共查询到20条相似文献,搜索用时 46 毫秒
1.
The thermalization of pµ atoms in protium and dµ atoms in deuterium is considered. Monte Carlo calculations are performed for gaseous (300 K) and solid (3 K) protium and deuterium targets. Complete sets of the total and differential cross sections for the scattering of pµ on protium targets and dµ on deuterium targets are used as an input to the Monte Carlo simulations. At 300 K, muonic atom scattering from single molecules of H2 and D2 is considered. In the case of solid hydrogen the correlation effects from all molecules of the sample are taken into account. In particular, the Bragg and phonon scattering cross sections are calculated. The spin states and average energy of the muonic atoms are shown as functions of time. It is shown that at energies below about 0.01 eV the solid-state effects influence strongly the calculated cross sections, and therefore the deceleration processes in the solids are much slower than in the gaseous targets. It is shown that the neutron spectrum due to ddµ formation and subsequent dd fusion is significantly affected by slow dµ thermalization in solid deuterium. 相似文献
2.
F. Mulhauser A. Adamczak G. A. Beer V. M. Bystritsky M. Filipowicz M. C. Fujiwara T. M. Huber R. Jacot-Guillarmod P. Kammel S. K. Kim P. Knowles A. R. Kunselman M. Maier V. E. Markushin G. M. Marshall A. Olin C. Petitjean T. A. Porcelli V. A. Stolupin J. Woźniak J. Zmeskal 《Hyperfine Interactions》2001,138(1-4):41-46
The TRIUMF E742 experiment has measured the energy dependence of the scattering cross-sections of muonic deuterium and tritium
on hydrogen molecules for collisions in the energy range 0.1–45 eV. The experimental setup permits the creation of muonic
atom (μd or μt) beams. The multilayered target system gives the possibility to choose the type of interactions to study and to isolate a
particular interaction. The scattering of μd or μt beams on H2 is analyzed via the muon transfer reaction to neon. The time-of-flight method is used to measure the scattering cross section
as a function of the energy of the muonic atom beam. The results are compared, using Monte Carlo simulations, with theoretical
calculations which have been recently performed with high accuracy.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
3.
S. G. Karshenboim V. G. Ivanov E. Yu. Korzinin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,39(3):351-358
In muonic atoms the Uehling potential (an effect of a
free electronic vacuum polarization loop) is responsible for the
leading contribution to the Lamb shift causing the splitting of
states with Δn=0 and Δl≠0. Here we consider the
Lamb shift in the leading nonrelativistic approximation, i.e.,
within an approach based on a certain Schr?dinger equation. That
is valid for low and medium Z as long as (Zα)2≪1. The
result is a function of a few parameters, including
κ=Zαmμ/me, n and l. We present various
asymptotics and in particular we study a region of validity of
asymptotics with large and small κ. Special attention is
paid to circular states, which are considered in a limit of
n≫1. 相似文献
4.
T.S. Jensen V.E. Markushin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,21(3):261-270
The deexcitation of exotic hydrogen atoms in highly excited states in collisions with hydrogen molecules has been studied
using the classical-trajectory Monte Carlo method. The Coulomb transitions with large change of principal quantum number n have been found to be the dominant collisional deexcitation mechanism at high n. The molecular structure of the hydrogen target is shown to be essential for the dominance of transitions with large Δn. The external Auger effect has been studied in the eikonal approximation. The resulting partial wave cross-sections are consistent
with unitarity and provide a more reliable input for cascade calculations than the previously used Born approximation.
Received 28 May 2002 Published online 15 October 2002
RID="a"
ID="a"e-mail: thomas@physik.unizh.ch 相似文献
5.
R. Gheisari 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(2):193-196
We calculate decay widths of the metastable ppμ*
ν,J molecular ion in non-adiabatic approach. The muonic molecular ion can be formed in collision of the excited pμ(2s) atoms
with H2. Then, decay of the ppμ*
ν,J system opens a path for the muon from pμ(2s) to pμ(1s). We employ trial wave function which includes non-adiabatic terms
to calculate some radiationless decay widths. The present results of the widths do not good agree with those given in our
previous work, while are more close to recent data of other researchers. 相似文献
6.
V. M. Bystritsky A. Adamczak G. A. Beer M. Filipowicz M. C. Fujiwara T. M. Huber R. Jacot-Guillarmod P. Kammel S. K. Kim P. Knowles A. R. Kunselman M. Maier V. E. Markushin G. M. Marshall F. Mulhauser A. Olin C. Petitjean T. A. Porcelli V. A. Stolupin J. Woźniak J. Zmeskal 《Hyperfine Interactions》2001,138(1-4):47-53
We present the study of μp atom scattering in solid hydrogen. Anomalously large emission of E
pμ≤1.9 meV μp's from a solid H2 layer was observed for the first time. This three times greater μp atom yield is due to non-elastic phonon scattering. As a result, it becomes possible to generate an ultracold flux of μp atoms. The recent calculations of the total and differential cross sections agree with all experimental results of μp atom scattering in solid H2.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
7.
M. K. Pandey R. K. Dubey D. N. Tripathi 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(2):275-279
The Classical Trajectory Monte Carlo (CTMC) Method has
been used to calculate the differential, partial and total single electron
capture cross sections for the collision of H+/D+ with Ca and Mg
atoms in the energy range of 1–100 keV. The differential cross sections
at angles near the diffraction limit (<0.1○) in both systems
show a forward peak followed by an asymptotic fall at higher angles. Total
and partial capture cross sections are found to be in good agreement with
the experimental observations. Oscillations in the partial capture cross sections have been explained due to the swapping
of the field electron.
Isotope effect in the electron transfer is reported to be negligible. 相似文献
8.
J. Piilo E. Lundh K.-A. Suominen 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,40(2):211-222
We have developed Monte Carlo wave function simulation schemes to study
cold collisions between magnesium atoms in a strong red-detuned laser field.
In order to address the strong-field problem, we extend the Monte Carlo wave function framework to include the partial wave
structure of the three-dimensional system. The average heating rate due to radiative collisions is calculated with two different
simulation schemes which are described in detail.
We show that the results of the two methods
agree and give estimates for the radiative collision heating rate for 24Mg atoms in a magneto-optical trap based on the 1S0–1P1 atomic laser cooling transition. 相似文献
9.
Dr. Minakshi L. K. Jha S. N. Chatterjee B. N. Roy 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(3):331-339
H+ and He2+ impact single and double ionization cross
sections of ground state lead atoms have been calculated in the binary
encounter approximation. Calculations of direct double ionization cross
sections have been performed in the modified double binary encounter model.
The accurate expressions of σΔE (cross-section for energy
transfer ΔE) and Hartree-Fock velocity distributions for the target
electrons have been used throughout the calculations. Contributions to
double ionization from Auger effect following ionization of inner shells
have been considered in the present work. Our H+ impact single and
double ionization cross sections are in good agreement with the experimental
observations. In calculations of He2+ impact cross sections, the
present theoretical approach shows limited success in the experimentally
investigated region (50–350 keV amu-1). 相似文献
10.
Woźniak J. Bystritsky V. M. Jacot-Guillarmod R. Mulhauser F. 《Hyperfine Interactions》1996,101(1):573-582
A technique of neutral muonic atom beams is proposed in the TRIUMF E742 experiment for measuring the scattering cross sections of muonic hydrogen isotopes in solid hydrogen. We present the results of Monte Carlo modeling of pµ and dµ atoms transport under the conditions of this experiment, taking into account the main physical as well as the geometrical aspects. The optimization of set-up parameters is performed in order to choose the most sensitive experimental conditions. 相似文献
11.
L. Chatterjee G. Das A. Chakravorty R. Goswami S. K. Mondal 《Hyperfine Interactions》1993,82(1-4):143-148
Interesting surprises in some exotic atom kinetics have been reported recently. These involve muonic atom transfer cross sections, nuclear pion capture and theq 1s effect in CF. These can be explained if the exotic atom population contains a contributing fast component. Such fast atoms can be formed by radiative continuum to bound transitions of fast (keV) muons or pions. Cross sections for formation of such fast pionic and muonic atoms and their velocity distributions are reported. The possibility of these processes competing with the thermalisation channels and contributing effectively to the exotic atom population is discussed. 相似文献
12.
J. S. Bakos G. P. Djotyan P. N. Ignácz M. Á. Kedves M. Serényi Zs. Sörlei J. Szigeti Z. Tóth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(1):141-149
The displacement of Rb atoms in a magneto-optical trap (MOT) caused by the force of a finite time series of counter-propagating
frequency modulated light pulse pairs is measured as a function of the chirp of the pulses. The frequency modulated light
pulses induced 85Rb 52S1/2 F=3 ↔ 85Rb 52P3/2 F'=2, 3, 4 excitation and de-excitation of the atoms. The result of this excitation
de-excitation process is a force causing the acceleration and, consequently, the displacement of the maximum of the spatial
distribution of the trap atoms. The time dependence of the populations of the levels of the atom are calculated — including
also the 85Rb 52S1/2 F=2 and F'=1 states — as
the result of the interaction with the finite train of counter propagating frequency modulated light pulses by the solution
of the Bloch equations. As the result of the measurement the interval of the chirp of the frequency modulated light of given
intensity where the transitions take place, are determined. The results of the experiment and the expectation on the basis
of model calculations are in qualitative agreement. 相似文献
13.
P. Barletta 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,53(1):33-40
This paper presents a comparative analysis of complexes made of one rare gas (Rg) atom and molecular hydrogen, for five different
Rg atoms. In particular, the vibrational band origins have been calculated, as well as the structural properties of the associated
wavefunctions. The study is extended to ultra-cold Rg–H2 collisions, object of a recent experiment aimed at producing ultra-cold H2 [1]. The molecular systems are studied variationally using a simple, yet effective, isotropic trial wavefunction. A large
number of potential energy surfaces available from the literature is considered. A comparative analysis shows that differences
of up to two orders of magnitude exist for the zero-energy elastic cross sections of the five complexes. Corrections to the
isotropic model have also been considered, showing no significant effect. 相似文献
14.
Cross sections for elastic and spin-flip scattering of metastable 2s muonic hydrogen on hydrogen atoms are calculated for
the symmetric systems pμ+p, dμ+d and tμ+t. The calculations are performed in the two-level approximation of the adiabatic
method with inclusion of the Lamb shift and electron screening. Due to the large polarizability of the 2s state, the obtained
cross sections significantly exceed their counterparts for the ground-state muonic hydrogen. 相似文献
15.
The QCMC scheme created earlier for cascade calculations in heavy hadronic atoms of hydrogen isotopes has been modified and
applied to the study of cascade processes in the μp muonic hydrogen atoms. The distribution of μp atoms over kinetic energies has been obtained and the yields of K-series X-rays per one stopped muon have been calculated.
Comparison with experimental data indicated directly that for muonic and pionic atoms new types of non-radiative transitions
are essential, while they are negligible for heavy (kaonic, antiprotonic, etc.) atoms. These processes have been considered
and their probabilities have been estimated.
This revised version was published online in August 2006 with corrections to the Cover Date. 相似文献
16.
A. Adamczak M. P. Faifman 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2009,51(3):341-345
The kinetics of muon-catalyzed-fusion processes (μCF) in pure D2 gas have been studied by means of Monte Carlo simulations for various target temperatures and densities. In particular, the
role of resonant and non-resonant ddμ formation in μCF has been investigated. It has been shown that non-resonant formation can be directly observed at very short times in the
neutron time spectra from μCF for low-density D2 targets. The time spectra of neutrons from the low-temperature ortho-D2 and para-D2 gas targets have been calculated. These spectra display a strong ortho-para effect, which agrees with experimental results
for the dilute-gas D2 targets. 相似文献
17.
J. S. Bakos G. P. Djotyan P. N. Ignácz M. Á. Kedves M. Serényi Zs. Sörlei J. Szigeti Z. Tóth 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2006,37(1):59-66
The spatial displacement of the 85Rb atoms in a
Magneto-Optical Trap (MOT) under the influence of series of frequency
modulated light pulse pairs propagating opposite to each other is measured
as a function of the time elapsed after the start of the pulse train, and
compared with the results of simulations. Adiabatic excitation and
consecutive de-excitation take place between the ground
52S1/2 (F=3) and the 52P3/2 (F'=2, 3, 4) excited levels as the result of
the interaction. The displacement of the 85Rb atoms is calculated as
the solution of simple equation of motion where the expelling force is that
arising from the action of the frequency modulated light pulses. The
restoring and friction forces of the MOT are taken into account also. The
system of Bloch equations for the density matrix elements is solved
numerically for transitions between six working hyperfine levels of the atom
interacting with the sequence of the frequency modulated laser pulses.
According to these simulations, the momentum transferred by one pulse pair
is always smaller than the expected 2ħk, (1) where ħ is the Plank constant and
k=2π/λ where λ is the wavelength, (2) having a maximum
value in a restricted region of variation of the laser pulse peak intensity
and the chirp. 相似文献
18.
M. Gupta K. L. Baluja 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,41(3):475-483
Electron-H2S collision process is studied using the R-matrix method. Nine low-lying states of H2S molecule are considered in the R-matrix formalism to obtain elastic integral, differential, momentum transfer and excitation cross sections for this scattering
system. We have represented our target states using configuration interaction (CI) wavefunctions. We obtained adequate representation
of vertical spectrum of the target states included in the scattering calculations. The cross sections are compared with the
experiment and other theoretical results. We have obtained good agreement for elastic and momentum transfer cross sections
with experiment for entire energy range considered. The differential cross sections are in excellent agreement with experiment
in the range 3–15 eV. A prominent feature of this calculation is the detection of a shape resonance in 2B2 symmetry which decays via dissociative electron attachment (DEA). Born correction is applied for the elastic and dipole allowed
transition to account for higher partial waves excluded in the R-matrix calculation. The electron energy range is 0.025–15 eV. 相似文献
19.
S.-U. Haq S. Mahmood M. A. Kalyar M. Rafiq R. Ali M. A. Baig 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,44(3):439-447
We present experimentally measured absolute values of the photoionization
cross sections from the 5s5p 1P1 and 5s5p 3P1 excited
states of strontium at the first ionization threshold as 11.4±1.8 Mb
and 10.7±1.7 Mb respectively using saturated absorption technique
along with a thermionic diode ion detector in conjunction with a Nd:YAG
pumped dye laser system. These threshold photoionization cross sections
values have been utilized to determine the oscillator strengths of the
5s5p 1P1↦5snd 1D2 and 5s5p 3P1↦5snd 3D2 Rydberg transitions. The oscillator strength densities in the
continuum corresponding to the 5s5p 3P1 excited state have also
been determined by measuring the photoionization cross sections at five
ionizing wavelengths above the first ionization threshold. Smooth merging of
the discrete f-values into the oscillator strength densities has been
observed for the 5s5p 3P1↦5snd 3D2 series across the
ionization threshold. 相似文献
20.
D. H. Shi J. F. Sun Z. L. Zhu H. Ma Y. F. Liu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2007,45(2):253-259
To quantify the changes in the geometric shielding effect in a molecule as the incident electron energy varies, an empirical
fraction, which represents the total cross section contributions of shielded atoms in a molecule at different energies, is
presented. Using this empirical
fraction, the total cross sections for electron scattering by
CH4, C2H6, C2H3F3, C2H4,
C2F4, C2Cl4 and C2Cl2F2 are
calculated over a wide energy range from 30 to 5000 eV by the
additivity rule model at the Hartree-Fock level. The quantitative
total cross sections are compared with those obtained by
experiment and other theories where available. Good agreement is
attained above 100 eV. 相似文献