Protons In Copper Research Articles

Organocopper(III) Phenanthriporphyrin-Exocyclic Transformations.

5,6-Dimethoxyphenanthriporphyrin 1 and 5,6-dioxophenanthriporphyrin 2 act as suitable organometallic ligands for copper(III), adopting trianionic [CCNN] coordination cores. Under oxidizing conditions, in the presence of methanol, copper(III) phenanthriporphyrin 1-Cu undergoes transformation to copper(III) phenanthriporphodimethene with methoxy substituents attached to two trans meso positions. Addition of acids to 1-Cu yields two isomeric copper(III) isophenanthriporphyrins protonated on one of the meso carbon atoms. Protonation of copper(III) 5,6-dioxophenanthriporphyrin 2-Cu yields the aromatic diprotonated complex 2-Cu-H22+. In the presence of HBF4 2-Cu undergoes borylation at the carbonyl oxygen atoms, forming an aromatic exocyclic boron(III) complex.

Electronic band structure effects in the stopping of protons in copper

We present an ab initio study of the electronic stopping power of protons in copper over a wide range of proton velocities $v = 0.02-10~\mathrm{a.u.}$ where we take into account non-linear effects. Time-dependent density functional theory coupled with molecular dynamics is used to study electronic excitations produced by energetic protons. A plane-wave pseudopotential scheme is employed to solve the time-dependent Kohn-Sham equations for a moving ion in a periodic crystal. The electronic excitations and the band structure determine the stopping power of the material and alter the interatomic forces for both channeling and off-channeling trajectories. Our off-channeling results are in quantitative agreement with experiments, and at low velocity they unveil a crossover region of superlinear velocity dependence (with a power of $\sim 1.5$) in the velocity range $v = 0.07-0.3~\mathrm{a.u.}$, which we associate to the copper crystalline electronic band structure. The results are rationalized by simple band models connecting two separate regimes. We find that the limit of electronic stopping $v\to 0$ is not as simple as phenomenological models suggest and it plagued by band-structure effects.

Experimental evaluation of the nuclide production cross sections for 50-GeV protons in copper

A thin target composed of copper and aluminum foils was placed in the accelerator vacuum tube and irradiated with circulating 50-GeV protons. The number of protons that hit the target during the accelerator run was determined by the activation of the monitor aluminum foil, and the radionuclide activities in each foil were measured. A set of the radionuclide production cross sections in 50-GeV proton interactions with copper nuclei were evaluated.

Proton-transfer reactions of copper(II)- and nickel(II) tetrapeptide complexes with bulky α-carbon substituents

Protonation of copper(II)- and nickel(II) tetrapeptide complexes with bulky α-carbon substituents has been studied. The pKa-values for the second and terminal metal–N(peptide) bond formation have been determined spectrophotometrically. More than one deprotonated peptide nitrogen exists in a complex but the individual protonation steps for the different CuII–N(tetrapeptide) positions could not be accounted for by the variation of the hydrogen ion concentration in the same experiment, as the protonation of the different metal–N(tetrapeptide) positions takes place at different wavelengths. For the NiII-tetra-alanine complex, the proton transfer to the terminal and second deprotonated peptide nitrogens have been detected by varying the hydrogen ion at the same wavelength. The proton transfer to the terminal metal–N(tetrapeptide) of CuII- and NiII-tetrapeptide complexes show first order kinetics with respect to the hydrogen ion and the peptide complex concentration and proceed via an outside protonation pathway. The relatively high pKa values for the terminal deprotonated peptide nitrogen indicate the instability of this metal–N(peptide) bond due to strain in the chelate ring because of atom overcrowding of the bulky α-carbon substituents.

Multiple-scattering distributions and angular dependence of the energy loss of slow protons in copper and silver

Measurements of angular distributions and of the angular dependence of the energy loss of 4-, 6-, and 9-keV protons transmitted through thin Cu and Ag polycrystalline foils are presented. By means of standard multiple-scattering model calculations it is found that a V(r){proportional_to}r{sup -2.8} potential leads to significantly better fits of the angular distributions than the standard Thomas Fermi, Lenz-Jensen, or Ziegler-Biersack-Littmark potentials. A theoretical model for the angular dependence of the energy loss based on considering geometric effects on a frictional inelastic energy loss plus an angular-dependent elastic contribution and the effects of foil roughness reproduces the experimental data. This agrees with previous results in Au and Al, therefore extending the applicability of the model to other metallic elements.

Elastic Scattering of Low-Energy Electrons, Positrons and Protons in Copper

Total cross section (TCS) and differential cross section (DCS) are calculated using the partial wave method for the elastic scattering of 0.1 eV-1 keV electrons, positrons and protons in solid copper. At low energies, because of the cancellation of the electrostatic potential by the polarization of a copper atom bound in the solid and the absence of an exchange effect, the TCS for positrons is much smaller than that for electrons, whereas the TCSs for positrons and for electrons are comparable at the highest energy (1 keV). The DCS for electrons shows oscillatory behavior, and the DCS for positrons is smooth, the minimum being found at the forward direction. The DCS for protons dramatically increases for very small scattering angles near zero degrees, whereas the DCS is equal to that of positrons for angles larger than 30°(>10 eV).

Dispersoid stability in a Cu-Al 2O 3 alloy under energetic cascade damage conditions

A commercial dispersion-strengthened Cu-Al 2O 3 alloy was irradiated with 750-MeV protons at 470 K to a damage level of about 2 displacements per atom (dpa). The density and size distribution of the Al 2O 3 particles was measured in nonirradiated and irradiated specimens using transmission electron microscopy. The mean primary knock-on atom (PKA) energy for 750-MeV protons in copper is 2.5 MeV, which is about 10 and 100 times higher than the average PKA energies in copper for fusion and fission neutrons, respectively. The irradiation caused only a slight decrease in the mean Al 2O 3 size, from 10.5 nm to 8.3 nm, and a slight decrease in the particle density from 4 × 10 22 / m 3 to 3 × 10 22/ m 3.

Production cross section of radionuclides in (p, x) reactions at copper and nickel nuclei

The authors measured the cross sections of the production of radionuclides by 10-100-MeV protons in copper and nickel targets of the natural isotope composition. The currently available data on these target nuclei are basically limited to a proton energy of approx. 50 MeV and some of the information is even inconsistent. The experiment was made on the linear injector of the Institute of High-Energy Physics. The targets were irradiated with the extracted proton beam of the linear injector with a beam current of 97 mA, a current-pulse duration of 57 ..mu..sec, and a pulse-repetition frequency of 0.25 Hz. In order to calculate the proton energy after the passage through a stack of foils, data on the stopping power and the ranges of protons in aluminium were used. The proton flux was monitored via the nuclear reactions /sup 65/Cu(p,n)/sup 65/Zn in the proton energy range 10-40 MeV and /sup 27/Al(p,x)/sup 24/Na in the proton energy range 40-100 MeV.

Measurement of the stopping cross section for protons in copper by backscattering using various methods for foil-thickness determination

Copper films evaporated on pyrolitic carbon are used to determine the stopping cross section of copper for protons in the energy range from 60 to 500 keV by evaluating the energy width of Rutherford backscattering (RBS)-spectra. For this purpose we need both the number of atoms per unit area of the copper-foils and the spectrum widths. The number of atoms per unit area is determined for all copper films by a quartz-thickness monitor during evaporation, by weighing on a microbalance and by RBS, where a reference target of known thickness has been used to obtain absolute values without the input of stopping cross section data. The results of the quartz monitor and of RBS always agree within 2%, they agree with the results obtained by weighing within a mean relative error of less than 6% for each target. From the width of the RBS-spectra the stopping cross section is extracted by an iteration procedure which starts with Warters' approximation [1] and afterwards corrects for the small systematic errors arising there. The resulting stopping cross section data lead to a maximum at 125 keV. They are in excellent agreement with the data of Luomajärvi [2] and in fair agreement with the data of Mertens and Krist [3], In comparison with the Andersen and Ziegler curve, our data are lower in the whole energy range.

Activation energy of protons in copper

The movement of protons in copper is studied using Ashcroft model potential and modified Hartree dielectric function. Octahedral position is found to be more favourable. The calculated activation energy is in good agreement with experiment for 0.31 e effective charge of the proton.