Inhibition of methicillin resistant Staphylococcus aureus by a plasma needle

In numerous recent papers plasma chemistry of non equilibrium plasma sources operating at atmospheric pressure has been linked to plasma medical effects including sterilization. In this paper we present a study of the effectiveness of an atmospheric pressure plasma source, known as plasma needle, in inhibition of the growth of biofilm produced by methicillin resistant Staphylococcus aureus (MRSA). Even at the lowest powers the biofilms formed by inoculi of MRSA of 10⁴ and 10⁵ CFU have been strongly affected by plasma and growth in biofilms was inhibited. The eradication of the already formed biofilm was not achieved and it is required to go to more effective sources.     

High-pressure Mössbauer spectroscopy using synchrotron radiation and radioactive sources

A high-pressure ⁵⁷Fe Mössbauer study of SrFeO₃ up to 74 GPa has been performed with diamond-anvil-cell (DAC) using synchrotron radiation and a radioactive point source of ⁵⁷Co in Rh. SrFeO₃ is known as a typical cubic perovskite with a high-valence state of Fe⁴⁺ and shows metallic conductivity at 0.1 MPa down to 4.2 K. Applying an external high pressure, SrFeO₃ has not shown any structural transformation up to 74 GPa keeping an Fe⁴⁺ state but the Néel temperature increases up to 300 K at 18 GPa. The external high pressure may induce the ferromagnetism in SrFeO₃ by a decrease of the interatomic distance of Fe or an increase of the d-band width. ⁵⁷Fe Mössbauer measurements under externally applied longitudinal magnetic field using radioactive ⁵⁷Co in Rh source and also nuclear forward scattering measurements with a linearly polarized synchrotron radiation under external magnetic field indicate the existence of the pressure induced ferromagnetism in SrFeO₃. In this work we compare high-pressure Mössbauer spectroscopy using synchrotron and radioactive sources and summarize the advantages and disadvantages of each method.     

Isotopic ratio of evaporated ions,critical ionization distances,and ionization regions in the process of the field evaporation of molybdenum at high temperatures

A magnetic mass spectrometer with a field ion source has been used to study the steady-state field evaporation of molybdenum at a temperature of 1000–2000 K. Ions of all seven molybdenum isotopes have been observed in the process of evaporation; only low-charge ions Mo⁺² and Mo⁺ have been detected. The critical ionization distances and ionization regions for single- and double-charge Mo ions have been identified based on the measured ion energies and the experimentally determined intensity of the evaporation field. It has been demonstrated that ions are produced in the process of field evaporation of surface atoms at certain distances from the emitter surface in a very narrow spatial region.     

Pulsed UV laser spectroscopy of thermal Eu2+ ions

An investigation of the radiative lifetimes of several excited Eu²⁺ levels has been performed using a novel ion source for the production of thermal, doubly charged positive ions in a continuous gas discharge. This ionization device, first applied to the generation of Eu²⁺, is suitable also for other elements with similar ionization potential and vapour pressure.     

Conversion electron spectroscopy of isobarically purified trapped radioactive ions

The feasibility of the JYFLTRAP for in-trap spectroscopy has been studied. Several internally converted transitions have been measured for isomers of fission products with good accuracy. High-resolution spectroscopic data free of source effects have been obtained proving that trapped radioactive ions can provide excellent conversion electron sources. The shortest-lived isomer studied in this work was ^117m Pd with a half-life of 19.1ms, for which a superior peak-to-total ratio and an excellent line shape at the 9.9keV conversion electron line have been observed. Detection efficiencies and related phenomena of the present setup are analyzed.     

Space-Charge Effects with REXTRAP

The beam quality of radioactive ion beams produced by present target ion source technology is often not sufficient for direct post-acceleration. Furthermore, pulsed beams insure a more efficient use of an accelerator. In the case of REX-ISOLDE, the post accelerator at the CERN ISOLDE facility, a gas-filled Penning trap (REXTRAP) has been chosen for accumulation of the radioactive ions and conversion into cooled bunches. Radial centering of the ions is achieved by applying an rf field with a frequency equal to the cyclotron frequency of the desired ion species. The efficiency achieved in the first tests with different isotopes covering nearly the entire mass range was already >20%. Going to total numbers of >10⁵ stored ions in the trap a shift of the centering frequency could be observed, which is most likely due to space charge effects. Despite this, it was possible to accumulate up to 10⁷ ions and deliver them as cooled bunches. This revised version was published online in July 2006 with corrections to the Cover Date.     

Towards optical spectroscopy of the element nobelium ({\sf Z }= \mathsf{102}) in a buffer gas cell

For the investigation of the atomic level structure of heavy elements which can only be produced at on-line facilities such as GSI, a novel experimental procedure has been developed. It is based on Radiation Detected Resonance Ionization Spectroscopy (RADRIS) and can be applied to elements like nobelium produced at rates of a few ions per second. Fusion reaction products are separated from the primary beam by the velocity filter SHIP at GSI, stopped in a buffer gas cell, collected on a tantalum filament and then re-evaporated as atoms. The ions produced by resonance ionization with tunable laser beams are detected via their characteristic α decay. First on-line experiments on α-active ¹⁵⁵Yb, which is supposed to have an atomic level structure similar to nobelium, were performed. These test experiments focused on the optimization of the collection and re-evaporation process of the radioactive ions, the laser ionization efficiency and the detection via α decay. An overall efficiency for RADRIS of 0.8% with respect to the target production rate was measured. While further improvements of this efficiency are in progress it should already be sufficient for the search for atomic levels in nobelium.     

Electric field perturbation caused by an increase in conductivity related to seismicity-induced atmospheric radioactivity growth

The influence of conductivity perturbation in the lower atmosphere on the DC electric field over a seismic region is investigated. This perturbation is related to the emanation of radon and other radioactive elements into the lower atmosphere as the seismic activity increases. An increase in the level of atmospheric radioactivity results in the appearance of additional ionization sources. The altitude dependence of the ion formation rate is calculated. An ionization source changes the atmospheric conductivity because of the appearance of ions with an equilibrium number density. The perturbation of the atmospheric conductivity is calculated as a function of the altitude. Lower atmosphere conductivity changes disturb the electric current that flows in the global atmosphere-ionosphere circuit. This disturbance is caused by an external current over a seismic region. DC electric field perturbations on the Earth’s surface and in the ionosphere are estimated. Published in Russian in Khimicheskaya Fizika, 2007, Vol. 26, No. 4, pp. 39–44. The text was translated by the authors.     

A hot cavity laser ion source at IGISOL

A development program is underway at the IGISOL (Ion Guide Isotope Separator On-Line) facility, University of Jyväskylä, to efficiently and selectively produce low-energy radioactive ion beams of silver isotopes and isomers, with a particular interest in N = Z ⁹⁴Ag . A hot cavity ion source has been installed, based on the FEBIAD (Forced Electron Beam Induced Arc Discharge) technique, combined with a titanium:sapphire laser system for selective laser ionization. The silver recoils produced via the heavy-ion fusion-evaporation reaction, ⁴⁰Ca(⁵⁸Ni, p3n)⁹⁴Ag , are stopped in a graphite catcher, diffused, extracted and subsequently ionized using a three-step laser ionization scheme. The performance of the different components of the hot cavity laser ion source is discussed and initial results using stable ^{107, 109}Ag are presented.     

MIS-1 electron-beam ion source

The Institute of Nuclear Physics (INP) has developed and produced electron-beam multiply charged ion sources. These ion sources give the electron beam its high density in the ionization area, at the ion trap ≥10³ A/cm². They produce multiply charged ions of various elements, both gaseous and solid ones. These ion sources successfully employ the technique of the dozed inlet of solid-element atoms into the ion trap.     

Integrated target-ion source unit for on-line production of radioactive short-lived isotopes

A new version of integrated target-ion source unit (ionising target) has been developed for the on-line production of radioactive single-charged ions. The target is able to withstand temperatures up to 2500 ^°C and acts also as an ion source of the surface and laser ionisation. Off-line and on-line experiments with the ionising target, housing tantalum foils as a target material, have been carried out at the IRIS (Investigation of Radioactive Isotopes on Synchrocyclotron) facility. The off-line surface ionisation efficiency measured for stable atoms of Li, Rb and Cs was correspondingly 6% , 40% and 55% at the target temperature of 2000 ^°C and 3-10% for atoms of rare-earth elements Sm, Eu, Tm and Yb at a temperature of 2200 ^°C. The off-line measured values of the ionisation efficiency for stable Gd and Eu atoms by the laser beam ionisation inside the target were 1% and 7%, respectively. The radioactive beam intensities of neutron-deficient rare-earth nuclides from Eu to Lu produced by the integrated target-ion source unit have been measured at a temperature of 2500 ^°C. The results of the integrated target-ion source unit use for on-line laser resonance ionisation spectroscopy study of neutron-deficient Gd isotopes have been also presented.     

Composition of a non-self-sustained discharge plasma in an N2: O2: H2O mixture at atmospheric pressure

The plasma composition of a discharge sustained by a pulsed ionization source of μs duration is computed. It is shown that, within a time interval of ∼10⁻⁶ s after the ionization pulse, the dependences of the ion densities on the electric field and ionization source power show features that should be taken into account when developing laser systems for controlling electric discharges in long air gaps. The effect of the plasma composition on the efficiency of electron photodetachment from negative O ₂ ⁻ ions is investigated by the example of a discharge initiation system consisting of two lasers with different pulse durations and wavelengths. Plasmochemical processes under conditions of enhanced electron photodetachment from negative O ₂ ⁻ ions are simulated. It is shown that photodetachment can increase the electron density for a time of <10⁻⁵ s.     

强激光与高密度气体相互作用中电子和离子加速的数值模拟

在现有的一维粒子模拟程序的基础上发展了带光电离和碰撞电离及蒙特卡罗两体碰撞的模拟程序(1D PIC-MCC). 用此程序模拟研究了短脉冲激光与He气靶相互作用时电子和离子的加速过程. 研究表明当强激光与过临界密度的微米厚度的平面靶相互作用时，靶前表面物质将被激光脉冲前沿迅速离化；新生的电子被激光场有质动力加速成为高能电子，这些电子穿入到靶内，通过电子碰撞电离离化靶内物质；一部分高能电子穿透靶后，会在靶的后表面形成强的电荷分离场，该场迅速离化靶后表面物质，同时使得后表面离子得到加速. 部分穿透靶的超热电子将被电荷分离场重新拉回靶内，在靶的前后表面振荡. 一些振荡电子在此过程中得到电荷分离场加速，离开前表面，在前表面也形成电荷分离场，使前表面离子得到加速. 关键词： 激光等离子体 光电离和碰撞电离 电子加速 离子加速     

Carbon-cluster mass calibration at SHIPTRAP

A carbon-cluster ion source has been installed and tested at SHIPTRAP, the Penning-trap mass spectrometer for precision mass measurements of heavy elements at GSI. Carbon-cluster ions ¹²C_n ⁺, 5 ≤n ≤23, were produced by laser-induced desorption and ionization from a carbon sample. They were tested for the first time as reference ions in an on-line mass measurement of the radionuclides ¹⁴⁴Dy, ¹⁴⁶Dy and ¹⁴⁷Ho. In addition, carbon clusters of various sizes were used for an investigation of the systematic uncertainty of SHIPTRAP covering a mass range from 84 u to 240 u. The mass-dependent uncertainty was found to be negligible for the case of (m-m _ref)< 100 u. However, a systematic uncertainty of 4.5 ×10^-8 was revealed.     

The theoretical and experimental study of the ionization processes during the low energy ion sputtering

The process by which atoms are ionized as they are sputtered from a metal surface has been analyzed both theoretically and experimentally. In the theoretical part the expressions for ionization coefficient R⁺ of atoms having the ionization energy much larger than the metal work function have been derived using a molecular orbital method. The effect of the level crossing was estimated in an approximate way. In the experimental part the SIMS experiments on clean Ni and Al surfaces and on Ni surface covered with a submonolayer of adsorbed K, Na and Al are reported. It has been found and it is for the first time reported that the energy distribution of ions sputtered from a submonolayer of adatoms is independent of energy (200–2500 eV) and mass (Ar⁺ Xe⁺ of incident ions and depends only upon the adsorption energy of the adatom. The energy distribution of ions sputtered from bulk samples has been found dependent on the primary ion energy. The measurement of the absolute value of R⁺ has shown that there is a strong correlation between the number of the adatom valence d-electrons and the value of R⁺, the value of R⁺ being smaller for atoms with more d-electrons. These experimental data have been compared with the theoretical expressions and the important role of the mechanism which takes into account the bending of the adatom energy level has been assessed.     

A reliable noble gas duoplasmatron for the 10 mA range

Duoplasmatrons have been employed at GSI as accelerator sources of multiply charged heavy ions, but extensive experience was collected also with singly charged noble gas ions. Other ion species can be produced from volatile compounds. provided that the cathode is protected from aggressive vapours by an additional noble gas. In a second source modification. the sputter duoplasmatron, ions are directly obtained from solid material.

Recently the GSI-duoplasmatron has been equipped with plasma expansion cups in order to raise the ion current output. Generally, at least a factor of three is gained in beam intensity and other aspects of source performance are improved, too.

A new cathode design considerably enhances life-time and reliability, permitting uninterrupted operation for a few hundred hours. Tables of measured ion beam currents are given.     

Multiphoton ionization of CF<Subscript>3</Subscript>I clusters by ultraviolet laser radiation

The results of the investigation of the multiphoton ionization of (CF₃I) _n clusters by ultraviolet laser radiation are reported. The yields of the I₂⁺ and I⁺ ions, which are the products of the multiphoton ionization, have been measured as functions of the intensity of the ultraviolet radiation at the wavelengths of 308 and 232.5 nm. The degree of multiphoton ionization has been determined and appears to depend on the wavelength of radiation. The velocity distributions of the products have been measured in detail for various wavelengths and various polarizations of radiation. The anisotropy parameters of the velocity distributions of the produced ions and their kinetic energy have been determined. After analysis of the data, a mechanism of the multiphoton ultraviolet ionization of the clusters under investigation has been proposed. This mechanism depends on the used wavelengths.     

Charge distribution of the daughter atom in α decay of 210Po

The evaporation model developed by Russek and collaborators for multiple ionization of outer-shell electrons in ion-atom collisions has been applied to the charge distribution of the daughter atom produced by α decay of ²¹⁰Po. The calculated result indicates that most of the daughter atoms are positively charged ions with a mean charge of + 1.41. The other ionization mechanisms, the recoil effect and the shake-off effect, are also considered. In comparison with the recent experimental results, it is shown that the evaporation model predicts more adequately than the recoil effect and the shake-off effect.     

Desorption/ionization of acrylamide in aqueous solutions in atmospheric pressure air using a microdischarge with vortex focusing of ions

A method of desorption/ionization in a microdischarge with ion vortex focusing (vortex focusing microdischarge, VFM) is suggested. A glow microdischarge is initiated in an air flow, and resulting ions act on the surface of interest. As a model compound, an aqueous solution of acrylamide is taken. Desorption/ionization taking place under atmospheric pressure is followed by the mass-spectrometric identification of the ions. The operating parameters of the VFM system are studied and optimized. Upon optimization of the system, the detection limit of acrylamide trace amounts in aqueous solutions is determined using the suggested method of desorption/ionization and analyte ion focusing with a vortex (swirling) jet. The acrylamide detection limit is found to be 2 × 10^?3 g/L.     

The influence of discharge parameters on the generation of ions H<Subscript>3</Subscript><Superscript>+</Superscript> in the source based on reflective discharge with hollow cathode

For hydrogen ions source based on reflective discharge with hollow cathode the investigations of the effect of discharge current and gas pressure on the component composition of the ion beam have been performed. It has been shown that the optimization of the discharge parameters makes it possible to achieve up to 70% triatomic hydrogen ions H₃ ⁺ in the beam.