2005 Vol. 29, No. 1
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Excited states in odd–odd 126I have been studied via the heavy–ion induced fusion–evaporation reaction 122Sn(11B,5n2p) at beam energies of 55 and 60 MeV with beams provided by the HI–13 tandem accelerator of CIAE in Beijing.A level scheme consisting of 20 new γ transitions assigned to 126I is established.The assignment of the established level scheme to 126I is based on the observed coincidences between the newly identified γ–transitions and two previously known cascade γ transitions feeding the ground state of 126I, and supported by a cross measurement using the 124Sn(7lI,5n) reaction performed at UTTAC,Japan.The observed structures of 126I at high spins show typical properties of collective rotation in a deformed nucleus. their possible configurations are discussed briefly on the basis of knowledge from the neighboring nuclei.
The transition rate for the Cabibbo suppressed decay d0→π–e+ν e is calculated. This allows the extractions of the form factor |fπ +(0)| and the CKM matrix element |v cd| using the measured branching ratio.
The lightest meson π in meson cloud model gave a natural explanation for the observed large light flavor sea asymmetry in proton,but not a satisfied explanation for (x)/(x). here we take into account the σ meson cloud effect,which gives a better description of the data. meanwhile,our calculation implies a reasonable smaller probability of finding a physical proton in the fock state |Nω〉 with a smaller value of Λ ω.
The teleportation may become an important means for remote distance communications in the future,and the mechanism is based on entanglement of quantum states.but the entanglement is fragile.As the state is disturbed by the environment the entanglement may be broken down.in this work,we choose the electron–positron pair in an entangled state of spin 0 as an example to investigate the rate of breaking down of the entanglement by the Compton scattering with the background radiation photons or Bremstrahlung with strong magnetic fields of some astronomical objects which the electron or positron passes by.Since the spin projection of single electron (positron) is not physically measurable and the electron beams cannot keep its shape for long because of the coulomb repulsion among the charged particles in the beam,the only way is to shoot one electron–positron pair each time and continuously repeat the processes.With all the restraints this study has only pedagogic meaning, but may shed light on further studies where other information messagers are chosen.
In this paper,we generalize the Toda mechanics system with long range interaction to the case of Loop algebra l(Dr).by using a pair of ordered positive integer (X,y) to describe Toda chains,we extract the equation of motion and the hamiltonian structure of this system for (3,2) Toda chain.it turns out that both extra coordinates and standard Toda variables are Poisson non–commutative in the case of nontrivial generalization,and for some case,extra variables appear linearly on the right hand side of the Poisson bracket.
Through analyzing the data with high statistics from measuring high–fold prompt γ–ray coincidence events following the spontaneous fission of 252Cf with the Gammasphere detector array,the level schemes in neutron–rich odd–A 109,111Ru nuclei have been extended up to higher spin states.Based on the data analysis of the coincidence matrices with different delay times,the life times for many low excited levels have been obtained in 107,109,111,113Ru nuclei,among them,the 96.4 keV level in 109Ru is an isomer with life time value 1300ns.It is shows that the observed backbending in the yrast band of the neighboring even-even 110Ru is indeed originated from the alignment of a pair of neutrons through analyzing the moments of inertia J(1)vs.rotational frequencies hω of the observed collective bands in 107,109Ru nuclei.Triaxial rotor plus particle model has been employed to calculate some levels of the collective bands as well as the B(M1)/B(E2) values.The calculated results basically accord with the experimental ones.
20Ne was used as primary beam to bombard Be target to produce RIB 17Ne, which is a candidate of proton halo nuclei in theoretical prediction.The total reaction cross section of 17Ne on Si target was measured.No enhancement was observed compared with that of its neighbors.The calculation with modified glauber model is consistent with the experimental results.No exotic structure of 17Ne is confirmed.
The triaxial superdeformed band in nucleus 164Lu are identified by three dimensional self–consistent TRS calculation.The calculated results agree with the data.The configuration of the triaxial superdeformed band is assigned as (π1/2,α=1/2)(ν5/2,α=1/2).
We study the possible signals of the pion string associated with the QCD chiral phase transition in LHC Pb–Pb collision at energy s=5.5 TeV.We follow the Kibble–Zurek mechanism to discuss the production and evolution of the pion string.We will show that if the QCD chiral phase transition really takes place in the LHC Pb-Pb collision process and the phase transition is in the second order,the pion string will be inevitably produced and subsequently decay.The main effect of this phenomenon is that there is a generation of a large number of pions in the final state produced by the decay of the pion string, and these pions are mostly distributed in a low momentum region with p～143MeV; also there are lots of neutral pions distributed in a low momentum region with the mean momentum at p～21MeV.
By using an improved isospin dependent quantum molecular dynamics model, the fusion reaction near coulomb barrier is studied for the 16O+16O system.The surface energy of the system is improved by a switch function method,which combines the surface energies of projectile and target with the one of compound nucleus in a proper way.The calculated fusion cross section increases obviously by using this method, which turns away the unphysical nucleon emission in the process of projectile and target approaching since the deformation effect of the surface has been embodied by the switch function method.
We examine the two–pion interferometry for the expanding sources of spherical quark–gluon plasma evolution. The quark–gluon plasma evolution is described by relativistic hydrodynamics with the equation of state of entropy density.The two–pion Hanbury-brown-twiss (HBT) correlation functions are calculated using quantum probability amplitudes in a path–integral formalism.We find the spatial parameter extracted by the two–pion interferometry is sensitive to the phase–space distribution of the pion–emitting source. the expanding velocity of the source leads to a smaller hbt radius and changes the relationship between the HBT radius and the freeze–out temperature.
Shandong University is in charge of the research and production of T9 type TGC (Thin Gap Chamber)detectors for ATLAS experiment.in this paper,the stability and the leak current of the detectors working at 3200V voltage were measured, and the plateau curves of the detectors were measured too.The counting rate of each channel was measured with same working condition and counting time interval for all the TGC detectors, in order to check the consistency of all signal channels. the performance of T9 type TGC detectors produced by Shandong University has met the requirement of the ATLAS experiment according to the preliminary results of measurement.
The 2Q2D magnetic spectrometer operating at the BEPC-Linac test beam site consists of 2 quadrupole magnets,2 dipoles and 2 position sensitive detectors.The spectrometer has a maximum acceptance of solid angle 5×10-4sr,a momentum range 0.2—1.3gev/c.Beam cross section and momentum spectra have been measured on the focal plane.A reference method for momentum measurement based on the TOF difference of proton and electron is introduced.
A“full coverage”air shower array,ARGO (Astrophysical Radiation with Groundbased Observatory) experiment is under construction currently at YangBaJing in Tibet,China.Its altitude of 4,300m above see level is equivalent to an atmospheric depth of 606g/cm2.ARGO experiment makes use of a full–coverage detector consisting of a layer of single gap Resistive Plate Chambers (RPC).The phase Ⅰ detector, including a central (74×78m2) part and a guard ring in size of 6400m2,will be operated in 2005. one of the main goals of ARGO is to detect VHE gamma ray emission from galactic and extragalactic sources. With full Monte-Carlo simulation we studied the detector's angular resolution and found that the angular resolution strongly depends on the number of fired pads npads.With three statistical methods we estimated ARGO's sensitivity in detecting Crab Nebula.According to our simulation, in one year's operation,Crab Nebula will be detected by ARGO with a statistical significance of about 18 standard deviation without appeying any gamma/hadron identification technique.
A prototype of X-ray imaging device based on triple Gas Electron Multiply detector is studied,which has an effective gain up to 105 and can be used in high rate X-rays imaging.The precise method of micro–strip readout is designed for X-rays localization, and the crate controller of high–speed SCSI interface is applied for the data acquisition.The test results show that the position resolution of measurement system is less than 90μm and the stability of its effective gain is better than 1% under the X-ray flux of 105Hz/mm2.
The design of large area neutron array detector at RIBLL for the study of neutron–rich nuclei is presented. The neutron detection efficiency, timing resolution and position distribution of this detecting system have been obtained by detailed Monte Carlo simulation based on Geant4 package.Meanwhile, the cross–talk of the detector system has been investigated.The design of the detector is described.
Recently intensive studies have been done on superconducting cavities (e.g. spoke cavity, reentrant cavity, and ch cavity), which are used as accelerating structures in the low and medium energy part of high power high intensity proton or ion accelerators. many experiments have shown that spoke cavity is a good candidate for low energy part. it is also promising to be used for the medium β area. so a β=0.45 spoke cavity is being studied at Peking university. in this paper, the structural and electromagnetic design of a β=0.45, f=350mhz spoke cavity is reported in detail. the calculated rf parameters (e.g. Q, r/Q, peak surface fields and dissipated power) indict a potential of good acceleration.
The beijing electron Positron collider upgrade Project (bePcⅡ) requires its injector linac to upgrade the beam energy and current. thus the accelerating structures in the positron production region must be newly designed and constructed to meet the high gradient demand. these new structures must be tested and conditioned with the high rf power before their installation into the linac tunnel. this paper describes the design and construction of the high power rf test stand, the tuning of the rf power source, the progress and the final results of the rf test and conditioning.
In order to easily measure the beam spot size of high energy electron accelerators with internal target enclosed,a real–time system, based on thick pinhole imaging technique, is employed. The experimental result on a 15MeV electron linear accelerator is also presented. In this paper the principle of thick pinhole imaging and the processing of data are introduced. The usual "sandwich" method needs to develop X-ray films, while debugging the accelerator parameters it will take a lot of time. On the contrary, X–ray pinhole imaging method can make a real–time measuring: as the accelerator parameters change, we can observe the beam profile's variation on the computer screen. Then when debugging we can have a definite object in view, and adjust the accelerator parameters more efficiently.
It is important for hirfl to improve the whole operation level if SSC accelerating voltage can be increased. In order to increase the voltage, it should firstly analyze the maximum voltage that SSC RF cavity can achieve in theory. SSC RF cavity was thoroughly analyzed and the main parameters of the cavity were obtained by using a three–dimensional electromagnetic calculation code. Based on the simulation results and the practical operation parameters the possibility of increasing the voltage is discussed. since the little power loss in high–power operation may affect the stability of the cavity–amplifier system, the power coupling system was also analyzed. The limit of power reflection is got and the improving methods are discussed too.
a tracking algorithm using grid–based space charge fields is studied for the analysis of secondary emission microwave electron gun(semeg). the poisson equations of the space charge forces are determined in the bunchs rest frame with a multi–grid method. the particles equations of motion are solved with a fifth–order embedded runge–Kutta method. the results of the semeg by this algorithm are presented and compared with these by mafia algorithm.
For storage–ring free electron laser (SR-FEL) and KrF laser driver of inertial confinement fusion(ICK KrF Laser), the mechanism of laser production is fully different from each other, but they have a nearly same requirement to the resonator mirror. The multi–layer interference coatings of the resonator mirror must suit for ultra–violet and extreme ultra–violet laser, and have a high reflectivity, wide frequency band, stable optical properties, long life–time. Today, a resonator mirror, consisting of oxides and fluoride (al2O3/SiO2/MgF2),has been developed successfully.Its optical reflectivity at 248nm reaches up to 96.83%, its frequency band–width is larger than 19.5nm, and its damage–resistant threshold is (5.36±0.30)J/cm2 to 23ns pulsed laser at 248nm. It will be able to be applied to the tunable high power SR-FEL and kJ ICF Krf laser.
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