共查询到20条相似文献,搜索用时 22 毫秒
1.
D.Q. Fang W.Q. Shen J. Feng X.Z. Cai Y.G. Ma H.Y. Zhang P.Y. Hu W.L. Zhan Z.Y. Guo G.Q. Xiao J.X. Li M. Wang J.F. Wang Z.J. Ning J.Q. Wang J.S. Wang Q.J. Wang Z.Q. Chen 《The European Physical Journal A - Hadrons and Nuclei》2001,10(4):381-385
Fragments produced in the reactions of 69 MeV/nucleon 36Ar and 55 MeV/nucleon 40Ar on a Be target have been measured experimentally. The isotopic distributions from fragmentation reaction for both projectiles
are compared with modified statistical abrasion-ablation model calculations. A strong isospin effect exhibits in the fragment
distributions produced in 36Ar and 40Ar fragmentation. Experimental evidence for the disappearance of the isospin effect in the isotopic distributions produced
by projectile fragmentation is observed with the increase of the violence of nuclear reaction.
Received: 15 November 2000 / Accepted: 11 April 2001 相似文献
2.
W. Christen U. Even 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,16(1):87-90
This contribution addresses the inelastic interaction of positively charged molecular cluster ions with a solid surface at
kinetic energies up to 30 eV/molecule. We report experimental results on the scattering of mass-selected, protonated methanol
cluster cations (CH3OH)nH+, n = 4-32, off a diamond-coated silicon surface. In particular we provide fragment size distributions of methanol cluster ions
following their impact on the target, as well as surface-induced neutralization probabilities of methanol cluster ions as
a function of the size and the kinetic energy of the parent clusters.
Received 30 November 2000 相似文献
3.
Z. Sosin R. Płaneta T. Ciszek J. Brzychczyk W. Gawlikowicz K. Grotowski S. Micek P. Pawłowski A. Wieloch A.J. Cole D. Benchekroun E. Bisquer A. Chabane M. Charvet B. Cheynis A. Demeyer P. Désesquelles E. Gerlic A. Giorni D. Guinet D. Heuer P. Lautesse L. Lebreton A. Lléres M. Stern L. Vagneron J.B. Viano 《The European Physical Journal A - Hadrons and Nuclei》2001,11(3):305-310
The shape of the velocity distributions of charged particles projected on the beam direction can be explained if emissions
from the hot projectile-like fragment and the target-like fragment are supplemented by an emission from an intermediate velocity
source located between them. The creation of this source is predicted by a two-stage reaction model where, in the second stage,
some of the nucleons identified in the first stage as participants form a group of clusters located in the region between
the colliding nuclei. The cluster coalescence process is governed on the average by the maximum value of entropy, although
its fluctuations are also significant. The properties of the intermediate velocity source are precisely described, including
the isotopic composition of the emitted particles.
Received: 12 March 2001 / Accepted: 20 June 2001 相似文献
4.
U. Galster P. Kaminski M. Beckert H. Helm U. Müller 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(3):307-318
We have performed kinematically complete investigations of molecular photodissociation of triatomic hydrogen in a fast beam
translational spectrometer recently built in Freiburg. The apparatus allows us to investigate laser-induced dissociation of
neutral molecules into two, three, or more neutral products. The fragments are detected in coincidence and their vectorial
momenta in the center-of-mass frame are determined. We demonstrate the potential of the method at the fragmentation of the
3 s
2
A
1
′
(
N
= 1,
K
= 0) state of triatomic hydrogen. In this state, three-body decay into ground state hydrogen atoms H+H+H, two-body predissociation
into H+H
2
(v
,
J), and photoemission to the H
3
ground state surface with subsequent two-body decay are competing channels. In the case of two-body predissociation, we determine
the rovibrational population in the H
2
(v
,
J) fragment. The vibrational distribution of H
2
is compared with approximate theoretical predictions. For three-body decay, we measure the six-fold differential photodissociation
cross-section. To determine accurate final state distributions, the geometric collection efficiency of the apparatus is calculated
by a Monte Carlo simulation, and the raw data are corrected for apparatus efficiency. The final state momentum distribution
shows pronounced correlation patterns which are characteristic for the dissociation mechanism. For a three-body decay process
with a discrete kinetic energy release we have developed a novel data reduction procedure based on the detection of two fragments.
The final state distribution determined by this independent method agrees extremely well with that observed in the triple-coincidence
data. In addition, this method allows us to fully explore the phase space of the final state and to determine the branching
ratios between the two- and three-body decay processes.
Received 29 March 2001 相似文献
5.
Molecular (or granular) dynamics methods are used to study the gravity-driven flow of granular material through a horizontal
aperture in three dimensions. The grains are spherical and modeled using a short-range repulsive interaction, together with
normal and tangential frictional damping forces. The material is contained in a rough-walled cylindrical container with a
circular hole in its base, and to permit flow measurements under steady-state conditions a continuous feed approach is employed
in which exiting grains are replaced at the upper surface of the material. The dependence of flow velocity and discharge rate
on aperture diameter is found to agree with experiment; other quantities such as the kinetic energy and pressure distributions
are also examined.
Received 5 June 2000 and Received in final form 21 September 2000 相似文献
6.
R. Płaneta W. Gawlikowicz A. Wieloch J. Brzychczyk T. Ciszek A.J. Cole P. Désesquelles K. Grotowski P. Hachaj S. Micek P. Pawłowski Z. Sosin D. Benchekroun E. Bisquer A. Chabane M. Charvet B. Cheynis A. Demeyer E. Gerlic A. Giorni D. Guinet D. Heuer P. Lautesse L. Lebreton A. Lléres M. Stern L. Vagneron J.B. Viano 《The European Physical Journal A - Hadrons and Nuclei》2001,11(3):297-304
The creation of hot Ca-like fragments was investigated in the 40Ca + 40Ca reaction at 35 AMeV. Using the AMPHORA 4π detector system, the primary projectile-like fragment was reconstructed and its
properties were determined. Both primary and secondary distributions are compared with the predictions of a Monte Carlo code
describing a heavy-ion collision as a two-step process. Some of the nucleons which are identified as participants in the first
step are transferred in the second step to these final states, which correspond on the average to the maximum value of entropy
(thermodynamic probability). The model allows for competition between mean-field effects and nucleon-nucleon interactions
in the overlap zone of the interacting nuclei. The analysis presented here suggests a thermalized source picture of the decay
of the projectile-like fragment. The validity of the reconstruction procedure for projectile-like fragments is discussed.
Received: 12 March 2001 / Accepted: 20 June 2001 相似文献
7.
P. Cacciani F. Brandi I. Velchev C. Lyngå C.-G. Wahlström W. Ubachs 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(1):47-56
Rotationally resolved spectral lines in the C
-
X
(1, 0) band of carbon monoxide are investigated under high resolution using a coherent vacuum ultraviolet laser source, continuously
tunable near 107 nm. Transition frequencies are determined by calibrating against a reference standard of iodine lines, recorded
with saturation spectroscopy in the visible range, yielding an absolute accuracy of 0.003 cm-1 in the vacuum ultraviolet. Improved molecular constants for the excited state are derived and no effects of perturbation
are found at the present level of accuracy. Line broadening measurements result in information on the excited state lifetime
of the C
1
Σ
+
,
v
= 1 state for five natural isotopomers of carbon monoxide: τ(
12
C
17
O
) = 280 ps, τ(
12
C
18
O
) = 210 ps, τ(
13
C
16
O
) = 295 ps, τ(
13
C
17
O
) = 160 ps, and τ(
13
C
18
O
) = 150 ps. Within the accuracy of the present measurements no effects of J-dependent lifetimes were observed, for neither of the isotopomers. In addition direct time domain measurements of the lifetime
of the C
1
Σ
+
,
v
= 0 and v
= 1 states of the main isotopomer are performed in a pump-probe experiment using a picosecond VUV-laser, yielding τ(
12
C
16
O
) = 1780 ps for v
= 0 and τ(
12
C
16
O
) = 625 ps for v
= 1. For C
1
Σ
+
,
v
= 0 in 12C16O and 13C16O the same lifetime is found; this lifetime matches experimental values of the oscillator strength and hence supports previous
results showing pure radiative decay in this state; the error margins however do not exclude some low level of predissociation.
The measurements indicate that the C
1
Σ
+
,
v
= 0 state of the 13C18O isotopomer is predissociated with an estimated yield of 17% (i.e. above the level of predissociation for 12C16O.) From the combined data predissociation yields upon excitation of the C
1
Σ
+
,
v
= 1 state are derived, lying in the range 0.84-0.91 for the five less abundant isotopomers; for the main 12C16O isotopomer a strongly deviating predissociation yield of 0.65 is deduced.
Received 21 December 2000 and Received in final form 26 March 2001 相似文献
8.
V.S. Malinovsky J.L. Krause 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,14(2):147-155
We present a general theory of adiabatic rapid passage (ARP) with intense, linearly chirped laser pulses. For pulses with
a Gaussian profile and a fixed bandwidth, we derive a rigorous formula for the maximum temporal chirp rate that can be sustained
by the pulse. A modified Landau-Zener formula displays clearly the relationships among the pulse parameters. This formula
is used to derive the optimal conditions for efficient, robust population transfer. As illustrations of the theory, we present
results for two- and four-level systems, and selective vibronic excitation in the I2 molecule. We demonstrate that population transfer with chirped pulses is more robust and more selective than population transfer
with transform-limited pulses.
Received 6 September 2000 and Received in final form 25 September 2000 相似文献
9.
R. V. Jolos A. K. Nasirov G. G. Adamian A. I. Muminov 《The European Physical Journal A - Hadrons and Nuclei》2000,8(1):115-124
The effect of shell structure on the distribution of the excitation energy between fragments of the deep inelastic collisions
is analysed in the microscopic approach. It is shown that the density of the single-particle levels of the proton and neutron
subsystems near the Fermi surface determines the ratio between the excitation energies of fragments at the initial stage of
the collision. It is shown also that the shell structure strongly influences the correlations between the width of the charge
distributions and the total kinetic energy losses. Calculations are performed for the 40,48Ca+248Cm reactions. The results obtained suggest a possible interpretation for the observed concentration of the excitation energy
in the light fragment in deep inelastic collisions for a wide range of the total kinetic energy losses.
Received: 27 July 1999 / Accepted: 29 March 2000 相似文献
10.
N. Liu W. Gao J. Yin 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2002,19(2):137-145
A new scheme to magnetically guide cold, neutral atoms using a V-shaped current-carrying conductor is proposed. The spatial
distributions of the magnetic fields, potentials and forces generated by the V-shaped current-carrying conductor are calculated,
and the relationship between the magnetic field and the parameters of the V-shaped current-carrying conductor are analyzed
in detail. Our study shows that the V-shaped current-carrying conductor proposed here can be used to guide cold atoms in the
weak-field-seeking state, and to construct various atom-optical elements, such as atomic funnel, atomic beam-splitter and
atom interferometer and so on, and even to realize a single-mode atomic waveguiding under certain conditions.
Received 17 November 2000 and Received in final form 26 May 2001 相似文献
11.
K. H. Schmidt 《The European Physical Journal A - Hadrons and Nuclei》2000,8(1):141-145
A new statistical test procedure is described to evaluate whether a set of radioactive-decay data is compatible with the assumption
that these data originate from the decay of a single radioactive species. Criteria to detect contributions from other radioactive
species and from different event sources are given. The test is applicable to samples of exponential distributions with two
or more events.
Received: 24 March 2000 / Accepted: 13 April 2000 相似文献
12.
X.H. Yan J.W. Ding Q.B. Yang 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(2):157-163
Developing a renormalization group approach, we study the hopping conductivity of nanocrystalline chains with different site
energies. Exact calculations show that many parameters including nano-sizes, randomness of grain distributions, lattice distortions,
site energies, transition rates, Fermi energy, and temperature influence the conductivity. Some new singular features, for
example the frequency shift, the amplitude fluctuations, and the interchange between “peak” and “valley” behavior of the imaginary
part of the conductivity can be caused by certain parameters mentioned above, while the interface distortions modulate mainly
the overall amplitudes of the conductivity at the whole frequency region.
Received 13 January 2000 and Received in final form 12 September 2000 相似文献
13.
A.B. Larionov W. Cassing M. Effenberger U. Mosel 《The European Physical Journal A - Hadrons and Nuclei》2000,7(4):507-518
The proton–charged pion correlated emission is studied in the reactions Au (1.06 AGeV) + Au, Ni (1.06 and 1.93 AGeV) + Ni
and Ni (1.97 AGeV) + Cu within the BUU approach. The associated invariant mass distributions are shifted to smaller energies
with respect to the free Δ(1232) mass distribution due to kinematical reasons. We find that the existing and partly conflicting
experimental data do not allow to draw definite conclusions on the in-medium modification of the Δ(1232).
Received: 18 October 1999 / Revised version: 4 February 2000 相似文献
14.
J. Tempere J.T. Devreese 《The European Physical Journal B - Condensed Matter and Complex Systems》2001,20(1):27-33
A sum rule for the first frequency moment of the optical absorption of a many-polaron system is derived, taking into account
many-body effects in the system of constituent charge carriers of the many-polaron system. In our expression for the sum rule,
the electron-phonon coupling and the many-body effects in the electron (or hole) system formally decouple, so that the many-body
effects can be treated to the desired level of approximation by the choice of the dynamical structure factor of the electron
(hole) gas. We calculate correction factors to take into account both low and high experimental cutoff frequencies.
Received 26 April 2000 and Received in final form 5 December 2000 相似文献
15.
G. Durand F. Spiegelmann 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,13(2):237-243
The stability against fragmentation and possible relaxation of the lowest excited states of the Na5F4 cluster (representative of cubic non stoechiometric clusters with an excess sodium atom, also called sodium-tail) is investigated
by means of one-electron pseudopotential calculations with particular reference to photoabsorption processes from the ground
state. Whereas the equilibrium configuration of the ground state has C3v symmetry, the doubly degenerate 12E excited state is affected by a conical intersection and a Jahn-Teller effect associated with the rotation of the sodium
tail around the C3-axis. This yields a “Mexican hat" topology for the lowest sheet with three equivalent Cs minima. Alternatively the 22A1 state has a minimum retaining the C3v symmetry. The dissociation paths of the cluster along the C3-axis into respectively Na4F4 + Na and Na4F3 + NaF are also investigated. Among the former paths, the excited states are found adiabatically stable with respect to the
products. However in the A1 symmetry, fragmentation into NaF exhibits an interesting avoided crossing between configurations correlated respectively
with Na4F3
+ + NaF- and Na4F3 + NaF. Such interaction, similar to the well-known charge exchange processes in elementary molecules might induce non adiabatic
predissociation of the 22A1 state. This mechanism is invoked to explain the differences between R2PI and depletion spectra, correlated with the dissociation
or relaxation of the excited states.
Received 24 March 2000 and Received in final form 11 July 2000 相似文献
16.
Pioneering experiments with stored and cooled exotic nuclei at relativistic energies have been performed using the combination
of the fragment separator FRS with the storage-cooler ring ESR. Exotic nuclei created in peripheral collisions are spatially
separated in-flight and injected into the storage ring for high-precision mass and unique lifetime measurements. Lifetimes
of stored bare and few-electron nuclei have been measured to study the influence of the electron density on the β decay. This
condition, relevant for stellar plasma, can now be systematically investigated in the laboratory for the first time. Characteristic
experiments of the present FRS-ESR system are presented and perspectives for a next-generation facility are briefly outlined.
Received: 1 May 2001 / Accepted: 4 December 2001 相似文献
17.
F.X. Gadéa Ph. Durand T. González-Lezana G. Delgado-Barrio P. Villarreal 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,15(2):215-219
The wave operator theory of quantum dynamics is applied to characterize coupled metastable states. The theory extends to quasi
bound states methods which are standard for dealing with bound levels. It is shown that interacting resonances can be investigated
by means of small-dimensional effective Hamiltonians containing all the significant information of intrinsic properties which
drive the various dynamical processes taking place. The study of the vibrational predissociation of I2Ne, mediated by intramolecular energy redistribution, illustrates the power of the method. In addition to its accuracy to
determine spectroscopic profiles and survival probabilities, it results more efficient than usual energy or time-domain numerical
calculations.
Received 25 January 2001 and Received in final form 11 May 2001 相似文献
18.
C.P. Sun X.F. Liu D.L. Zhou S.X. Yu 《The European Physical Journal D - Atomic, Molecular, Optical and Plasma Physics》2001,17(1):85-92
To account for the phenomenon of quantum decoherence of a macroscopic object, such as the localization and disappearance of
interference, we invoke the adiabatic quantum entanglement between its collective states (such as that of the center-of-mass
(CM)) and its inner states based on our recent investigation. Under the adiabatic limit where motion of the CM does not excite
the transition of inner states, it is shown that the wave function of the macroscopic object can be written as an entangled
state with correlation between adiabatic inner states and quasi-classical motion configurations of the CM. Since the adiabatic
inner states are factorized with respect to each component of the macroscopic object, this adiabatic separation can induce
the quantum decoherence. This observation thus provides us with a possible solution to the Schr?dinger cat paradox.
Received 24 October 2000 and Received in final form 8 March 2001 相似文献
19.
P.V. Degtyarenko M.V. Kossov H.-P. Wellisch 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):411-420
An event generator based on the CHIPS model is implemented in the GEANT4 simulation toolkit. Nuclear fragment production in
the process of pion capture on nuclei is used to tune the parameters of the CHIPS model describing clusterization of nucleons
in nuclei. The spectra of nucleons and nuclear fragments in pion capture and in photonuclear reactions at 60 MeV are compared
with experimental data.
Received: 30 May 2000 / Accepted: 2 November 2000 相似文献
20.
W. Nörenberg G. Papp P. Rozmej 《The European Physical Journal A - Hadrons and Nuclei》2000,9(3):327-343
The diabatic approach to dissipative collective nuclear motion is reformulated in the local-density approximation in order
to treat the normal modes of a spherical nuclear droplet analytically. In a first application the adiabatic isoscalar modes
are studied and results for the eigenvalues of compressional (bulk) and pure surface modes are presented as function of density
and temperature inside the droplet, as well as for different mass numbers and for soft and stiff equations of state. We find
that the region of bulk instabilities (spinodal regime) is substantially smaller for nuclear droplets than for infinite nuclear
matter. For small densities below 30% of normal nuclear matter density and for temperatures below 5 MeV all relevant bulk
modes become unstable with similar growth rates. The surface modes have a larger spinodal region, reaching out to densities
and temperatures way beyond the spinodal line for bulk instabilities. Essential experimental features of multifragmentation,
like fragmentation temperatures and fragment-mass distributions (in particular the power-law behavior) are consistent with
the instability properties of an expanding nuclear droplet, and hence with a dynamical fragmentation process within the spinodal
regime of bulk and surface modes (spinodal decomposition).
Received: 4 September 2000 / Accepted: 14 November 2000 相似文献