Evaporation residue cross sections from the fusion of52Cr+110Pd

Evaporation residue cross sections for the fusion of⁵²Cr and¹¹⁰Pd were studied at four energies close to the barrier (up toE _CM ?E _B =26 MeV). The cross sections were analysed using a multiple-chance fission/evaporation calculation. Agreement with the data is obtained with a fission barrier reduced by 40 to 20%, depending on incident energy.     

Measurements of evaporation residues and fission for 40Ar + 110Pd

Fusion cross sections for the reaction ⁴⁰Ar + ¹¹⁰Pd have been measured in the bombarding energy range 164–262 MeV. Evaporation residues and fission fragments have been detected by ΔE-E telescopes. We compare the fusion cross sections to various theoretical models with special attention to the high-energy data. An analysis is also given for entrance-channel spin zones for evaporation residues and fission.     

Levels in 110Pd, 112Pd, 114Pd and 116Pd from the beta decays of the on-line mass separated Rh isotopes

The energy levels of even ^110–116pd nuclei have been studied from β-decays of odd-odd ^110–116Rh isotopes produced at the on-line isotope separator IGISOL. Two β-decaying states with I^π = 1⁺ and I ⩾4 have been identified in all the cases. New level schemes with preliminary spin assignments have been constructed for ¹¹²Pd, ¹¹⁴Pd and ¹¹⁶Pd. Similarities with the level structures of their Xe isotones have been pointed out.     

Measurement of the mass of110Pd and114Pd using the (14C,16O) reaction

A measurement of the mass excess of¹¹⁰Pd and¹¹⁴Pd has been made by detecting emergent¹⁶O ions in aQ3D magnetic spectrometer using the¹¹²Cd(¹⁴C,¹⁶O)¹¹⁰Pd and¹¹⁶Cd(¹⁴C,¹⁶O)¹¹⁴Pd reactions at 60 MeV. The results are compared with theoretical predictions.     

Absolute coverages for the various surface phases of CO and O adsorbed on Pd(110)

The absolute surface coverages of CO and O on Pd(110) have been measured by nuclear reaction analysis (NRA) using the ¹²C(d, p)¹³C and ¹⁶O(d, p₁)¹⁷O¹ reactions. The CO coverages of the (2 × 1) and (4 × 2) phases of CO on Pd(110) are 1.00 ±0.05 and 0.73 ±0.05 ML (1 ML = 1 monolayer = 9.4 × 10¹⁴ CO molecules cm⁻²) respectively. The oxygen coverage in the c(4 × 2) phase of O on Pd(110) is 0.50 ±0.05 ML.     

Isomeric cross section ratio for110Pd(n,2n)109Pd reaction at 14.7 MeV

Reaction¹¹⁰Pd(n, 2n)¹⁰⁹Pd has been investigated at 14.7 MeV neutrons. Cross sections for the formation of^109m Pd and^109g Pd were measured. Experimental value of the isomeric cross section ratio has been compared with the theoretical calculation performed with the Huizenga and Vandenbosch method.     

Fractional-order desorption of D2 from a Pd(110) surface

The desorption of deuterium from the low temperature (α₂) state on a Pd(110) surface was studied by TDS, LEED and Δφ. Simultaneous measurements of the isothermal desorption of the α₂ state, intensity of a half-order beam of the (1 × 2) phase and work function change show clearly that the desorption of this low temperature state is associated with the phase transition (1 × 2) to (2 × 1). This transition correlation with a work function change of ∼ 70 mV. The desorption follows nearly zero-order kinetics with an activation energy of ∼ 71 kJ mol⁻¹. The desorption kinetics are thus closely analogous to those on Ni(110).     

Electron spectroscopy of surfaces by impact of metastable He atoms: CO on Pd(110)

Deexcitation of metastable He1 2¹S (excitation energy E1 = 20.6 eV) or 2³S (E* =19.8 eV) atoms at a clean Pd(110) surface proceeds through a two-stage process (resonance ionization + Auger neutralization, RI + AN). The measured electron energy distribution reflects the self-convolution of the local density of states of the outmost atomic layer. A CO adlayer suppresses the RI step and the spectra are caused by Auger deexcitation (Penning ionization). Comparison with corresponding UPS data allows identification of the valence orbitals of the adsorbate. Emission up to the Fermi level is ascribed to contributions from the 5σ level. The effectively available excitation energy in front of the adlayer is lowered by 0.5 eV. Extensive data on the variation of the intensities from the adsorbate valence levels with angle of incidence as well as of emission are presented and are analyzed in terms of an empirical model.     

High-spin states in112Cd from the110Pd(α, 2n γ)-reaction

The decay scheme of¹¹²Cd has been studied by γ-ray spectroscopy with the¹¹⁰Pd(α, 2nγ) reaction. Spin and parity assignments were made on the basis of coincidence measurements, angular distributions and excitation functions. Twelve new energy levels were established. A vibrational-like positive-parity band up to spin 8⁺ and a negativeparity side band 5^?, (7^?), (9^?) were found. For the negative-parity states a (v_j, vh_11/2) configuration is suggested. Nuclear Reactions:¹¹⁰Pd(α,2nγ),E _α =15–22.5 MeV; measuredE _γ ,E _γ , (E,E _γ ),E _γ (θ),γ-γ- coincidence;¹¹²Cd deduced levels,J; enriched target.     

The low-lying quadrupole collective excitations of Ru and Pd isotopes

Quadrupole excitations of even-even Ru and Pd isotopes are described within a microscopic approach based on the general collective Bohr model which includes the effect of coupling with the pairing vibrations. The excitation energies and E2 transition probabilities observed in ^104–114Ru and ^106–110Pd are reproduced in the frame of the calculation containing no free parameters. Particularly interesting are ¹⁰⁴Ru and ^106–110Pd where good agreement to very rich information based on Coulomb excitation experiments is achieved.     

MgH2(110)表面Pd单原子催化氢脱附反应的第一性原理研究

本文采用第一性原理密度泛函理论计算研究了MgH₂(110)表面吸附单原子Pd后的氢脱附反应. 计算发现,在吸附一个Pd单原子后,MgH₂(110)表面氢脱附反应的能垒可以从1.802 eV显著地降低到1.154 eV,表明Pd单原子对于氢脱附具有很强的催化效应. 并且,Pd单原子催化还可以将氢脱附的温度从573 K显著地降低到了367 K,从而使MgH₂(110)表面的氢脱附反应更加容易和快速地发生. 此外,通过MgH₂(110)表面氢溢出机制的反向过程来讨论了氢脱附反应的微观过程. 该研究表明Pd/MgH₂薄膜在未来的实验中可作为良好的储氢材料.     

A procedure for clean deposition of100Pd on surfaces

For a program of surface and interface experiments with the PAC isotope¹⁰⁰Pd, a procedure has been developed to chemically separate¹⁰⁰Pd from irradiated rhodium and deposit it on surfaces by evaporation under UHV conditions. First results have been obtained for¹⁰⁰Pd on an Ni(111) surface.     

Search for ferromagnetic ordering in Pd doped wide band gap semiconductors GaN and ZnO

GaN and ZnO are possible candidates for dilute magnetic semiconductors with Curie temperatures above room temperature. Doping with transition metals like Co, Mn or Fe could be a simple way to create such systems. The perturbed angular correlation (PAC) probe ¹⁰⁰Pd/¹⁰⁰Rh is isoelectronic to cobalt and therefore a perfect tool to investigate the incorporation of transition metals into these compounds as well as the influence of other impurities on internal magnetic fields. The (0001) and (10 $\bar{1}$ 10) surfaces of ZnO single crystals, freestanding GaN films, and GaN thin films (6 μm) on sapphire substrates were recoil-implanted with the ¹⁰⁰Pd/¹⁰⁰Rh probe. The probe was produced using the fusion evaporation reaction ⁹²Zr(¹²C, 4n)¹⁰⁰Pd at a beam energy of 69 MeV. Subsequently, the incorporation of the probe was studied by PAC spectroscopy during an isochronal annealing program. First results without and with an applied external magnetic field are indicative of a strongly disturbed lattice vicinity of Pd impurities in both hosts. No signs of spontaneous ferromagnetic ordering were observed.     

Cross section of metastable state population in the photoneutron decay of the E1 giant resonance for 110Pd, 112Cd, and 113In nuclei

The cross sections of isomeric state excitation in the ¹¹⁰Pd(γ, n)^109m Pd, ¹¹²Cd(γ, n)^111m Cd, and ¹¹³In(γ, n)^112m In reactions have been investigated. The measurements were performed in the γ-ray energy range 9–18 MeV with a step ΔE = 0.5 MeV. The dependences of the isomeric ratios on the γ-ray energy are obtained. The experimental data are compared with the results of calculations within the cascade-evaporation model.     

Investigation of the fusion of heavy nearly symmetric systems

Excitation functions in the vicinity of the Coulomb barrier have been measured for the formation of evaporation residues in¹⁰⁰Mo-induced fusion reactions with^{90, 92, 96}Zr,^{92, 96, 98, 100}Mo,¹⁰⁴Ru and¹¹⁰Pd as well as for the system⁹⁶Zr+⁹⁶Zr. From these data the fusion probability in central collisions was extracted covering a range of 4 orders of magnitude. At the fusion barriers expected from systematics we find that the fusion probability is suppressed by one to three orders of magnitude. It is rising very gradually at higher energies and reaches for the heaviest systems saturation only at energies as high as 30 MeV above the barrier. The observed hindrance of the fusion process increases roughly with the growing Coulomb repulsion between the collision partners, but there is also a distinct influence of their individual nuclear structure. The data are compared to the extra-push model, the surface-friction model and the diabatic fusion model. A parameterisation of the extra-push energy and its fluctuation in terms of a macroscopic quantity like the Coulomb repulsion combined with a microscopic quantity characterizing the nuclear structure is proposed. As a byproduct of this work a new alpha emitter,¹⁹¹Po, could be identified. Its half-life is (15.5 _–2.5 ⁺⁶ ) ms, the alpha energy is (7314±20) keV.     

Allowance for the shell structure of the 42100 Mo and 46110 Pd nuclei in the synthesis of 84200 Po, 88210 Ra, and 92220 U

The effect of the shell structure of colliding nuclei in calculating the entrance channel on the ensuing evolution of the product system is investigated. The entrance channel is calculated under the assumption of the nose-to-nose orientation of colliding nuclei. The following three reactions involving nuclei that are deformed in the ground state are considered: ₄₂¹⁰⁰Mo + ₄₂¹⁰⁰Mo → ₈₄¹⁰⁰Po, ₄₂¹⁰⁰Mo + ₄₆¹⁰⁰Pd → ₈₈²¹⁰Ra, and ₄₆¹¹⁰Pd + ₄₆¹¹⁰Pd → ₉₂²²⁰U. The state of the system at the point of touching is determined by the results obtained by calculating the entrance reaction channel. The shape of the system is specified by three collective coordinates (deformation parameters). The evolution of collective coordinates of the system is described in terms of Langevin equations. The potential energy of the system of colliding nuclei is calculated with allowance for their shell structure. It is shown that allowance for individual features of interacting nuclei in the entrance channel of the fusion-fission reactions makes it possible to obtain, for the reactions being considered, cross sections for evaporation-residue formation that are closer to available experimental data than their liquid-drop counterparts.     

“Forking” of ground state bands in 102Pd and 100Pd

A new phenomenon is observed in the level schemes of ¹⁰²Pd and ¹⁰⁰Pd, populated by heavy ion induced reactions: the ground state bands of these nuclei reach J = 14, but “fork” into two branches, at the 8+ state in ¹⁰²Pd and at the 6+ state in ¹⁰⁰Pd. A ground state band in the near-magic nucleus ⁹⁸Pd, whose level energies were previously unknown, was populated to J = 8.     

Mechanism of formation and decay of the compound nuclei150Gd produced by two entrance channels (16O+134Ba) and (40Ar+110Pd)

Excitation functions have been drawn for evaporation residues issued from¹⁵⁰Gd, a compound nucleus produced either by¹⁶O ions on¹³⁴Ba, or by⁴⁰Ar on¹¹⁰Pd. Absolute cross sections were measured for^145–147Gd,^145–147Eu,^141m Sm,^143m Sm,^140m Pm and^139m Nd. Complete fusion cross sections have been obtained and compared to calculated estimations based, at low energies, on the simple expressionσ _CF=πR _Fuss ² (1?V _Fus/E) whereR _Fus andV _Fus are respectively the distance and the potential for fusion atdV/dr=0. For high energies σ_CF=πR _cr ² (1?V_cr/E) with the model of critical distanceR _cr and critical potentialV _cr. Thresholds energies have been determined with a particular care. The analysis of the shape and the width of excitation functions, particularly for the emission of 4 and 5 neutrons, has been carried out and compared to calculated values. The difference between argon and oxygen induced reactions has been attributed to the difference inl population in the entrance channel.     

The preparation, characterisation and oxygen adsorption on Ir/Pd(110) alloys

Ir-Pd alloys were formed on Pd(110) by evaporation of Ir and subsequent heating in vacuo. Ir overlayers were stable up to 600 K. At higher temperatures Pd diffusion to the surface occurred, which resulted in a Pd-dominated surface over a range of Ir coverages. The transformation of the surface initially dominated by Ir to one where a more homogeneous distribution of the two metals was obtained was probed with angle-resolved XPS. This showed that above 600 K a rapid loss of Ir from the surface region took place, which was followed by a slower loss at higher temperatures. Mixed surface layers could thus be formed which varied in composition depending on the initial amounts of Ir deposited. At low Ir coverages, these surfaces showed an oxygen adsorption behaviour resembling that of Pd(110) in terms of desorption temperatures, but with an increased amount of oxygen desorbing from subsurface sites.     

g-factor experiments on the first excited 2 states in Ru,Pd and Cd

The g-factors of the first 2⁺ levels in ¹⁰²Ru, ¹⁰⁶Pd and ¹¹⁰Cd have been remeasured with increased accuracy, using the perturbed angular correlation method and the radio-active mother isotopes dissolved in ferromagnetic lattices. The results are g = ± 0.408 + 0.034, g = + 0.399 ± 0.029 and g = + 0.35 ± 0.07 respectively. Possible sources of error in the use of internal fields are discussed.