Coincidence Intensity Research Articles

Evaluation Method for Complex Electromagnetic Environment

To perform a complexity evaluation for an electromagnetic environment (EME), a new method based on the S-transform is proposed, which can simultaneously count the time occupancy, frequency occupancy, and energy occupancy in the time–frequency domain. The frequency coincidence, modulation similarity, and background noise intensity are selected as important evaluation indices, and their physical interpretations are analyzed and calculated. The Extreme Learning Machine (ELM) method is adopted to evaluate the environmental complexity. The proposed method (S-ELM) requires less training time and has a fast convergence rate. The simulation and experimental results confirm that the proposed method is accurate and efficient.

In-beam spectroscopic study of Zn63

Investigation on the excited states of $^{63}\mathrm{Zn}$ was done through in-beam $\ensuremath{\gamma}$-ray spectroscopic techniques using the $^{52}\mathrm{Cr}(^{18}\mathrm{O},\phantom{\rule{4pt}{0ex}}\ensuremath{\alpha}3n)$ fusion-evaporation reaction at a beam energy of 72.5 MeV. Detection of the emitted $\ensuremath{\gamma}$ rays from the excited nuclei was performed in the coincidence mode using 14 Compton suppressed Ge clover detectors of the Indian National Gamma Array. Based on the $\ensuremath{\gamma}\ensuremath{-}\ensuremath{\gamma}$ coincidence data, 13 new transitions have been placed in the level scheme following their coincidence relationship and intensity balance. Spin and parity assignments of the excited levels have been carried out by extracting the directional correlation from oriented states ratio and polarization asymmetry values of the emitted $\ensuremath{\gamma}$ rays. Shell model calculations have been performed in the ${f}_{5/2}p{g}_{9/2}$ model space with a $^{56}\mathrm{Ni}$ core using the jj44bpn interaction, to interpret the observed excited states of the nucleus. A reasonable agreement is found between the experimental findings and the shell-model calculations. In order to understand the evolution of a collective shape built on the $9/{2}^{+}$ (1704 keV) state, we have performed total Routhian surface calculations with a $1{g}_{9/2}$ quasineutron and found reasonable agreement.

Double electron emission from surfaces via low-energy positrons

We have studied the electron pair emission process from surfaces due to the impact of a primary low-energy positron. The existence of this process implies a two-step scattering event. We find that the electron pair intensity is on the same scale as the positron-electron pair intensity. This suggests that a significant contribution of the pair intensity is actually due to the emission of three particles, of which two are detected. We also observe a strong material dependence of the coincidence intensity. Similarly to our previous studies with primary electron excitation or photon absorption, NiO is the material that displays the highest coincidence rates. We also note that the electron pair intensity scales with the single electron rate. This was also observed in electron pair emission with primary photons or electrons. This suggests that the coincidence intensity may provide a measure of the electron correlation strength.

High spin γ -ray spectroscopy in Ca41

High spin states in $^{41}\mathrm{Ca}$ have been investigated by using $\ensuremath{\gamma}$-ray spectroscopic techniques following the $^{27}\mathrm{Al}(^{16}\mathrm{O},pn)^{41}\mathrm{Ca}$ fusion-evaporation reaction. Around twelve new transitions belonging to $^{41}\mathrm{Ca}$ have been observed and placed in the level scheme, which now has been extended up to ${E}_{x}\ensuremath{\sim}9$ MeV. The spin-parity assignments for the observed levels were arrived at following the analysis of both the coincidence intensity anisotropies and linear polarization measurements. The established 5p-4h band was extended up to ${J}^{\ensuremath{\pi}}=19/{2}^{\ensuremath{-}}$. The observations of Doppler shape and shifts facilitated the estimation of the level lifetimes by using the Doppler shift attenuation method. The lifetimes were validated with respect to previous measurements and lifetime of a few levels has been arrived at for the first time. Shell-model calculations were carried out to explain the observed level structure of the nucleus and are indicative of both single-particle and collective degrees of freedom in this $N\ensuremath{\sim}Z\ensuremath{\sim}20$ nucleus.

Electron pair emission from surfaces: Intensity relations

The emission of an electron pair upon single-photon absorption requires a finite electron-electron interaction. Therefore, double photoemission is a particularly sensitive tool to study the electron correlation in matter. This is supported by a recent theoretical work which predicts that the pair intensity is a direct reflection of the correlation strength. In order to explore the validity of this statement, we performed a study on a variety of materials. Among them are noble metals, transition metals, and insulators. The latter include transition metal oxides such as CoO and NiO which are also termed highly correlated. We find an increased pair emission rate of NiO and CoO compared to the metals which reach a factor of 10. We also discovered that an increase of the coincidence intensity is accompanied by an increase in the singles count rate. This demonstrates that the electron pair emission is an efficient process at surfaces contributing up to $15%$ to the single-electron emission in double photoemission. We performed also electron pair emission studies upon primary electron impact and find similar intensity relations.

Structure of 207Pb populated in 208Pb + 208Pb deep-inelastic collisions

The yrast structure of 207Pb above the 13=2+ isomeric state has been investigated in deep-inelastic collisions of 208Pb and 208Pb at ATLAS, Argonne National Laboratory. New and previously observed transitions were measured using the Gammasphere detector array. The level scheme of 207Pb is presented up to ∼ 6 MeV, built using coincidence and γ-ray intensity analyses. Spin and parity assignments of states were made, based on angular distributions and comparisons to shell model calculations.

Structure of $^{207}$Pb Populated in $^{208}$Pb + $^{208}$Pb Deep-inelastic Collisions

The yrast structure of 207Pb above the 13/2+ isomeric state has been investigated in deep-inelastic collisions of 208Pb and 208Pb at ATLAS, Argonne National Laboratory. New and previously observed transitions were measured using the Gammasphere detector array. The level scheme of 207Pb is presented up to ~ 6 MeV, built using coincidence and γ-ray intensity analyses. In addition, the spin and parity assignments of states were made, based on angular distributions and comparisons to shell model calculations.

High-Statistics Study of theβ+/EC-Decay of110In

A study of the 110In β+/EC decay was performed at the TRIUMF Isotope Separator and Accelerator (ISAC) facility to probe the nuclear structure of 110Cd. The data were collected in scaled-down γ-ray singles, γ − γ coincidence, and γ-electron coincidence mode. The data were sorted and a random-background subtracted γ − γ matrix was created containing a total of 850 million events. We expanded the level scheme of 110Cd significantly by identifying 75 levels under 3.8 MeV, including 12 new ones, and increased the number of previously observed transitions from these levels to 273. The γ-ray branching intensities have been extracted through an analysis of the coincidence intensities. The branching ratios were combined with a reanalysis of lifetimes measurements obtained in an (n, n'γ) reaction with monoenergetic neutrons for the calculation of B(E2) values and these results have lead to the proposal of a γ-soft rotor, or O(6) nucleus, rather than a vibrational, or U(5) pattern for the nature of the low-lying, low-spin levels in 110Cd.

Effect of stimulus intensity on response time distribution in multisensory integration

To increase the efficiency of multimodal user interfaces, one has to design them according to how multimodal features appear in the real world. Although spatial coincidence and matching intensity levels are important for perception, these factors received little attention in human–computer interaction studies. In our present study we aimed to map how spatial coincidence and different intensity levels influence response times. Sixteen participants performed a simple auditory localization task, where sounds were presented either alone or together with visual non-targets. We found that medium intensity visual stimuli facilitated responses to low intensity sounds. Analyses of response time distributions showed that intensity of target and non-target stimuli affected different parameters of the ex-Gaussian distribution. Our results suggest that multisensory integration and response facilitation may occur even if the non-target has low predictive power to the location of the target. Furthermore, we show that the parameters of the ex-Gaussian distribution can be related to distinct cognitive processes. The current results are potentially applicable in the design of an intelligent warning system that employs the user’s reaction time to adapt the warning signal for optimal results.

Exploring highly correlated materials via electron pair emission: the case of NiO/Ag(100)

Metal oxides like NiO are usually termed ‘highly correlated’, because the material properties are decisively determined by the electron–electron interaction. This makes them interesting candidates for electron pair spectroscopy which is particularly sensitive to the electron correlation. We have prepared ultrathin NiO/Ag(100) films and studied the electron pair emission upon electron impact. Compared to the metal substrate we observe an increase of the coincidence intensity by a factor of 8 for NiO. Thickness dependent measurements prove that this enhancement is an intrinsic effect rather than due to a mean free path increase of the oxide. The Néel temperature TN of NiO films displays a thickness dependence which allows us to tune TN. We performed temperature dependent measurements and observed no temperature dependence of the coincidence spectra. This proves that the electron pair emission probes the local correlation rather than long range order. An enhanced coincidence intensity was also found for other oxide phases compared to their corresponding metal phases.

Spin-parity assignments and extension of the 02+band in158Er

Low and medium spin collective structures in 158 Er have been studied using the 150 Sm(12 C,4nγγ ) fusion-evaporation reaction at a beam energy of E lab = 65 MeV. A band built on the 02 + excitation has been established and extended to J π = 18+ from the analysis of γ -γ coincidence relationships, intensity arguments and DCO ratios. The 02 + band in 158 Er presents a similar trend to the 02 + bands in the lighter N = 90 isotones but lies about 125 keV higher. This systematic trend supports a similar configuration for the 02 + bands in the N = 90 isotones.

Coincidence photoelectron and Auger-electron spectral behaviors of Auger cascade decay

Abstract The Auger-photoelectron coincidence spectroscopy (APECS) and Auger Auger-electron coincidence spectroscopy (AAECS) spectral behaviors of Auger cascade decay are discussed by a many-body theory. There is a significant difference in the coincidence intensity distribution in a two-dimensional map according to whether a pair of coincidence electrons are generated, respectively, by creation and annihilation of the same n -hole state ( n ⩾ 1 ) . The difference manifests as a line narrowing and a peak KE shift of the coincidence spectrum compared to the singles (noncoincidence) one. We discussed the inherent mechanism of APECS (AAECS), which causes the difference.

Correlation-induced non-Abelian quantum holonomies

In the context of two-particle interferometry, we construct a parallel transport condition that is based on the maximization of coincidence intensity with respect to local unitary operations on one of the subsystems. The dependence on correlation is investigated and it is found that the holonomy group is generally non-Abelian, but Abelian for uncorrelated systems. It is found that our framework contains the Lévay geometric phase (2004 J. Phys. A: Math. Gen. 37 1821) in the case of two-qubit systems undergoing local SU(2) evolutions.

Sensing the electron–electron correlation in solids via double photoemission

AbstractWe discuss the electron pair emission from surfaces upon the absorption of a single photon, also called double photoemission (DPE). This experiment is particular sensitive to the electron–electron interaction, because for independent electrons the DPE intensity is zero. We outline the experimental development of this technique over the past decade. Going beyond the mere detection of pairs we advanced the instrumentation. Now we are able to measure the kinetic energies and emission angles of a wide angular acceptance. We will show how the available energy is distributed among the electrons and how the angular distributions look like. The latter enabled us to make contact to an important concept of modern solid state theory, namely the exchange–correlation hole. We demonstrate that the exchange–correlation hole manifests itself in a depletion zone of the coincidence intensity around the fixed emission direction of one electron. The experiments were performed at the synchrotron facilities BESSY I and BESSY II. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Electronic correlation spectroscopy in condensed matter

On the basis of formal analysis and the perturbation many-body theory we point out the conditions under which short and long-range electronic correlations in condensed matter can be mapped by means of two-particle coincidence spectroscopy. For particle-impact induced electron emission we show that the coincidence intensity integrated over the slow ejected electron is related to the density-density time correlation function. In the case of a fast incoming and outgoing projectile and a slow emitted electron we relate the intensity to the two-particle and higher order correlations. Erects of two-particle correlations on the two-particle spectral density are investigated by means of the dynamical mean field theory (DMFT) applied to the Hubbard model.

Electron pair emission from a Cu(111) surface upon photon absorption

We studied the electron pair emission from a Cu111 surface upon photon absorption. We found that the energy sharing depends on the angle between the trajectories of the two emitted electrons. The angular distribution of the coincidence intensity displays a zone of reduced intensity, if the emission direction of one electron is fixed. We are able to observe the full extension and shape of this depletion zone. It has an angular extension of 1.2 rad, which is independent of the electron energy. This depletion zone is a manifestation of the exchange-correlation hole. The experimental results are discussed in connection with a detailed theoretical description.

Transition strengths and degree of deformation inSr79

High-spin states in $^{79}\mathrm{Sr}$ were studied using the $^{54}\mathrm{Fe}$($^{28}\mathrm{Si}$,$2p$$n$) reaction at 90 MeV, with a thick 14-mg/${\mathrm{cm}}^{2}$ $^{54}\mathrm{Fe}$ target used to stop all recoils. Prompt $\ensuremath{\gamma}\text{\ensuremath{-}}\ensuremath{\gamma}$ coincidences were detected using the Florida State University Compton-suppressed Ge array consisting of three Clover detectors and seven single-crystal detectors. The most recent $^{79}\mathrm{Sr}$ level scheme has been confirmed in three separate band structures up to a spin as high as the $({\frac{37}{2}}^{+})$ yrast state based on \ensuremath{\gamma}-ray coincidence relations, intensity and effective lifetime measurements, and directional correlation of oriented nuclei ratios. Lifetimes of 33 excited states were measured using the Doppler-shift attenuation method, with the experimental line shapes obtained at two separate observation angles and by gating from above the transitions of interest whenever possible. Transition quadrupole moments ${Q}_{t}$ inferred from the lifetimes indicate a high degree of collectivity and deformation over a rather wide range of spins in all three observed bands, with evidence for modest reductions in the values with increasing spin. The changes in ${Q}_{t}$ are attributed to the onset of quasiproton alignment and are supported qualitatively by the predictions of the projected shell model and cranked Woods-Saxon calculations in conjunction with the cranked shell model. Lifetimes measured in a band based on the [431]${\frac{1}{2}}^{+}$ intrinsic Nilsson configuration suggest a large quadrupole deformation (${\ensuremath{\beta}}_{2}\ensuremath{\approx}0.41$) associated with this band, providing another example of the strong deformation-driving properties of the ${d}_{5/2}$ intruder orbital in the mass 80 region.

Normalization of γ–γ angular correlation coincidence counts using characteristic X-rays

A new method to normalize coincidence counts for γ–γ angular correlations measured with a multiple-Ge detector system is described. This method uses characteristic KX-rays emitted following internal conversion or electron capture, which exhibit a coincidence with γ-rays and an isotropic KX-γ angular correlation. Only the ratios between KX-ray counts and γ-ray counts of interest in the same gated spectra are used to deduce normalized coincidence intensities, and any other quantities such as detector efficiencies, γ-ray singles counts and other kinds of efficiencies are not required. Performance of this method was tested in on-line experiments using mass-separated 126 La and 128 La sources.

The role of defects at low concentrations in the NH3/TiO2(110) adsorption system: An Auger–photoelectron coincidence spectroscopy study

We present Auger–photoelectron coincidence spectra from the stoichiometric and reduced (by vacuum annealing) TiO2(110) surfaces after saturation exposure to NH3 at room temperature. The Ti 3p coincidence photoemission spectrum shows substantial emission from residual (or intrinsic) defects on the stoichiometric surface and additional emission from thermally-induced bridging oxygen vacancies on the reduced surface. Changes in the line shape of the coincidence Ti 3p spectrum upon adsorption show that NH3 binds to the five-fold coordinated Ti ions and the rosette structures of both surfaces, and at bridging oxygen vacancies of the reduced surface, but not at intrinsic defects. Quantitative analysis of the spectra supports a structural model where on the stoichiometric surface NH3 adsorbs at every other five-fold coordinated Ti site and at every other Ti site of the rosettes. On the reduced surface, NH3 adsorbs at bridging oxygen vacancies preventing adsorption on neighboring five-fold coordinated Ti sites, suggesting that the saturation coverage of NH3 is smaller for the reduced surface. We observe a correlation between the density of bridging oxygen vacancies and the coincidence intensity from five-fold coordinated Ti ions that gives an internally consistent account of these data.

Coherent excitation of the singlet-triplet mixed 1s4f state of helium.

In this paper, we present a detailed theoretical description for the coherent electron-impact excitation, the subsequent time evolution, and the cascading decay process of the singlet-triplet mixed $1s4f$ state of helium. The excitation amplitude and phase of each sublevel of this state are related to measurable coincidence intensities and polarizations of the emitted photons. It is found that the intensity and polarization of the emitted photons are time modulated due to the singlet and triplet mixing in the $1s4f$ state.