Low-velocity Protons Research Articles

Experimental low velocity proton and 28Siq+ induced X-ray production cross sections for select elements within 24 ≤ Z ≤ 83

Particle Induced X-ray Emission (PIXE) spectroscopy is an effectively well-established analytical technique in the low projectile mass (Z < 3) regime. This is in part due to the availability of fairly accurate theoretical models of fundamental interaction parameters such as the X-ray production cross section (XPCS). Continual development of widely used theoretical models such as the ECPSSR theory with adapted corrections in the United Atom limit (UA), Electron Capture (EC) and Multiple Ionisation (MI); requires a rich database of experimental X-ray production cross sections. Beyond the scope of proton PIXE, validated reliable theoretical models may be useful for the accurate approximation of heavy ion induced X-ray production cross sections for Heavy Ion PIXE. This requires persistent efforts aimed at contributing to the currently sparse heavy ion induced X-ray production cross section database. In this work, we report on a new experimental dataset of low energy XPCS in the 0.3 MeV/u – 1.0 MeV/u ion velocity range in Cr, Ni, Ge, Mo, Sn, W, Au and Bi due to proton and 28Siq + ion impact, with an aim at enriching and updating the current database.

Design and fabrication of stripline BPM for the ESS MEBT

Beam Position Monitors (BPM) are non-destructive diagnostics devices used in particle accelerators to measure the transverse beam position (beam center of mass) and phase of the accelerated beam. There are various ways of realization of the BPMs in accelerators having different measurement requirements, particle type or energy. Several types of BPM pickups have been studied including the button type, grounded striplines and matched striplines. The choice and final design is based on a matched stripline to accommodate the signal transmission to electronics and provide relatively higher signal level for low velocity (β=0.088) proton beam within MEBT. Due to mechanical space limits, all the BPMs are embedded inside quadrupoles; hence it is required to use non-magnetic materials in the BPM sensor, in particular the feedthroughs. The BPM sensor is composed of several components, which are separately machined with tolerances of 10μm, and then welded together by the use of electron beam welding. The analysis show for long bunches, the multi bunch transfer impedance is different than of single bunch due to bunch signals overlapping. The design, fabrication and tests of the BPM sensors were performed at ESS-Bilbao and their installation and the electrical checks at ESS-Lund. Prior to installation in the ESS accelerator tunnel, one BPM stripline was installed and the BPM system tested with the CEA-IPHI beam. This paper gives an overview of the electromagnetic and mechanical design and the fabrication of BPM striplines. Furthermore, the results of the RF measurements are compared with the simulations.

Stopping power of fluorides and semiconductor organic films for low-velocity protons

A combined experimental and theoretical study of the energy loss of protons in fluorides and organic films is presented. The measurements were performed in fresh ${\mathrm{AlF}}_{3}$, LiF, and $N$,${N}^{\ensuremath{'}}$-bis(1-ethylpropyl)-perylene-3,4,9,10-tetracarboxdiimide (EP-PTCDI) evaporated in situ on self-supported C or Ag foils, covering the very low energy range from $25$ keV down to $0.7$ keV. The transmission method is used in combination with time-of-flight (TOF) spectrometry. In the case of fluorides with large band gap energies (${\mathrm{AlF}}_{3}$ and LiF), the experimental stopping power increases almost linearly with the mean projectile velocity showing a velocity threshold at about $0.1$ a.u. These features are well reproduced by a model based on quantum scattering theory that takes into account the velocity distribution and the excitation of the active 2$p$ electrons in the ${F}^{\ensuremath{-}}$ anions, and the properties of the electronic bands of the insulators. In the case of the semiconductor organic film with a lower gap, the experimental stopping power increases linearly with the mean projectile velocity without presenting a clear threshold. This trend is also reproduced by the proposed model.

Stopping power of fluorides for low-velocity protons

A combined experimental and theoretical study of the energy loss of protons in fluorides is presented. The measurements were performed in fresh $\mathrm{Al}{\mathrm{F}}_{3}$ evaporated in situ on self-supported C foils, extending the low-energy range from 25 down to $0.7\phantom{\rule{0.3em}{0ex}}\mathrm{keV}$. The transmission method is used in combination with time-of-flight spectrometry. The experimental stopping power increases almost linearly with the mean projectile velocity, showing a velocity threshold at about $0.1\phantom{\rule{0.3em}{0ex}}\mathrm{a.u.}$ These features are well reproduced by a model based on quantum scattering theory that takes into account the velocity distribution and the excitation of the active $2p$ electrons in the ${\mathrm{F}}^{\ensuremath{-}}$ anions, and the properties of the electronic bands of the insulators. The model also reproduces the threshold behavior measured previously on LiF.

Ponderomotive instabilities and microphonics—a tutorial

Phase and amplitude stabilization of the fields in superconducting cavities in the presence of ponderomotive effects and microphonics was one of the major challenges that had to be surmounted in order to make superconducting rf accelerators practical. This was of particular concern in low-velocity proton and ion accelerators since the beam loading was often negligible, but was usually not relevant in electron accelerators since the beam loading was often high and the gradients low. More recent or future applications of electron linacs—for example JLab upgrade, energy recovering linacs (ERLs)—will operate at increasingly higher gradients with little beam loading, and the issues associated with microphonics and ponderomotive instabilities will again become relevant areas of research. This paper will describe the ponderomotive instabilities and the conditions under which they can occur, and review the methods by which they, and microphonics, can be overcome.

Simulation of Proton Neutralization Effect for Neutron Dosimetry

Neutron dose is transferred to biological materials through the recoil protons produced by elastic scattering. When a low-velocity proton collides with the atoms or molecules of a target, it changes to a hydrogen atom by electron capture; this hydrogen atom then changes to a proton by losing the electron. Because the hydrogen atom has a different ionization cross section from that of a proton, the charge exchange processes need to be considered to calculate stopping power for low energy protons. The proton neutralization effect has been simulated by using a proton track structure code developed by taking into account charge exchange processes. The microdosimetric spectrum for 1 MeV neutrons was calculated by assuming a continuous slowing down approximation (csda) and the results of the proton track code. It was found that hydrogen atoms after proton neutralized by electron capture contribute about 24% to neutron dose.

Electronic energy loss of slow protons channeled in metals

The electronic energy loss for low-velocity protons channeled in the $〈$100$〉$ direction of single-crystal Au and Al is calculated. The proton trajectories are determined by solving the equation of motion. In the proton dynamics two forces are included, a repulsive term arising from the nuclei and core electrons and a friction force, depending on proton velocity, arising from the valence electrons. The repulsive force on the proton is evaluated using a superposition of conservative potentials. The friction coefficient is evaluated by using the local density of valence electrons, and a quantum-mechanical transport cross-section approach with a self-consistent model based on Friedel's sum rule. The results allow us to describe the nonlinear behavior of energy loss with ion velocity observed experimentally in Au, as well as the linear behavior observed in Al.

Single ionization of He by low-velocity protons and C6+: Ejected electron momentum distributions.

A technique for electron spectroscopy which yields full two-dimensional momentum distributions for continuum electrons has been used to study ejected electrons from single ionization of He by ${\mathrm{C}}^{6+}$ and proton projectiles at low velocities. Projectile velocities of 1.63, 1.38, and 1.16 a.u. for ${\mathrm{C}}^{6+}$ and 2.39, 1.71, 1.15, .85, and 0.63 a.u. for protons were used. All spectra show much broader distributions along the beam than transverse to the beam. For the case of proton bombardment, the spectra are strongly influenced by both target and projectile potentials, maximizing near the velocity of the saddle in the potential between the two receding ion cores for the lowest projectile velocities. For ${\mathrm{C}}^{6+}$ projectiles, the spectra appear to be dominated by the projectile potential and the center of the distribution is strongly shifted toward the projectile velocity. Theoretical results from the continuum-distorted-wave--eikonal-initial-state and classical-trajectory--Monte Carlo methods are in rather good agreement with the proton data but do not agree well with the ${\mathrm{C}}^{6+}$ data. \textcopyright{} 1996 The American Physical Society.

Energy loss of slow protons channeled in Au.

The electronic energy loss for low-velocity protons channeled in the 〈100〉 direction of single-crystal Au is calculated. The spatial distribution of valence electronic density in Au is calculated by using the tight-binding linear muffin-tin method [O. K. Andersen and O. Jepsen, Phys. Rev. Lett. 53, 2571 (1984); O. K. Anderson, Z. Pawlowska, and O. Jepsen, Phys. Rev. B 34, 5253 (1986)]. The proton trajectories are determined by numerical integration of the classical equation of motion, and the energy loss is evaluated by using a quantum-mechanical transport cross-section approach with a self-consistent model based on Friedel's sum rule. The results allow us to describe the nonlinear behavior of energy loss with ion velocity observed experimentally. \textcopyright{} 1996 The American Physical Society.

K-shell X-ray production in vanadium, cobalt, copper, molybdenum and silver by low velocity protons

K-shell X-ray production cross sections have been measured for thick foil targets of V, Co, Cu, Mo, and Ag at incident proton beam energies of 75 to 550 keV. The overall agreement of these cross sections with previous work is generally within the experimental uncertainty. The K-shell X-ray production cross sections are compared with the predictions of the energy-loss Coulomb-deflection, perturbed stationary state relativistic (ECPSSR) theory.

Influence of Damping on the Energy Loss Straggling of Low Velocity Protons in an Electron Gas

AbstractWhen damping is included in an electron gas, an increase in the straggling parameter of low energy ions is predicted. The magnitude of this effect is estimated. The calculations provide a step forward towards a better understanding of experimental data on low energy straggling, which appears to be consistently higher than existing calculations based on the (undamped) free electron gas model. More experiments for low velocities would be desirable in order to check the theoretical predictions.

Investigation of L-subshell ionization of gold by low velocity proton bombardment

Proton induced X-ray emission was used to measure absolute L-subshell and total L-shell ionization cross sections of gold in the energy range 0.2–0.6 MeV. The experimental results were compared with the predictions of two versions (RPWBA-BC, CPSSR) of the plane wave Born approximation.

Bethe-bloch stopping power parameters for light projectiles at energies near the stopping power maximum

Recent measurements of the stopping power of H 2, He, O 2, N 2, Ne, Ar, Kr and Xe for protons and alpha particles near the stopping power maximum have been analyzed with modified Bethe—Bloch theory in conjunction with an effective charge factor. Satisfactory fits were attained with a single charge state parameter, in general, although the shell corrections used required an increase in prescribed values of about 22% for low velocity protons traversing Ar, Kr, and Xe targets.

K-shell ionisation cross sections for W, Au and U by low-velocity protons

Proton-induced K-shell ionisation cross sections for W, Au and U by low-velocity protons were obtained from thick-target measurements. For the first time the lowest incident energy reached a value less than ten times the binding energy of the K-shell electron (less than nine times in the case of Au). Possible sources of error are thoroughly examined and a comparison with other available experimental results and theoretical values is presented and discussed.

Atomic orientation effects in proton stopping at low velocity

The energy of moving ions in solid is dependent on the electronic density as well as the atomic structural properties of the target material. These factors contribute to the observable effects in polycrystalline material using the scanning ion microscope. Here we outline a method to investigate the dependence of low velocity proton stopping on interatomic distances and orientations.The interaction of charged particles with atoms in the frame work of the Fermi gas model was proposed by Lindhard. For a system of atoms, the electronic Lindhard stopping power can be generalized to the formwhere the stopping power function is defined as

Application of pixe to the measurement of sputter deposits

On the basis of angular distribution measurements of sputtered copper and aluminium deposits improvements of the experimental method are presented which led to a higher angular resolution and a reduction of error. The applicability of especially low velocity proton- and hydrogen molecule-induced X-rays is shown.

Molecular polarizability as a basis for energy partitioning estimates in ordinary radiolysis

Independent assessments of relative energy depositions in mixtures based upon low velocity proton stopping cross sections or upon radiolytic ionization yields suggest that the effective energy deposition during radiolysis is proportional to molecular polarizability. The results indicate that energy partitioning estimates based upon the Simple Mixture Law will be grossly inaccurate in systems containing halocarbons or rare gases.

Ranges and Energy-Loss Processes of Heavy Ions in Emulsion

The range-energy relations for C, N, O, Ne, and A ions in nuclear-track emulsion have been measured for energies up to 10 Mev/nucleon. The ions, accelerated by the heavy-ion linear accelerator, were suitably degraded and subsequently analyzed by a 180\ifmmode^\circ\else\textdegree\fi{} double-focusing magnetic spectrometer. The heavy-ion ranges were measured relative to those of alpha particles which were employed to calibrate the instrument. Within the energy interval studied, it has been found that a general expression for the range of a heavy ion is $R=(\frac{M}{{z}^{2}})\ensuremath{\lambda}(\ensuremath{\beta})+M{z}^{\frac{2}{3}}{C}_{z}(\frac{\ensuremath{\beta}}{z})$, where $\ensuremath{\lambda}(\ensuremath{\beta})$ is the range of a particle of proton mass and charge at velocity $\ensuremath{\beta}c$, ${C}_{z}(\frac{\ensuremath{\beta}}{z})$ is an empirical function that corrects for the extension in range caused by neutralization of the ionic charge as electrons are captured at low velocities, and $M$ and $z$ are the ionic mass and charge in units of the proton. The range data are sufficiently complete and accurate to allow detailed analyses of rates of energy loss and effective charge of the heavy ions as they come to rest. The relative importance of primary and secondary ionization processes in producing the taper in the track of a multicharged ion has been studied by examining the ions in emulsions of various sensitivities. Buckling-type distortions of heavily ionizing tracks in strongly developed emulsions are also discussed. The range-energy relation for low-velocity protons is re-examined and an improved range point at 0.585 Mev is reported.

The Stopping Power for Protons in Several Metals

The rate of energy loss of low velocity (i.e., from 50 to 400 kev) protons has been measured in five different stopping materials: Be, Al, Cu, Ag, and Au. Agreement with previous measurements at higher velocities (greater than 400 kev) is good where such measurements have been published. The stopping measurements were made on foils prepared by an evaporation technique and are believed to be more accurate than measurements made on the usual (hammered or rolled) foils; the results give a value for stopping about 15 percent higher (in Au) and about 7 percent lower (in Al) than those published by Wilcox. A comparison to existing theory at very low and at high velocities (the critical velocity being defined as $\frac{{e}^{2}}{\ensuremath{\hbar}}$ was made with good agreement shown at the low end. The high end theory is of doubtful validity and gives a stopping power about 10 percent higher than observed. It is argued that this discrepancy cannot be accounted for by a proton charge less than unity due to the electron capture-loss process.

Low Velocity Hydrogen Ion Scattering in Hydrogen, Water and Ammonia

Improved technique has enabled more precise measurements to be made of the effective cross section for scattering of hydrogen, water, and ammonia for low velocity protons and of hydrogen for low velocity H2+ and H3+. From the measurements of proton scattering in hydrogen and ammonia and H3+ scattering in hydrogen, and the use of certain assumptions, the average force laws can be evaluated and the energy of combination estimated in the first two cases. The proton affinities thus calculated for hydrogen and ammonia agree with previous estimates. For H2+ in H2 an evaluation of force law and an estimate of energy of combination cannot be made, but the large interaction is a phenomenon of some interest. Further increase in precision, separation of scattering from neutralization, and extension of measurements to lower velocities of ions is necessary also to evaluate the force law and proton affinity of water. As measurements of this kind can be made using many kinds of ions, each of which can be scattered in a great variety of gases, much information of value can be obtained such as force laws, proton affinity or absolute basicity of substances, energies of solvation of ions, etc.