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1.
Measurements of relative cross sections of K- and L-shell ionization of silver and gold targets by positron and electron impact
at projectile energies of 30–70 keV are reported. The experiments were performed at the slow positron source TEPOS at the
linac of the Strahlenzentrum. This source and the experimental equipment will be described briefly and the experimental results
will be presented in detail. In addition, plane wave Born (PWBA) calculations were performed. They include an electron exchange
term and the deceleration or acceleration of the incident projectile in the nuclear field of the target atom. The present
experimental results agree well with these calculations; for L-shell ionization, they are at variance with a previous experiment
where a different energy dependence was observed. 相似文献
2.
Cross section ratios for K- and L-shell ionization of thin silver and gold targets by positron and electron impact have been determined at projectile energies of 30–70 keV. The experimental results are confirmed by calculations in plane wave Born approximation (PWBA) which include an electron exchange term and account for the deceleration or acceleration of the incident projectile in the nuclear field of the target atom. We report first absolute cross sections for K- and L-shell ionization of silver and gold targets by lepton impact in the threshold region. We have measured the corresponding cross sections for electron (e–) impact with an electron gun and the same experimental set-up. 相似文献
3.
Yu. A. Fainberg Ya. A. Teplova N. V. Novikov 《Journal of Surface Investigation: X-ray, Synchrotron and Neutron Techniques》2010,4(3):494-497
The energy and charge distributions of protons and hydrogen atoms reflected from the Cu surface in the case of grazing incidence
angles are measured at energies of incident particles (H+ and H0) of 200 and 250 keV. The charged fractions of reflected particles are analyzed. A weak dependence of the neutral fraction
of reflected particles on the scattering angle is discovered for incidence angles of 1°–2° and an energy of scattered particles
of 60 keV or less. It is shown that the neutral fraction of reflected particles with an energy of 60–80 keV or more is independent
of the scattering angle and is determined by the ratio of the cross sections for the electron capture and loss by ions in
the material. 相似文献
4.
Thin films Backscattering Coefficients (BSCs) for 1 to 4 keV electron and positron normally incident beams are stochastically modeled and calculated by the Monte Carlo
method. We suggest a new function BSC(δ) depending only of one free parameter (to be determined) and which can describe very well the variation of the backscattering
coefficient versus the film thickness (δ). Moreover, this paper aims at discussing the observed differences between the electron and positron properties impinging
on solid targets. 相似文献
5.
In this paper, we report a new method to determine the effective atomic number, Z
eff, of composite materials for Compton effect in the γ-ray region 280–1115 keV based on the theoretically obtained Klein–Nishina scattering cross-sections in the angular range
50°–100° as well as a method to experimentally measure differential incoherent (Compton) scattering cross-sections in this
angular range. The method was employed to evaluate Z
eff for different inorganic compounds containing elements in the range Z = 1–56, at three scattering angles 60°, 80° and 100° at three incident gamma energies 279.1 keV, 661.6 keV and 1115.5 keV
and we have verified this method to be an appropriate method. Interestingly, the Z
eff values so obtained for the inorganic compounds were found to be equal to the total number of electrons present in the sample
as given by the atomic number of the elements constituting the sample in accordance with the chemical formula of the sample.
This was the case at all the three energies. 相似文献
6.
M. Behar C. D. Denton R. C. Fadanelli I. Abril E. D. Cantero R. Garcia-Molina L. C. C. Nagamine 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2010,59(2):209-213
We report the results of an experimental-theoretical study on the stopping
power of ZrO2 films for swift H and He ion beams. The experiments,
using the Rutherford Backscattering technique, were done for protons with
incident energies in the range 200–1500 keV and for α-particle beams
with energies in the range 160–3000 keV. The theoretical calculations were
done in the framework of the dielectric formalism using the MELF-GOS model
to account for the ZrO2 target electronic response. It is shown that
for both ion beams, the agreement between theory and experiment is quite
remarkable. 相似文献
7.
Total electron yields for perpendicular impact of C+ ions on W have been measured for projectile energies from 0.2 keV to 7 keV. The data are compared with the data of C+ bombardment of gold and graphite in order to demonstrate general trends in kinetic electron yields at low projectile velocities. The total electron yields in the studied combinations of projectiles and substrates show a similar exponential dependence Γ ∝ (v/A) exp(−A/v), where A is a constant and v is the projectile velocity. 相似文献
8.
A. Bentabet 《Applied Surface Science》2007,253(21):8725-8728
The backscattering coefficient of 1-4 keV electron and positron beams normally incident impinging on Al thin film targets is stochastically modeled within a Monte Carlo frame work. The aim of the present paper is to study the behavior of the backscattering coefficient as a function of the Al film thickness. To the authors’ knowledge, no theoretical or experimental work on the dependence of the positron backscattering coefficient on film thickness targets has been reported so far. It is found that the backscattering coefficient for both electron and positron beams presents different behaviors when the Al film thickness belongs to the nano-scale. Beyond this scale, the behavior becomes qualitatively similar. 相似文献
9.
K. S. Mann K. S. Kahlon N. Singh K. L. Allawadhi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):455-456
The total M shell relative photoionization
cross-sections for Au, Pb, Th and U have been measured in the energy region
6–12 keV. External conversion K X-rays of suitable elements has been employed
as incident photons to photo ionize the total M shell of elements under
investigation. The method provides relative cross-sections therefore does
not make use of theoretically calculated average M shell fluorescence yields
which involve uncertainties of the order of 20%. No evidence of deviation
from calculated values of cross-sections have been observed within
experimental errors for all incident photon energies. 相似文献
10.
In order to study the depth-dependent characteristics of open-volume defects in thin surface layers, the variable-energy positron lifetime spectroscopy (VEPLS) has been enabled by pulsing a continuous positron beam. The buncher is a quarter-wave coaxial resonator and the RF-signal is fed in by a coupling loop with a frequency of 149.89 MHz and the reflection factor of 0.05 measured by a Network Analyzer. Three synchronic signals with their phases and amplitudes adjusted independently are supplied for start signal of the positron lifetime measurement and the power signal by an electronic system. The stop signal is derived from a detector, a BaF2 scintillator coupled to a photomultiplier-tube (Hamamatsu). The time resolution of 295 ps (FWHM) was achieved for a Kapton film and a Ti sample at positron energies in the range between 1 keV and 30 keV. 相似文献
11.
The behavior of disordered isolated volumes (zones) in InP under electron action was characterized by TEM observations. The
total areal fraction of the disordered zones in initial InP pre-irradiated by 100 keV heavy Au ions decreased as a function
of irradiating electron fluence (time of TEM electron beam irradiation) within all the investigated electron energy range
(100–300 keV), Disappearance of disordered zones shows that these zones are sensitive to electron beam irradiation and recover
even under electron energies not sufficient to directly elastically displace lattice atoms In and P. 相似文献
12.
V.B. Gavrikov V.P. Likhachev J.D.T. Arruda-Neto A.L. Bonini 《The European Physical Journal A - Hadrons and Nuclei》2001,12(4):487-493
Differential and integral features of incoherent X-radiation, induced by relativistic electrons in crystals, are studied for
observation angles θγ several times greater than γ-1, where γ is the projectile Lorentz factor. The existence of sharp maxima and a minimum of the five-folded incoherent differential
cross-section as a function of the final electron angles, and a dip minimum when the cross-section is taken as a function
of the photon energies, is demonstrated. At near backward observation angles the three-folded cross-section shows a maximum
in the region of several keV photon energies. The obtained results allow us to optimize the conditions for coincidence experiments,
minimizing the incoherent contribution to the total radiation yield, and helping to analyse results of finite-size detector
experiments with crystal targets.
Received: 2 July 2001 / Accepted: 26 November 2001 相似文献
13.
B. Nath S. Chattopadhyaya C. Sinha 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2000,11(1):31-36
Triple differential cross-sections (TDCS) of a hydrogenic (He+) ion has been studied by positron impact using coplaner geometry for both symmetric and asymmetric kinematics in the intermediate
and medium high incident energy region. TDCS has also been studied of He+ ion by electron impact for symmetric kinematics taking account of the electron exchange effect. The final state wavefunction
is chosen as the correlated 3-body Coulomb wavefunction satisfying the exact asymptotic boundary condition. The long range
Coulomb interaction in the initial channel between the ionic target and the projectile has also been taken into account properly.
For positron impact, the collision is found to be almost recoilless at lower incident energies, in contrast to the strong
recoil peak noted in the case of electron impact ionisation. For electron impact, the exchange effect is found to be significantly
high for equal energy sharing in the final channel.
Received 10 July 1999 and Received in final form 7 December 1999 相似文献
14.
V. L. Bratman Yu. K. Kalynov V. N. Manuilov 《Radiophysics and Quantum Electronics》2009,52(7):472-481
We review briefly the main ideas and achievements in the field of physics related to shortwavelength large-orbit gyrotrons,
in which the coupling of electrons with the working mode and the discrimination of parasitic modes in the case of resonance
at the high cyclotron harmonic are more efficient compared with conventional gyrotrons. The results of studying a new large-orbit
gyrotron with moderate electron energies of 50–80 keV and comparatively low magnetic fields of 10.5–14 T are presented. In
this gyrotron, high-power single-mode generation was obtained at the second and third cyclotron harmonics in the frequency
range 0.55–1.00 THz. The prospects of development and application of short-wavelength large-orbit gyrotrons are discussed. 相似文献
15.
Summary Elastic and inelastic collisions of fast non-relativistic electrons with positronium atoms have been studies in the Born-Ochkur
approximation. It has been shown that exchange plays an important role for transitions between states with the same parity
as in this case the direct scattering amplitude vanishes. Numerical results for the total and ortho-para conversion cross-sections
for the 1s→1s, 1s→2s and 1s→2p transitions have been presented for projectile energies varying from 0.1 to 10 keV. According to charge symmetry, presented
results apply also to positron projectiles. 相似文献
16.
It is shown experimentally that under energetic electron bombardment the backscattered electrons from solid targets contribute
significantly (∼80%) to the observed total electron yield, even for targets of high backscattering coefficients. It is further
found that for tungsten (Z = 74) with a backscattering coefficient of about 0.50, about 20% of the total electron yield is contributed by the total
secondary electrons for impact energies in the range of 8–28 keV. The yield of true backscattered electrons at normal incidence
(η
0), total secondary electrons (δ) and the total electron yield (δ
tot) produced in collisions of 8–28 keV electrons with W have been measured and compared with predictions of available theories.
The present results indicate that the constant-loss of primary electrons in the target plays a significant role in producing
the secondary electrons and that it yields a better fit to the experiment compared to the power-law.
相似文献
17.
Based on new experimental investigations of elastic p
6Li scattering at energies 500–1150 keV and angles 30–170°, a phase analysis is performed and interaction potentials for p
6Li-system in 2,4S- and 2P-states are constructed. 相似文献
18.
A.M. Samant S. Kailas A. Chatterjee A. Shrivastava A. Navin P. Singh 《The European Physical Journal A - Hadrons and Nuclei》2000,7(1):59-64
The fission fragment angular distributions have been measured for the system 19F +209Bi over a range of bombarding energies from 88.0 MeV to 125.6 MeV. The measured fission fragment anisotropies are in agreement
with the saddle point statistical model calculations in the above energy range. Combining these data with those available
for 11B, 12C, 14N, 16O and 18O +209Bi, 208Pb systems, it is concluded that the spherical target plus projectile systems behave “normal” from near- to above – barrier
energies. This observation is in contrast to the “anomalous” anisotropies exhibited by the deformed actinide target – projectile
systems at near – barrier energies.
Received: 5 May 1999 / Revised version: 25 July 1999 相似文献
19.
O. Sueoka C. Makochekanwa M. Kimura 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,37(3):377-383
Total cross-sections (TCSs) for 0.2–1000 eV positrons and 0.4–1000 eV
electrons colliding with normal-octane and cyclo-octane molecules have been
studied using a relative measurement method. The TCS curves for positron and
electron vary smoothly and compare well with other alkane molecules, in
order of increasing carbon number. For positron scattering, weak humps at
1.5–2.5 eV for both normal- and cyclo-octane were observed. In the energy
range lower than 2.2 eV, positron TCSs are roughly equal to or larger than
electron TCSs. For electron scattering, a resonance peak at 8 eV and a
shoulder at 25.0 eV were observed for both molecules. Over all the energy
range, the TCS values for normal-octane are larger than those of
cyclo-octane. The positron and electron TCS data for normal- and
cyclo-octane molecules are briefly compared with those for normal- and
cyclo-hexane. 相似文献
20.
Measurements of the secondary electron energy spectra resulting from very low-energy positron bombardment of a polycrystalline Au surface are presented. The low-energy part of the secondary spectra contain significant contributions from two processes: (1) annihilation-induced Auger electrons that have lost energy before leaving the surface and (2) secondary electrons resulting from direct energy exchange with an incident positron. Our data indicate that the second process (direct energy exchange with the primary positron) is still important at and below 3 eV incident beam energy. Since energy conservation precludes secondary electron generation below an incident beam energy equal to the difference between the electron and positron work functions (∼3 eV), the fact that we still observe significant secondary electron emission at energies at or below this value provides strong evidence that the incident positrons are falling directly into the surface state and transferring all of the energy difference to an outgoing secondary electron. These measurements were also used to obtain the first experimentally determined upper limit on the intensity of the spectrum of Auger-induced secondary electrons. 相似文献