中子、γ射线在稀土-高分子材料中的输运(英文)

为研究新型复合屏蔽材料的最佳厚度与各种成分最佳配比, 用MCNP计算了中子、 γ射线在稀土 高分子与重金属复合材料中的通量。 对中子、 γ射线在屏蔽体中变化规律进行了深入探索, 同传统复合屏蔽材料的屏蔽性能进行了对比。 结果表明, 中子和γ射线通过屏蔽体时, 其强度遵循指数衰减规律。 新型屏蔽材料对中子的屏蔽效果均优于铅硼聚乙烯, 对γ射线的屏蔽效果均劣于W Ni合金, 且并非稀土含量越高, 材料对中子辐射屏蔽能力越强。 A series of shielding analyses have been performed to estimate the material composition and optimum thickness required for a new radiation shield with various rare earth doped polymer and heavy metal mixtures. The neutron and γ photon fluxes have been calculated by Monte Carlo N Particle(MCNP) transport code. The results indicate that the relative fluxes of γ photon and neutron in both traditional and new composite materials follow an exponential decay rule with the distance of penetration. It can be seen that the composite material consisting of rare earth doped polymer and heavy metal has stronger neutron shielding performance than lead boron polyethylene, but weaker γ shielding effectiveness than W Ni alloy. It is also found that materials with more components of rare earth elements don’t always provide better neutron shielding performance.     

Study on the novel neutron-to-proton convertor for improving the detection efficiency of a triple GEM based fast neutron detector

A high-efficiency fast neutron detector prototype based on a triple Gas Electron Multiplier(GEM) detector, which, coupled with a novel multi-layered high-density polyethylene(HDPE) as a neutron-to-proton converter for improving the neutron detection efficiency, is introduced and tested with the Am-Be neutron source in the Institute of Modern Physics(IMP) at Lanzhou in the present work. First, the developed triple GEM detector is tested by measuring its effective gain and energy resolution with55 Fe X-ray source to ensure that it has a good performance.The effective gain and obtained energy resolution is 5.0×104and around 19.2%, respectively. Secondly, the novel multi-layered HDPE converter is coupled with the cathode of the triple GEM detector making it a high-efficiency fast neutron detector. Its effective neutron response is four times higher than that of the traditional single-layered conversion technique when the converter layer number is 38.     

A novel acquisition method for nuclear spectra based on pulse area analysis

A novel simple method based on pulse area analysis (PAA) is presented for acquisition of nuclear spectra by a digitizer. The PAA method can be used as a substitute for the traditional method of pulse height analysis (PHA). In the PAA method a commercial digitizer was employed to sample and sum in the pulse, and the area of the pulse is proportional to the energy of the detected radiation. The results of simulation and experiment indicate the great advantages of the PAA method, especially as the count rate is high and the shaping time constant is small. When the shaping time constant is 0.5 μs, the energy resolution of PAA is about 66% better than that of PHA.     

Collective Transverse Flow in Intermediate Energy Heavy-Ion Collisions

Within the hadronic transport model IBUU04, we study the density-dependent symmetry energy by using the neutron-proton differential flow from the 132Sn＋124Sn reactions at beam energies of 200, 400, 600 and 800MeV per nucleon. The strong effect of the symmetry energy is shown at the incident beam energy of 400MeV/A. The small medium-effect of the neutron-proton differential flow is also found. We also study the neutron-proton differential flows with impact parameters of 3, 5, 7fm. It is found that in semi-central collisions the sensitivity of the neutron-proton differential flow to the symmetry energy is larger.     

Monte Carlo studies of micromegas as a neutron detector and its track reconstruction

In this paper a two dimensional readout micromegas detector with a polyethylene foil as converter was simulated on GEANT4 toolkit and GARFIELD for fast neutron detection. A new track reconstruction method based on time coincidence technology was developed in the simulation to obtain the incident neutron position. The results showed that with this reconstruction method higher spatial resolution was achieved.     

Application of the HKS in the identification of kaons produced in the reaction （e,e＇K^＋）

At Jefferson Laboratory the experiment E02-017 was carried out to investigate the fission associated with kaons in the hypernuclei-producing interaction p（e,K^＋e＇）A. The newly installed high resolution kaon spectrometer （HKS） in Hall C was used as a key instrument to identify kaons. This paper introduces the HKS hardware and describes the way the kaons are identified. Maintaining most of the kaons （nearly 100%） in the data, HKS identifies kaons with a purity of -67% in this experiment. The resolution of the kaon target time reconstructed by HKS reaches 0.42 ns.     

A new fully quantum-mechanical method used to calculate the collisional broadening coefficients and shift coefficients of Rb D_1 lines perturbed by noble gases He and Ar

In this work, a new full quantum method is proposed to calculate the broadening and shift coefficients of the D_1 line in neutral collision. Based on the variable phase approach and Baranger theory, this method calculates the scattering phase shift instead of scattering matrix elements in order to simplify the calculation. As an illustration, this method is used to calculate the broadening and shift coefficients of the absorption lines of alkali metal atom Rb, as it collides with buffer gas He and Ar, in a temperature range from 150 K to 800 K. With a comparison with other calculations and experiment measurements, the reasonable agreements in all cases demonstrate the validity and simplicity of this method.     

基于极化氦三靶的原子核散射实验

利用极化的氦三气体靶可以显著地拓展传统的核物理实验研究,观察初态自旋自由度对核反应过程动力学的影响。本文通过列举极化三体核力实验以及极化的重离子电荷交换反应实验,介绍了极化氦三靶在核物理实验研究中的独特优势。在质子散射实验中,通过测量不同极化方向下的多种末态产物角分布,可以进一步检验手征有效场理论对于三体核力的描述;而在与重离子的电荷交换反应中,通过控制靶极化方向可以分离π介子交换与ρ介子交换对于核子自旋同位旋激发的贡献,从而为研究核子在不同核环境中的动力学演化提供独一无二的契机。结合我国新一代大科学装置的建设背景,尤其是以加速器驱动嬗变系统（ADS）和强流重离子加速器装置（HIAF）和中国散裂中子源（CNS）为代表的先进实验平台为原子核物理实验研究提供了理想的机遇。新的实验技术手段将明显拓展在这些大型核科学装置上开展实验研究的深度与广度。极化氦三靶做为其中具有独特优势的研究手段,必将具有广阔的应用前景。     

Supercontinuous high harmonic generation from asymmetric molecules in the presence of a terahertz field

We have investigated high-order harmonic generation from asymmetric molecules. It is found that supercontinuous high harmonics,which are produced from asymmetric molecules by significantly steering the ionization,are broken down when the electric field of the 5-fs driving laser pulse is increased to 0.16 a.u. The high harmonic generation from asymmetric molecules with the presence of a terahertz field is also investigated. This reveals that the terahertz controlled laser pulse significantly increases the energy difference between photons,emitted from the ejected electrons,in the first and second halves of the optical cycle at the centre of the driving laser pulse. In this way,a 200-eV broadband supercontinuum can be produced in the plateau,from which a 60-as pulse with a bandwidth of 60 eV can be directly obtained with a minor post-pulse.     

被动法高浓铀年龄测量技术研究

利用HPGe-γ谱仪测量了多个年龄段的HEU样品, 获得了样品中N(214Bi)/N(234U)的值, 从而计算得到了HEU的年龄,其测量结果与参考值吻合较好。最后结合实验结果,系统分析了其它可能用于测量高浓铀年龄的方法,并对各种方法的可行性进行了分析。 结果表明, 214Bi/234U比值法是最佳的选择。N(231Pa)/N(235U)法中对γ谱如何解谱还需作进一步研究。 The HEU sample was measured by HPGe- γ spectrometry. By analyzing the detected γ spectrum, the N(214Bi)/N(234U) of the HEU sample was acquired, and the age of HEU samples was determined, which was coincided with the reference value. At last, the other potential methods of determining the age of HEU were analyzed systematically. N(214Bi)/N(234U) is more feasible,and algorithm of spectrum decomposition in N(231Pa)/N(235U) should be studied further.