有机染料CSPI的双光子吸收和上转换荧光性质

报道了一种有机染料Trans 4 [p carbazol 9 ylstyryl] ] N methylpyridiniumiodide的线性和非线性光学性质。当用 830nm皮秒激光激发时 ,可以得到强烈的黄绿色上转换荧光 ,中心波长在 538nm附近。该染料的双光子荧光寿命为 95 .6ps。测试了该染料在 72 0～ 1 0 50nm的非线性透过率 ,并求出了该染料在上述波长时的双光子吸收截面。双光子吸收最强在 80 0nm ,吸收截面为 9.2× 1 0 - 48cm4 ·s/ photon。     

整体考虑靶和均整器的设计来提高医用加速器剂量率的方法

通常低能医用加速器靶的设计遵从厚靶原则, 即采用厚度等于或大于电子射程的靶, 使靶后无电子污染. 本文提出了新的靶设计概念：设计靶时, 将靶与相关系统(初级准直锥、均整器)作为一个整体考虑, 通过减小靶厚来提高光子剂量率, 利用初级准直锥、均整器来减少电子污染. 采用这种设计概念, 用蒙特卡罗方法对BJ-6—6MV单光子医用电子直线加速器的靶进行优化设计. 模拟计算10cm×10cm野, 30cm×30cm野的深度剂量曲线, 结果表明：较之现有的厚靶, 治疗剂量提高了10%, 同时表面剂量、X射线的品质仍满足国标的要求. 通过薄靶、厚靶的加速器整机对比实验, 已验证了此结论的正确性.     

一种新型有机染料HEASPS在不同波长时的双光子吸收和频率上转换性质研究

报道了一种新型双光子吸收染料 ,即反式 - 4- [4′- (N-羟乙基 - N-乙基胺基 )苯乙烯基 ]- N-甲基吡啶对甲苯磺酸盐的非线性光学性质 ;测试了染料在 72 0～ 110 0 nm波段的非线性透过率曲线。结果发现 :双光子吸收最强波长相对线性吸收峰波长的两倍处有明显蓝移 ;计算出的相应波长的双光子吸收截面在 930 nm处染料有最大双光子吸收截面(2 .0 6× 10 - 4 7cm4·s/ photon) ;测量了染料在 90 0～ 110 0 nm波段的上转换效率 ,在 10 2 0 nm处有最高效率 (5 .1% ) ,最高激射效率的波长相对最强双光子吸收的波长有明显红移     

神龙二号加速器及其关键技术北大核心CSCD

神龙二号加速器是一台以M H z 猝发率猝发工作的三脉冲直线感应电子加速器.该加速器输出的三脉冲电子束,相邻两脉冲间最小时间间隔300 n s ,而且可调,每个脉冲电子束的电子能量1 8 -20 M e V 、束流强度大于等于2 k A .当电子束与轫致辐射转换靶相互作用时,可产生三个强X 光脉冲,X 光斑点尺寸小于等于2 m m （ F W H M ）,距靶1 m 处照射量大于等于7 . 7 4 × 1 0^- 2C /k g （ 0 0 R ）.该加速器涉及的主要关键技术包括三脉冲功率源设计、三脉冲强流高品质电子束源的产生、加速场建造、束流传输线设计、轫致辐射转换靶设计、测量与诊断技术等.     

质子直线加速器设计研究

当前质子直线加速器发展的两个重要方向是强流质子直线加速器和小型质子直线加速器.前者主要用于核能领域,后者主要用于质子治疗.两类加速器有着共同的特点:1.采用一些新型加速结构,它们是传统结构的组合和发展;2.加速小发射度的质子束;3.加速器应有高度的可靠性.但前者的建造难度远大于后者,它还要求具有很低的束流损失率和尽可能高的能量利用效率.研究了两类加速器设计中的一些重要问题,提出了一些设计方案.     

BEPC de前前后后

 80年代是我国高能物理事业的一个转折点.BEPC按计划高质量地完成,为我国高能物理实验研究提供了一个极其重要的手段;也表明我国的加速器事业已在世界高技术领域中占有了一席之地.BEPC的成就凝聚着几代人的心血.早在1957年,在王淦昌教授的领导下。选派了一批年青的科学家,赴苏学习高能加速器的设计及建造.一年后,在苏联专家的指导下,进行1-2GeV电子同步加速器的设计,这一设计在1958年的大跃进中被认为是保守落后的,而把方案改成15GeV的质子同步加速器.     

1MV多级气体开关

本文叙述了一个为1MV强流脉冲电子束加速器配置的主开关.多级气体开关的设计和实验结果。是国内首次将此种类型的开关应用于兆伏级加速器。     

我国低能加速器的发展

为发展我国的基础学科研究而建造的几台大型加速器工程已相继完成，同时，各类具有广泛用处的小型低能加速器也得到了发展，这标志着我国加速器技术具有相当的水平．本文简要地回顾了我国低能加速器发展的历史，并介绍了几种典型的低能加速器的性能和有关技术的发展情况．     

750keV射频四极注入器水冷设计

750 keV,201.25 MHz的射频四极注入器为四杆型,电极长度124 cm,共16个支撑板。根据加速器射频结构设计的结果进行了水冷管道的结构设计,理论分析了管路的流体力学特性和传热学特性。在忽略结构形变的情况下,利用射频计算软件的稳态热分析功能计算了加速腔的温度分布,降低了模拟计算的难度。计算结果表明:加速腔的最大温升控制在1 K以内,水冷系统能够使加速器在适宜的温度下长时间稳定运行,设计结果很好地满足了物理需求。     

中国加速器驱动次临界系统主加速器初步物理设计

中国加速器驱动次临界系统（C-ADS）计划采用一个平均流强为10 mA的连续波质子加速器作为次临界堆的驱动器,驱动加速器的束流功率为15 MW,最终能量1.5 GeV,其中主加速器是驱动加速器的一个重要部分,完成束流能量从10 MeV到1.5 GeV的加速,所有加速腔均采用超导结构。为了避免频繁束流中断对反应堆的损坏,设计要求驱动加速器在运行过程中束流可以中断的次数非常有限,因此加速器在设计过程植入了容错机制,尝试了各种可能的方法以最大程度地满足C-ADS加速器的高可靠性和稳定性的要求。介绍了C-ADS主加速器的基本设计: 总长度306.4 m, 束流的归一化RMS发射度增长控制在5%以内。总结了各个重要参数选择过程中的考虑以及整个加速段多粒子跟踪模拟的束流动力学结果。     

Regge couplings and intercepts from the planar dual bootstrap

Planar unitarization of dual models is examined in terms of renormalized diagrams. The shift of the Reggeon intercept 1 ? α(0) and the renormalized coupling $\text{g}{}^2\text{N}\text{16π}$ are both expected of order unity in a model with SU(N) Chan-Paton factors. In four space-time dimensions Regge behaviour makes the shift of the dual photon mass reminiscent of Schwinger's mechanism.     

Scaling in a dual model for single particle inclusive electroproduction

Single particle inclusive electroproduction is studied by means of dual resonance models for currents making use of Müller's theorem. Generalized scaling behaviour holds when the photon mass goes to infinity in the target fragmentation region. When the photon mass is kept fixed the two current vertex factorises and the distribution of fragments becomes independent of the mass value.     

High energy pion photoproduction amplitudes from fixed-t dispersion relations and duality

Contributions to the high energy imaginary parts of the charged and neutral pion photoproduction amplitudes from degenerate ? and A₂ exchanges and ω and B exchanges are parametrized similarly to the dual absorptive model. These contributions together with the imaginary parts of the amplitudes found at low energies from partial-wave analyses are then used to evaluate the high energy real parts of the photoproduction amplitudes from fixed-t dispersion relations. A fit is made to data on pion photoproduction at 3.4 and 16 GeV incident photon energies, for momentum transfers up to ?1(GeV/c)². It is shown that much of the data is reproduced both qualitatively and quantitatively by our model. The high energy imaginary parts of the photoproduction amplitudes given by the fit are shown to be in accord with their average low energy behaviour.     

Center-of-Mass Tomography and Wigner Function for Multimode Photon States

Tomographic probability representation of multimode electromagnetic field states in the scheme of center-of-mass tomography is reviewed. Both connection of the field state Wigner function and observable Weyl symbols with the center-of-mass tomograms as well as connection of the Grönewold kernel with the center-of-mass tomographic kernel determining the noncommutative product of the tomograms are obtained. The dual center-of-mass tomogram of the photon states are constructed and the dual tomographic kernel is obtained. The models of other generalized center-of-mass tomographies are discussed. Example of two-mode even and odd Schrödinger cat states is presented in details.     

Effects of long-wavelength fluorescence excitation in liquid solutions of N-pyrrolobenzonitrile

The absorption, dual fluorescence, and fluorescence excitation spectra of N-pyrrolobenzonitrile (P5C) in a set of solvents with different polarities are studied upon irradiation of solutions by light with different photon energies. The dual fluorescence from the locally excited Frank-Condon and charge-transfer states are recorded in all cases. The change in the excitation photon energy does not affect the fluorescence band positions, but noticeably changes the intensity ratio between the bands in favor of the long-wavelength band belonging to the charge-transfer state. The effects observed are explained using the data of quantum-mechanical calculations, which demonstrate that the solutions of these systems can very likely contain rotational isomers with different pyrrole orientations with respect to the benzene ring. In the excited state, these isomers have different charge-transfer reaction rates, which leads to different intensity ratios of the recorded fluorescence bands.     

The influence of field size and off-axis distance on photoneutron spectra of the 18 MV Siemens Oncor linear accelerator beam

At present, high energy electron linear accelerators (LINACs) producing photons with energies higher than 10 MeV have a wide use in radiotherapy (RT). However, in these beams fast neutrons could be generated, which results in undesired contamination of the therapeutic beams. These neutrons affect the shielding requirements in RT rooms and also increase the out-of-field radiation dose to patients. The neutron flux becomes even more important when high numbers of monitor units are used, as in the intensity modulated radiotherapy. Herein, to evaluate the exposure of patients and medical personnel, it is important to determine the full radiation field correctly. A model of the dual photon beam medical LINAC, Siemens ONCOR, used at the University Hospital Centre of Osijek was built using the MCNP611 code. We tuned the model according to measured photon percentage depth dose curves and profiles. Only 18 MV photon beams were modeled. The dependence of neutron dose equivalent and energy spectrum on field size and off-axis distance in the patient plane was analyzed. The neutron source strength (Q) defined as a number of neutrons coming from the head of the treatment unit per x-ray dose (Gy) delivered at the isocenter was calculated and found to be 1.12 × 10¹² neutrons per photon Gy at isocenter. The simulation showed that the neutron flux increases with increasing field size but field size has almost no effect on the shape of neutron dose profiles. The calculated neutron dose equivalent of different field sizes was between 1 and 3 mSv per photon Gy at isocenter. The mean energy changed from 0.21 MeV to 0.63 MeV with collimator opening from 0 × 0 cm² to 40 × 40 cm². At the 50 cm off-axis the change was less pronounced. According to the results, it is reasonable to conclude that the neutron dose equivalent to the patient is proportional to the photon beam-on time as suggested before. Since the beam-on time is much higher when advanced radiotherapy techniques are used to fulfill high conformity demands, this makes the neutron flux determination even more important. We also showed that the neutron energy in the patient plane significantly changes with field size. This can introduce significant uncertainty in dosimetry of neutrons due to strong dependence of the neutron detector response on the neutron energy in the interval 0.1–5 MeV.     

Electron-hole plasma in pulse photoexcited single quantum wells

We report photoluminescence studies of MOCVD grown, GaAsAl_xGa_1?xAs single quantum wells which were intensly excited with a pulse dye laser at T=2K. For a well width of d～40Å, the spectra are interpreted as due to the radiative recombination of a hot electron-hole plasma confined to the well. The density of charge carriers and their temperature depend upon the excitation intensity, and vary in the range of 10¹¹–10¹³ cm^?2 and 100–500K for an absorbed photon flux of 10¹³–10¹⁶ photons-cm^?2 per pulse, respectively. The observed spectral features are identified as the e1-hh1 and e1-lh1 transitions and two additional bands which are tentatively assigned to transitions involving virtual bound states of either the electron or the hole. The electron-hole plasma spectra of the d～40Å sample are strongly polarized perpendicular to the well quantization axis. For wider wells (d～80 and 150Å) smaller photoexcited carrier densities were observed for the same absorbed photon flux. It is thus concluded that the capture efficiency of the well is small.     

双散射光合成场动态散斑的统计性质

本文研究了在两束高斯光束照明条件下,由旋转散射体产生的双散射光合成的远场动态散斑的统计性质.这种动态散斑的统计性质由它的强度涨落的空-时相关函数描述.文中推导了这个函数的解析表达式,并采用了光子计算及光子相关技术,从实验上证实了这个表达式的正确性.     

Single-Photon Counting Multicolor Multiphoton Fluorescence Microscope

We present a multicolor multiphoton fluorescence microscope with single-photon counting sensitivity. The system integrates a standard multiphoton fluorescence microscope, an optical grating spectrograph operating in the UV–Vis wavelength region, and a 16-anode photomultiplier tube (PMT). The major technical innovation is in the development of a multichannel photon counting card (mC-PhCC) for direct signal collection from multi-anode PMTs. The electronic design of the mC-PhCC employs a high-throughput, fully-parallel, single-photon counting scheme along with a high-speed electrical or fiber-optical link interface to the data acquisition computer. There is no electronic crosstalk among the detection channels of the mC-PhCC. The collected signal remains linear up to an incident photon rate of 10⁸ counts per second. The high-speed data interface offers ample bandwidth for real-time readout: 2 MByte -stacks composed of 16 spectral channels, 256× 256 pixel image with 12-bit dynamic range can be transferred at 30 frames per second. The modular design of the mC-PhCC can be readily extended to accommodate PMTs of more anodes. Data acquisition from a 64-anode PMT has been verified. As a demonstration of system performance, spectrally resolved images of fluorescent latex spheres and ex-vivo human skin are reported. The multicolor multiphoton microscope is suitable for highly sensitive, real-time, spectrally-resolved three-dimensional imaging in biomedical applications.