2011 Vol. 35, No. 11
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We report that a general principle of physical independence of mathematical background manifolds brings a replacement of common derivative operators by co-derivative ones. Then we obtain a new Lagrangian for the ordinary minimal standard model with supplementary terms containing the Lorentz invariance violation information measured by a new matrix, denoted as the Lorentz invariance violation matrix. We thus provide a new fundamental theory to study Lorentz invariance violation effects consistently and systematically.
It is well known that the spin operators of a quantum particle must obey uncertainty relations. We use the uncertainty principle to study the Larmor clock. To avoid breaking the uncertainty principle, Larmor time can be defined as the ratio of the phase difference between a spin-up particle and a spin-down particle to the corresponding Larmor frequency. The connection between the dwell time and the Larmor time has also been confirmed. Moreover, the results show that the behavior of the Larmor time depends on the height and width of the barrier.
Using the phenomenological relativistic harmonic model (RHM) for quarks, we have obtained the masses of S wave charmonium and bottomonium states. The full Hamiltonian used in the investigation has Lorentz scalar plus vector confinement potential, along with the confined one gluon exchange potential (COGEP). A good agreement with the experimental masses for the ground and the radially excited states is obtained both for the triplet and singlet S wave mesons. The decay properties of the ground state charmonium and bottomonium are investigated.
We perform a Hamiltonian analysis of the Green-Schwarz sigma model on a supercoset target with Z4m grading. The fundamental Poisson brackets between the spatial component of the flat currents depending on a continuous parameter, which can be thought of as a first step in the complete calculation of the algebra of the transition matrices, are obtained. When m=1, our results are reduced to the results of the type IIB Green-Schwarz superstring on AdS5 × S5 background obtained by Das, Melikyan and Sato.
High spin states in 107Ag are studied via the 100Mo(11B, 4n)107Ag reaction at an incident beam energy of 60 MeV. Prompt γ-γ coincidence and DCO ratios are measured by the detector arrays in CIAE. The level scheme has been updated and a new negative band belonging to 107Ag is identified. The new negative side band has been constructed and its configuration is tentatively assigned to πg9/2 νh11/2(g7/2/d5/2).
Fission cross sections strongly depend on the ratio of the level density parameter in fission to neutron emission, af/an. In this work, a cascade-exciton model implemented in the code CEM95 has been used to observe this effect for proton induced fission cross sections of tungsten, lead and bismuth. The method was employed using different level density parameter ratios for each fission cross section calculation. The calculated fission cross sections are compared with the available experimental data in the literature. It has been observed that a change of the ratio of the level density parameter, af/an, is necessary with the incident energy of the proton, to best estimate the fission cross sections in CEM95.
By investigating the cross section distributions of fragments produced in the 140 A MeV 40,48Ca+9Be and 1 A GeV 124,136Xe+Pb reactions, the isospin dependence of projectile fragmentation in fragment production is studied. In the framework of the statistical abrasion-ablation model, the 1 A GeV 136Xe+208Pb reaction is calculated. By adjusting the diffuseness parameter in neutron density distribution of 136Xe, we find the isospin dependence of projectile fragmentation in fragment production is sensitive to the neutron-skin thickness of the projectile nucleus.
The Gamow-Teller transitions for pf shell nuclei with proton number less than 40 and neutron number larger than 40 were believed to be blocked, due to the full filling of the neutron orbit. However, recent experimental research shows that the Gamow-Teller transitions for these kinds of nuclei are not blocked. In this paper, we systematically calculate the GT transition of pf shell nuclei 76Se in different truncations, and the results are compared with experimental results. It is shown that, due to correlations, the believed blocked GT transition occurs, and the shell model calculations reproduce the experimental GT strength. In addition, the electron capture rates in a stellar environment are calculated and discussed.
Linear Alkyl Benzene (LAB) is a promising liquid scintillator solvent in neutrino experiments because it has many appealing properties. The timing properties of LAB-based liquid scintillator have been studied through ultraviolet and ionization excitation in this study. The decay time of LAB, PPO and bis-MSB is found to be 48.6 ns, 1.55 ns and 1.5 ns, respectively. A model can describe the absorption and re-emission process between PPO and bis-MSB perfectly. The energy transfer time between LAB and PPO with different concentrations can be obtained via another model. We also show that the LAB-based liquid scintillator has good (n, γ) and (α, γ) discrimination power.
We report on the recent test results of a MICROMEGAS detector in terms of position resolution, time resolution and efficiency. With a Ar + CO2 (10%) gas mixture and a strip pitch of 200 μm an accuracy of 80 μm in sigma on the position has been measured. The time resolution is better than 20 ns and a cosmic ray detection efficiency of 94% was obtained. A Monte Carlo simulation indicates that transverse diffusion, gain fluctuation and electronic noise limit the position resolution.
Film ZnO:In crystal is a good candidate for a scintillation recoil proton neutron detection system and the response of ZnO:In to protons is a crucial point. The energy response of ZnO:In to mono-energetic protons in the range of 10 keV-8 MeV was measured. The experiment was carried out in current mode, and Au foil scattering was employed, where the forward scattering protons were used for exciting the sample, and the backward scattering protons were used for monitoring the beam intensity. According to the result, the yield of light non-linearly depends on proton energy, and drops significantly when proton energy is low. The scintillation efficiency as a function of proton energy was obtained, which is very useful for researching the scintillation recoil proton neutron detection system.
A four-rod radio frequency quadruple (RFQ) cavity has been built for the Peking University Neutron Imaging Facility (PKUNIFTY). The rf tuning of such a cavity is important to make the field distribution flat and to tune the cavity's resonant frequency to its operating value. Plate tuners are used to tune the RFQ, which have an effect on both the cavity frequency and field distribution. The rf performance of the RFQ and the effect of plate tuners are simulated. Based on the simulation, a code RFQTUNING is designed, which gives a fast way to tune the cavity. With the aid of the code the cavity frequency is tuned to 201.5 MHz and the flatness deviation of the field distribution is reduced to less than 5%.
The analytical linear transfer matrices for different quadrupole fringes including quadratic, high order power and exponential models are deduced in this paper. As an example, the transfer matrices of the quadrupole BEPCⅡ/ 105Q are computed for the above three models and compared with hard edge and slice-by-slice models in cases of near 60° and 90° FODO cells. These models' results are much better than the hard edge model's, and can meet the requirement of accurate calculation.
A new procedure for the design and simulation of a Radio Frequency Quadrupole (RFQ) accelerator has been developed at the Argonne National Laboratory. This procedure is integrated with the beam dynamics design code DESRFQ and the simulation code TRACK, which are based on three-dimensional field calculations and the particle-in-cell mode beam dynamics simulations. This procedure has been applied to the development of a 162.5 MHz CW RFQ which is capable of delivering a 10 mA proton beam for the Accelerator Driven System (ADS) of the CAS. The simulation results show that this RFQ structure is characterized by the stable values of the beam acceleration efficiency for both the zero current beam and space charge dominated beam. For an average beam current of 10 mA, there is no transverse rms emittance growth, the longitudinal rms emittance at the exit of RFQ is low enough and there is no halo formation. The beam accelerated in the RFQ could be accepted easily and smoothly by the following super-conducting linear accelerator.
Emittance is an important characteristic of describing charged particle beams. In hadron accelerators, we often meet irregular beam distributions that are not appropriately described by a single rms emittance or 95% emittance or total emittance. In this paper，it is pointed out that in many cases a beam halo should be described with very different Courant-Snyder parameters from the ones used for the beam core. A new method — the Courant-Snyder invariant density screening method - is introduced for analyzing emittance data clearly and accurately. The method treats the emittance data from both measurements and numerical simulations. The method uses the statistical distribution of the beam around each particle in phase space to mark its local density parameter, and then uses the density distribution to calculate the beam parameters such as the Courant-Snyder parameters and emittance for different beam boundary definitions. The method has been used in the calculations for beams from different sources, and shows its advantages over other methods. An application code based on the method including the graphic interface has also been designed.
A C-band accelerator structure is one promising technique for a compact XFEL facility. It is also attractive in beam dynamics in maintaining a high quality electron beam, which is an important factor in the performance of a free electron laser. In this paper, a comparison between traditional S-band and C-band accelerating structures is made based on the linac configuration of a Shanghai Soft X-ray Free Electron Laser (SXFEL) facility. Throughout the comprehensive simulation, we conclude that the C-band structure is much more competitive.
In this work we studied the feasibility of detecting the depth of interaction (DOI) with two layers of crystal arrays of LYSO and BGO scintillators coupled to a position-sensitive photomultiplier tube (PS-PMT) R8900-C12. A front-end electronics was designed, with which we got different pulse shapes for different crystals to obtain depth information. With the double integration method, we got the DOI histogram of a divided integration ratio of two crystals as the standard to determine the layer-of-interaction. The DOI accuracy, measured by scanning a 22Na slit source along the side of the module, was 98% for the LYSO layer and 95% for the BGO layer. The energy resolution at 511keV was 13.1% for LYSO and 17.1% for BGO. We obtained good crystal separation in 2D position histograms of both layers. These results could be useful in the manufacture of PET scanners with high spatial resolutions.
A high energy digital radiography (DR) testing system has generated diverse scientific and technological interest in the field of industrial non-destructive testing. However, due to the limitations of manufacturing technology for accelerators, an energy fluctuation of the X-ray beam exists and leads to bright and dark streak artifacts in the DR image. Here we report the utilization of a new software-based method to correct the fluctuation artifacts. The correction method is performed using a high pass filtering operation to extract the high frequency information that reflects the X-ray beam energy fluctuation, and then subtracting it from the original image. Our experimental results show that this method is able to rule out the artifacts effectively and is readily implemented on a practical scanning system.
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