Beijing Radiation Center

Beijing, China

Beijing Radiation Center

Beijing, China
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Sitiwaldi I.,Beijing Normal University | Xie B.-S.,Beijing Normal University | Xie B.-S.,Beijing Radiation Center
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2017

We investigate the electron–positron pair production process in an oscillating field with modulated amplitude in the quantum kinetic formalism. By comparing the number density in the oscillating field with and without modulation, we find that the pair production rate can be enhanced by several orders when the photon energy just reaches the threshold with the help of shifted frequency due to modulation. We also detect the same effect in a pulse train with subcycle structure. We demonstrate that the frequency threshold can be lowered by the frequency of the pulse train due to the modulation effect. We also find that the momentum distribution for a N-pulse train can reach N2 times the single pulse at the maximum value and the number density as a function of pulse number follows the power law with index 1.6 when the modulation effect is maximized. © 2017 The Authors


Su J.,Beijing Normal University | Su J.,Beijing Radiation Center | Zhang F.-S.,Beijing Normal University | Zhang F.-S.,Beijing Radiation Center | Zhang F.-S.,Accelerator Centre
Physical Review C - Nuclear Physics | Year: 2013

The non-equilibrium in momentum space of fragmenting sources in central heavy-ion collisions at Fermi energy is reproduced by partly compensating for the fermionic feature in the isospin-dependent quantum molecular dynamics model. A memory loss ratio is defined to investigate the degree of entrance channel memory loss. The incomplete memory loss and the linear correlation between the memory loss ratio and the normalized radial flow energy are found both from experimental data and calculations. The residual memory indicates that the global equilibrium is not achieved in central collisions. The local equilibrium is achieved only in a very small central region of the fragmenting source. Both the asymmetry distribution of the expansive flow and the deformation of the fragmenting source are the consequences of the residual memory. A method to extract the transversal-to-longitudinal axis ratio of the expanding fragmenting source is suggested. © 2013 American Physical Society.


Jiang X.,Beijing Normal University | Yan S.,Beijing Normal University | Yan S.,Beijing Radiation Center | Maruhn J.A.,Goethe University Frankfurt
Physical Review C - Nuclear Physics | Year: 2013

The dynamics of energy dissipation in head-on fusion reactions of mass-symmetric systems at low bombarding energies is studied by exploiting the improved quantum molecular dynamics model. The results indicate that the form and magnitude of the mass parameter and friction coefficient show strong dependence on system size, bombarding energy, and relative distance. The dynamical mass parameter has almost no effect on the friction coefficient. Two-body collisions play an important role in energy dissipation even when the incident energy is much lower than the Fermi energy. The nucleon-nucleon collisions not only attenuate the energy dissipation but also hinder the nucleon transfer process. © 2013 American Physical Society.


Xie W.-J.,Beijing Normal University | Xie W.-J.,Yuncheng University | Zhang F.-S.,Beijing Normal University | Zhang F.-S.,Beijing Radiation Center | Zhang F.-S.,Accelerator Centre
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2014

The isospin-dependent quantum molecular dynamics model is used to investigate the nuclear collective flow observables in semicentral 197Au+197Au collisions at 400A MeV. It is found that the calculated results can reproduce both the experimental data and the other theoretical calculations. We find that the cluster production influences the rapidity dependence of directed flow of protons but less influences the results of tritons. Neutron-proton differential collective flows have larger values when taking the neutron effective mass less than the one of protons as compared with the case of neutron effective mass greater than the one of protons at larger rapidities and transverse momenta. Thus neutron-proton differential collective flows are proposed to be a useful probe to the neutron-proton effective mass splitting and the momentum-dependent symmetry potential. © 2014 Elsevier B.V.


Li Y.,Beijing Normal University | Yan S.,Beijing Normal University | Yan S.,Beijing Radiation Center | Jiang X.,Beijing Normal University | Wang L.,Beijing Normal University
Nuclear Physics A | Year: 2013

By using the improved quantum molecular dynamics model, the mechanism of ternary breakup reactions is systematically studied with several symmetrical colliding systems. The result shows that the nearly symmetrical ternary breakup occurs in central and semiperipheral reactions and experiences an extremely and sufficiently inelastic collision with the intense nucleon exchanges. The dynamical effects and nucleon-nucleon correlations play very important roles for determining the outcome of the reactions. © 2013 Elsevier B.V.


Xie W.-J.,Beijing Normal University | Xie W.-J.,Beijing Radiation Center | Xie W.-J.,Yuncheng University | Su J.,Beijing Normal University | And 6 more authors.
Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics | Year: 2013

Based on the improved isospin-dependent Boltzmann-Langevin model which incorporates the dynamical fluctuations, we study the π production in central heavy ion collisions at different incident energies from 250 to 1200AMeV. It is found that the π multiplicity is sensitive to the nuclear equation of state. At π subthreshold energy, the fluctuations have a larger effect on the π multiplicity. The π-/π+ ratios as a probe of nuclear symmetry energy are calculated with different stiffness of symmetry energy. The results favor a supersoft symmetry energy of the potential term in comparison with the FOPI data, which supports the one obtained by the usual Boltzmann-Uehling-Uhlenbeck model. © 2012 Elsevier B.V.


Sheng Y.-B.,Beijing Normal University | Deng F.-G.,Beijing Normal University | Zhou H.-Y.,Beijing Normal University | Zhou H.-Y.,Beijing Radiation Center
Quantum Information and Computation | Year: 2010

We present a single-photon entanglement concentration protocol for long-distance quantum communication with quantum nondemolition detector. It is the first concentration protocol for single-photon entangled states and it dose not require the two parties of quantum communication to know the accurate information about the coefficient α and β of the less entangled states. Also, it does not resort to sophisticated single-photon detectors, which makes this protocol more feasible in current experiments. Moreover, it can be iterated to get a higher efficiency and yield. All these advantages maybe make this protocol have more practical applications in long-distance quantum communication and quantum internet. © Rinton Press.


Su J.,Beijing Normal University | Su J.,Beijing Radiation Center | Zhang F.-S.,Beijing Normal University | Zhang F.-S.,Beijing Radiation Center | Zhang F.-S.,Accelerator Centre
Physical Review C - Nuclear Physics | Year: 2011

A systematic study of isotope temperatures has been presented for heavy-ion collisions at 600 MeV/nucleon via the isospin-dependent quantum molecular dynamics model in the company of the statistical decay model (GEMINI). We find that the isospin dependence of the isotope temperatures in multifragmentation is weak; however, this effect is still visible over a wide isotopic range. The isotope temperatures for the neutron-rich projectiles are larger than those for the neutron-poor projectiles. We also find that the isotope temperatures calculated by the model decrease with increasing nuclear mass. © 2011 American Physical Society.


Wang T.-J.,Beijing Normal University | Wang T.-J.,Beijing Radiation Center | Deng F.-G.,Beijing Normal University
Communications in Theoretical Physics | Year: 2011

We present a remote three-party quantum state sharing (QSTS) scheme with three-atom Greenberger - Horne - Zeilinger (GHZ) states assisted by cavity QED and flying qubits. It exploits some photons to act as the flying qubits for setting up the quantum channel securely with three-atom systems in a GHZ state, which maybe make this remote QSTS scheme more practical than some other schemes based on atom systems only or ion-trap systems as photons interact with their environments weakly. The coherence of the stationary atom qubits in cavities provides the convenience for the parties in QSTS to check eavesdropping, different from entangled photon systems. Moreover, the present scheme works in a collective-noise condition and it may be more practical than others in applications in future. © 2011 Chinese Physical Society and IOP Publishing Ltd.


Bai Y.-J.,CAS Institute of Botany | Bai Y.-J.,University of Chinese Academy of Sciences | Chen L.-Q.,China Agricultural University | Ranhotra P.S.,University of Lucknow | And 3 more authors.
Global Change Biology | Year: 2015

The Earth has undergone a significant climate switch from greenhouse to icehouse during the Plio-Pleistocene transition (PPT) around 2.7-2.4 million years ago (Ma), marked by the intensification of the Northern Hemisphere glaciation (NHG) ~2.7 Ma. Evidence based on oceanic CO2 [(CO2)aq], supposed to be in close equilibrium with the atmospheric CO2 [(CO2)atm], suggests that the CO2 decline might drive such climate cooling. However, the rarity of direct evidence from [CO2]atm during the interval prevents determination of the atmospheric CO2 level and further assessment on the impact of its fluctuation. Here, we reconstruct the [CO2]atm level during 2.77-2.52 Ma based on a new developed proxy of stomatal index on Typha orientalis leaves from Shanxi, North China, and depict the first [CO2]atm curve over the past 5 Ma by using stomata-based [CO2]atm data. Comparisons of the terrestrial-based [CO2]atm and the existed marine-based [CO2]aq curves show a similar general trend but with different intensity of fluctuations. Our data reveal that the high peak of [CO2]atm occurred at 2.77-2.52 Ma with a lower [CO2]aq background. The subsequent sharp fall in [CO2]atm level might be responsible for the intensification of the NHG based on their general temporal synchronism. These findings shed a significant light for our understanding toward the [CO2]atm changes and its ecological impact since 5 Ma. © 2014 John Wiley & Sons Ltd.

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