摘要:

In this work we report calculations of the impact parameter dependent energy loss and charge exchange cross section of4He+ions on atomic neon by taking into account the dynamics of both electrons and nuclei. The results are obtained for projectiles energies ranging from a few eV/amu up to 100 keV/amu. We also report the nuclear and electronic contribution to the total stopping cross section. Comparison of the present results for this channel with the available experimental data shows good agreement. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1395235

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Energy spectra of &agr;-particles channeling along the optical axis (c-axis) of a quartz crystal in the energy regionE&agr;=3.0–3.5&hthinsp;Mevin the backscattering geometry were taken and analyzed. Computer simulations based on the assumption that the dechanneling of &agr;-particles follows an exponential law are in good agreement with the measured spectra, yielding electronic stopping powers for the specific crystal orientation that vary between 17.82 and 16.12 eV/Å respectively for the energy interval into consideration. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1395236

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Previously published measurements of stopping powers of four organic (co)polymers for protons, alpha particles, and7Liions have been analyzed in terms of modified Bethe-Bloch theory. This procedure allows extraction of values of various parameters which constitute an integral part of the formalism, most notably the target mean excitation energy (I) and Barkas-effect parameter (b). Normally one can expect the extracted I-value to exceed by a few per cent the value based on the additivity assumption(IB),whereas the extracted b-value should lie within the expected interval of about 1.3–1.5. Results of one series of measurements with the same experimental arrangement, utilizing thin target foils of formvar (a polyvinylformyl resin), polysulfone, kapton (a polymide), and vyns (a vinylchloride-vinylacetate copolymer), yielded results quite consistent with expectation except that the extracted I-value for formvar lay about 20&percent; below the value ofIB.This salient anomaly will be examined in detail. Moreover, trends in extracted I- and b-values suggesting a dependence on projectile will be considered. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1395237

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

We investigate the influence of the dechanneling process on the parameters of undulator radiation generated by ultra-relativistic positrons channelling along a crystal plane, which is periodically bent. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1395238

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

Neutral Ne atoms with keV energies are scattered under channeling conditions, i.e. at a glancing angle of incidence, from a LiF(001) surface. By means of a time-of-flight method with a pulsed neutral beam we record energy distributions for scattered projectiles. For this specific system the small energy transferred to the crystal lattice (“nuclear energy loss”) during channeling via binary collisions with large impact parameters dominates the dissipation of projectile energy. All other excitations of the solid can be brought to a negligible level. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1395239

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The stopping powers of 2–10 MeV Si, P and S ions in Ni, Cu and Ge thin films has been measured using a novel technique based on elastic recoil detection (ERD). This technique eliminates the need to recalibrate the silicon surface barrier detector while changing the incident ion species. Results have been compared to SRIM 2000 and other theoretical predictions and experimental measurements. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1395240

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

A theoretical treatment of the exchange contributions in Bethe’s theory of the stopping of electrons is presented. The effects of the binding of the electron within the atom are systematically evaluated. Starting with the first Born approximation, an expansion in powers of the ratio of the electronic energy of the target atom to the incident electron’s kinetic energy is obtained, and the leading contribution recovers Bethe’s results. The approach involves the use of sum rules that are generalizations of the Bethe sum rule, specifically dealing with the contributions from electron exchange. Though the discussion is restricted to the stopping power here, the approach is quite general and may be applied to the calculation of the exchange contributions to other quantities related to the cross sections of electron-atom scattering. Our results indicate that there may be significant corrections when one accounts for the binding of the target electrons. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1395241

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The yields of the dissociation products of water ionized by fast proton impact were measured relative toH2O+using the coincidence time-of-flight method. The relative yields following single ionization were found to be independent of the collision velocity over the range of collision velocities measured and similar to the values reported for ionization by equal velocity electron impact, except for a higher rate ofH2+production. Double ionization of water leads predominantly to two dissociation channels, namelyH++OH+andH++O++H,which are equally likely and also independent of the collision velocity. TheO2+fragment was found to be always in coincidence withH+,thus suggesting it is only a product of triple (or higher) ionization of water. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1395242

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

The charge state and energy dependences of Transfer Ionization (TI) and Single Capture (SC) processes are being investigated. The collision systems reported here areO(4–8)+ions interacting with Helium. The measurement is being made for beam energy 1 MeV/u using a supersonic He jet with two-stage collimation. A recoil ion momentum spectrometer is used to separate TI and SC by recording the longitudinal momentum transfer and time-of-flight of the recoil ions. A magnetic field is used to control the position of the recoil ions on the detector. The ratios of TI to SC are determined with high accuracy and are compared with previous results. Higher Z-ions are under investigation. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1395243

出版商:AIP    

年代:1901

数据来源: AIP

摘要:

A Johann-type single crystal spectrometer(2R=1500&hthinsp;mm)with a high resolution was equipped in BL01B1 in Spring-8. This has an excitation source over an energy range more than 3.1 keV for a core level investigation and material sciences. The experimental results with fluorescence x-ray spectra on copper and tungsten are first time presented here. The features inKandLemission spectra of copper and tungsten excited near threshold, and a clear relationship between them and spectral structures usually obtained in the laboratory, are mentioned. The monochromator uses the Si double-crystal system, in which the energy resolution is within the width of Rocking curve in Bragg reflection. The spectrometer has a resolving power of&Dgr;E/E=2×10−4forFe&hthinsp;K&agr;1spectra. Si(100) crystal was used for the copper and Si(111) used for the tungsten, respectively. ©2001 American Institute of Physics.

ISSN:0094-243X    

DOI:10.1063/1.1395244

出版商:AIP    

年代:1901

数据来源: AIP