Ferroelectric domain structure and evolution, as well as phase transition, of [001]-oriented 34Pb(In1/2Nb1/2)O-3-0.25Pb(Mg1/3Nb2/3)O-3-0.41PbTiO(3) single crystal has been studied through temperature and frequency-dependent relative permittivity characterization. Under dc bias, the transition temperature from rhombohedral-to-tetragonal phases becomes lower and the transition temperature from macrodomain to microdomain structures increases. Phase transition from rhombohedral to tetragonal is confirmed by temperature-dependent x-ray diffraction. These results are also well supported by direct domain observation by means of piezoresponse force microscopy under dc bias at different temperatures, as well as polarization-electric field hysteresis loop measurement. (C) 2011 American Institute of Physics. [doi:10.1063/1.3525163]

采用离子注入法及退火工艺,在硅基二氧化硅薄膜中制备了镶嵌结构的天然Ge纳米晶样品.通过退火实验研究,发现随着退火温度的升高,纳米晶的晶态峰峰位红移,这意味着Ge纳米晶受到的应力减小.当退火温度达到700℃时,纳米晶的晶态峰强度显著增强,而且薄膜中与Ge有关的缺陷发光减弱.采用中子嬗变掺杂法对天然Ge纳米晶进行了掺杂,X射线荧光光谱数据表明,样品中成功的引入了Ga杂质和As杂质.薄膜中形成的与Ge有关的缺陷具有稳定的结构,中子辐照之后其发光仍然存在,而且,掺杂后的样品中没有发现与Ga或As有关的缺陷发光.

In this paper, 1-3 composites based on Pb(In1/2Nb1/2)-Pb(Mg1/3Nb2/3)-PbTiO3 (PIMNT) single crystal and high-temperature epoxy were fabricated with various volume fractions of PIMNT single crystal ranging from 0.4 to 0.9. The electrical properties were studied as functions of PIMNT volume fraction and temperature, and it revealed that the nature of ultrahigh electromechanical coupling coefficient (0.82-0.93) and low acoustic impedance (17-19 MRayl) of the composites can be retained within a wide temperature range from room temperature to 185 degrees C. Single element ultrasonic transducer using the PIMNT 1-3 composite was fabricated and characterized as a function of temperature. It was found that the transducer can still work normally at high temperatures, such as 165 degrees C, possessing a bandwidth of 95% and insertion loss of -27 dB. (C) 2011 American Institute of Physics. [doi:10.1063/1.3583746]

It's difficult to carry out the on-site calibration of the measuring equipment of nuclear reactor control and protection system,especially to carry out calibration of power measuring protection equipment and period measuring protection equipment,the input signals range from reactor intermediate range to reactor full level,or from 10-11A to 10-4A,the output period signal scaled by 1/T function.Because of the errors introduced during signal measurement,conversion and transmission,the same signal has difference display value in the protection system and the distributed control system(DCS).This paper presents a calibration method of Neutron Flux Measurement Instrumentation(NFMI) based on author's experience calibrating NFMI in the commissioning of research reactors.Through modifying measurement software,we can ensure the signals keep 1.05∶1.1 relation between the alarm system and protection system.The period protection trigger action point calibrated by specific software to ensure the protection system sending accident trigger action once the reactor power period below 10s.Results of calibration meet the accuracy requirements of the protection system triggering,the monitoring parameter values also display more consistent in different systems.

Cold neutron radiography (CNR) is a new neutron radiography technique. And the research of CNR is just started in China. The cold neutron converter is a key subassembly of the CNR facility. The simulate method of cold neutron converters is studied. The principle of the interaction between cold neutrons and converters is analyzed. The calculate model of the simulation is set up and the point spread function (PSF) of the converter is resolved. At last, the simulation of the light output image of cold neutron converters under the particular sample has been realized.

Burn-down of fuel assemblies is chosen as the initial event for the first comprehensive emergency practice for the research reactor.The highest response level of the practice is on-site emergency status.The practice is organized by the institute in charge of the reactor.All personnel of the reactor participates the practice.It is simulated that a fuel assembly burns down suddenly while the reactor runs on full power in daytime.Through the practice,some problems are found and solved.It is verified that the emergency response plan for the reactor is effective.

Crystal structure, electronic structure and bonding characteristics of LaNi(5-x)Co(x)(x=0, 0.5) and its hydride were investigated by the density functional theory based on general gradient approximation (GGA) and the ultra-soft plane-wave pseudopotential method. The total energy, energy band structure, density of states and Mulliken population were obtained. The results show that the interaction between Ni2c and La atoms is larger than that between Ni3g and La atoms in LaNi(5) alloy. There is obvious covalent interaction between Ni2c-Ni2c and Ni3g-Ni3g. However, the covalent interaction is reduced after introduction of Co and H atoms. The interaction between H and Ni3g atoms is larger than that between H and Ni2c atoms. The expansion along a axis is larger than that along c axis because the lattice expansion results in outward moving of Ni2c atoms after hydrogen atom enters the tetrahedron.

First-principle calculation was carried out on the Ti of hcp structure and Ti-H system supercells by a total-energy plane-wave ultrasoft pseudopotential method based on density functional theory (DFT), which combined generalized gradient approximation(GGA). Lattice parameters, total energy, energy band structure, density of states (DOS) and Mulliken population of the system were obtained. The calculated results reveal that after H atom introduction into the crystal cell of Ti8, Ti16 and Ti32, the formation energy of crystal impurity was decreased and the volume of crystal cell was swollen; the distortion would become serious and the volume would be increased obviously along with increase of the hydrogen concentration in the crystal cell. The intensity of the great mass of Ti-Ti bonds were enhanced in the octahedron storing H atom of crystal cell. The Femi energy level moved to the direction of low energy of DOS. The activity of Ti alloys was improved, and the transferred electrons were mainly those on the P orbit of Ti.

通过离子注入及中子嬗变掺杂制备了Ga(镓)掺杂70Ge(锗)纳米晶,并对样品进行了质子激发X射线荧光分析谱(PIXE)、光致发光谱(PL)、激光拉曼散射谱(LRS)的测量与研究.结果表明:随着Ga杂质浓度的增加,580 nm附近的荧光峰的发光强度不断地下降,这可能是非辐射的俄歇复合过程与纳米晶数量的减少共同作用的结果.此外,从PL上面看到580 nm附近的荧光峰蓝移则可能是由纳米晶尺寸的减小和非辐射的俄歇复合过程引起的.

The calculations of total energy,energy band structure,electronic density of states and Mulliken population of LaNi5M(M=0,D,Al) were performed by adopting the method of total energy combined with ultra-soft Pseudopotential technology.The trend of electronic structure for LaNi5、LaNi5D and LaNi4Al,which was analyzed,the Al element is inclined to substitute for 3g-site Ni.The change rules of band structure and density of states were analyzed,and calculated the model by Reflex in Material studio,the theoretical results of Power Diffraction spectrum accord well with that of the experiments spectrum.

Samples of nanocrystalline 74Ge embedded in amorphous SiO2 film were prepared by 74Ge ion implantation and subsequent primary thermal annealing. These samples were irradiated by neutron flux in a nuclear reactor then the second annealing followed. Irradiation with thermal neutrons leads to doping of nanocrystalline 74Ge with As impurities due to nuclear transmutation of isotope 74Ge into 75As. Transmission electron microscope, X-ray fluorescence, X-ray photoelectron spectroscopy, laser Raman scattering and photoluminescence of the obtained samples were measured. It was observed that with the increase in As-donors concentration, photoluminescence intensity first increased but then significantly decreased. An explanatory model of this non-monotonic behavior was discussed.

Phase contrast imaging which is based on the wave character of neutron beam,is an advanced technique in neutron imaging field. When we investigate the neutron phase contrast,a simulation is necessary. But so far no software can provide the function to simulate neutron wave. In the paper,we discuss the feasibility of simulating neutron phase contrast imaging process by ZEMAX,a sophisticated optics simulation software. The influences of sample-source distance,sample-detector distance,point neutron source size and sample size on imaging are investigated. The result of the simulation accords with the phase contrast theory,which indicates that ZEMAX is feasible to simulate neutron phase contrast imaging.

The prompt neutron decay constant was measured by using reactor noise technology at delayed criticality for 300# pool research reactor.The reactor core uses irradiated low-enrichment fuel loading.The prompt neutron decay constant is obtained from nonlinear least-squares fitting of the cross-power spectral densities measured between two detectors placed adjacent to the core.The measured prompt neutron decay constant αc at delayed criticality with a power of 4 kW is(83.4±0.7) s-1.

We have succeeded in doping arsenic (As) impurities into isotope germanium nanocrystals (nc-Ge-74) uniformly dispersed in a SiO2 matrix by using the neutron transmutation doping (NTD) method. The samples' inner structural transmutation is studied by combining Raman scattering, Xray fluorescence (XRF), X-ray photoelectron spectroscopy (XPS) and Transmission electron microscope (TEM) methods. The Raman spectrum of the doped sample exhibits a relative intensity increase of the low frequency tail, blue shift of the main Raman peak (similar to 300 cm(-1)) and a high frequency tail, while the undoped sample does not. Together with the XRF, XPS and TEM, we believe that the relative intensity increase of the low frequency tail arises from an increase of amorphous Ge-74 (a-Ge-74) induced by the irradiation damage. The blue shift of the main Raman peak comes from the mismatch of the crystal lattice which arose from the As impurity introduction. And the high frequency tail is due to transmuted-impurities (As) in the nc-Ge-74 which was introduced by NTD. (c) 2006 Elsevier Ltd. All rights reserved.

Samples of Ge nanocrystals (Ge-ncs) embedded in amorphous SiO2 film were prepared by Ge ion implantation and subsequent primary thermal annealing. These samples were irradiated by neutron flux in a nuclear reactor followed by the second annealing. Irradiation with thermal neutrons leads to doping of nanocrystals with Ga, As and Se impurities due to nuclear transmutation of isotope Ge-70 into Ga-71, isotope 74 Ge into 75 As, isotope 76 Ge into 77 Se, respectively (neutron transmutation doping, NTD). Irradiation with fast neutrons leads to appearance of radiation damages, which are expected to be removed after the second annealing. Photoluminescence (PL) measurements show that PL is quenched after neutron irradiation, and restored after annealing higher than 500 degrees C. The PL spectra of doped Ge-nes samples show more intense exciton radiative luminescence than of undoped Ge-ncs sample, which is related to that the donor and acceptor impurities recombine the nonradiative centers in the interface of Ge-ncs and SiO2 matrix, and enhance the probability of exciton recombination. (c) 2007 Elsevier B.V. All rights reserved.

The principle for neutron phase contrast is this paper. Emphases Discuss In-line neutron imaging principle. The experiment technique and condition of neutron phase contrast imaging are discussed. At last, introduce the research project on SPRR-300 neutron imaging system.

The neutron flux distribution in the concrete shielding of SPRR-300 reactor is achieved with MCNP code and ANISN code,and it is well accorded with the result of the low neutron flux outsides the concrete shielding which is gained by solid state nuclear track detector.The credibility of the calculation result is confirmed and the data is provided to calculate the radioactivity source for the retiring of the SPRR-300 reactor.

The issue predigests geometric structure of SPRR-300 reactor core with repeated structure geometry feature of MCNP code and sets up the irradiation channel mathematical model to calculate the neutron flux.The calculated results accorded well with the experimental data shows that the mathematical model in this issue is reasonable and feasible.

The source and characteristic of several rays, such as X-ray,γ-ray,ray of the neutron and the other electriferous particles,which are often meet with in radioactive jobs,are reviewed.It is pointed out that the most applied and best means is looking for proper shielding material.The kinds and shielding cause of these materials are briefly introduced.It is proposed that the researchful direction of present shielding materials is looking for the rare-earth composite,and increasing the shielding efficiency of these rare-earth elements in this composite.

In order to modify the simple one-dimension model,the neutron fluence rate distribution calculated with ANISN code was checked with that calculated with(MCNP) code.To modify the error caused by ignoring the neutron landscape orientation leaking,the reflector that can't be modeled in a simple one-dimension model was dealt by extending landscape orientation scale.On this condition the neutron fluence rate distribution and the energy spectrum in the thermal column of SPRR-300 reactor were calculated with one-dimensional code ANISN,and the results of Cd ratio are well accorded with the experimental results.The deviation between them is less than 5% and it isn't above 10% in one or two special positions.It indicates that neutron fluence rate distribution and energy spectrum in the thermal column can be well calculated with one-dimensional code ANISN.