Probing Balance Energy Using Momentum- and Isospin-Dependent Potential

Using the momentum- and isospin-dependent Boltmann-Uehling-Uhlenbeck （BUU） model, we investigate the transverse flow and balance energy in two isotopic colliding systems ^48Ca＋^58Fe and ^48Cr＋^58Ni by adopting different symmetry potentials. By comparing the results between the two colliding systems, we find that the difference between the balance energies of two isotopic systems can be considered as a sensitive probe to the density dependence of symmetry energy.     

Hard gamma as probe of nuclear dynamics

Experimental results concerning the ⁵⁸Ni + ⁵⁸Ni at 30 MeV/u and ⁵⁸Ni + ¹⁹⁷Au at 30 and 45 MeV/u reactions are presented. The emission mechanism of hard photons has been exploited to get information on the time evolution of the reactions. From the measured hard gamma multiplicity associated to different classes of heavy residues a quantitative estimate of the reaction centrality has been obtained. Moreover, evidence of a prompt Intermediate Mass Fragment (IMF) emission is shown for the Ni + Au reaction at 45 MeV/u for central collisions exploring the correlation function between thermal photons and IMF’s.     

中能重离子碰撞中平衡能的同位旋效应

利用同位旋相关的量子分子动力学模型,计算了⁵⁸Fe+⁵⁸Fe和⁵⁸M+⁵⁸Ni两个反应系统在不同碰撞参数下的平衡能.观察到在不同碰撞参数下丰中子反应系统⁵⁸Fe+⁵⁸Fe比⁵⁸Ni+⁵⁸Ni有更高的平衡能.计算结果能与实验数据定性符合.     

197Au Mössbauer study of Au/Ni and Au/Fe metallic superlattices

¹⁹⁷Au Mössbauer measurements have been performed for Au/Ni and Au/Fe metallic superlattices at below 75 K. For Au/Ni superlattices, the area ratio in a spectrum between a superlattice component and that of the pure Au buffer layer has been determined at 25, 50 and 75 K. From the area ratios, it is found that the recoil-free fraction of Au in Au(10 Å)/Ni(10 Å) is larger than that of the bulk Au, suggesting the existence of the supermodulus effect in this superlattice. The¹⁹⁷Au Mössbauer spectrum obtained from Au(5 Å)/Fe(8 Å) is entirely magnetic at 16 K, suggesting the existence of a magnetic hyperfine interaction at¹⁹⁷Au nuclei through the transferred electron spin polarization.     

Radial Expansion Flow in Reactions of 40Ca+58Fe and 40Ca+58Ni

By means of using an isospin-dependent Boltzmann-Langevin equation which includes isospin-dependent symmetry energy, Coulomb energy, isospin-dependent nucleon-nucleon cross sections, Pauli blocking, and initialization, the radial expansion flow of reaction systems ⁴⁰Ca+⁵⁸Ni and ⁴⁰Ca+⁵⁸Fe at 53, 100, 150, and 200 MeV/u in the central collisions were studied. It has shown that the more neutron rich system exhibits smaller radial expansion flow. It was found that the neutron rich system had smaller threshold energy which may provide a new method to determine the isospin dependent nuclear equation of state from calculated result and linear fitting result.     

Forward and backward electron emission cross-sections for 23 MeVu<Superscript>-1</Superscript> C,Ni and Au projectiles traversing C,Al , Ni,Ag , Au and Bi foils

A rather complete experimental study of forward and backward electron velocity spectra from thin foils bombarded with ions at constant velocity of 30 atomic units (23MeV u^-1) was performed. Three different beams ( ¹²C³⁺ , ⁵⁸Ni¹⁴⁺ and ¹⁹⁷Au³⁶⁺ and six different targets ( ¹²C , ²⁷Al , ^natNi , ^natAg , ¹⁹⁷Au and ²⁰⁹Bi of approximately 90μg cm^-2 thickness were used. This procedure allowed to study the evolution of electron emission (velocity and angular distributions) for the [projectile; target] matrix [ C , Ni , Au ; C , Al , Ni , Ag , Au , Bi ] in a wide angular range. The projectile and target dependence of absolute cross-sections for binary encounter-, Auger- and backward-emitted electrons are analyzed.     

The new beta-delayed proton precursors103Sn and105Sn

Using⁵⁸Ni+⁵⁰Cr and⁵⁸Ni+⁵⁴Fe reactions and on-line mass separation, the new isotopes¹⁰³Sn and¹⁰⁵Sn with half-lives of 7±3 s and 31±6 s, respectively, were identified via their beta-delayed proton decays. The relative yields and the possibility of reaching¹⁰¹Sn are discussed.     

Azimuthal Distributions of K + Mesons in Heavy-Ion Collisions

Strange mesons are considered to be sensitive to in-medium modifications. Theory predicts a repulsive K ⁺ N potential and an attractive K ^? N potential in dense matter. A repulsive K ⁺ N potential would repel the K ⁺ mesons from the bulk of the nucleons and therefore cause a preferred out-of-plane emission of K ⁺ mesons at midrapidity and a directed flow opposite to the nucleons at target and projectile rapidity. One of observables to probe in-medium effects is the azimuthal emission pattern of K ⁺ mesons in heavy ion collisions. KaoS collaboration has measured the azimuthal distributions of K ⁺ mesons in Au + Au reactions at 1.5 A GeV and Ni + Ni reactions at 1.93 A GeV. Data show that K ⁺ mesons exhibit a pronounced enhancement at ${\phi = {90}^\circ}$ , i.e. perpendicular to the reaction plane. The data have also been fitted using the first two components of a Fourier series to get the directed flow v ₁ and elliptic flow v ₂. We used the quantum molecular dynamics model based on the covariant kaon dynamics to simulate the Au + Au collisions at 1.5 A GeV and the Ni + Ni collisions at 1.93 A GeV, to analyze the azimuthal distributions of K ⁺ mesons, and to calculate v ₁ and v ₂ of K ⁺ mesons. Calculated results with a repulsive in-medium K ⁺ N potential can reasonably describe the features of KaoS data. This indicates that the azimuthal distribution is one of sensitive probes to extract information on in-medium properties at high densities.     

Fe掺杂对溶胶凝胶法制备的ZnO: Ni薄膜结构及发光特性的影响

采用溶胶凝胶法在玻璃基片上制备了ZnO及Ni, Fe共掺杂的Zn_0.95-xNi_0.05Fe_xO (x=0, 0.005, 0.01, 0.03, 0.05) 薄膜. 通过扫描电镜(SEM) 和X射线衍射(XRD) 研究了薄膜样品的表面形貌和晶体结构. 结果表明所有样品都具有(002) 择优取向, Fe掺杂导致ZnO: Ni薄膜的晶体质量变差, 晶粒尺寸减小, 但适当的Fe掺杂有利于获得致密、 均匀的薄膜. XPS测试结果表明样品中Ni离子的价态为+2价, Fe离子的价态为+2价和+3价.室温光致发光(PL) 测量表明, 所有样品均观察到较强的紫外发光峰, 蓝光双峰和绿光发光峰. ZnO: Ni薄膜的发光强度可以通过Fe掺杂进行有效调节. 进而我们讨论了Ni, Fe共掺杂ZnO样品的发光机理.     

Hyperfine structure of highly charged ions

¹⁹⁷Au Mössbauer spectra from Au/TM (TM = Fe, Co, Ni) multilayers consist mainly of two components. One component shows a large hyperfine magnetic field due to the hybridization at the interface between Au and ferromagnetic layers. The other component is nonmagnetic arising from the middle part of the Au layers. From the fractional area of the magnetic components in each spectrum, the Au atoms in 0.4 nm Au layers are perturbed by the Fe and Ni layers, and Co layers perturb 0.3 nm Au layers at the interface.     

Hard photons and neutral pions as probes of hot and dense nuclear matter

The dynamics of heavy-ion collisions is studied in an energy domain in the vicinity of the Fermi energy. The early history of the collision is analyzed from the theoretical and experimental point of view in which the message conveyed by bremsstrahlung photons and neutral pions is exploited. The Boltzmann-Uehling-Uhlenbeck model and the Dubna Cascade Model, both based on similar principles but each adopting different computation technics, are briefly described and their respective predictions are discussed. In particular the emission pattern of bremsstrahlung photons is discussed. The photon production has been measured in the systems ⁸⁶Kr+⁵⁸Ni at 60A MeV, ¹⁸¹Ta+¹⁹⁷Au at 40A MeV and ²⁰⁸Pb+¹⁹⁷Au at 30A MeV and energy spectra, angular distributions and two-photon correlations have been analyzed. We find that bremsstrahlung photons are emitted from two distinct sources that can be correlated with nuclear-matter density oscillations. The properties of photon emission are discussed in terms of collective properties of nuclear matter. The high energy tail of the photon spectrum is interpreted by π⁰ and Δ decay but predominantly by radiative capture of pions. The π⁰ absorption in the nuclear medium is further analyzed by examining their emission pattern.     

The role of phase separation for self-organized surface pattern formation by ion beam erosion and metal atom co-deposition

We investigate the ripple pattern formation on Si surfaces at room temperature during normal incidence ion beam erosion under simultaneous deposition of different metallic co-deposited surfactant atoms. The co-deposition of small amounts of metallic atoms, in particular Fe and Mo, is known to have a tremendous impact on the evolution of nanoscale surface patterns on Si. In previous work on ion erosion of Si during co-deposition of Fe atoms, we proposed that chemical interactions between Fe and Si atoms of the steady-state mixed Fe _x Si surface layer formed during ion beam erosion is a dominant driving force for self-organized pattern formation. In particular, we provided experimental evidence for the formation of amorphous iron disilicide. To confirm and generalize such chemical effects on the pattern formation, in particular the tendency for phase separation, we have now irradiated Si surfaces with normal incidence 5 keV Xe ions under simultaneous gracing incidence co-deposition of Fe, Ni, Cu, Mo, W, Pt, and Au surfactant atoms. The selected metals in the two groups (Fe, Ni, Cu) and (W, Pt, Au) are very similar regarding their collision cascade behavior, but strongly differ regarding their tendency to silicide formation. We find pronounced ripple pattern formation only for those co deposited metals (Fe, Mo, Ni, W, and Pt), which are prone to the formation of mono and disilicides. In contrast, for Cu and Au co-deposition the surface remains very flat, even after irradiation at high ion fluence. Because of the very different behavior of Cu compared to Fe, Ni and Au compared to W, Pt, phase separation toward amorphous metal silicide phases is seen as the relevant process for the pattern formation on Si in the case of Fe, Mo, Ni, W, and Pt co-deposition.     

Evidence of non-statistical structures in the elastic and inelastic scattering of58Ni+58Ni and58Ni+62Ni and intermediate dinuclear states

Excitation functions and angular distributions of⁵⁸Ni+⁵⁸Ni and⁵⁸Ni+⁶²Ni scattering at energies just above the Coulomb barrier have been measured aroundθ _cm=90° in energy stepsΔE _cm=0.25 MeV fromE _cm ? 110 MeV toE _cm ? 120 MeV for⁵⁸Ni+⁵⁸Ni and fromE _cm ? 110 MeV toE _cm ? 118 MeV for⁵⁸Ni+⁶²Ni. Evidence for structure of non-statistical character has been found in the angle-summed excitation functions; this evidence is corroborated by the analysis of the angular distributions. This is the first time that non-statistical structure in elastic and inelastic scattering is reported with high confidence level for this mass and excitation energy ranges. Attempts are presented to understand the nature of this structure, including the presence of intermediate dinuclear states and virtual states in a potential well.     

A rutherford scattering study of the diffusion of heavy metal impurities in silicon to ion-damaged surface layers

Rutherford backscattering of 1.75 and 2 MeV ⁴He⁺ ions has been utilized to study the high temperature gettering of Fe, Co, Ni, Cu and Au from silicon by ion-damaged surface layers. In a typical experiment a metal film was evaporated onto one side of a silicon wafer (125 microm thick) which had received ion implantation damage (10¹⁶/cm² Si⁺ ions at 100 keV) on the opposite side; the wafer was then annealed at 900°C, usually for 30 min. The results of such experiments show that the metals studied may be divided into two classes, those which are gettered slowly - Fe, Co, and Au, and those gettered rapidly - Cu and Ni. Fe, Co, and Au were found at levels of 1×10¹³?1×10¹⁴/cm² in the damaged layer, whereas Cu and Ni appeared at levels of 6×10¹⁴ to 5 ×10¹⁶cm². The gettered level of Au, one of the “slow” group, was increased ten-fold by an equal increase in the anneal time to 300 min. The gettered Cu and Au exhibited double peaks in the scattered ion spectra, corresponding to metal concentrated at the most heavily damaged region (end of range for Si implant) and also at the outer surface, with a separation of ~ 1300 Å. A simple model is proposed to explain the slow and fast gettering, based on published interstitial diffusivities and solubilities of the five elements studied.Rutherford scattering has proven to be well suited for the quantitative identification of low levels of impurities on Si surfaces and for impurities gettered at damaged layers close to the surface.     

Elliptic flow of ν ands <Emphasis Type="Italic">π</Emphasis><Superscript>0</Superscript> mesons in heavy-ion collisions at 2 <Emphasis Type="Italic">A</Emphasis> GeVmesons in heavy-ion collisions at 2 <Emphasis Type="Italic">A</Emphasis> GeV

Elliptic flow of ν and π ⁰ mesons emitted at midrapidity are studied in collisions of 1.9 A GeV ⁵⁸Ni+⁵⁸Ni and 2 A GeV ⁴⁰Ca+^natCa. The observed anisotropy corresponds to a negative elliptic flow signal for ν mesons, indicating a preferred emission perpendicular to the reaction plane. In contrast, only small azimuthal anisotropies are observed for π ⁰ mesons. This may indicate that ν mesons freeze out earlier from the central interaction region than pions.     

Cross-section measurements for the 58,60,61Ni(n, α)55,57,58Fe reactions at 8.50, 9.50 and 10.50 MeV neutron energies

Cross sections of the ^58,60,61Ni(n, α)^55,57,58Fe reactions were measured at 8.50, 9.50 and 10.50 MeV neutron energies based on the HI-13 tandem accelerator of China Institute of Atomic Energy (CIAE) with enriched ⁵⁸Ni, ⁶⁰Ni, and ⁶¹Ni foil samples with backings. A twin gridded ionization chamber (GIC) was used as the charged particle detector, and an EJ-309 liquid scintillator was used to obtain the neutron energy spectra. The relative and absolute neutron fluxes were determined via three highly enriched ²³⁸U₃O₈ samples inside the GIC. The uncertainty of the present data of the ⁵⁸Ni(n, α)⁵⁵Fe reaction is smaller than most existing measurements. The present data of ⁶⁰Ni(n, α)⁵⁷Fe and ⁶¹Ni(n, α)⁵⁸Fe reactions are the first measurement results above 8 MeV. The present experimental data could be reasonably reproduced by calculations with TALYS-1.9 by adjusting several default values of theoretical model parameters.     

NiO-thickness dependent magnetic anisotropies in Fe/NiO/Au(001) and Fe/NiO/MgO(001) systems

The in-plane magnetic anisotropy of Fe/NiO bilayers was studied quantitatively as a function of NiO thickness using the magneto-optical Kerr effect with a rotating field. For NiO thicker than the ordering transition thickness, the total in-plane fourfold anisotropy of the Fe layer decreases with NiO thickness in Fe/NiO/Au(001), but increases in Fe/NiO/MgO(001). Our result indicates that the exchange coupling in an Fe/NiO bilayer might induce an additional in-plane fourfold anisotropy, and the opposite thickness dependent behaviors may be attributed to the different Ni²⁺ antiferromagnetic spin orientations for NiO films grown on Au(001) and MgO(001) surfaces.     

Baryon flow at SIS energies and beyond

We calculate the baryon flow P_x/A(y) in the energy range from 0.25 to 4.0A GeV in a relativistic transport model for Ni + Ni and Au + Au collisions employing various models for the baryon self-energies. We find that to describe the flow data of the FOPI Collaboration above 1A GeV the strength of the vector potential has to be reduced at high relative momentum or at high density. The latter phenomenon leads to a softening of the nuclear equation of state at high density.