2001 Vol. 25, No. 3
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The erraticity analysis of the pseudorapidity gaps is performed for the experimental data of multiparticle production in pp collisions at 400GeV/c.The entropy-like quantities Sq and ∑q which have been proposed by Hwa et al .are calculated. It is found that Sq and ∑q deviate significantly from 1. The 1nSq versus q has a quite linear behavior ,but the 1n∑q versus q has only an approximate linear behavior. The same calculations are performed for the event sample simulated using FRITIOF program. The results have a rather large deviation from experimental data.
Contributions of fermion loops,W-boson loops and their sum to the high energyγγ→γγ scattering total cross section (｜cosθ｜<COS30)are calculated numerically by using the analytic expressions ofγγ→γγ scattering helicity amplitude from previous paper.These contributions may be observed in the future Photon Linear Collider,and may be used to test standard model.
The orthogonal qs-coherent state is constructed and its nonclassical properties such as squeezing property,antibunching effect are studied.The effects of q and s variables on these nonclassical properties are calculated numerically.
The nuclide 129Ce was produced by a (16O,4n) reaction with an enriched 117Sn target. With the aid of a helium-jet tape transport system, the reaction products were transported to a shielded location,where Ce samples were prepared after chemical separation. The neighboring isotopes of 117Sn,116Sn and 118Sn,were also bombarded with 16O beam. Different isotopes of Ce were further separated by comparing the products in the above three reactions. An activity with a half life of 4.1 min in the chemically purified cerium samples was identified as 129Ce. Based on X-γ-t and γ-γ-t coincidence measurements, the EC/β+ decay scheme of 129Ce, including 51 γ lines,was proposed. Using the observed growth decay curve of an intense 278.6keV γ line of 129La decay, the β feeding branch from the ground state of 129Ce directly to the ground state of 129 La was estimated to be (26±7)%. In addition, the γ spectra gated by both La-Kα-X ray and intense 68.2keV γ ray of 129Ce decay as well as the time spectra of typical γ rays were also presented here.
Five superdeformed bands observed in 149Tb were investigated comprehensively. A large-amplitude fluctuation in the observed transition energies and hence in the extracted dynamic moments of inertia was found in most of these bands. The smoothed transition energies were deduced by removing the fluctuation. The spins of these bands were assigned conclusively by the ab-fitting and/or its modification. Two pairs of superdeformed bands in 149Tb, i.e. bands 3,5 and bands 2,4,were proposed to be signature partners. The exit spins are 59/2 and 61/2 for the former pair,and 49/2 and 63/2 for the latter pair. These values are different by one unit from those given from a comparison with 150Tb(1). In fact,the spins of 150Tb(1), which have not been determined experimentally,are different by different theoretical approaches of assignment. The de-coupling constants were extracted from the modified ab-fitting. Responsible Ω=1/2 orbit in the vicinity of the Fermi surface of 149Tb seems to be ν↑ for bands 2 and 4,and π↓ for bands 3 and 5. The exit spin of band 1 was assigned as 53/2 or 55/2,which may be picked out from the observation of its signature partner. Good correspondence between these bands(especially bands 2,4 and 5) and their identical bands was obtained.
With q-deformed three-parameter formula,the ground rotational bands of 29 even-even rare-earth and actinium nuclei have been calculated,and the fitting parameters have been analyzed. The calculated results show that the ground rotational bands of even even nuclei may be described well by the rigid rotor with q-deformed moment of inertia.
In this paper a mapping of the collective state subspace in a microscopic IBM onto the fermion collective state subspace is achieved. A microscopic theoretical method (ME method),which is suitable to deduce the boson one-body operator from the fermion one body operator,is proposed by supposing the form of the boson operator and making equal the matrix elements of physical operator between the coressponding normal basis vectors of the two different collective state subspaces. In the context, the procedure of obtaining the boson structure function,i.e. the determination of the boson transition charge/current density operator,is taken as an example to give a detailed statement of the method. Thereafter, calculations of the nuclear charge/current densities can be carried out in the boson state space by taking advantage of the eigenfuncitons of the microscopic IBM. Associated with the formal theories of electron nucleus scattering and nuclear electromagnetic transition,a microscopic approach,which can be used to study nuclear transition charge/current densities,various form factors,differential cross sections,reduced transition rates,electromagnetic multipole moments, g factors, and so on,can be built up. Preliminary calculations of transition charge density and reduced transition probability from 2+1 to 0+1 in 146Nd are carried out in terms of the approach in the framework of microscopic sdgIBM 1. It is found that the theoretical results fit the experimental data quite well.
Based on the statistical theory and available measured isomeric cross section ratio, a systematic formula of the isomeric cross section ratio with one parameter for neutron induced reactions was developed. This formula is applicable for the mass region 44≤A≤197,spin region of isomeric and ground states 0≤Jm≤12 and 0.5≤Jg≤8 of the residual nucleus, respectively. Fair agreement was obtained between the systematics predictions and measurements. Within the range of nuclides and spins the systematics predictions can provide useful isomeric cross section ratio information where experimental data are of large discnepancy or where experimental data are not available.
The multiparticle Bose-Einstein correlations of pions and kaons produced by a surface hadronization of the quark-gluon plasma droplets are calculated. For finite initial baryon density, the multiparticle correlations of K+ are weaker than those of π, and the average multiparticle correlation intensities of K－ decrease rapidly with the increase of the number of the droplets Nd. For zero initial baryon density the differences between the correlation intensities of K+ and π become obvious with Nd increase.
The isospin dependence of preequilibrium nucleon emission for the neutron-deficient colliding system and neutron-rich system has been studied in the wide beam energy region. The calculation results show that the ratio of preequilibrium emission neutrons to protons is sensitive to the symmetrical potential and insensitive to the isospin dependence of in-medium nucleonnucleon collision cross section from low beam energy region to high energy region, in which nucleonnucleon collision dynamics is dominant, namely the isospin dependence of in medium nucleonnucleon cross section excites neutron and proton to be emitted with about the same probability in wide beam energy region. At the same time, the neutrons and protons are excited to be emitted with the same probability for Pauli potential, momentum dependence interaction and impact parameter, even though their effects on preequilibrium neutron number and proton number are obvious. The ratio of preequilibrium neutrons to protons for neutron rich colliding system is larger than the initial value of neutron proton ratio of colliding system, but that for neutron-deficient system is less than the initial value. In this case, one can compare the theoretical results with the experimental data systematically to extract information on the symmetrical potential.
A beam photoelectron instability may arise in high energy storage rings when the multibunch positron beam interacts with the photoelectrons which are produced in the beam tube by synchrotron radiation. This instability gives rise to a big interest for the accelerator physicists in recent years as a new mechanism has been involved in this phenomenon study. It is very important for the particle factories as there are strong multi-bunch positron beams to be operated. The experimental observations are carried out in the Beijing Electron Positron Collider (BEPC) under the cooperation between IHEP, China and KEK, Japan, and the simulation studies are presented in this paper.
An ion induced coupled-bunch instability observed in the Beijing Electron-Positron Collider (BEPC) is analyzed in the paper, with the given side-band of the instability. A linear two-beam theory of ion trapping is applied to calculate the threshold current and growth time of the instability. A simulation program based on the strong weak model is developed to track the interaction process between the beam and the ion cloud. The simulation results successfully reproduce the side-band and give a reasonable growth time of the instability.
The stray field of eddy current septum magnets is analyzed theoretically and also simulated by a computer program. The results from theoretical analysis agree well with those simulated from OPERA program. The maximum of stray field varies inversely with the thickness of septum. It delays some time with respect to the maximum of main field, and the delay time is proportional to square of the thickness of the septum. After stray field increases to its maximum, it starts to decrease very slowly to zero. To reduce stray field fast, one can adopt full sine wave pulse current to power the magnet, The stray field can be reduced to 0.2% at any position and any time by using composite septum (2.4mm Cu+0.6mm Fe). The homogeneity of the main field is superior to 1%.
The proton therapy is a new developing method in the radiation oncology. The superior dose localization capabilities of proton beams suggest the possibility of depositing a higher dose into the cancer while reducing the unwanted radiation damage in surrounding normal tissues. The merit can be realized with the aid of the beam delivery system, whose functions are energy adjustment, energy modulation, beam spreading and collimation. In this paper a new soft-modulating and double-scattering beam delivery system is proposed. It uses a program-controlled modulator to change proton energy and thereby the proton range in the body so that the Bragg peak is spread out. Moreover, a larger treatment field can be obtained with two scatterers. The delivery system has high reliability and flexibility, and is especially good for conformal therapy.
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