Time evolution of ion guiding through nanocapillaries in a PET polymer

We measured the time evolution of the guided transmission of 3 keV Ne⁷⁺ ions through nanocapillaries in insulating PET polymers. Capillaries with a diameter of 200 nm and a density of 4 × 10⁶ cm⁻² were used. The angular distribution of the transmitted ions was measured as a function of the charge deposited on the sample surface, which is a measure of time. The evolution of the angular transmission profiles was acquired for different tilt angles ranging from 0° to 5°. The transmission profiles appear as a superposition of essentially 3 localized peaks which exhibit significant changes in intensity as time varies. This observation provides evidence for the formation of temporary charge patches produced in the interior of the capillary besides the primary charge patch created in the entrance region.     

Interferences in electron emission from O2 by 30 MeV O impact

Interference structures in the ejected electron spectra for 30 MeV O^5,8+ + O₂ are investigated. The measured electron yields were studied for electron energies from 5 to 400 eV and observation angles of 30°, 60°, 90°, 120° and 150° with respect to the incident beam direction. Experimental molecular cross-sections were normalized to theoretical molecular one-center cross-sections revealing oscillatory structures suggestive of secondary interferences as evidenced by the independence on the observation angle. An oscillation interval for 30 MeV O^5,8+ + O₂ of Δk ∼ 4 a.u. is found, a value two times larger than that previously observed for 3 MeV H⁺ + N₂. No obvious evidence for primary Young-type interferences was seen.     

Interferences in coherent electron emission from diatomic molecules

Recent studies of electron emission from molecular hydrogen by the impact of fast ions have shown the existence of interference effects. The interferences are manifested as oscillations in the velocity (or energy) distributions of the ejected electrons, and are analogous to the interference of light in Young’s two-slit experiment. The frequencies of the oscillatory structures depend strongly on the electron observation angle and to a lesser extent on the collision velocity. Additionally, secondary oscillations with ∼2-3 times higher frequencies attributed to scattering of the primary electron “wave” at the other atomic center are found to be superimposed on the primary oscillations. More recently, electron interference studies have focused on diatomic molecules more complex than H₂, including N₂ and O₂, for which only structures due to secondary interferences are apparently observed. Here, these various results are reviewed, outstanding questions identified, and future directions indicated.     

The influence of the charged back side on the transmission of highly charged ions through PC nanocapillaries

We have measured the fraction of the ions transmitted through nanocapillaries with their initial charge state for 200 keV Xe⁷⁺ ions impact on a polycarbonate (PC) foil with a thickness of 30 μm and a diameter of 150 nm. An Au film was evaporated on both the front and back side. It is found that more than 97% of the transmitted ions remain in their initial charge state. Then, the transmitted ion fraction and the characteristic tilt angle of 40 keV Xe⁷⁺ ions through this foil and another one with the same thickness and diameter, but evaporated by Au only on the front side, were measured. By comparing the results of these two foils, the influence of the ions deposited in the capillary exit region on the transmitted ion fraction and the characteristic tilt angle is studied. In comparison with the foil evaporated by Au on both sides, the maximum transmitted ion fraction of the foil evaporated by Au on the front side only is nearly 4 times smaller. Also, the characteristic tilt angle is slightly decreased. These results are discussed within the models for the guiding effect.     

Fully differential cross section for single ionization of helium by 1 KeV electrons in the eikonal approximation

We report new results for fully differential cross sections for the single ionization of helium by 1 KeV electron impact at the ejection energy of 10 eV. Investigations have been made for both the scattering and perpendicular planes. The present calculation is based on the eikonal approximation due to Glauber. Here we have also incorporated the effect of classical post collision interaction (PCI) in the Glauber approximation (GA). A comparison is made of the present calculation with the results of other theoretical methods and the recent experiment [M. Dürr, C. Dimopoulou, B. Najjari, A. Dorn, K. Bartschat, I. Bray, D.V. Fursa, Z. Chen, D.H. Madison, J. Ullrich, Phys. Rev. A 77 (2008) 032717]. The Glauber results are in good agreement with the experiment in the scattering plane, but strong discrepancies are observed in the plane perpendicular to it. The effect of PCI is not substantial in the present kinematics.     

Determination of K shell absorption jump factors and jump ratios in the elements between Tm(Z = 69) and Os(Z = 76) by measuring K shell fluorescence parameters

The K shell absorption jump factors and jump ratios have been measured in the elements between Tm (Z = 69) and Os(Z = 76) without having any mass attenuation coefficient at the upper and lower energy branch of the K absorption edge. The jump factors and jump ratios for these elements have been determined by measuring K shell fluorescence parameters such as the total atomic absorption cross-sections, the K_α X-ray production cross-sections, the intensity ratio of the K_β and K_α X-rays and the K shell fluorescence yields. We have performed the measurements for the calculations of these values in attenuation and direct excitation experimental geometry. The K X-ray photons are excited in the target using 123.6 keV gamma-rays from a strong ⁵⁷Co source, and detected with an Ultra-LEGe solid state detector with a resolution 0.15 keV at 5.9 keV. The measured values have been compared with theoretical and others’ experimental values. The results have been plotted versus atomic number.     

K-shell absorption jump factors and jump ratios in elements between Tm (Z = 69) and Os (Z = 76) derived from new mass attenuation coefficient measurements

The K-shell absorption jump factors and jump ratios were derived from new mass attenuation coefficients measured using an energy dispersive X-ray fluorescence (EDXRF) spectrometer for Tm, Yb elements being Tm₂O₃, Yb₂O₃ compounds and pure Lu, Hf, Ta, W, Re and Os. The measurements, in the region 56-77 keV, were done in a transmission geometry utilizing the K_α1, K_α2, K_β1 and K_β2 X- rays from different secondary source targets (Yb, Ta, Os, W, Re and Ir, etc.) excited by the 123.6 keV γ-photons from an ⁵⁷Co annular source and detected by an Ultra-LEGe solid state detector with a resolution of 150 eV at 5.9 keV. Experimental results have been compared with theoretically calculated values. The measured values of Tm, Yb, Lu, Hf, Ta, W, Re and Os are reported here for the first time.     

L-subshell ionization of heavy elements by S ions with energy of 0.4-3.8 MeV/amu

The L-shell X-ray production cross sections have been measured for sulphur ions in the energy range of 12.8-120 MeV for Au and Bi elements. The experimental L X-ray spectra were analyzed using the method that takes into account the multiple ionization in outer shells. The L-subshell ionization cross sections have been obtained from measured X-ray production cross sections for resolved Lα_1,2 Lγ₁ and Lγ_2,3 transitions using the L-shell fluorescence and Coster-Kronig yields modified by the multiple ionization effects in the M and N shells. The results are compared with the predictions of ECUSAR theory, which is the modified ECPSSR approach describing both direct ionization and electron-capture processes and the semiclassical approximation (SCA) calculations for direct ionization. These approaches were modified by the L-subshell coupling effects within the “coupled-subshell model” (CSM). Both modified approaches are in good agreement with the data. Remaining discrepancies are discussed in terms of the L-shell decay rates modified for the multiple ionization effects.     

Measurement of K-L radiative vacancy transfer probabilities in selected rare earth elements bombarded with 3-4 MeV protons

K-shell X-ray intensity ratios for selected rare earth elements were measured following irradiation with proton beams having energies between 3 and 4 MeV. Using the X-ray intensity ratios, the radiative vacancy transfer probabilities from the shell K to the L sub-shells were determined. The experimental data were compared to theoretical predictions for X-ray line intensities and radiative vacancy transfer probabilities. The results showed a good agreement between theory and experiment.     

Effective atomic numbers for photon energy absorption of essential amino acids in the energy range 1 keV to 20 MeV

Effective atomic numbers for photon energy-absorption (Z_PEAeff) of essential amino acids histidine, leucine, lysine, methionine, phenylalanine, threonine, tryptophan and valine have been calculated by a direct method in the energy region of 1 keV to 20 MeV. The Z_PEAeff values have been found to change with energy and composition of the amino acids. The variations of mass energy-absorption coefficient, effective atomic number for photon interaction (Z_PIeff) and Z_PEAeff with energy are shown graphically. Significant differences exist between Z_PIeff and the Z_PEAeff in the energy region of 8-100 keV for histidine and threonine; 6-100 keV for leucine, lysine, tryptophan, phenylalanine and valine; 15-400 keV for methionine. The effect of absorption edge on effective atomic numbers and the possibility of defining two set values of these parameters at the K-absorption edge of high-Z element present in the amino acids are discussed. The reasons for using Z_PEAeff rather than the commonly used Z_PIeff in medical radiation dosimetry for the calculation of absorbed dose in radiation therapy are also discussed.     

Stopping force of 0.5-3.5 MeV/u Cl ions in polymers

The stopping force of Cl ions in LR-115 and Kapton polymers, at energies 0.5-3.5 MeV/u, has been measured. These measurements have been performed using 15UD Pelletron accelerator facility at Inter University Accelerator Centre, New Delhi, India. The measured stopping force values have been compared with the corresponding computed values based on the semi-empirical formulations viz. Ziegler et al., Paul and Schinner, Hubert et al., Diwan et al., and standard data tables viz. Northcliffe and Schilling, ICRU-73 report. The aim of the present study is to measure stopping force around Bragg’s peak and to check the compatibility of the widely used semi-empirical formulations and standard data tables through comparison with the experimentally measured values.     

Total bremsstrahlung spectral photon distributions in metallic targets in the photon energy range of 5-10 keV by Tl beta particles

Total bremsstrahlung spectral photon distributions produced by beta particles of the ²⁰⁴Tl beta emitter in thick targets of Al, Ti, Sn and Pb targets were evaluated at photon energies from 5 keV to 10 keV. Experimental measurements were compared with the theoretical total bremsstrahlung spectral photon distributions obtained from Elwert corrected (non-relativistic) Bethe-Heitler theory and modified Elwert factor (relativistic) Bethe-Heitler theories for ordinary bremsstrahlung, and the modified Elwert factor (relativistic) Bethe-Heitler theory which includes polarization bremsstrahlung in the stripped atom approximation. The experimental results show better agreement with the modified Elwert factor (relativistic) Bethe-Heitler theory which includes the contribution of polarization bremsstrahlung. The contributions of polarization bremsstrahlung decrease with increased photon energy, particularly for medium and high Z elements. Hence its contribution cannot be neglected while studying the total bremsstrahlung spectral photon distributions in thick targets, produced by continuous beta particles in the studied energy region.     

Microstructural investigation of alumina implanted with 30 keV nitrogen ions

Among ceramics, alumina is being widely used as biomaterials now these days. It is being used as hip joints, tooth roots etc. Ion implantation has been employed to modify its surface without changing it bulk properties. 30 keV nitrogen with varying ion dose ranging from 5 × 10¹⁵ ions/cm² to 5 × 10¹⁷ ions/cm² is implanted in alumina. Surface morphology has been studied with optical microscope and atomic force microscope (AFM). Improvement in brittleness has been observed with the increase in ion dose. Compound formation and changes in grain size have been studied using X-Ray diffraction (XRD). AlN compound formation is also observed by Fourier transform infrared spectroscopy (FTIR). The change in the grain size is related with the nanohardness and Hall-Petch relationship is verified.     

380 keV proton irradiation effects on photoluminescence of Eu-doped GaN

The effect of 380 keV proton irradiation on the photoluminescence (PL) properties has been investigated for undoped and Eu-doped GaN. As the proton irradiation exceeds , a drastic decrease of PL intensity of the near band-edge emission of undoped GaN was observed. On the other hand, for Eu-doped GaN, the PL emission corresponding to the ⁵D₀→⁷F₂ transition in Eu³⁺ kept the initial PL intensity after the proton irradiation up to . Present results, together with our previous report on electron irradiation results, suggest that Eu-doped GaN is a strong candidate for light emitting devices in high irradiation environment.     

Measurement of the energy deposition profile for U ions with specific energy 500 and 950 MeV/u in stainless steel and copper targets

The paper presents the results of precision measurements of the total stopping range and energy deposition function of ²³⁸U ions with specific energies E = 500 and 950 MeV/u in stainless steel and copper targets. The experiment was performed at the SIS-18 facility (GSI Darmstadt) in the experimental area Cave A in September 2004-May 2005.The measured energy deposition profiles are compared with calculations using the codes ATIMA, PHITS, SHIELD and SRIM.     

Be AMS measurements at low energies (E < 1 MeV)

The longlived isotope ¹⁰Be is of great importance in earth sciences for dating applications, reconstruction of the solar activity or in climate research. Routine AMS measurements with BeO samples are performed on accelerators with a terminal voltage above 2 MV. Applying the degrader foil technique for boron suppression, first tests with BeO samples on the 0.6 MV ETH/PSI machine were limited by background to a ¹⁰Be/⁹Be ratio of 10⁻¹³. The background was identified as ⁹Be which reaches the detector by scattering processes. By applying an additional magnetic mass filter to the high energy mass spectrometer the background was effectively removed. A ¹⁰Be/⁹Be background ratio of <5 × 10⁻¹⁵ was achieved. The overall efficiency (detected ¹⁰Be compared to BeO⁻ injected into the accelerator) was 7-8%.     

Off-line studies of the laser ionization of yttrium at the IGISOL facility

A laser ion source is under development at the IGISOL facility, Jyväskylä, in order to address deficiencies in the ion guide technique. The key elements of interest are those of a refractory nature, whose isotopes and isomers are widely studied using both laser spectroscopic and high precision mass measurement techniques. Yttrium has been the first element of choice for the new laser ion source. In this work, we present a new coupled dye-Ti:Sapphire laser scheme and give a detailed discussion of the results obtained from laser ionization of yttrium atoms produced in an ion guide via resistive heating of a filament. The importance of not only gas purity, but indeed the baseline vacuum pressure in the environment outside the ion guide is discussed in light of the fast gas phase chemistry seen in the yttrium system. A single laser shot model is introduced and is compared to the experimental data in order to extract the level of impurities within the gas cell.     

K-shell X-ray fluorescence cross-sections and intensity ratios for some pure metals at 59.5 and 123.6 keV

K-shell X-ray fluorescence cross-sections for some pure metals such as Cr, Fe, Co, Cu, Zn, Ga, Se, Y, Mo, Cd, In, Sn, Te, Ba, Ta, W and Bi have been theoretically and experimentally determined. The Cr, Fe, Co, Cu, Zn, Ga, Se, Y, Mo, Cd, In, Sn, Te and Ba metals were excited by 59.5 keV γ-ray from 50 mCi ²⁴¹Am radioactive source and the Ta, W and Bi targets were excited by 123.6 keV γ-ray from 25 mCi ⁵⁷Co radioactive source. The characteristic K X-rays emitted by samples were detected by using a super Si(Li) detector having a resolution of 150 eV at 5.9 keV. In addition, the I_Kβ/I_Kα intensity ratios for these metals were studied. The obtained experimental values of the K-shell X-ray fluorescence cross-sections and the I_Kβ/I_Kα intensity ratios have been compared with theoretical values. The measured values were in good agreement with theoretical values.     

Threshold effects in the ionization of atoms by positron impact

We employ different theoretical models, both classical and quantum-mechanical, to explore the recoil-ion momentum distribution in positron-atom collisions. We pay special attention to the vicinity of the kinematical threshold between ionization and positronium formation. We demonstrate that it is intertwined by dynamical constraints to the formation of highly excited and low-lying continuum electron-positron states. Finally we discuss how the study of recoil-ion momentum distribution, which is characteristic of a reaction microscopy technique, might represent an alternative approach to the standard spectroscopy of electrons and positrons.