共查询到20条相似文献,搜索用时 15 毫秒
1.
The fission cross section and fission probability of 197Au, induced by (1665 MeV) π-, have been studied using CR-39 track detectors. A 4π-geometry was used to count track statistics. A beam of negative pions of 1665 MeV was produced at AGS of Brookhaven National Laboratory, USA, and allowed to fall normally on the stack. Two detectors from the stack were scanned for fission fragment tracks after etching in 6N NaOH at 70℃. The statistics of fission fragment tracks in both detectors were obtained. It was found that there was a marked asymmetry of registered tracks with respect to the forward and backward hemispheres. This asymmetry could be partly accounted for on the basis of momentum transfer to the struck nucleus. On the basis of counting statistics fission cross section was measured, and fission probability was determined by dividing the fission cross section with the reaction cross section. The fission cross-section and fission probability were compared with the computed values using the cascade-exciton model code CEM95. 相似文献
2.
M. Ablikim et al 《中国物理 C》2012,36(11)
The decay ψ(2S)→Ω-Ω+ is analyzed using 14×106 ψ(2S) events recorded by the Beijing Spectrometer Ⅱ (BESⅡ) at the Beijing Electron Positron Collider (BEPC). Based upon events with no missing charged tracks and a satisfactory four-constraint kinematic t, we determine the upper limit for the branching fraction of ψ(2S)→Ω-Ω+ to be 1.5×104 at a 90% confidence level. By including events with one missing charged track, we are able to report the first evidence of an Ω+ signal with a statistical signi cance of 3.1|σ. The branching fraction of ψ(2S)Ω+ is determined to be (4.80±1.56(stat)±1.30(sys))105. 相似文献
3.
M. Ablikim et al 《中国物理C(英文版)》2012,36(11):1040-1045
The decay ψ(2S)→Ω-Ω+ is analyzed using 14×106 ψ(2S) events recorded by the Beijing Spectrometer Ⅱ (BESⅡ) at the Beijing Electron Positron Collider (BEPC). Based upon events with no missing charged tracks and a satisfactory four-constraint kinematic t, we determine the upper limit for the branching fraction of ψ(2S)→Ω-Ω+ to be 1.5×104 at a 90% confidence level. By including events with one missing charged track, we are able to report the first evidence of an Ω+ signal with a statistical signi cance of 3.1|σ. The branching fraction of ψ(2S)Ω+ is determined to be (4.80±1.56(stat)±1.30(sys))105. 相似文献
4.
Extended Measurement of the v2 (1- ←0+) Band of H3O+ by Mid-Infrared Diode Laser Spectroscopy
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Twenty-five new R-branch lines of the v2(1^-← 0^+) band of H3O^+ are measured using diode laser velocity modulation spectroscopy between 1070 and 1230 cm^-1. The H3O^+ ions are produced in a high voltage ac discharge with water diluted in helium. The observed lines together with all the previously published measurements are fit to the standard vibration-rotational Hamiltonian of an oblate symmetric top, yielding a set of improved molecular constants. All the sextic centrifugal distortion constants for both 0^+ and 1^- states are determined precisely. The observed R(13, 0) transition is shifted about -0.129 cm^-1 from its calculated value, indicating that a near degeneracy exists between the (13, 0)^+ and (13, 3)^- ground-state rotation-inversion levels. 相似文献
5.
In this paper, we calculate the branching ratios of Λb→pK- and pπ- decays in the avor changing Z' model. We nd that the branching ratios for these two decay modes are sensitive to the contributions of the Z' boson. For Λb→pK- decay, if the left-handed couplings are equal to the right-handed couplings, the branching ratio of this decay could match up to the currently experimental data for ξs=0.01 and -52°<φsL<132°, or ξs=0.004 and 0°<φsL<84°; if only the left-handed couplings are considered, it could match up to the experimental data for ξs=0.01 and -10°φsL<138°. And for Λb→pK- decay, if the left-handed and right-handed couplings are equal, the branching ratio of Λb→pK- decay may be consistent with the currently experimental data with ξd=0.05 and -135°φdL<43°, if only the left-handed couplings are considered, it may be consistent with ξd=0.05 and -114°φdL<8°. 相似文献
6.
In this paper, we calculate the branching ratios of Λb→pK- and pπ- decays in the avor changing Z' model. We nd that the branching ratios for these two decay modes are sensitive to the contributions of the Z' boson. For Λb→pK- decay, if the left-handed couplings are equal to the right-handed couplings, the branching ratio of this decay could match up to the currently experimental data for ξs=0.01 and -52°<φsL<132°, or ξs=0.004 and 0°<φsL<84°; if only the left-handed couplings are considered, it could match up to the experimental data for ξs=0.01 and -10°φsL<138°. And for Λb→pK- decay, if the left-handed and right-handed couplings are equal, the branching ratio of Λb→pK- decay may be consistent with the currently experimental data with ξd=0.05 and -135°φdL<43°, if only the left-handed couplings are considered, it may be consistent with ξd=0.05 and -114°φdL<8°. 相似文献
7.
using the isospin–and momentum–dependent transport model, for three different symmetry energies, we have calculated the π–/π+ ratio as a function of time and tranverse–momentum in central 132sn+124 sn collision at e_beam/A=400mev. the results show that the π–/π+ ratios is very sensitive to the stiffness of the symmetry energy. thus we can probe the stiffness of the symmetry energy at high densities by using the π–/π+ ratio at different time or transverse momentum more accurately than before. comparing experimental data with the calculations will reveal crucial information about the stiffness of the symmetry energy more accurately.hadronic transport model, symmetry energy, π–/π+ ratio 相似文献
8.
M. Ghergherehchi H. Afarideh Y.S. Kim S.Y. Park S.B. Lee D.H. Shin J.S. Chai X.J. Mu B.N. Lee 《Radiation measurements》2012,47(6):410-416
High- and intermediate-energy protons are not able to directly form a track in a CR-39 etch detector (TED). Such detectors, however, can be used for the detection and dosimetry of the beams of these particles through the registration of secondary charged particles with sufficiently high values of linear energy transfer (LET). High-energy protons (72–220 MeV) and Intermediate-energy protons (10–30 MeV) with low LET values ranging from 1.1 down to 0.4 keV/μm and 5.87 down to 2.40 keV/μm, respectively are considered in this study. It seems to be sufficient to create secondary particles, although the LET values are low. This phenomenon can modify the characteristics of the energy transfer process due to these particles, which should be taken into account when such particles are used for radiobiology studies or for radiotherapy. The importance of these secondary particles was investigated experimentally by means of an LET spectrometer based on a chemically etched track detector in which the tracks of the primary protons are not revealed. Experiments were performed with proton beams available at the Nuclear Research Center for Agriculture and Medicine (NRCAM) in Karaj, Iran and at the National Cancer Center (NCC) in Seoul, Korea with protons of primary energies of about 10–30 MeV and 72–220 MeV respectively. The contribution of the secondary particle dose increases as the proton energy decreases. The origin of the secondary particles in interactions with protons having high and intermediate energies due to various nuclear reactions was calculated by the both ALICE and TALYS computer codes. The secondary microdosimetry doses were also calculated by GEANT4 code. There is large discrepancy between experimental and calculated results in low proton energies. It has been verified that there is a good correlation between the experimentally obtained results and the reaction cross sections predicted by ALICE and TALYS codes. 相似文献
9.
The resistivity of conventional glass is quite high and is unacceptable in a high rate environment. Low resistive glass-electrodes could be a solution for this problem. The present study reports the e^+/e^- simulation results of an RPC detector made from low resistive phosphate glass electrodes. The detailed geometrical configuration of the content materials which are the essential components of the glass of the RPC detector have been created with the GEANT4 simulation code. Two different types of particle sources, i.e. for e^+/e^- , have been located on the detectors surface to evaluate the performance of the phosphate glass RPC. Both of the particles have been simulated as a function of their respective energies in the range of 0.1 MeV 1.0 GeV. The present simulation work has shown that the resistive electrode plays an important role for the particle production in the RPC configuration. 相似文献
10.
Q. Wang L. D. Chen X. J. Liu W. D. Yu X. M. Li 《Applied Physics A: Materials Science & Processing》2009,96(3):643-653
Melting, vaporization and resolidification processes of thin gold film irradiated by a femtosecond pulse laser are studied
numerically. The nonequilibrium heat transfer in electrons and lattice is described using a two-temperature model. The solid–liquid
interfacial velocity, as well as elevated melting temperature and depressed solidification temperature, is obtained by considering
the interfacial energy balance and nucleation dynamics. An iterative procedure based on energy balance and gas kinetics law
to track the location of liquid–vapor interface is utilized to obtain the material removal by vaporization. The effect of
surface heat loss by thermal radiation was discussed. The influences of laser fluence and duration on the evaporation process
are studied. Results show that higher laser fluence and shorter laser pulse width lead to higher interfacial temperature,
deeper melting and ablation depths. 相似文献
11.
Study of n-γ discrimination for 0.4-1 MeV neutrons using the zero-crossing method with a BC501A liquid scintillation detector
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CHEN Yong-Hao LEI Jia-Rong ZHANG Xiao-Dong AN Li ZHENG Pu WANG Xin-Hua ZHU Chuan-Xin HE Tie 《中国物理C(英文版)》2013,37(4):046202-046202
An experimental system aimed at n-γ discrimination using the zero-crossing method with a φ3"× 2" BC501A liquid scintillation detector was established and tested with an Am-Be neutron source. Two-dimensional plots of energy versus zero-crossing time were obtained. The quality of n-γ discrimination was checked by the figure-of-merit (FOM), the neutron peak-to-valley ratio, and the proportion of leaked neutrons over all neutron events. The performance of n-γ discrimination in terms of FOM was compared with previous work done by other groups. The n-γ discrimination in four different energy regions with an interval of 0.1 MeV between 0.3 MeV and 0.7 MeV was studied, and the results indicate that the n-γ discrimination threshold can go down to 0.4 MeV. 相似文献
12.
An experimental system aimed at n-γ discrimination using the zero-crossing method with a φ3’’×2’’ BC501A liquid scintillation detector was established and tested with an Am-Be neutron source. Two-dimensional plots of energy versus zero-crossing time were obtained. The quality of n-γ discrimination was checked by the figure-of-merit (FOM), the neutron peak-to-valley ratio, and the proportion of leaked neutrons over all neutron events. The performance of n-γ discrimination in terms of FOM was compared with previous work done by other groups. The n-γ discrimination in four different energy regions with an interval of 0.1 MeV between 0.3 MeV and 0.7 MeV was studied, and the results indicate that the n-γ discrimination threshold can go down to 0.4 MeV. 相似文献
13.
Wave function is important for determining decay constants fDS- and fD-. Using the 5 types of D meson wave functions in the heavy quark limit, we studied the uncertainties of radiative pure-leptonic decays of DS-(D-) mesons. The branching ratios are (1.025390—1.706812) × 10-5 and (0.953498—1.576725) × 10-6 for DS- and D- decays, respectively, which are sensitive to the type of wave function. 相似文献
14.
A semi-empirical detector response function (DRF) model of a Si (PIN) detector is proposed to fit element Kα and Kβ X-ray spectra, which is based on the statistical distribution analytic (SDA) method. The model for each single peak contains a step function, a Gaussian function, and an exponential tail function. Parameters in the model are obtained by the weighted nonlinear least-squares fitting method. In the application, six kinds of elements’ characteristic X-ray spectra are obtained by using the Si (PIN) detector, and fitted by the established DRF model. Reduced chi-square values are at the interval of 1.11-1.25. Other applications of the method are also discussed. 相似文献
15.
V. G. Kohn I. V. Kohn É. A. Manykin 《Journal of Experimental and Theoretical Physics》1999,89(3):500-507
The energy dependence of the back reflectivity in the dynamical diffraction of x rays at a Bragg angle of π/2 (back diffraction)
in perfect crystals of cubic symmetry (silicon) is investigated theoretically. In this case strict backscattering is realized
only under the conditions of multiple diffraction. The features of the influence of multiple diffraction on back reflection
in the energy range near the nuclear resonance radiation energy of 14.41 keV for 57Fe nuclei, specifically in the six-wave case, including the silicon (1,9,9) reflection (with an energy of 14.57 keV), which
can be investigated experimentally with high energy resolution (1 meV) using synchrotron radiation and a monochromator developed
for nuclear resonant absorption, are thoroughly studied. It is shown that the back reflectivity observed under the conditions
of multiple diffraction has several maxima on the plot of its energy dependence with a value at each maximum smaller than
half, in contrast to two-wave diffraction, where there is one maximum with a value close to unity.
Zh. éksp. Teor. Fiz. 116, 940–952 (September 1999) 相似文献
16.
BES Collaboration 《中国物理C(英文版)》2002,26(1):8-16
The decay mode of J/ψ→π03(π+π-) was studied very little before. There are no informations except branching ratios for this channel in PDG book which based on less than 0.2×106J/ψ events of MARKⅠ. Now, BESⅠ has a data sample of 7.8×106J/ψ events, we can make more accurate results than MARKⅠ. Total of 3290±43 J/ψ→π03(π+π-) events including 1275±86 J/ψ→ω2(π+π-) events are selected. J/ψ→π03(π+π-) and J/ψ→ω2(π+π-) events have been generated with MC simulition for calculating events selection efficiency. BESⅠ result is: Br(J/ψ→π03(π+π-))=(2.52±0.06±0.43)% and Br(J/ψ→π03(π+π-))=(1.31±0.09±0.21)%. Meanwhile, we studied the invariant mass of 4π and ωππ to find interesting signals. It seems that there is a peak at about 1.74GeV in the invarianat mass spectrum of 4π, and a enhancement was also found at about 1.9GeV in the invariant mass spectrum of ωππ. It is not clear whether they are from resonances or background. Therefore, more work in detail is still going on. 相似文献
17.
Belle Collaboration reported a new observed value of K*-(892) mass by studying τ-→ KSπ-ντ decay, which is significantly different from the current world average value given by Particle Data Group 2006. Motivated by this new data, we revisit the issue on the K*0(892)-K*±(892) mass splitting. Our theoretical estimation favors the new measurement by Belle Collaboration. Therefore further experimental efforts are urgently needed to improve our understanding of these issues. 相似文献
18.
BES Collaboration< BR> BAI Jing-Zhi BAN Yong BIAN Jian-Guo CAI Xiao CHANG Jin-Fan CHEN Hai-Xuan CHEN He-Sheng CHEN Hong-Fang CHEN Jiang-Chuan CHEN Jin CHEN Jun CHEN Ma-Li CHEN Yuan-Bo CHI Shao-Peng CHU Yuan-Ping CUI Xiang-Zong DAI Hong-Liang DAI You-Shan DENG Zi-Yan DONG Liao-Yuan DU Shu-Xian DU Zhi-Z 《中国物理C(英文版)》2004,28(4):325-331
Evidence of ψ(3770) decays to a non-DD final state is observed. A total of 6.8±3.0 ψ(3770)→J/ψ→π+π— events are obtained from a data sample of 8.0±0.5 pb-1 taken at center-of-mass energies around 3.773GeV using the BES-Ⅱ detector at the BEPC. The branching fraction is determined to be BF(ψ(3770)→J/ψ→π+π—)=(0.59±0.26±0.16)%, corresponding to the partial width of Γ(ψ(3770)→J/ψπ+π—)=(139±61±41)keV. 相似文献
19.
π-核双电荷交换反应的强度与反应过程的两核子转移的核谱振幅直接联系着. 本文讨论了这类反应与它们的核谱因子的关系. 并以26Mg(π+, π-)26Si为例, 用两种核结构讨论了它的激发函数和微分截面. 我们所用的理论方法能够解释实验数据. 相似文献
20.
TiO2 μ-donuts have been fabricated on glass and silicon substrates using polymer masks in combination with a sol-gel technique. Cylindrical poly(methyl methacrylate) (PMMA) nanopillars have been created using a composite polymer of polystyrene (PS) and PMMA followed by careful removal of the PS. Atomic force microscopy (AFM) analyses show that the height and diameter of the PMMA cylinders used as the mask are 440 ± 5 nm and 2.1 ± 0.2 μm, respectively. The cylindrical PMMA nanopillars have been coated with the sol of the TiO2 precursor by a spin coating technique and annealed in air at elevated temperature to remove the PMMA mask. Removal of the PMMA mask has resulted in the formation of well ordered μ-donuts of TiO2 on silicon surfaces. The interior and exterior heights of the TiO2 μ-donuts are found to be 373 ± 152 nm and 457 ± 136 nm, respectively; and the interior and exterior diameters of the TiO2 μ-donuts are found to be 1.33 ± 0.63 μm and 2.82 ± 0.50 μm, respectively. X-ray photoelectron spectroscopy (XPS) spectra of the TiO2 μ-donuts as well as the smooth TiO2 thin film showed signals from Ti and O confirming the presence of TiO2 with Ti 2p3/2 and O 1s peaks at 458.8 eV and 530.4 eV, respectively. The O 1s peak of the TiO2 μ-donuts shows another peak at binding energy 532.0 eV due to SiO2, as during annealing, the PMMA evaporates and the Si substrate is exposed. The X-ray diffractometer (XRD) pattern of the smooth TiO2 thin film indicates that the anatase phase is present, with the characteristic peaks observed at 2θ values of 25.4°, 37.4°, and 48° corresponding to (1 0 1), (0 0 4), and (2 0 0) planes, respectively. UV-vis absorption spectra of TiO2 μ-donuts on glass showed an unusual absorption of light in the visible region at ∼524 nm in addition to the usual UV absorption at ∼337 nm. 相似文献