shapes is proposed in ${}^{82}$Ge. These deformed rotational bands can be formed by two-particle, two-hole excitations with the 0${}^{+}$ pairing energy states of the $\ensuremath{\nu}9/2{[404]}^{\ensuremath{-}2}\ensuremath{\bigotimes}1/2{[431]}^{2}$ configuration across the $N=50$ closed shell.

Exchange and polarization effect in high-order harmonic imaging of molecular structures

We analyze the importance of exchange, polarization, and electron-electron correlation in high-order harmonic generation in molecules interacting with intense laser fields. We find that electron exchange can become particularly important for harmonic emission associated with intermediate excitations in the molecular ion. In particular, for orbitals associated with two-hole one-particle excitations, exchange effects can eliminate structure-related minima and maxima in the harmonic spectra. Laser-induced polarization of the neutral molecule may also have major effects on orbital structure-related minima and maxima in the harmonic spectra. Finally, we show how exchange terms in recombination can be viewed as a shakedownlike process induced by sudden electronic excitation in the ion.

Multi-particle–hole excitations in many-body Fermi systems

We formulate a microscopic theory for calculating the dynamic structure function of 3 He and other strongly interacting Fermi liquids. The theory is a generalization of the correlated basis function theory for the dynamics of 4 He and includes time-dependent two-particle—two-hole excitations. It may also be interpreted as a systematic extension of the random-phase approximation (RPA). Comparison of numerical results with experiments show a significant improvement of the excitation spectrum over RPA predictions while maintaining the accuracy of prediction of ground-state quantities like the static structure function.

Intruder bands and configuration mixing in lead isotopes

A three-configuration mixing calculation is performed in the context of the interacting boson model with the aim to describe recently observed collective bands built on low-lying ${0}^{+}$ states in neutron-deficient lead isotopes. The configurations that are included correspond to the regular, spherical states as well as two-particle two-hole and four-particle four-hole excitations across the $Z=82$ shell gap.

Spherical-deformed shape coexistence for thepfshell in the nuclear shell model

A spherical-deformed shape coexistence for semimagic pf-shell nuclei is investigated. Deformed states can arise by breaking the ${f}_{7/2}$ submagic shell, and coexist with spherical yrast states for ${}^{54}\mathrm{Fe}.$ These states are shown to be primarily two-particle two-hole excitations on top of the respective correlated ground states. In addition to these modes, a four-particle--four-hole excitation can be found for ${}^{54}\mathrm{Fe},$ which is related to the deformed band of doubly magic ${}^{56}\mathrm{Ni}.$ To investigate this shape coexistence, we use the conventional shell-model diagonalization, constrained Hartree-Fock, generator coordinate, variation-after-projection, and Monte Carlo shell-model methods.

Numericalstudies of the two-leg Hubbard ladder

The Hubbard model on a two-leg ladder structure has been studied bya combination of series expansions at T = 0 and the density-matrixrenormalization group. We report results for the ground-stateenergy E0 and spin gap Δs at half-filling, as well asdispersion curves for one- and two-hole excitations. For small Uboth E0 and Δs show a dramatic drop near t/t⊥~0.5, which becomes more gradual for larger U. This represents acrossover from a `band insulator' phase to a strongly correlatedspin liquid. The various features are collected in a `phasediagram' for the model.

Multistep variational approach to collective excitations

We discuss a multistep variational approach to collective excitations. The approach is developed in a boson formalism (bosons representing particle-hole excitations) and based on an iterative sequence of diagonalizations in subspaces of the full boson space. Purpose of these diagonalizations is that of searching for the best approximation of the ground state of the system. The procedure also leads us to define a set of excited states and, at the same time, of operators which generate these states as a result of their action on the ground state. We examine the cases in which these operators carry one-particle one-hole and up to two-particle two-hole excitations. We also explore the possibility of associating bosons to Tamm-Dancoff excitations and of describing the spectrum in terms of only a selected group of these. Tests within an exactly solvable three-level model are provided.

Many-body correlations in a multistep variational approach

We discuss a multistep variational approach for the study of many-body correlations. The approach is developed in a boson formalism (bosons representing particle-hole excitations) and based on an iterative sequence of diagonalizations in subspaces of the full boson space. Purpose of these diagonalizations is that of searching for the best approximation of the ground state of the system. The procedure also leads us to define a set of excited states and, at the same time, of operators which generate these states as a result of their action on the ground state. We examine the cases in which these operators carry one-particle one-hole and up to two-particle two-hole excitations. We also explore the possibility of associating bosons to Tamm-Dancoff excitations and of describing the spectrum in terms of only a selected group of these. Tests within an exactly solvable three-level model are provided.

Deformed intruder bands in113Sn

High-spin states in the odd-$A{ }^{113}\mathrm{Sn}$ nucleus have been investigated with the ${}^{100}\mathrm{Mo}{(}^{18}\mathrm{O}, 5n)$ reaction at 94 MeV using the Chalk River $8\ensuremath{\pi}$ array. Three decoupled $(\ensuremath{\Delta}I=2)$ rotational bands extending to spins $I$ in the range $(63/2--69/2)\ensuremath{\Elzxh}$ have been identified and connected to known low-lying states. Experimental observations for the most extended band have been interpreted as evidence for smooth band termination. Theoretical calculations performed within a configuration-dependent shell-correction approach suggest that all three bands are built upon deformed two-particle--two-hole proton excitations across the $Z=50$ shell gap.

Spectral Decorrelation of Nuclear Levels in the Presence of Continuum Decay.

The fluctuation properties of nuclear giant resonance spectra are studied in the presence of continuum decay. The subspace of quasibound states is specified by one-particle--one-hole and two-particle--two-hole excitations, and the continuum coupling is generated by a scattering ensemble. It is found that, with an increasing number of open channels, the real parts of the complex eigenvalues quickly decorrelate. This appears to be related to the transition from power-law to exponential time decay of the survival probability of an initially nonstationary state.

High-spin rotational bands in doubly odd

Three rotational bands have been established to high spin in doubly odd using high-fold -ray coincidence data collected with the Eurogam II spectrometer. Two of the bands are linked by dipole transitions at low spin and are believed to be signature partners built on the structure. A low-spin signature inversion is observed and taken as evidence for a triaxial shape with , which is supported by TRS cranking calculations. The third band, seen at higher spin/frequency, is tentatively associated with a deformed five-particle - two-hole configuration, whereby two proton holes result from two-particle - two-hole excitations across the Z = 50 shell gap.

JUSTIFICATION OF EFFECTIVE PARTICLE NUMBERS FOR DESCRIBING INTRUDER BANDS

The standard theoretical explanation of low-lying, deformed, intruder bands in even-even nuclei near closed shells is in terms of two-particle, two-hole excitations across the major-shell gap. One normally ignores the difference between particles and holes and assumes that the effective proton (or neutron) number has increased by four. We provide a justification of this approximation by comparing two F-spin multiplets having the same F value, where one multiplet is for the ground-band levels of a set of nuclei, while the second multiplet is for the intruder-band levels of another set of nuclei.

Electronically stimulated adsorbate dissociation in the presence of an electronegative coadsorbate: (NO2+O) on Pt(111).

The effects of an electronegative coadsorbate on the stimulated dissociation of a chemisorbed molecule are investigated using state-resolved laser-ionization spectroscopy of those dissociation fragments which leave the surface. Specifically, we examine the NO${(}^{2}$${\mathrm{\ensuremath{\Pi}}}_{\mathrm{\ensuremath{\Omega}}=1/2,3/2}$) and O${(}^{3}$${\mathit{P}}_{\mathit{J}}$) fragment energies and yields resulting from electron- (6--350 eV) stimulated dissociation of chemisorbed ${\mathrm{NO}}_{2}$ as a function of preadsorbed atomic O coverage. The most dramatic effect associated with O coverage (up to ${\mathrm{\ensuremath{\Theta}}}_{\mathrm{O}}$=0.75 monolayer) is a large (a factor of 26) enhancement in the specific ${\mathrm{NO}}_{2}$ dissociation yield. There is also an O-induced narrowing of the translational energy distributions and a decrease in both the rotational and vibrational energy of the NO fragment. The dissociation threshold of \ensuremath{\sim}10 eV, together with lifetime arguments, suggest that the dominant excitation(s) are shallow-valence two-hole excitations. The above observations can be understood in terms of reduced substrate charge-transfer screening of these excitations. In addition, we observe a distinct propensity (>4:1 at low J) for populating the upper (\ensuremath{\Omega}=3/2) over the lower (\ensuremath{\Omega}=1/2) level of the spin-orbit-split NO${(}^{2}$${\mathrm{\ensuremath{\Pi}}}_{\mathrm{\ensuremath{\Omega}}}$) ground state, whereas the spin-orbit population of the O${(}^{3}$${\mathit{P}}_{\mathit{J}}$) fragment is statistical (2J+1) within experimental error. The O${(}^{3}$${\mathit{P}}_{\mathit{J}}$) yield derives from dissociation of nitro-bound ${\mathrm{NO}}_{2}$ (N end down); no O${(}^{3}$${\mathit{P}}_{\mathit{J}}$) yield can be associated with side-bonded ${\mathrm{NO}}_{2}$.

Auger Spectroscopy and Electronically-stimulated Surface Processes

Electronic excitationsin adsorbate layers stimulate desoprtion and dissociation of adsorbed melecules as well as chemical reactions between adsorbates. The highest-probability stimulated processes produce neutral desorbates and determine how surface composition is altered by elctron or photon radiation. A basic understanding has emerged, due largely to laser resonance-enhanced multiphoton ionization (REMPI) experiments, which provide quantum-state resolution of the gas-phase products.Auger phenomena enter this understanding in several ways. For example, CVV Auger spectroscopy determines the screened hole-hole interaction, U, in adsorbates, which in turn provides insight into the degree of charge-transfer screening from the substrate. In those systems where screening charge is used in excitation Auger decay, screening direcly determines the lifetime, which in turn can exponentially affect the yield. Reductions in screening, e.g. induced by coadsorption of electro-negative species, thus can result in giant yield enhancements. As separate issues, a finite U may prevent the fast resonant decay and this increase the yield from two-hole excitations, as has been suggested for NO2 dissociation on Pt(111), or may assist in the localization (self-trapping) of two-hole excitations in dense adsorbate layers, as apparently is the case for NO desorption from the same surface. The latter causes the yields from one- and two-hole excitations to differ in their coverage dependence. Finally, CVV Auger spectroscopy, of course, measures the energies of two-hole excitations, which can be correlated with observed stimulated thresholds.