Proton Charge Density Research Articles

Determination of the moments of the proton charge density

Determination of the moments of the proton charge density

Impact of secondary particles on the magnetic field generated by a proton pencil beam: a finite-element analysis based on Geant4-DNA simulations.

To investigate the static magnetic field generated by a proton pencil beam as a candidate for range verification by means of Monte Carlo simulations, thereby improving upon existing analytical calculations. We focus on the impact of statistical current fluctuations and secondary protons and electrons. We considered a pulsed beam (10 s pulse duration) during the duty cycle with a peak beam current of 0.2 A and an initial energy of 100MeV. We ran Geant4-DNA Monte Carlo simulations of a proton pencil beam in water and extracted independent particle phase spaces. We calculated longitudinal and radial current density of protons and electrons, serving as an input for a magnetic field estimation based on a finite element analysis in a cylindrical geometry. We made sure to allow for non-solenoidal current densities as is the case of a stopping proton beam. The rising proton charge density toward the range is not perturbed by energy straggling and only lowered through nuclear reactions by up to 15%, leading to an approximately constant longitudinal current. Their relative low density however (at most 0.37 protons/mm3 for the 0.2 A current and a beam cross-sectionof 2.5mm), gives rise to considerable current density fluctuations. The radial proton current resulting from lateral scattering and being two orders of magnitude weaker than the longitudinal current is subject to even stronger fluctuations. Secondary electrons with energies above 10eV, that far outnumber the primary protons, reduce the primary proton current by only 10% due to their largely isotropic flow. A small fraction of electrons (<1%), undergoing head-on collisions, constitutes the relevant electron current. In the far-field, both contributions to the magnetic field strength (longitudinal and lateral) are independent of the beam spot size. We also find that the nuclear reaction-related losses cause a shift of 1.3mm to the magnetic field profile relative to the actual range, which is further enlarged to 2.4mm by the electron current (at a distance of mm away from the central beam axis). For mm, the shift increases linearly. While the current density variations cause significant magnetic field uncertainty close to the central beam axis with a relative standard deviation (RSD) close to 100%, they average out at a distance of 10cm, where the RSD of the total magnetic field drops below 2%. With the small influence of the secondary electrons together with the low RSD, our analysis encourages an experimental detection of the magnetic field through sensitive instrumentation, such as optical magnetometry orSQUIDs.

Comparing a Local Potential with a Non-Local Potential for the Bound States of ^(16)O and ^(40)Ca

Using the non-local nuclear potentials, we calculate the binding energies and radial wave functions of a single particle, and the proton charge density for ^(16)O and ^(40)Ca nuclei. In order to obtain them, we use a matrix equation method generated from the integral form of the Schrodinger equation and find the best parameter set, which includes the potential depth, diffuseness, radius, and non-local parameter, by fitting the experimental data. The proton charge densities for the non-local potential are repulsive in comparison with those for the local potential. It is also found that the radius of the non-local potential is greater than that of the local one due to the non-local parameter (β). In addition, using the trivially equivalent local potential (TELP) method, we compare the local potentials with the non-local potentials and then find that the non-local potentials are repulsive.

Troubles with the Proton rms-Radius

Due to the peculiar shape of the proton charge density ρ(r) the value of the rms-radius r rms determined from electron scattering data depends strongly on the density ρ(r) at large radii, which is not fixed by scattering data. Supplementing the data with the large-r shape of ρ(r) resulting from the Fock components (n + π, . . .) dominating the large-r behavior produces a more reliable value. This radius agrees with the one we previously extracted, but disagrees with the one recently obtained from muonic Hydrogen. The origin of the discrepancy is not understood.

The electric charge and magnetisation distribution of the nucleon: evidence of a subatomic Turing wave pattern

Subquantum kinetics, a physics methodology that applies general systems theoretic concepts to the field of microphysics has gained the status of being a viable unified field theory. Earlier publications of this theory had proposed that a subatomic particle should consist of an electrostatic field that has the form of a radial Turing wave pattern whose form is maintained through the ongoing activity of a non-linear reaction–diffusion medium that fills all space. This subatomic Turing wave prediction now finds confirmation in recent nucleon scattering form factor data which show that the nucleon core has a Gaussian charge density distribution with a peripheral periodicity whose wavelength approximates the particle's Compton wavelength and which declines in amplitude with increasing radial distance. The subquantum kinetics explanation for the origin of charge correctly anticipates the observation that the proton's charge density wave pattern is positively biased while the neutron's is not. The phenomenon of beta decay is interpreted as the onset of a secondary bifurcation leading from the uncharged neutron solution to the charged proton solution. The Turing wave dissipative structure prediction is able to account in a unitary fashion for nuclear binding, particle diffraction, and electron orbital quantisation. The wave packet model is shown to be fundamentally flawed implying that quantum mechanics, although mathematically workable, does not realistically represent the microphysical world. This new conception points to the possible existence of orbital energy states below the Balmer ground state whose transitions may be tapped as a new source of energy.

Importance of surface charge characteristics when selecting soils for wastewater re-use

Land application represents a viable option in the management of wastewater such as landfill leachate. The surface charge and ion adsorption characteristics of the receiving soil will play an important role in the success of this disposal strategy. The surface charge characteristics of 6 soils with contrasting chemical and physical properties were studied using charge balance principles. The point of zero net proton charge density, point of zero salt effect and point of zero net charge, and the concentrations of permanent and variable charge as a function of pH, were determined for each soil. The presence and magnitude of permanent negative surface charge was largely dependant on clay mineralogy. All soils displayed increasing negative surface charge density with increasing pH. The magnitude of increase for any particular soil was dependent on the type and amount of colloids exhibiting variable surface charge. The increased negative surface charge was attributed to the ionisation of functional groups on organic matter, hydrous Fe and Al oxides, and edge sites of kaolinite and smectite. The variation in surface charge with pH conformed to charge balance principles for soils containing a mixture of both permanent and variable surface charge, but not for soils containing predominantly permanent surface charge. Proton-consuming processes (e.g. adsorption on permanent charge sites, neutralisation of inherent alkalinity) influenced the overall charge balance, particularly for soils with predominantly permanent surface charge. Ammonium adsorption from landfill leachate was measured as a function of pH for each soil type. Increased negative surface charge resulted in increased ammonium adsorption, and for most soils the preference of the newly created adsorption sites for ammonium remained relatively constant. Since many soils contain a mixture of colloids with permanent and variable surface charge, these charge characteristics and their effect on individual soil properties, contaminant availability, and contaminant mobility must be taken into account when evaluating the suitability of land for wastewater re-use.

Solid state NMR investigation of hydrous ruthenium oxide

Amorphous hydrous ruthenium oxide (RuO 2· xH 2O) with different composition x has been studied using solid-state nuclear magnetic resonance (NMR) spectroscopy. The 2 D NMR spectra at different temperatures illustrate that the water molecules undergo fast molecular motion even if the temperature is as low as 213 K. The static 1 H NMR spectra indicate the composition dependent proton–proton dipolar interaction. It is demonstrated that the mobility of the water molecules and their interaction with ruthenium oxides play an important role in the proton charge density. In conclusion, the competition between these two antithetical effects provides a mechanism for the proton charge storage of the RuO 2· xH 2O materials.

Adsorption of polyelectrolytes onto oxides — the influence of ionic strength, molar mass, and Ca 2+ ions

The paper presents results concerning the adsorbate structure and the adsorption mechanism of polyelectrolytes (polyacrylic acid, polymethacrylic acid and humic acid) onto the oxides gibbsite, goethite and alumina. The investigations deal with the influence of different parameters such as ionic strength, divalent cations and molar mass of the polyacids. The observed adsorption isotherms of every polyacid all show the same high affinity type typical of polymer adsorption. The maximum adsorbed amount is correlated linearly with the proton charge density σ H of the oxides at low ionic strength of 0.01 M NaCl. During the adsorption process the surface charge of the oxides turns from positive to negative. An increase in the ionic strength or the addition of divalent cations causes an increase of the maximum adsorbed amount of polyacid. Due to higher ionic strength or divalent cations the repulsion of the negatively charged polyelectrolyte segments is reduced. Therefore loops and tails in the adsorption layer are stabilized. Additionally, the increase of the maximum adsorbed amount with ionic strength indicates a chemical bond between polyacid and surface. Irrespective of molar mass, polyacrylic acid adsorbs in a flat conformation if the ionic strength is low. Above a certain threshold of the ionic strength higher molar masses are better adsorbed than lower ones. Under these conditions the polyacrylic acid adsorbs in a coiled conformation.

Proton Binding by Groundwater Fulvic Acids of Different Age, Origins, and Structure Modeled with the Model V and NICA−Donnan Model

The proton binding properties of four fulvic acids from pristine groundwater and leachate-polluted groundwater were measured at four different ionic strengths (0.005−0.12 M) and modeled by the Model V and the NICA−Donnan model in order to evaluate the necessity of detailed proton binding parameters for groundwater fulvic acids. The proton binding parameters derived from the various fulvic acids were very similar, and on the basis of these parameters, it was not possible to distinguish between pristine and polluted groundwater. Normalization of the proton charge density by the proton charge density at pH 7 for each fulvic acid made all four fulvic acids regress to the same curve. The effects of varying the proton binding parameters were evaluated by simulating cadmium complexation using sets of proton binding parameters for the four fulvic acids and default sets of proton binding parameters available in the models WHAM (based on Model V) and Ecosat (based on NICA−Donnan). The Model V was rather indifferent with respect to specific characteristics of fulvic acids proton binding, and for most practical uses, the default values available in the model can be used. The NICA−Donnan model resulted in larger deviations between simulations based on default values and specific parameters. However, the NICA−Donnan database is still rather limited, and specific proton binding parameters should be used until the database providing default values has been extended.

Nucleon-nucleon correlations and the Coulomb Displacement Energy

Coulomb Displacement Energies (CDE) are accurately known for a wide range of nuclear masses. Assuming isospin independence in the nuclear Hamiltonian, the CDE can in first instance be interpreted as the Coulomb interaction energy between the density of the excess neutrons and the proton charge density in the parent nucleus. However, when using reasonable meanfield models for the proton and neutron density one underestimates the CDE by about 8% on average. This discrepancy is known as the Nolen-Shiffer anomaly, and various explanations have been put forward in the past. In this work we reexamine the role of nucleon-nucleon correlations. We present calculations for the pair density functions in various nuclei. Preliminary results suggest that the modifications to the mean-field pair density functions cause an enhancement of the CDE in the order of 4%, which is ratherA-independent.

Molecular-dynamics study of adiabatic proton-transfer reactions in solution

A molecular-dynamics study of adiabatic proton transfer between two ions in a polar solvent is presented. The proton is treated as a quantum particle in three dimensions and the polar solvent is composed of classical rigid, dipolar molecules. The coupled Schrödinger and Newton’s equations are solved to determine the proton charge density and solvent configuration. The rate coefficient for the proton transfer is computed from correlation function expressions and corrections to transition-state theory due to recrossing of a free-energy barrier are determined. The simulation results are compared with a simple two-state model.

High pressure phase transitions and hydrogen-bond symmetry in ice polymorphs

A recently developed ground state variational wave function theory of hydrogen-bonded crystals is employed to investigate the high pressure behavior of several ice polymorphs. The theory accurately accounts for short and long range proton correlations and quantum mechanical tunneling, all of which are important in the high pressure regime. Attention is focused on pressure induced order–disorder phase transitions and hydrogen-bond symmetrization for the ices VII, VIII, and Ic. We find a strongly first order transition (driven by proton tunneling) at approximately 330 kbar from the antiferroelectrically ordered ice VIII phase to a highly ionized form of proton disordered ice VII. Despite the large degree of ionization, significant short range proton order remains at the transition as indicated by the bimodality of the proton charge density along the bond. The crossover to a unimodal situation, i.e., hydrogen-bond symmetrization, is predicted to occur at 450 kbar. The effects of deuterium isotope substitution on these phenomena are also studied. Calculations for the lower density cubic form of ice indicate that it may be possible to observe symmetrical hydrogen bonds in this material at a significantly lower pressure than those required for the dense ices.