Mean Emission Angle Research Articles

Fragmentation of carbon on elemental targets at 290AMeV

The total charge-changing cross-sections and the partial cross-sections for projectile fragments (PFs) production for the fragmentation of 12C on C, Al, Cu, Pb and CH2 targets at the highest energy of 290[Formula: see text]A[Formula: see text]MeV were studied. It was found that the total charge-changing reaction cross-sections and the partial reaction cross-sections of PFs production were independent of the beam energy, and increased with increase of mass of target for the same beam energy. The total charge-changing reaction cross-section was the same as the prediction of Bradt–Peters semi-empirical formula, PHITS and NUCFRG2 simulation models. The partial cross-section of PFs production increased with the increase of the mass of target, and it was the same as the prediction of NUCFRG2 models. The mean scattering angle of projectile particle was smaller than the average emission angle of PF, and the width of scattering angle distribution of projectile particle was smaller than that of emission angle distribution of PFs. The mean emission angle of PFs does not obviously depend on the target mass and beam energy in our studied beam energy regions.

Simulations of Ion-Guiding Through Insulating Nanocapillaries of Varying Diameter: Interpretation of Experimental Results

The guiding of highly charged ions through a single nanocapillary is simulated in comparison with previous experiments performed with highly insulating polyethylene terephthalate (PET). The simulations are carried out using 3-keV Ne7+ ions injected into capillaries with diameters ranging from 100 nm to 400 nm. In the calculations, non-linear effects are applied to model the charge transport along the capillary surface and into the bulk depleting the deposited charges from the capillary walls. In addition to the surface carrier mobility, the non-linear effects are also implemented into the bulk conductivity. A method is presented to determine the parameters of the surface charge transport and the bulk conductivity by reproducing the oscillatory structure of the mean emission angle. A common set of charge depletion rates are determined with relatively high accuracy providing confidence in the present theoretical analysis. Significant differences in the oscillatory structures, experimentally observed, are explained by the calculations. Experimental and theoretical results of the guiding power for capillaries of different diameters are compared. Finally, dynamic non-linear effects on the surface and bulk relaxation rates are determined from the simulations.

Fragmentation of 400 A MeV carbon ions on Cu target

The total charge-changing cross-section and the partial cross-section of projectile fragments (PFs) production for the fragmentation of 12C on Cu target at the highest energy close to about 400 A MeV is investigated. It is found that the total charge-changing cross-sections of PFs production is independent of the beam energy, but the partial cross-sections of PFs production increase with decrease beam energy for the same target. The total charge-changing reaction cross section is in agreement with the prediction of Bradt-Peters semi-empirical formula, PHITS and NUCFRG2 models. The partial cross section of PFs production is larger than the prediction of PHITS model. The average scattering angle of beam particle is smaller than the mean emission angle of PF, and the width of scattering angle distribution of beam particle is smaller than that of emission angle distribution of PF.

X-ray emission reduction and photon dose lowering by energy loss of fast electrons induced by return current during the interaction of a short-pulse high-intensity laser on a metal solid target

During the interaction of a short-pulse high-intensity laser with the preplasma produced by the pulse's pedestal in front of a high-Z metal solid target, high-energy electrons are produced, which in turn create an X-ray source by interacting with the atoms of the converter target. The current brought by the hot electrons is almost completely neutralized by a return current j→ driven by the background electrons of the conductive target, and the force exerted on the hot electrons by the electric field E→ which induces Ohmic heating j→.E→, produced by the background electrons, reduces the energy of the hot electrons and thus lowers the X-ray emission and photon dose. This effect is analyzed here by means of a simple 1-D temperature model which contains the most significant terms of the relativistic Fokker-Planck equation with electron multiple scattering, and the energy equations of ions, hot, and cold electrons are then solved numerically. This Ohmic heating energy loss fraction τOh is introduced as a corrective term in an improved photon dose model. For instance, for a ps laser pulse with 10 μm spot size, the dose obtained with a tantalum target is reduced by less than about 10% to 40% by the Ohmic heating, depending upon the plasma scale length, target thickness, laser parameters, and in particular its spot size. The laser and plasma parameters may be optimized to limit the effect of Ohmic heating, for instance at a small plasma scale length or small laser spot size. Conversely, others regimes not suitable for dose production are identified. For instance, the resistive heating is enhanced in a foam target or at a long plasma scale length and high laser spot size and intensity, as the mean emission angle θ0 of the incident hot electron bunch given by the ponderomotive force is small; thus, the dose produced by a laser interacting in a gas jet may be inhibited under these circumstances. The resistive heating may also be maximized in order to reduce the X-ray emission to lower the radiation level for instance in a safety radiological goal.

Projectile fragment emission in the fragmentation of silicon on carbon and polyethylene targets at 775 A · MeV

The emission angle and the transverse momentum distributions of projectile fragments (PFs) produced in fragmentation of 28Si on C and CH2 targets at 775 A. MeV are measured. It is found that the mean emission angle and the mean transverse momentum increase with the decrease of the charge of PFs for the same target, and no obvious dependence of angular and transverse momentum distribution on the mass of target nucleus are found for the same PF. The cumulative squared transverse momentum distribution of PF can be well explained by a single Rayleigh distribution. The temperature of PF emission source do not depend on the size of PF and mass of target for PF with charge 5 ≤ Z < 13.

Experiments and simulations of ion guiding through nanocapillaries in insulating polymers

Recent experimental studies of dynamic properties concerning ion guiding through nanocapillaries etched in polyethylene terephthalate (PET) and polycarbonate (PC) are reviewed. The temporal evolution of the intensity and the angular distribution of the transmitted ions have been measured as function of the charge inserted into the capillaries. The mean emission angle exhibit pronounced oscillatory structures both for PET and PC. The experimental results are interpreted by simulations of the ion trajectories guided in 3 dimensions by the electrostatic field within the capillaries. This field was determined from the charge deposited at the walls of the capillaries taking into account the transport of the charges by means of the surface conductivity. The experimental oscillations of the mean emission angle are well reproduced by the simulations. Differences between results using PET and PC are attributed to differences in the surface conductivity.

Model for oscillations in the guidance of ions through insulating nanocapillaries

The pre-equilibrium period of the ion guiding through insulating nanocapillaries is characterized by the production of temporary charge patches inside the capillaries. The dynamics of the charge patch creation is revealed by oscillations of the mean emission angle of the emerging ions. To understand the oscillations, we propose a phenomenological model based on the retardation between charging and discharging of the patches.

Dynamics of ion guiding through nanocapillaries in insulating polymers

We review recent studies of dynamic properties concerning the ion guiding through nanocapillaries etched in polyethylene terephthalate (PET) and polycarbonate (PC). Typical lengths of the capillaries were 10 μm with diameters ranging from ~100 - 400 nm. The temporal evolution of the intensity and the angular distribution of the transmitted ions were studied by measuring transmission profiles as a function of the charge inserted into the capillaries. Tilt angles of the capillaries axis with respect to the incident beam direction were 3° and 5°. The mean emission angle of the transmission profiles exhibit pronounced oscillatory structures both for PET and PC. However, for PC nearly an order of magnitude more charge is required to induce the oscillations. In contrast to PET, with capillaries in PC we observed a strong decrease of the profile intensities with irradiation time. This observation provides evidence for blocking effects on the ion transmission. The experimental results are interpreted by simulations of the ion trajectories guided in 3 dimensions by the electrostatic field within the capillaries. This field was determined from the charge deposited at the walls of the capillaries taking into account the removal of the charges by means of a non-linear conductivity law.

Classical study of ultrastrong nonperturbative-field interactions with a one-electron atom: Validity of the dipole approximation for the bound-state interaction

We present a classical, relativistic Monte Carlo calculation investigating the role of the magnetic field in bound-state dynamics and ionization for atoms in ultrastrong external radiation fields. Atoms with atomic numbers $1\ensuremath{\leqslant}Z\ensuremath{\leqslant}20$ in external fields from 0.01 to ${10}^{3}$ a.u. are studied. We show that, when calculating ionization rates, the dipole approximation yields accurate values compared to a full classical electromagnetic laser field for intensities up to ${10}^{23}$ W/cm${}^{2}$. The calculations indicate that the quasistatic approximation is valid for external-field frequencies less than 1/20 of the Kepler-orbit time for the ionizing state. For ionization at fields above 100 a.u., the magnetic field affects the atom by altering the portion of the bound state that ionizes and deflecting the mean emission angle of the photoelectron angular distributions, although no change in the width of the final-state angular emission about this mean occurs. The photoelectron distribution and change in the ionizing bound state are seen as an indication of nonperturbative magnetic field effects for atoms in ultrastrong radiation fields.

Evidence of blocking effects on 3-keV Ne7+ions guided through nanocapillaries in polycarbonate

We studied the dynamic properties of ion guiding through nanocapillaries etched in insulating polycarbonate (PC). Capillaries with diameters of 95 and 165 nm and a length of 10 mu m were used. In a further sample, the capillaries had a diameter of 175 nm and a length of 30 mu m. A few additional measurements were made using capillaries in polyethylene terephthalate (PET). The temporal evolution of the intensity and the angular distribution of the transmitted ions were studied by measuring transmission profiles as a function of the charge deposited on the sample surface. The tilt angle of the capillary axis was varied from 0 degrees to 5 degrees. The mean emission angle of the transmission profiles exhibit pronounced oscillations, similarly as in previous measurements using PET. However, for PC, nearly an order of magnitude more charge needs to be inserted into the capillaries to accomplish the oscillations. In contrast to PET, with PC, we observed a strong decrease of the profile intensities with irradiation time. This observation provides evidence of blocking effects on the ions, which are likely to be due to a repulsive field produced by significant charge deposition inside the PC capillaries.

Ion guiding accompanied by formation of neutrals in polyethylene terephthalate polymer nanocapillaries: Further insight into a self-organizing process

A relatively large yield of neutralized atoms was observed when 3 keV Ar${}^{7+}$ ions were guided trough polyethylene terephthalate nanocapillaries. Time and deposited-charge dependence of the angular distribution of both the guided ions and the neutrals was measured simultaneously using a two-dimensional multichannel plate detector. The yield of neutrals increased significantly faster than that of guided ions and saturated typically at a few percent level. In accordance with earlier observations, both the yield and the mean emission angle of the guided ions exhibited strong oscillations. For the atoms, the equilibrium was achieved not only faster, but also without significant oscillations in yield and angular position. A phase analysis of these time dependencies provides insight into the dynamic features of the self-organizing mechanisms, which leads to ion guiding in insulating nanocapillaries.

Experimental test of Monte Carlo proton transport at grazing incidence in GEANT4, FLUKA and MCNPX

The ability of the Monte Carlo (MC) particle transport codes GEANT4.8.1 and GEANT4.8.2, FLUKA2006 and MCNPX2.4.0 to model proton transport at grazing incidence onto tungsten blocks has been tested and compared to experimental measurements. The test geometry consisted of a narrow proton beam of two energies, 98 MeV and 180 MeV, impinging on a thick tungsten alloy block at grazing incidence. The distribution of forward out-scatter from the tungsten alloy block was measured with a fluorescent screen viewed with a CCD camera via a mirror. In the MC simulations, the experimental setup was modelled and the dose deposited to the fluorescent screen material was scored. Simulations and measurements were made for four different incidence angles (3.5, 5.0, 7.5 and 10°). Several different sets of calculations were performed, studying the impact of different user-defined settings in the different MC packages. The study of different parameters settings in the GEANT4.8.1 simulation showed a strong dependence of the calculated out-scatter probability on the maximum allowed step length. For the largest incidence angle an increase of 60% in the out-scatter probability was found when restricting the maximum allowed step length to 0.05 cm. We also observed that the stepping algorithm of GEANT4.8.1 and 4.8.2 introduces a small non-physical directional and positional asymmetry at the exit boundary of the tungsten alloy block. The shape of the energy spectrum of protons being out-scattered agreed between the codes. The dose-weighted forward out-scatter probability, i.e. the ratio between the total signal from the unscattered beam and the out-scattered beam, showed a qualitative agreement of simulations compared to measurements. Quantitatively, the deviation of the simulations reached as high as 37%, while the experimental uncertainty was 14%. The mean emission angle of the simulations was within 16% of the measurement for all incidence angles with a measurement uncertainty of 8%.

H2+, H3+ and H− emission by MeV ion impact: charge state dependence of energy and angular distributions

A 1MeV/n127Iq+ beam of the Tandem accelerator at Orsay, France, has been used to study the dependence of hydrogen ion emission on the charge state of the incident primary ions. The samples investigated were bare gold and carbon foils and a 150 nm glycine film vacuum-evaporated on an Au foil. The measurements were performed at a vacuum pressure of about 10−7 mbar; the sample surfaces were covered by a contamination layer. The linear time-of-flight instrument used was equipped with two acceleration grids and a position sensitive stop detector, in order to measure the initial velocity components and the angle of emission for each detected ion. The results were axial, radial and total energy distributions and angular distributions for the hydrogen ions H+, H2+, H3+ and axial energy distributions for H−, all measured at constant beam energy for the charge states 17+, 20+, 26+, 30+ or 32+ under an angle of incidence of 55° against the surface normal.The angular distributions of all ions were asymmetric relative to the surface normal, for the glycine target more than for the bare metals. The mean energies increase slightly with the charge state, the increase was in the order of 0.5–2% per charge state. The change of the mean emission angle had negative as well as positive values in the order of 0–0.2° per charge state. Comparing glycine and metal targets, the angular distributions obtained with the metals seemed to be wider around the main direction of emission. A few suggestions about possible desorption/ionization processes are given.

Critical study of source size extractions from p-p correlations in 20Ne reactions at 30 MeV/nucleon.

Two proton correlation functions have been measured at 30 MeV/nucleon for various systems ${(}^{20}$Ne${+}^{12}$C${,}^{27}$Al${,}^{59}$Co${,}^{197}$Au) in the forward hemisphere. Source radii extracted by comparisons to the final state interaction model of Koonin turn out to be independent of the mean emission angle of the protons as well as of the size of the studied system, and little affected by energy cuts on the detected proton pairs. Typical size (\ensuremath{\sim}5.5--6 fm) exceeds the radius of the compound nucleus for almost all studied systems, suggesting significant time delays between proton emissions. However, similarity of transverse and longitudinal correlation functions seems to eliminate the existence of a long lifetime. Due to the poor sensitivity of the proton-proton correlation function, this method seems not well suited for source size measurements in this energy domain.

Electron emission from ion bombardment of high Tc superconductors

We have performed first studies of secondary electron energy- and angular distributions (0 eV ≤ E ≤ 40 eV, 25 ° ≤ θ ≤ 90 °) from H + and C + (2 MeV) bombardment of single crystals of YBa 2Cu 3O 7− x and EuBa 2Cu 3O 7− x high T c supercondu distributions N( θ) have been measured at sample temperatures above ( T = 300 K) and below ( T = 35 K) the superconducting transition temperature ( T c ≈ 90 K) as a function of the angle of incidence (δ = 55 °, 65 °, 70 °, 75 °) of the projectiles. The rat R = N(C +) N(H +) of electron intensities from heavy C + ion impact to the electron intensities from proton impact sho peaks ( Δθ ≈ 25 °) at low electron energies E < 20 eV. The mean emission angle θ em of the excess electrons belonging to this peak shifts to higher angles 8 with increasing δ. Within the framework of a model for the refraction of low energy electrons at surfaces this can be explained by the directed emission of shock electrons perpendicular to the conical charge density fluctuations caused by the ion induced wake shock front. Furthermore, the influence of the superconducting phase transition at T = T c on the emission of electrons is discussed.

A detailed investigation of the thermal neutron induced ternary fission of 235U

The energy and angular distributions of the long-range α-particles released in the thermal neutron induced fission of 235U have been measured as a function of the mass and kinetic energy of the fission fragments. Only one of the fission fragments was detected, its mass being determined by kinetic energy and time-of-flight measurements. The dependence of the light particle kinetic energy spectra on its final direction is examined as a function of mass and kinetic energy of the fission fragments. The angular distribution of all α-particles with respect to the light fragment direction has a most probable value of 81.3°±0.5° with a dispersion (FWHM) of 18.5°±0.8° which compares very well to the angular spread measured in the spontaneous fission of 252Cf. Other striking similarities between the ternary fission of 236U and 252Cf are pointed out. A positive correlation between the mean emission angle and the mass of the light fragment resolves the controversy which remained on this point up to now. The influence of the total fragment kinetic energy on the width of the angular distribution is investigated in detail. A preliminary interpretation of our data shows that α-accompanied fission should no longer be considered as contradictory to the semi-statistical models of fission.

Characteristics of nonannihilation interactions of 5 GeV/c antiprotons with emulsion nuclei

The energy and angular characteristics of surviving\(\bar p\) at 5 GeV/c are presented. The mean inelasticity in the centre-of-mass system for these events is found to be 0.45±0.03. A smaller heavy-prong number of parent stars (〈Nh〉=2.10±0.26) indicates that the secondary\(\bar p\) survive mainly from those collisions which take place on the nuclear periphery. The nonannihilation events are characterized by a smaller shower multiplicity (〈ns〉=1.65±0.06) compared with the annihilation events (〈ns〉=4.50±0.74). The mean emission angle of the surviving\(\bar p\) is correlated, whilst its energy is anticorrelated with the shower multiplicity of parent stars. Then mean transverse momentum of surviving\(\bar p\) is found to be (334±20) MeV/c.

A magnetic lens spectrometer for electron-gamma and electron-electron directional correlation measurements

A magnetic lens spectrometer has been adapted for electron-gamma and electron-electron directional correlation measurements. One electron channel has magnetic momentum selection provided by a medium short magnetic lens spectrometer. The lens spectrometer is iron-free with the exception of two steel end plates which decouple the already weak magnetic field in the lens from the electron detector and from the movable gamma or electron detector. The source sits outside the magnetic field and is accessable through 180° to a movable detector. Directional correlations of electrons with gamma-rays or electrons have been carried out by using a NaI(Tl) detector or an anthracene scintillation detector, respectively. A special source holder was designed for the electron-electron work. Electron energies down to 20 keV have been measured in the lens. A proportional counter may be used to lower energies. The maximum lens energy is ≈ 5 MeV. The spectrometer mean emission angle was chosen to be 13.5°. The resolution can then be varied from 1 to 5 per cent with a corresponding transmission of 0.4 to 1.5 per cent.

Ring Detection in a Thin-Lens Magnetic Spectrometer

Ring detection has been carried out in a thin-lens beta-ray spectrometer by locating anthracene crystals at the ring focus of the electron trajectories. The geometry of the electron focusing has been investigated for gathering powers of 1.6, 1.1, and 0.7% at mean emission angle tangents of 0.400, 0.385, and 0.352 and the resolutions obtained have been tabulated. At a gathering power of 1.6% a line width of better than 1.37% in momentum has been achieved. A comparison of this instrument with other helical spectrometers is made.

Instrument for electron-gamma directional correlation experiments with magnetic momentum selection

A medium thick lens spectrometer was adapted for electron-gamma angular correlation experiments. The requirements to be filled are discussed. It has been found that the necessary mutual independence between spectrometer and gamma-counter can be obtained by suitable iron and mu-metal shielding. A transmission of 1.5% at 3% resolution has been obtained, when utilizing a mean emission angle of 11°.5.