碳化硅(SiC)中子探测器属于一种宽禁带半导体探测器,适合在高温强辐射环境下的测量.本文利用标准放射源建立了SiC中子探测器的实验测试系统,分别研究了SiC中子探测器在252Cf标准源及60Co标准源照射下的响应情况.通过实验测试发现,SiC中子探测器可以在低偏置电压下工作,在252Cf标准源照射下探测器的计数率与中子通量之间具有非常好的线性关系,其线性拟合R2值为0.9998.此外,SiC中子探测器在60Co源照射下的计数主要是在低能区,可以通过甄别阈值设置有效地分辨γ射线的影响.

为了确保2D位敏核探测器的成像性能,需要对探测器各个像素通道进行增益标定和刻度匹配,为此对2D位敏核探测器检测平台进行研究,设计开发了基于激光光源的二维平面光学检测平台.实验证明了该检测平台能够准确的刻度光电倍增管(PMT)元件各个通道的增益差异,为组装匹配和电子学调试提供数据支持.

A new long counter has been constructed and calibrated with the inherent efficiency of 11.5 cm2 in the 2.5 MeV neutron field, and a relative flat energy response of 20% disparity within 0.5 MeV–15 MeV. Using this detector and another commercial DePangher counter, the departure of “point” assumption at near distance and the scattering background influence are investigated by performing three groups of experiments in low, middle and high scattering room. Simulation studies are also performed to supplement the experimental data.

Neutron holography is a new imaging technique based on the recording of the interference pattern of two coherent waves emitted by the same source, which allows observing the spatial order of microscopic objects like molecules or atoms in crystal sample. Two approaches can be used in neutron holography measurements. One is called inside-source holography, in which both the reference wave and object wave come from embedded atoms in the sample and propagate toward the detector outside the sample. The second approach called inside-detector holography is the inverse method of inside-source holography, in this case the reference wave is the initial neutron beam coming from a distant source outside the sample, while the atoms embedded in the sample act as detectors. In an ideal inside-source holography experiment, the sample should be fixed and the detector moves on a sphere, which is not practical because the detector system is usually heavy and far from the sample. In order to minimize the operation space, the detector always moves on a circle around sample or is located at a fixed position, while the sample rotates in an appropriate way to imitate the motion of the detector in a sphere. However, the orientation of the sample relative to the incident neutron beam is changed during sample rotation, and part of the inverse hologram is recorded together with the inside-detector hologram, which can cause distortion in the holographic reconstruction. In this paper, we simulate neutron holograms and reconstructions based on three different sample/detector rotations. In the first case, the detector moves on a circle, while the sample rotates about an axis perpendicular to the detector moving surface. In the second case, the detector is fixed, while the sample rotates around two perpendicular axes, the θ axis rotating the sample through πradians is perpendicular to the incident beam-detector plane, while the θ axis rotating the sample through 2πradians moves on a circle parallel to the incident beam-detector plane, this rotation can be carried out on a 3-axis spectrometry. In the third case, the detector is also fixed and the sample rotates around two perpendicular axes, but the θ axis is parallel to the sample-detector direction, while the θ axis moves on a circle perpendicular to the incident beam-detector plane, this rotation can be carried out on a 4-cycle spectrometry. The distortions and corresponding correcting methods of three kinds of rotations are discussed. The result shows that most distortions can be corrected by using special measurement or reconstruction techniques. Furthermore, pure sample rotation based on 3-axis spectrometer can achieve the best reconstruction result, so this rotation approach is preferred if conditions permit.

The thickness and dielectric constants of thin films usually have certain correlation in the fitting procedure of spectroscopic ellipsometry (SE). The choice of different dispersion models may also influence the results and cause errors. As the fitting is influenced by the dispersion models adopted in the analysis, the uniqueness test has been introduced into SE fitting. The results of uniqueness test have been compared with different dispersion models, different film thicknesses, different wavelength ranges and different incident angles using titanium dioxide samples as an example. It is indicated that uniqueness test is efficient in evaluating the fitting for SE measurement. Uniqueness test can also provide quantitative comparison among different dispersion models and contribute to fitting precision.

Effcient thermal neutron detectors with large area, two-dimensional position sensitive, high coun-ting rate high detection effciency and low gamma sensitivity are required to satisfy the demands for the China Spallation Neutron Source (CSNS). Compared with the traditional analog readout method, the digital readout method has the advantages of higher counting rate, smaller quantity of data transmission, simpler readout system and higher signal to noise ratio. The theoretical analysis of the digital readout method is reported in this paper. Used the raw data of GEM detector, the relationship between the position resolution and the width of the readout strip was studied. The results indicate that the digital readout method could be a good choice for the large area position sensitive detector where the requirement of position resolution is less than 4 mm, e.g. the detector of Small-Angle Neutron Scattering (SANS) diffractometer of CSNS.

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.

<正>肿瘤的重离子束治疗是目前放射治疗领域中的最先进、最有效技术之一。重离子治疗终端剂量校准系统担负对束流照射剂量的准确监测和控制任务,是成功实施重离子束

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.

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.

MCNP simulation method of neutron radiography is introduced.The process that Maxwell thermal neutron penetrates the samples is simulated,and clear images are obtained.The contrast of simulation results and actual neutron radiography is also given.The simulation images are very similar to the experimental images.The analyse of the effect of scattered neutrons is included.As the distance between objects and scintillation screen increases,the scattered component decreases.For a distance of double object size,the influence of the scattered neutrons to the image can be ignored.The ability that thermal neutrons penetrates Al,Pb,Fe and Cu is discussed.The reason for the difference between simulation and experimental results is studied.The conclusion can be drawn that the MCNP simulation method of the neutron radiography is credible and can be used to supervise neutron radiography investigation.

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.

Numerical Simulation of NR(neutron radiography) images is of unquestionable importance.This paper introduce MCNP(Monte Carlo program) application in NR.In this paper,we present the simulation results of thermol NR obtained with MCNP4B.The program is used for assessment of the scattered neutron component in NR.The conclusion is important to the NR experiment in future.

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.

A new image transform, namely, the contourlet transform is introduced,which can capture the intrinsic geometrical structure of image. Furthermore, a novel image denoising scheme based on contourlet is presented. Via calculating variance homogeneous measurement (VHM), the locally adaptive window is determined to estimate the shrinkage factor optimally, then the contourlet coefficient is shrunk using the shrinkage factor. The scheme utilizing the correlation of contourlet coefficients in the same subband along the edge or contour of the image, which can get the tradeoff between “noises removing” and “details preserving”. In numerical comparisons with various methods, the presented scheme outperforms the traditional contourlet denoising method based on hard-thresholding and Wiener filter in terms of PSNR. Experiments also show that this scheme could not only remove the noises effectively, but also suit for the neutron radiography system.

Ge nanocrystals embedded in an amorphous SiO 2 film on Si matrix were prepared by ion implantation and subsequent annealing. Neutron transmutation doping (NTD) technique was used for doping Ge nanocrystals with As impurities. The microstructure, phase and photoluminescence of NTDed Ge nanocrystals were analyzed and compared with undoped Ge nanocrystals. A new photoluminescence peak related to As impurities was found. It is discovered that impurities are expelled from larger clusters resulted from Ge nanocrystal aggregation on the sample surface. To prevent nanocrystal aggregation and assure uniform doping of As, it is necessary to adopt appropriate implantation and annealing conditions.