Deep Hole States Research Articles

Theoretical studies on the cascade decay processes of 1s-core-hole state of Ar ion

The cascade decay processes from the 1s-core-hole state of Ar ion have been studied theoretically via straightforward construction of de-excitation trees and high-accuracy level-to-level calculations using the flexible atomic code (FAC). The final charge state distribution (FCSD), contributions of different cascade routes to the FCSD, and the main production pathways of each Ari+ ion which are never discussed before are analyzed carefully. It is found that the de-excitation processes is very complex and Auger decay is the predominant channel, the most probable final charge state is 4, while Ar+ to Ar6+ ions can be produced in the 5-step Auger cascade decay processes for Ar+1s−1 hole state. Ar+ is mainly derived from KM23 channel, Ar2+ is associated mainly with KL23 channel, when Ar3+, Ar4+, Ar5+ and Ar6+ions are mainly coming from KL23M23, KL23L23, KL1L23 and KL1L1 channels, respectively. Present studies would be helpful for further researches on the cascade decay processes of deep inner-shell hole states, and for the interaction between x-ray free-electron lasers and matter.

Improved rectification and transport properties of hybrid PEDOT:PSS/Ge/Si heterojunctions with Ge nanoclusters

The electrical characteristics and deep-level transient spectroscopy of a hybrid poly(3,4-ethylene dioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/GeNCs/Si heterojunction with Ge nanoclusters grown by molecular beam epitaxy on a p-type Si(001) substrate are investigated. The heterostructure shows good rectifying J–V characteristics, the dark current exhibits an activation energies of 280 meV and 550 meV, while the reverse bias leakage current is suppressed due to the coating of Ge nanoclusters with PEDOT:PSS. We show that recombination via deep hole states close to grain boundaries can be partly suppressed by the PEDOT:PSS thin films, leading to a decrease in the saturation current and an improvement of the rectification without deterioration of forward current.

Damping of simple modes of high-energy nuclear excitations: dispersive optical models and their implementations

The particle-hole dispersive optical model, proposed recently to describe the main properties of high-energy particle-hole-type excitations in medium-heavy mass spherical nuclei, is briefly presented. Unique features of the model, new developments and some implementations are discussed. In applying to the description of deep-hole states, an unitary version of the single-quasiparticle optical model is also briefly presented.

Atomistic Design of CdSe/CdS Core-Shell Quantum Dots with Suppressed Auger Recombination.

We design quasi-type-II CdSe/CdS core-shell colloidal quantum dots (CQDs) exhibiting a suppressed Auger recombination rate. We do so using fully atomistic tight-binding wave functions and microscopic Coulomb interactions. The recombination rate as a function of the core and shell size and shape is tested against experiments. Because of a higher density of deep hole states and stronger hole confinement, Auger recombination is found to be up to six times faster for positive trions compared to negative ones in 4 nm core/10 nm shell CQDs. Soft-confinement at the interface results in weak suppression of Auger recombination compared to same-bandgap sharp-interface CQDs. We find that the suppression is due to increased volume of the core resulting in delocalization of the wave functions, rather than due to soft-confinement itself. We show that our results are consistent with previous effective mass models with the same system parameters. Increasing the dot volume remains the most efficient way to suppress Auger recombination. We predict that a 4-fold suppression of Auger recombination can be achieved in 10 nm CQDs by increasing the core volume by using rodlike cores embedded in thick shells.

On the excitation energy of deep-hole states in medium-heavy-mass spherical nuclei

Within the particle-hole dispersive optical model it is shown that the spreading effect determines a significant part of the anomalously large excitation energy of deep-hole states in the 90 Zr and 208 Pb parent nuclei.

Exclusive measurements of quasi-free proton scattering reactions in inverse and complete kinematics

Quasi-free scattering reactions of the type (p,2p) were measured for the first time exclusively in complete and inverse kinematics, using a 12C beam at an energy of ∼400 MeV/u as a benchmark. This new technique has been developed to study the single-particle structure of exotic nuclei in experiments with radioactive-ion beams. The outgoing pair of protons and the fragments were measured simultaneously, enabling an unambiguous identification of the reaction channels and a redundant measurement of the kinematic observables. Both valence and deeply-bound nucleon orbits are probed, including those leading to unbound states of the daughter nucleus. Exclusive (p,2p) cross sections of 15.8(18) mb, 1.9(2) mb and 1.5(2) mb to the low-lying 0p-hole states overlapping with the ground state (3/2−) and with the bound excited states of 11B at 2.125 MeV (1/2−) and 5.02 MeV (3/2−), respectively, were determined via γ-ray spectroscopy. Particle-unstable deep-hole states, corresponding to proton removal from the 0s-orbital, were studied via the invariant-mass technique. Cross sections and momentum distributions were extracted and compared to theoretical calculations employing the eikonal formalism. The obtained results are in a good agreement with this theory and with direct-kinematics experiments. The dependence of the proton–proton scattering kinematics on the internal momentum of the struck proton and on its separation energy was investigated for the first time in inverse kinematics employing a large-acceptance measurement.

On an optical-model description of the relaxation of deep hole states in medium-heavy-mass spherical nuclei

The Green’s function method is used to formulate the single-quasiparticle dispersive optical model with the aim of semimicroscopically describing the relaxation of deep hole states in medium-heavy-mass spherical nuclei. The results of the calculations performed on the basis of this model for the 208Pb parent nucleus are compared with experimental data.

Hypernuclei and Deep Hole States

A close connection of nuclear-core deep hole states with the production, structure and decay of hypernuclei is discussed together with the structure analysis of the deep hole states. We found theoretically a selection rule for fragmentation of s-hole states in light nuclei. The selection rule tells us that s-hole states in light nuclei can be fragmented into non-α channels such as 3He or t, while the fragmentation into α channel is largely suppressed, reflecting the space symmetry of the s-hole states. The characteristic decay pattern of a Λ12C(sn−1sΛ) state into a Λ9Be+3He channel and the two-body single-Λ hypernuclear production reaction through Ξ−-atomic capture, 12C(stopped Ξ−, Λ9Be)Λ4H, might suggest the possible existence of the selection rule for fragmentation s-hole states in light nuclei.

Spectroscopic factors and strength distributions for the deeply bound orbitals inCa40obtained from the(p⃗,2p)reaction at392 MeV

The cross sections and analyzing powers for the $^{40}\mathrm{Ca}$($\mathrm{pP\vec},2p$) reaction were measured. The strength distributions for the deep-hole states were obtained by a multipole decomposition analysis. The centroid energies and widths of the hole-state strengths of the $1p$ and $1{s}_{1/2}$ orbitals in $^{40}\mathrm{Ca}$ were determined. The spectroscopic factors for the deeply bound $1p$ and $1{s}_{1/2}$ orbitals were extracted as $49\ifmmode\pm\else\textpm\fi{}10%$ and $78\ifmmode\pm\else\textpm\fi{}14%$ of the sum-rule limits of the independent-particle shell model, respectively. A strong influence of the nucleon-nucleon correlations on the spectroscopic factors is suggested.

Kinetic energy sum spectra in nonmesonic weak decay of hypernuclei

We evaluate the coincidence spectra in the nonmesonic weak decay (NMWD) $\ensuremath{\Lambda}N\ensuremath{\rightarrow}\mathit{nN}$ of \ensuremath{\Lambda} hypernuclei ${}_{\ensuremath{\Lambda}}^{4}\mathrm{He}$, ${}_{\ensuremath{\Lambda}}^{5}\mathrm{He}$, ${}_{\ensuremath{\Lambda}}^{12}\mathrm{C}$, ${}_{\ensuremath{\Lambda}}^{16}\mathrm{O}$, and ${}_{\ensuremath{\Lambda}}^{28}\mathrm{Si}$, as a function of the sum of kinetic energies ${E}_{\mathit{nN}}={E}_{n}+{E}_{N}$ for $N=n,p$. The strangeness-changing transition potential is described by the one-meson-exchange model, with commonly used parametrization. Two versions of the independent-particle shell model (IPSM) are employed to account for the nuclear structure of the final residual nuclei. They are as follows: (a) IPSM-a, where no correlation, except for the Pauli principle, is taken into account and (b) IPSM-b, where the highly excited hole states are considered to be quasistationary and are described by Breit-Wigner distributions, whose widths are estimated from the experimental data. All np and nn spectra exhibit a series of peaks in the energy interval 110 MeV $<{E}_{\mathit{nN}}<170$ MeV, one for each occupied shell-model state. Within the IPSM-a, and because of the recoil effect, each peak covers an energy interval proportional to ${A}^{\ensuremath{-}1}$ , going from $\ensuremath{\cong}4$ MeV for ${}_{\ensuremath{\Lambda}}^{28}\mathrm{Si}$ to $\ensuremath{\cong}40$ MeV for ${}_{\ensuremath{\Lambda}}^{4}\mathrm{He}$. Such a description could be pretty fair for the light ${}_{\ensuremath{\Lambda}}^{4}\mathrm{He}$ and ${}_{\ensuremath{\Lambda}}^{5}\mathrm{He}$ hypernuclei. For the remaining, heavier, hypernuclei it is very important, however, to consider as well the spreading in strength of the deep-hole states and bring into play the IPSM-b approach. Notwithstanding the nuclear model that is employed the results depend only very weakly on the details of the dynamics involved in the decay process proper. We propose that the IPSM is the appropriate lowest-order approximation for the theoretical calculations of the of kinetic energy sum spectra in the NMWD. It is in comparison to this picture that one should appraise the effects of the final-state interactions and of the two-nucleon-induced decay mode.

Structures and decay of deep-hole states in light nuclei populated by the (p, 2p 2p) reactions

Decay particles from the s-hole states in 11B and 15N have been measured in coincidence with the quasifree 12C(p, 2p) and 16O(p, 2p) reactions at E p =392 MeV. Triton decay is found to be dominant for the 11B(s-hole) state and also found to be larger than α decay for the 15N(s-hole) state despite its smaller Q value compared to α decay. Measured decay branching ratios are discussed in comparison with the results of statistical-model, SU(3)-model, and shell-model calculations. The energy spectra around the s-hole states in both 11B and 15N exhibit some bumplike structures, which can be qualitatively explained by recent shell-model calculations for both nuclei.

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.

Neutron decay of deep hole states and isobaric analog states in 115Sn populated by the (3He,α) reaction at 102 MeV

Neutron decay of excited hole states and isobaric analog states (IAS) populated by the 116Sn(3He,α) reaction at an energy of 102 MeV has been investigated. The α-particles were analysed in a magnetic spectrograph positioned at 1.4° and detected with a multiwire drift chamber. Excitation energies in 115Sn up to 23 MeV were studied. An array of neutron detectors was positioned around the target at angles ranging from 68° to 209°. The neutron data were analysed in terms of decay into final states, using statistical model calculations as a tool to extract lower limits of nonstatistical decay. Nonstatistical decay was observed from states up to an excitation energy of about 18 MeV. The neutron emission of the IAS is compatible with 100% statistical decay.

Space-charge-limited post transit currents spectroscopy in poly(methylphenylsilylene)

Transient space-charge-limited currents (T-SCLCs) were used as a method for examining drift mobility, recombination and transport mechanisms for a typical poly(silylene), poly(methylphenylsilylene) (PMPSi). It was found that T-SCLCs present a unique possibility for injecting constant charge into a material with strong dependence of the generation efficiency on the electric field strength. This charge is given by space charge limitations and is thus independent of the transport properties of the material. The post-transit T-SCLC hole emission signals from deep traps have been measured using post-transit T-SCLCs. A density-of-electron-states distribution for deep trapping hole states with a tail-like exponential and a Gaussian distribution centred at 0.55 eV were found. © 1997 John Wiley & Sons, Ltd.

Neutron decay of deep-hole states in 89Zr populated by the 90Zr(3He,α)89Zr reaction at 102 MeV

Neutron decay of excited hole states populated by the Zr-90(He-3,alpha) reaction at an incident energy of 102 MeV has been investigated. The alpha-particles were analysed in a magnetic spectrograph ...

Neutron decay of deep-hole states populated by the 208Pb(3He,α)207Pb reaction at 102 MeV

Neutron decay of excited hole states populated by the 208Pb(3He,α) reaction at an energy of 102 MeV has been investigated. The α-particles were analysed in a magnetic spectrograph positioned at 1.4° and detected with a multi-wire drift chamber. Excitation energies in 207Pb up to 25 MeV were studied. An array of neutron detectors was positioned around the target at angles ranging from 68° to 209°. The neutron data were analysed in terms of decay into final states, using statistical-model calculations as a tool to extract non-statistical decay.

Hypernuclei and Deep Hole States

Hypernuclei and Deep Hole States

Proton hole states in 208Pb, studied by means of a self-consistent solution of the second-order Dyson equation for single-particle propagators

The single-particle self-energy in finite nuclei is constructed in a microscopic way by means of the Green-function formalism. We present calculations for the 208 Pb system which are fully self-consistent up to second order in the residual interaction. This leads to an improved description of damping effects in the spectral function for deeply bound hole states. The theoretical results are compared with experimental (e, e'p) results. Global properties of the single-particle strength distributions for deep hole states, such as the centroids and widths, are well reproduced. Finally some comments are made about the meaning of occupation probabilities for shell-model orbits.

Onset of neutron single-particle strengths in the tin isotopic chain.

The stripping reaction (\ensuremath{\alpha}${,}^{3}$He) at 183 MeV bombarding energy has been used to study the neutron-particle response function on $^{124,122,120,118,116,112}\mathrm{Sn}$ target nuclei up to 25 MeV excitation energy. Strong transitions to high-lying neutron states are observed beyond 4 MeV excitation energy. These transitions, arising from neutron stripping to high-spin outer subshells, appear as a sharp and strong peak located around 5 MeV excitation energy for the heavier tin isotopes (125, 123, and 121) and a broader structure extending up to 10 MeV. A clear broadening of the whole structure and the disappearance of the sharp component is observed with decreasing mass number, leading to a structureless spectrum in the case of $^{113}\mathrm{Sn}$. Our investigation reveals a strong excitation of the 1${\mathit{i}}_{13/2}$ neutron strength, with possible mixture with the neighboring 1${\mathit{h}}_{9/2}$ and 2f subshells between 5 and 10 MeV excitation energy. The empirical data are compared with the theoretical predictions from the quasiparticle-phonon nuclear model. The present investigation, on a wide range of the tin isotopic chain, allows us to establish a comparison between the damping of high-lying particle and deep-hole states in heavy nuclei.

Aharonov-Bohm effect and vacuum polarization: Pawel Górnicki. Institute for Theoretical Physics, Polish Academy of Sciences, A1. Lotników 32/46, PL-02-668 Warsaw, Poland

The structure of light hypernuclei with strangeness S=−1 and −2 is investigated with the microscopic cluster model and the Gaussian expansion method (GEM). We emphasize that the cluster picture as well as the mean-field picture is invaluable to understand the structure of Λ hypernuclei, Σ hypernuclei and double Λ hypernuclei. A variety of aspects of Λ hypernuclei is demonstrated through a systematic study of p-shell hypernuclei (Λ6He,Λ6Li, Λ7Li, Λ8Li, Λ8Be, Λ9Be, Λ13C) and sd-shell ones (Λ20Ne, Λ21Ne): for example, the appearance of genuine hypernuclear states with new spatial symmetry which cannot be seen in ordinary nuclei, the glue-like role of the Λ particle which shrinks the size of nuclear core and thus reduces the B(E2) value, and the halo and skin structures in Λ6He and Λ6Li etc. The typical light hypernucleus Λ9Be is thoroughly investigated, including its production, structure and decay. Precise three-body and four-body calculations of Λ7Li, Λ9Be and Λ13C using GEM provide important information on the spin structure of the underlying ΛN interaction, by comparing with recent experimental data from γ-ray hypernuclear spectroscopy. The Λ–Σ coupling effect is studied in Λ4H and Λ4He. The binding mechanism of Σ4He is discussed together with the possible existence of Σ7Li, emphasizing the fact that the study of Σ7Li is useful for extracting information on the ΣN interaction differing from that from Σ4He. A systematic study of double-Λ hypernuclei, constrained by the NAGARA data (ΛΛ6He) within a four-body cluster model indicates that the recently observed Demachi–Yanagi event can be interpreted as the 2+ state of ΛΛ10Be. The effect of hyperon mixing in ΛΛ6He and ΛΛ10Be is investigated using one-boson-exchange potentials and quark-cluster-model interactions for the S=−2 sector. A close relation between nuclear deep hole states and hypernuclei is discussed, emphasizing the selection rule for fragmentation of the s-hole in light nuclei, which is promising for understanding the production mechanism of double-Λ and twin-Λ hypernuclei via Ξ-atomic capture.