HIRFL-CSR实验环中束流损失机制及寿命研究

分析了在储存环中回旋的离子束与残余气体分子、 内靶和冷却电子束相互作用时的损失机制及相应的束流寿命, 针对兰州重离子加速器冷却储存环实验环内靶模式, 计算了50—500 MeV/u 12C6+, 36Ar18+, 132Xe54+和 238U92+等束流在各种损失机制影响下所对应的束流寿命和总的束流寿命。 结果表明: 影响束流寿命的主要因素是与内靶分子（原子）之间的电荷交换及与冷却电子束之间的辐射复合; 对于重离子束 132Xe54+和 238U92+, 与冷却电子束之间的辐射复合是影响其储存寿命的主要因素。The loss mechanism and lifetime of ion beams in collisions with residual gas, internal target and electrons in e cooler in heavy ion cooler storage rings were studied. The partial beam lifetimes resulting from various loss mechanisms and the total beam lifetimes of 50—500 MeV/u12C6+, 36Ar18+, 132Xe54+ and 238U92+ stored in the experimental ring of the Cooler Storage Ring at the Heavy Ion Research Facility in Lanzhou (HIRFL CSR) were calculated. The calculations indicate that the charge exchange process between ion beams and the internal target, as well as the radiative recombination process with the electrons in e cooler restrict the beam lifetime considerably. For heavy ion beams such as 132Xe54+ and 238U92+, the radiative recombination is the dominant loss mechanism     

Structural response of aluminum core–shell particles in detonation environment

Natural aluminum particles have the core–shell structure. The structure response refers to the mechanical behavior of the aluminum particle structure caused by external influences. The dynamic behavior of the structural response of aluminum core–shell particles before combustion is of great importance for the aluminum powder burning mechanism and its applications. In this paper, an aluminum particle combustion experiment in a detonation environment is conducted and analyzed; the breakage factors of aluminum particles shell in detonation environment are analyzed. The experiment results show that the aluminum particle burns in a gaseous state and condenses into a sub-micron particle cluster. The calculation and simulation demonstrate that the rupture of aluminum particle shell in the detonation environment is mainly caused by the impact of the detonation wave. The detonation wave impacts the aluminum particles, resulting in shell cracking, and due to the shrinkage-expansion of the aluminum core and stripping of the detonation product, the cracked shell is fractured and peeled with the aluminum reacting with the detonation product.     

Measurement and analysis of fission rates in a spherical mockup of uranium and polyethylene

Measurements of the reaction rate distribution were carried out using two kinds of Plate Micro Fission Chamber （PMFC）. The first is a depleted uranium chamber and the second an enriched uranium chamber. The material in the depleted uranium chamber is strictly the same as the material in the uranium assembly. With the equation solution to conduct the isotope contribution correction, the fission rate of 238U and 235U were obtained from the fission rate of depleted uranium and enriched uranium. Then, the fission count of 238U and 235U in an individual uranium shell was obtained. In this work, MCNP5 and continuous energy cross sections ENDF/BV.0 were used for the analysis of fission rate distribution and fission count. The calculated results were compared with the experimental ones. The calculation of fission rate of DU and EU were found to agree with the measured ones within 10% except at the positions in polyethylene region and the two positions near the outer surface. Because the fission chamber was not considered in the calculation of the fission counts of 238U and 235U, the calculated results did not agree well with the experimental ones.     

Dynamic Localization of a One—Dimensional Quantum Dot Array in an ac Electric Field

We investigate the dynamics of two interaction electrons confined to one-dimensional quantum dot array in an ac electric field.We find that initially localized electrons will remain localized in the absence of coulomb interaction if the ratio of the ac field magnitude to the frequency is a root of the ordinary zero-order Bessel function.In contrast to the case without Coulomb interaction,no matter what the value is,the electrons are delocalized and the delocalization effect depends on the ratio U/ω and eaE/ω,where U is the strength of Coulomb interaction,a is the lattice constant,and E and ω are the ac field amplitude and frequency,respectively.     

Measurement of Ξ_(cc)~(++) production in pp collisions at s~(1/2)=13 TeV

The production of Ξ_(cc)~(++) baryons in proton-proton collisions at a centre-of-mass energy of s~(1/2)=13 TeV is measured in the transverse-momentum range 4 pT15 GeV/c and the rapidity range 2.0 y4.5.The data used in this measurement correspond to an integrated luminosity of 1.7 fb~(-1),recorded by the LHCb experiment during2016.The ratio of the Ξ_(cc)~(++) production cross-section times the branching fraction of the Ξ_(cc)~(++)→Λ_c~+K~-π~+π~+ decay relative to the prompt Λ_c~+production cross-section is found to be(2.22±0.27±0.29)×10~(-4),assuming the central value of the measured Ξ_(cc)~(++) lifetime,where the first uncertainty is statistical and the second systematic.     

Spin—Other—Orbit Effect in Two—Mode Multiphoton Ionization

A previously unknown “spin-other-orbit” effect of photon modes is predicted by solving a Schrodinger-like equation for a non-relativistic electron interacting with a two-mode intense photon field propagating in two perpendicular directions.A multiphoton ionization experiment to test this effect is suggested.Transition rates which manifest this effect to be measured in the experiment are calculated and presented graphically.A detailed comparison between this effect and the well-known spin-other-orbit effect of electrons is included.     

Investigation of Λ+c- and Λb-Hypernuclei in Relativistic Mean-Field Model

We investigate the properties of Λc+- and Λb-hypernuclei within the framework of the relativistic mean-fieldmodel (RMF). It is found that no Λc+ bound states can exist if the Λc+ potential well depth |Uλc+| in nuclear matter isless than 10 MeV. If |Uλc+| is less than 20 MeV, Λc+ cannot bind to the heavier nuclei with atomic number larger than100. We suggest it is preferable to search the Λc+-hypernuclei from medium-heavy nuclear systems in experiment. Verysmall spin-orbit splitting for the Λc+ in hypernuclei is also observed, and for the Λb it is nearly zero.     

Study of the data taking strategy for a high precision τ mass measurement

To achieve a high precision τ mass measurement at the high luminosity experiment BESIII,Monte Carlo simulation and sampling technique are utilized to simulate various data taking cases for single and multiparameter fits by virtue of which the optimal scheme is determined. The optimized proportion of luminosity distributed at selected points and the relation between precision and luminosity are obtained. In addition,the optimization of the fit scheme is confirmed by scrutinizing a variety of fit possibilities.     

A puzzle of the radio-quiet quasar PG 1407+265: Are optical and X-ray emissions produced from a relativistic jet?

PG 1407+265 is a radio quiet quasar that has a relativistic jet.In this report,we show some peculiar properties of its optical and X-ray emissions,which indicate possible non-thermal origins produced from the jet.We use a simple synchrotron + synchrotron self Compton (SSC) model to fit the emissions with different ratios of energy densities between the magnetic field and electrons (η≡U B/U e),which predicts a different γ-ray luminosity.The First LAT AGN Catalog (1LAC) did not include PG 1407+265,which indic...     

Electronic structure and magnetic properties of rare-earth perovskite gallates from first principles

The density functional calculation is performed for centrosymmetric(La–Pm) GaO_3 rare earth gallates, using a full potential linear augmented plane wave method with the LSDA and LSDA+U exchange correlation to treat highly correlated electrons due to the very localized 4f orbitals of rare earth elements, and explore the influence of U = 0.478 Ry on the magnetic phase stability and the densities of states. LSDA+U calculation shows that the ferromagnetic(FM) state of RGaO_3 is energetically more favorable than the anti-ferromagnetic(AFM) one, except for LaGaO_3 where the NM state is the lowest in energy. The energy band gaps of RGaO_3 are found to be in the range of 3.8–4.0 eV, indicating the semiconductor character with a large gap.     

VIP-2 —High-Sensitivity Tests on the Pauli Exclusion Principle for Electrons

The VIP collaboration is performing high sensitivity tests of the Pauli Exclusion Principle for electrons in the extremely low cosmic background environment of the underground Gran Sasso National Laboratory INFN (Italy). In particular, the VIP-2 Open Systems experiment was conceived to put strong constraints on those Pauli Exclusion Principle violation models which respect the so-called Messiah–Greenberg superselection rule. The experimental technique consists of introducing a direct current in a copper conductor, and searching for the X-rays emission coming from a forbidden atomic transition from the L shell to the K shell of copper when the K shell is already occupied by two electrons. The analysis of the first three months of collected data (in 2018) is presented. The obtained result represents the best bound on the Pauli Exclusion Principle violation probability which fulfills the Messiah–Greenberg rule.     

Precision luminosity for Z^0 lineshape measurements with a silicon-tungsten calorimeter

The measurement of small–angle Bhabha scattering is used to determine the luminosity at the OPAL interaction point for the LEP I data recorded between 1993 and 1995. The measurement is based on the OPAL Silicon-Tungsten Luminometer which is composed of two calorimeters encircling the LEP beam pipe, on opposite sides of the interaction point. The luminometer detects electrons from small–angle Bhabha scattering at angles between 25 and 58 mrad. At LEP center-of-mass energies around the Z, about half of all Bhabha electrons entering the detector fall within a 79 nb fiducial acceptance region. The electromagnetic showers generated in the stack of 1 radiation length tungsten absorber plates are sampled by 608 silicon detectors with 38,912 radial pads of 2.5 mm width. The fine segmentation of the detector, combined with the precise knowledge of its physical dimensions, allows the trajectories of incoming 45 GeV electrons or photons to be determined with a total systematic error of less than 7 microns. We have quantified all significant sources of systematic experimental error in the luminosity determination by direct physical measurement. All measured properites of the luminosity event sample are found to be in agreement with current theoretical expectations. The total systematic measurement uncertainty is , significantly below the theoretical error of currently assigned to the QED calculation of the Bhabha acceptance, and contributes negligibly to the total uncertainty in the OPAL measurement of , a quantity of basic physical interest which depends crucially on the luminosity measurement. Received: 28 September 1999 / Published online: 14 April 2000     

Radiative ionization in slow ion-atom collisions

Bremsstrahlung from the ionization of inner shell electrons in slow ion atom collisions is considered. The yield predicted by the binary encounter approximation is small compared with experiment in 12–33 MeV O + Zr and O + Au collisions.     

Particle acceleration in ultra-intense laser plasma interaction

The acceleration of electrons in laser plasma interaction has been observed since the seventies, when it was initially considered as a deleterious effect, as, in the inertial fusion context, the so-called suprathermal electrons preheat the target. However, it has been quickly observed that a large benefit could be taken from these electrons. Two main directions are now followed. In the first direction, one tries to accelerate electrons to high energy, presently in the GeV range. The electrons may originate from a pre-accelerated beam, or directly from a gas target instantaneously transformed in a plasma by the ultra-intense laser pulse. In the second direction, one tries to transfer the energy of the electrons to fast ions, especially protons, presently in the few tens of MeV range. Thin targets are used for this transformation, the electrons being accelerated at the front of the target, while the ions may originate from the front part or the back part of the target, or from inside the target, depending on the parameters of the experiment. While the maximum energy was the initial goal of the pioneer experiments, there are now strong experimental efforts to improve the quality of the beams, in terms of luminosity, emittance, and energy spectrum. In the recent years, quasi-monoenergetic beams were obtained both for electrons and for ions.     

Nonstandard interactions in plasmon decay to a neutrino pair in a strongly magnetized medium

The neutrino luminosity of a stellar medium because of plasmon decay to a neutrino pair via nonstandard tensor interaction in a degenerate electron gas subjected to the effect of a magnetic field such strong that the electrons of the gas are in the lowest Landau level is calculated. Relative limits on nonstandard coupling constants are obtained from a comparison of the results of this calculation with the neutrino luminosity generated in the respective standard process proceeding under the same conditions.     

Novel internal target for electron scattering off unstable nuclei

A novel internal target has been developed, which will make electron scattering off short-lived radioactive nuclei possible in an electron storage ring. An "ion trapping" phenomenon in the electron storage ring was successfully utilized for the first time to form the target for electron scattering. Approximately 7 x 10(6) stable 133Cs ions were trapped along the electron beam axis for 85 ms at an electron beam current of 80 mA. The collision luminosity between the stored electrons and trapped Cs ions was determined to be 2.4(8) x 10(25) cm(-2) s(-1) by measuring elastically scattered electrons.     

Measurement of the ZZ production cross section and limits on anomalous neutral triple gauge couplings in proton-proton collisions at sqrt[s] = 7 TeV with the ATLAS detector

A measurement of the ZZ production cross section in proton-proton collisions at sqrt[s] = 7 TeV using data corresponding to an integrated luminosity of 1.02 fb(-1) recorded by the ATLAS experiment at the LHC is presented. Twelve events containing two Z boson candidates decaying to electrons and/or muons are observed, with an expected background of 0.3 ± 0.3(stat)(-0.3)(+0.4)(syst) events. The cross section measured in a phase-space region with good detector acceptance and for dilepton masses within the range 66 to 116 GeV is σ(ZZ → ?+ ?- ?+ ?-)(fid) = 19.4(-5.2)(+6.3)(stat)(-0.7)(+0.9)(syst) ± 0.7(lumi) fb. The resulting total cross section for on-shell ZZ production, σ(ZZ)(tot) = 8.5(-2.3)(+2.7)(stat)(-0.3)(+0.4)(syst) ± 0.3(lumi) pb, is consistent with the standard model expectation of 6.5(-0.2)(+0.3) pb calculated at the next-to-leading order in QCD. Limits on anomalous neutral triple gauge boson couplings are derived.     

Electronic structure of three-dimensional quantum dots

We study the electronic structure of three-dimensional quantum dots using the Hartree-Fock approximation. The confining potential of the electrons in the quantum dot is assumed to be spatially isotropic and harmonic. For up to 40 interacting electrons the ground-state energies and ground-state wavefunctions are calculated at various interaction strengths. The quadrupole moments and electron densities in the quantum dot are computed. Hund's rule is confirmed and a shell structure is identified via the addition energies and the quadrupole moments. While most of the shell structure can be understood on the basis of the unperturbed non-interacting problem, the interplay of an avoided crossing and the Coulomb interaction results in an unexpected closed shell for 19 electrons. Received 5 November 2001 / Received in final form 12 November 2002 Published online 1st April 2003 RID="a" ID="a"e-mail: vorrath@physnet.uni-hamburg.de     

Originalarbeiten / Travaux originaux / Original Papers

An account is given of a variational calculation to estimate the amplitudes of resonance factorsɛ in a recent theory to describe the enhancement of crystalline field potentials by conduction electrons in heavy rare earth metals. It is demonstrated that the values ofɛ obtained by minimising the energy of interaction between conduction electrons and rare earth ions are consistent with those previously used to form a comparison with experiment. These latter values were obtained by maximising theA ₂ ⁰ crystal field coefficient with respect toɛ. Consistency is exhibited in both the sign and order of magnitude of the resonance amplitudes and renders the theory parameterless. The values ofɛ show an approximate linear dependence with the number of electrons in the incompletef shell of the rare earth ions.     

(e,2e) and (e,3-1e) coincidence experiments for studying the PCI effect of low energy ionizing electrons in the Auger process of Ar

Our (e,3-1e) measurements for studying the post-collision interaction (PCI) after electron impact inner shell ionization of argon were continued and completed at different energy conditions. Emitted LMM Auger electrons are detected in coincidence with the ionizing scattered electrons and the energy of the slow PCI inducer ejected electron was calculated from energy conservation. Particularly the effect of the very low energy (i.e. 0–5 eV) ejected electrons (strongly asymmetric energy sharing) is studied at 500 and 460 eV primary electron energies. In the latter case, the background caused by outer-shell electrons was measured by itself and then removed from the coincident spectrum. Nevertheless, the evaluation of PCI distorted Auger lines is still considerably disturbed by the resonant Auger electrons from the high Rydberg states, their (e,2e) contribution was estimated in the paper.