Ni Nuclei Research Articles

Observation of isoscalar multipole strengths in exotic doubly-magic 56Ni in inelastic α scattering in inverse kinematics

The Isoscalar Giant Monopole Resonance (ISGMR) and the Isoscalar Giant Dipole Resonance (ISGDR) compression modes have been studied in the doubly-magic unstable nucleus 56Ni. They were measured by inelastic α-particle scattering in inverse kinematics at 50 MeV/u with the MAYA active target at the GANIL facility. The centroid of the ISGMR has been obtained at Ex=19.1±0.5 MeV. Evidence for the low-lying part of the ISGDR has been found at Ex=17.4±0.7 MeV. The strength distribution for the dipole mode shows similarity with the prediction from the Hartree–Fock (HF) based random-phase approximation (RPA) [1]. These measurements confirm inelastic α-particle scattering as a suitable probe for exciting the ISGMR and the ISGDR modes in radioactive isotopes in inverse kinematics.

High-energy mechanical milling-induced crystallization in Fe32Ni52Zr3B13

Amorphous Fe32Ni52Zr3B13, prepared by rapid solidification, undergoes crystallization during high-energy mechanical milling. The resulting structure consists of face-centered cubic (fcc) FeNi and Zr3Ni20B6 nanocrystallites. Structural evolution and defect analysis of as-solidified Fe32Ni52Zr3B13 ribbons with different milling times is investigated. From the differential thermal analysis (DTA) curve of amorphous ribbons, exothermic peaks were observed at 415°C and 475°C corresponding to the crystallization of fcc Zr3Ni20B6 phase and fcc FeNi phase, respectively. However, high-energy mechanical milling induces the formation of FeNi within the first 2h of mechanical milling. Further milling induces the crystallization of Zr3Ni20B6. Doppler broadening positron annihilation spectroscopy (DBPAS) was used to investigate vacancy-type defects. The milling-induced crystallization appears to be related to enhanced vacancy-type defect concentrations allowing growth of pre-existing Fe(Ni) nuclei. The milling and enhanced vacancy concentration also de-stabilizes the glass, leading to decreased crystallization temperatures for both phases, and ultimately eliminating the glass transition altogether.

Triton/3He ratio as an observable for neutron-skin thickness

Based on the framework of the Isospin-Dependent Quantum Molecular Dynamics (IQMD) model in which the initial neutron and proton densities are sampled according to the droplet model, the correlation between triton-to-$^{3}$He yield ratio (R(t/$^{3}$He)$=$Yield(t)/Yield($^{3}$He)) and neutron skin thickness (${\delta}_{np}$) in neutron-rich projectile induced reactions is investigated. By changing the diffuseness parameter of neutron density distribution in the droplet model for the projectile to obtain different ${\delta}_{np}$, the relationship between ${\delta}_{np}$ and the corresponding R(t/$^{3}$He) in semi-peripheral collisions is obtained. The calculated results show that R(t/$^{3}$He) has a strong linear correlation with ${\delta}_{np}$ for neutron-rich $^{50}$Ca and $^{68}$Ni nuclei. It is suggested that R(t/$^{3}$He) could be regarded as a good experimental observable to extract ${\delta}_{np}$ for neutron-rich nuclei because the yields of charged particles triton and $^{3}$He can be measured quite precisely.

A specific chemical activation pretreatment for electroless nickel plating on SiC ceramic powders

The electroless pretreatment of SiC ceramic powders through a specific chemical activation pretreatment method and room temperature ultrasonic auxiliary chemical deposition method can result in Ni layers on the surface of SiC ceramic powder. The growth mechanism of Ni layers and the surface morphologies and composition of initial SiC powders, pretreated SiC powders, and Ni-coated SiC powders were analyzed by field emission scanning electron microscopy (FE-SEM) and energy dispersion spectrometry (EDS). The results show that the uniformly Ni-coated SiC composite powders are successfully synthesized without conventional sensitization and activation steps by ultrasonic-assisted electroless plating at room temperature. The Ni layers on the powders have cell structures with dense uniform distribution. The growth process of Ni is as follows: the reactants in the chemical deposition solution absorb near the surface defects of SiC powder and the particles of Ni stick to the nucleation of surface defects of SiC powder through redox reaction. The Ni nucleus grows in three-dimensional direction to form cellular ‘Ni’ particles that accumulate into a film. On the surface of the Ni layer film, the Ni layer grows by superposition type.

Analysis of elastic scattering of pi-mesons by nuclei within the microscopic optical potential

Cross sections of inelastic scattering of π-mesons from Si, Ni, and Pb nuclei at energy T lab = 291 MeV are calculated using the distorted wave approximation. The microscopic direct and transition optical potentials are determined by specifying the pion-nucleon scattering amplitude and the nuclear density distribution, where we use the in-medium πN amplitude parameters obtained earlier by analyzing the elastic scattering data for the same nuclei. The cross sections are calculated on the basis of the relativistic wave equation. The deformation parameters of the nuclei are obtained by comparing inelastic scattering cross sections with the appropriate experimental data.

Tensor Effects in Dipole Excitations at Finite Temperature

Tensor e ects in the dipole excitation of neutron-rich Ni nucleus are investigated in the framework of Skyrme Hartree Fock plus random phase approximation at nite temperature. We calculate isovector giant and pygmy dipole strengths with nite temperature random phase approximation by using di erent tensor correlations. The e ect of both tensor and nite temperature on the giant dipole resonance pygmy dipole resonance energy region is analysed. Pygmy dipole resonance calculations with di erent proton neutron tensor coupling constants are also compared with the experimental results.

Probing core polarization around78Ni: intermediate energy Coulomb excitation of74Ni

The study of the evolution of nuclear shells far from stability provides fundamental information about the shape and symmetry of the nuclear mean field. Nuclei with large neutron/proton ratio allow to probe the density dependence of the effective interaction. Indeed, it was recently shown that tensor and three-body forces play an important role in breaking and creating magic numbers. Of particular interest is the region of 78 Ni where the large neutron excess coincides with a double shell closure.We have recently measured the B(E 2; 0+ → 2+ ) of the 74 Ni nucleus in an intermediate-energy Coulomb excitation experiment performed at the National Superconducting Cyclotron Laboratory of the Michigan State University. The 74 Ni secondary beam has been produced by fragmentation of 86 Kr at 140 AMeV on a thick Be target. Selected radioactive fragments impinged on a secondary 197 Au target where the measurement of the emitted γ -rays allows to extract the Coulomb excitation cross section and related structure information. Preliminary B(E2) values do not point towards an enhancement of the transition matrix element and the comparison to what was already measured by Aoi and co-workers in [1] opens new scenarios in the interpretation of the shell evolution of the Z=28 isotopes.

Gamow-Teller decay population of64Ni levels in the decay of1+64Co

The ${}^{64}$Co $\ensuremath{\beta}$-decay feeding levels in the well-studied ${}^{64}$Ni nucleus were investigated. Whereas the previously known ${}^{64}$Co decay scheme merely contained 2 $\ensuremath{\gamma}$ rays, the decay scheme established in this work contains $18,$ of which 5 are observed in this work and 6 were previously observed in an ($n$,$\ensuremath{\gamma}$) study but not placed in the ${}^{64}$Ni level scheme. Surprisingly, one additional level---placed at an excitation energy of $3578.7$ keV---could be determined. The observed $\ensuremath{\beta}$-decay paths involve allowed $\ensuremath{\nu}{f}_{5/2}\ensuremath{\rightarrow}\ensuremath{\pi}{f}_{7/2}$ and $\ensuremath{\nu}{p}_{1/2}\ensuremath{\rightarrow}\ensuremath{\pi}{p}_{3/2}$ transitions. Three strongly fed levels around 4 MeV are interpreted to possess possible proton-intruder character.

Alpha Emission Spectra of 27Al, 50,52Cr, 55Mn, 54,56Fe, 58,60Ni Nucleus for Neutron Induced Reaction

The design of novel nuclear facilities, fusion as well as fission reactors, requires the knowledge of all properties of relevant materials, including the nuclear differential cross sections for a careful selection. The nuclear cross sections data for gas production via particle (neutron, proton, alpha, etc.) induced reactions are great importance in the domain in the fusion reactor technology, particularly in the calculation of nuclear transmutation rates, nuclear heating and radiation damage due to gas formation. In fusion reactor structures, a serious damage mechanism has been gas production in the metallic resulting from diverse nuclear reactions, mainly through (n, p) and (n, α), (n, d), (n, t). In the present study, by using equilibrium reaction mechanisms, the (n, xα) reaction alpha emission spectra for 27Al, 50,52Cr, 55Mn, 54,56Fe, 58,60Ni isotopes were investigated from 9 to 15 MeV incident neutron energy. The equilibrium results have been calculated by using the hybrid model, the geometry dependent hybrid model. Calculation results have been also compared with the available measurements in literature.

Relaxation and modulation interference effects in two-pulse electron spin echo envelope modulation (ESEEM)

Two-pulse electron spin echo envelope modulation (ESEEM) line widths are influenced by transverse electron spin relaxation, which is in turn induced by local field fluctuations. Simultaneous analysis of the decays of the unmodulated and modulated parts of the ESEEM signal provides deeper insight into the relaxation of a spin system consisting of an electron spin 1/2 coupled to NI nuclei with spin 1/2. Standard two-pulse ESEEM formulas either do not account for relaxation or assume uniform relaxation for all lines. In general, the relaxation rates on allowed and forbidden transitions may not be the same. Experimental results obtained on a single crystal of Cu(II)-doped l-histidine suggest that such a difference exists. Theoretical considerations show that in such a case the product rule for two-pulse ESEEM does not extend to expressions including relaxation. Product rules in general do not properly account for relaxation in three-pulse ESEEM and HYSCORE experiments. Decay of the apparently non-oscillatory part of the two-pulse echo may be strongly affected by modulation interference. Such interference of difference frequencies of matrix nuclei may cause a rather flat initial feature, which was previously attributed solely to non-exponential phase relaxation of electron spin transitions due to spin diffusion of the matrix nuclei. In addition, the sometimes observed drastic initial decay of the time domain signal is related to modulation interference of multiple-quantum coherences that arise from a strong cross-suppression effect.

Ground-state properties of closed-shell nucleus 56Ni with realistic nucleon–nucleon interactions

We have calculated the ground-state energy of the doubly magic nucleus 56Ni within the framework of the Green’s function using the CD-Bonn and N3LO nucleon–nucleon potentials. For the sake of comparison, the same calculations are performed using the Brueckner–Hartree–Fock approximation. Both the continuous and conventional choices of single particle energies are used. Additional binding energy is obtained from the inclusion of the hole–hole scattering term within the framework of the Green function approach. In this study, comparison of the calculated ground-state energies, obtained by using the Brueckner–Hartree–Fock approach using continuous choice and different nucleon–nucleon potentials, with the experimental value is accomplished. The results show good agreement between the calculated values and the experimental one for the 56Ni nucleus. The sensitivity of our results to the choice of the model space is examined.

An update of the B(E2) evaluation for [formula omitted] transitions in even–even nuclei near [formula omitted

An update of the B(E2)↑ evaluation for even–even Cr, Fe, Ni, and Zn nuclei is presented. It is a continuation of work by Raman et al. on B(E2)↑ values and was motivated by a large number of new measurements. It extends the previous evaluation from 20 to 38 nuclei and includes a comprehensive shell-model analysis. Evaluation policies for the analysis of experimental data are discussed. Future plans for a complete B(E2)↑ evaluation of even–even nuclei are outlined.

The systematic study of the influence of neutron excess on the fusion cross-sections using different proximity-type potentials

Using different types of proximity potentials, we have examined the trend of variations of barrier characteristics (barrier height and its position) as well as fusion cross sections for 50 isotopic systems including various collisions of C, O, Mg, Si, S, Ca, Ar, Ti and Ni nuclei with $1\leq N/Z < 1.6$ condition for compound systems. The results of our studies reveal that the relationships between increase of barrier positions and decrease of barrier heights are both linear with increase of $N/Z$ ratio. Moreover, fusion cross sections also enhance linearly with increase of this ratio.

Recent experimental results on level densities for compound reaction calculations

Proton evaporation spectra from 6,7 Li induced reactions on 54,56,58 Fe nuclei have been measured and analyzed with Hauser-Feshbach compound reaction calculations with a Gilbert and Cameron input level density model. Level densities of residual 59 64 Ni nuclei have been extracted from proton spectra. Both level density and level density pa- rameter a have been compared against the respective values obtained from neutron res- onance spacing data. The discrepancy has been found in systematics behavior of level densities against the mass number of Ni isotopes.

Shape phase transition in neutron-rich even-even light nuclei with Z = 20–28

The E-Gamma Over Spin (E-GOS) analysis method is applied to the study of the shape phase transition of neutron-rich even-even light nuclei with Z = 20–28. Some valuable results are gained through analysing E-GOS curves of Ca, Ti, Cr, Fe and Ni nuclei.

Surface properties of neutron-rich exotic nuclei: A source for studying the nuclear symmetry energy

We study the correlation between the thickness of the neutron skin in finite nuclei and the nuclear symmetry energy for isotopic chains of even-even Ni, Sn, and Pb nuclei in the framework of the deformed self-consistent mean-field Skyrme HF + BCS method. The symmetry energy, the neutron pressure, and the asymmetric compressibility in finite nuclei are calculated within the coherent density fluctuation model using the symmetry energy as a function of density within the Brueckner energy density functional. The mass dependence of the nuclear symmetry energy and the neutron-skin thickness are also studied together with the role of the neutron-proton asymmetry. A correlation between the parameters of the equation of state (symmetry energy and its density slope) and the neutron skin is suggested in the isotopic chains of Ni, Sn, and Pb nuclei.

Clusterization in the shape isomers of the56Ni nucleus

The interrelation of the quadrupole deformation and clusterization is investigated in the example of the ${}^{56}$Ni nucleus. The shape isomers, including superdeformed and hyperdeformed states, are obtained as stability regions of the quasidynamical U(3) symmetry based on a Nilsson calculation. Their possible binary clusterizations are investigated by considering both the consequences of the Pauli exclusion principle and the energetic preference.

Urea-Melt Assisted Synthesis of Ni/NiO Nanoparticles Exhibiting Structural Disorder and Exchange Bias

An easy, inexpensive urea-melt assisted route was designed for the synthesis of ∼10 nm-sized Ni/NiO nanoparticles (NPs). The method consists of the thermal decomposition of a urea-melted medium containing a Ni2+-salt and involves the olygomerization and self-combustion of the organic matrix and the formation of the Ni/NiO NPs within it in a two stepped process of Ni2+ reduction yielding Ni crystallization and subsequent inward oxidation. Control over the microstructural features of the NPs within three typical regimes was accomplished by means of the initial urea quantity. Type A samples (0.2 g urea/0.2908 g nickel nitrate) consists of NiO nanostructures which might contain dispersed Ni nuclei of a few atoms; B NPs (2 g urea/0.2908 g nickel nitrate) are made of proper small Ni cores, in the limit of the coherence length of XRD, surrounded by thick NiO shells, while C (20 g urea/0.2908 g nickel nitrate) NPs correspond to relative big Ni cores and thin NiO shells. Further control over the thickness of the N...

Fabrication of micro-Ni arrays by electroless and electrochemical depositions with etched porous aluminum template

Nickel micro-arrays were fabricated by electroless and electrochemical deposition in an etched porous aluminum membrane. The aluminum membrane with metal characteristic could be fabricated from high-purity aluminium by electrochemical method. The aluminum reduced Ni2+ into Ni and the formed Ni nuclei served as the catalyst for further reduction of Ni2+ in electroless solution. With the help of the membrane, nickel micro-columns of about 1–2 μm diameter were obtained. The surface-deposited nickel layer served as a substrate for the nickel micro-columns, and the resulting material possessed strong mechanical strength. Electrochemical deposition was operated without preparing a conductive layer on the template due to the conductivity of the aluminum membrane. Nickel micro-tubes with an outer diameter of about 1–2 μm and a wall thickness in the order of tens of nm were obtained. The nickel micro-arrays were characterized by scanning electron microscope (SEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS).

Low-energy (p,γ) reactions in Ni and Cu nuclei using a microscopic optical model

Radiative capture reactions for low energy protons have been theoretically studied for Ni and Cu isotopes using the microscopic optical model. The optical potential has been obtained in the folding model using different microscopic interactions with the nuclear densities from Relativistic Mean Field calculations. The calculated total cross sections as well as the cross sections for individually low lying levels have been compared with measurements involving stable nuclear targets. Rates for the rapid proton capture process have been evaluated for astrophysically important reactions.