高能Xe离子辐照引起的注碳a:SiO2中新结构的形成

先用120keV的碳离子注入非晶二氧化硅a:SiO2薄膜，再用能量为1754MeV的Xe离子辐照。注碳量为5．0×10^16—8．6×10^17ion／cm^2，Xe离子辐照剂量为1．0×10^11和5．0×10^11ion／cm^2。辐照后的样品中形成的新结构用显微傅立叶变换红外光谱仪进行测试分析。结果表明，Xe离子辐照引起了注碳a:SiO2中Si—C，C—C，Si—O—C键以及CO和CO2分子的形成与演化。在注碳量较高时，Xe离子辐照在样品中产生了大量的Si—C键。与注入未辐照和辐照的低注碳量样品比较，增强的Si—C键的形成，预示着辐照可引起注碳a:SiO2样品中的SiC结构相变。Amorphous silicon-dioxide （a:SiO2） films were firstly implanted at room temperature （RT） with 120 keV C-ions to doses ranging from 5.0 × 10^16 to 8.6 × 10^17 ion/cm^2, and then the C-doped a:SiO2 films were irradiated at RT with 1 754 MeV Xe ions to 1.0 × 10^11 and 5.0 × 10^11 ion/cm^2, respectively. The information of new tex- ture formation in the C-doped SiO2 films after high-energy Xe ion irradiation was investigated using micro-FTIR measurements. The obtained results showed that Si--C, C--C, Si--O--C bonds as well as CO and CO2 molecules were formed in the C-doped a-SiO2 films after Xe ion irradiation. Furthermore, Xe-ion irradiation induced a plenteous formation of Si--C bonds in the high dose C-ion implanted a:SiO2 films. Compared with the C-implanted sampies without Xe-ion irradiation and the low dose C-implanted samples with Xe-ion irraddiation, the enhanced and plenty of Si--C bond formation implied that the phase of SiC structures may be produced by Xe-ion irradiation in the high dose C-ion implanted a:SiO2 films.     

双光子共振四波差频产生的真空紫外激光特性研究

介绍以惰性气体Xe为非线性介质、利用双光子共振四波混频差频方法产生的可调谐真空紫外激光(VUV)的特性研究 .实验中 ,传播方向和空间均相互重合的两束脉冲染料激光经透镜聚焦于Xe气混频池内 ,其中一束激光的波长 (2 4 9.6 2 6nm)对应于Xe原子 6P[1/2 ,0 ]←← 5P的双光子共振跃迁 ,通过调谐另一束激光的波长 ,产生在 15 1～ 171nm可连续调谐的VUV激光 .经估算 ,产生的VUV激光的强度约为每脉冲约 0 .2 μJ ,转换效率约为 0 .1% .通过测量超声射流冷却下CO分子的A1Π←X1Σ+ (0 ,0 )带的转动分辨激光诱导荧光 (LIF)光谱 ,确定出VUV激光的线宽为 0 .3cm-1.此外 ,还对VUV激光强度与惰性气体压力、染料激光强度等依赖关系进行了研究 .     

Laser-polarized 129Xe NMR at 1.88 T and 8.5 mT: a signal-to-noise ratio comparison

The signal-to-noise ratio of nuclear magnetic resonance signals from laser-polarized 129Xe gas was investigated at 8.5 mT and compared to that of signals acquired at 1.88 T. A dedicated 8.5 mT resistive magnet was constructed and used to acquire the signals. The SNR for 1 atm of xenon gas with a polarization of 1% was measured to be 1900 at a field of 1.88 T. Under identical acquisition conditions, the SNR at 8.5 mT was about 60 (or 32 times lower). After measuring and including all of the electrical factors of the detection systems at each field strength, theory indicates the SNR value measured at 8.5m T should be about 36 times lower. Considering the widely differing frequencies and completely different detection systems the agreement is quite good and indicates that extrapolating the frequency dependence of the SNR down to very low fields does work as long as the detection system parameters are carefully accounted for. This work suggests that magnetic resonance (MR) imaging is achievable on ideal gas samples at 8.5 mT using laser-polarized 129Xe gas down to the practical resolution limit of about 0.5mm, although the SNR will be very low (approximately 1.4). The feasibility of imaging small animals at 8.5 mT is discussed and it is suggested that a field of about 50 mT is required.     

MCM-41分子筛的合成及129Xe核磁共振的研究

ＭＣＭ４１中孔分子筛是１９９２年由Ｍｏｂｉｌ公司的科学家Ｋｒｅｓｇｅ［１］等人首次合成的,并在《自然》杂志发表。这种中孔分子筛具有六角形孔径,孔径２ｎｍ～１０ｎｍ,这种分子筛的孔径可以通过水晶模板来控制［２］。已报道的合成ＭＣＭ４１,孔径一般在２．０ｎｍ～３．５ｎｍ,使用的水晶模板一般是单一或两种阳离子季铵盐表面活性剂［３,４］。本论文通过引入第二种扩孔模板,与阳离子季铵盐协同作用,合成了孔径５．２ｎｍ（ＢＥＴ法测）的ＭＣＭ４１。通过氮气的吸脱附,测定了分子筛的比表面和孔径等性质。Ｊ．Ｆｒａｉｓｓａｒｄ…     

A Molecular Imaging Approach to Mercury Sensing Based on Hyperpolarized 129Xe Molecular Clamp Probe

Mercury pollution, in the form of mercury ions (Hg²⁺), is a major health and environmental hazard. Commonly used sensors are invasive and limited to point measurements. Fluorescence‐based sensors do not provide depth resolution needed to image spatial distributions. Herein we report a novel sensor capable of yielding spatial distributions by MRI using hyperpolarized ¹²⁹Xe. A molecular clamp probe was developed consisting of dipyrrolylquinoxaline (DPQ) derivatives and twocryptophane‐A cages. The DPQ derivatives act as cation receptors whereas cryptophane‐A acts as a suitable host molecule for xenon. When the DPQ moiety interacts with mercury ions, the molecular clamp closes on the ion. Due to overlap of the electron clouds of the two cryptophane‐A cages, the shielding effect on the encapsulated Xe becomes important. This leads to an upfield change of the chemical shift of the encapsulated Xe. This sensor exhibits good selectivity and sensitivity toward the mercury ion. This mercury‐activated hyperpolarized ¹²⁹Xe‐based chemosensor is a new concept method for monitoring Hg²⁺ ion distributions by MRI.     

Gradient-induced longitudinal relaxation of hyperpolarized noble gases in the fringe fields of superconducting magnets used for magnetic resonance

When hyperpolarized noble gases are brought into the bore of a superconducting magnet for magnetic resonance imaging (MRI) or spectroscopy studies, the gases must pass through substantial field gradients, which can cause rapid longitudinal relaxation. In this communication, we present a means of calculating this spatially dependent relaxation rate in the fringe field of typical magnets. We then compare these predictions to experimental measurements of (3)He relaxation at various positions near a medium-bore 2-T small animal MRI system. The calculated and measured relaxation rates on the central axis of the magnet agree well and show a maximum (3)He relaxation rate of 3.83×10(-3) s(-1) (T(1)=4.4 min) at a distance of 47 cm from the magnet isocenter. We also show that if this magnet were self-shielded, its minimum T(1) would drop to 1.2 min. In contrast, a typical self-shielded 1.5-T clinical MRI scanner will induce a minimum on-axis T(1) of 12 min. Additionally, we show that the cylindrically symmetric fields of these magnets enable gradient-induced relaxation to be calculated using only knowledge of the on-axis longitudinal field, which can either be measured directly or calculated from a simple field model. Thus, while most MRI magnets employ complex and proprietary current configurations, we show that their fringe fields and the resulting gradient-induced relaxation are well approximated by simple solenoid models. Finally, our modeling also demonstrates that relaxation rates can increase by nearly an order of magnitude at radial distances equivalent to the solenoid radius.     

Preclinical MRI Using Hyperpolarized 129Xe

Although critical for development of novel therapies, understanding altered lung function in disease models is challenging because the transport and diffusion of gases over short distances, on which proper function relies, is not readily visualized. In this review we summarize progress introducing hyperpolarized ¹²⁹Xe imaging as a method to follow these processes in vivo. The work is organized in sections highlighting methods to observe the gas replacement effects of breathing (Gas Dynamics during the Breathing Cycle) and gas diffusion throughout the parenchymal airspaces (3). We then describe the spectral signatures indicative of gas dissolution and uptake (4), and how these features can be used to follow the gas as it enters the tissue and capillary bed, is taken up by hemoglobin in the red blood cells (5), re-enters the gas phase prior to exhalation (6), or is carried via the vasculature to other organs and body structures (7). We conclude with a discussion of practical imaging and spectroscopy techniques that deliver quantifiable metrics despite the small size, rapid motion and decay of signal and coherence characteristic of the magnetically inhomogeneous lung in preclinical models (8).     

超极化129Xe磁共振波谱和成像及在生物医学中的应用

文章简要介绍了磁共振波谱和成像的基本原理和对限制其灵敏度的挑战,详细阐述了为增强磁共振信号而制备超极化129Xe的物理机制,论述了129Xe在生物组织中的溶解性以及化学位移的特异性,综述了当前超极化129Xe在肺部、脑部成像领域的研究进展和在临床方面应用所取得的有代表性的研究成果,并讨论了基于超极化129Xe分子生物探针的超灵敏磁共振技术的研究前景,最后对超极化129Xe在生物医学领域的应用与发展作了展望.     

双光子共振四波差频产生的真空紫外激光特性研究

The character of tunable Vacuum-Ultraviolet（VUV）laser generated by two-photon resonant four wave difference frequency mixing in Xenon was studied. The intense VUV laser was generated in the wavelength range of 151-171 nm using 6P［1/2,0］level of Xe atom as the two-photon resonant state. The pulse intensity of VUV laser was estimated to be 0.2 μJ,and the conversion efficiency relative to the wavelength-fixed laser was determined to be 0.1%. The line width of VUV laser was found to be 0.3 cm-1 from the laser-induced fluorescence spectrum of A-X（0,0）rotational line profiles of jet-cooled CO,which was much broader than those of the two employed dye lasers（0. 1 cm-1）,mainly due to the saturation broadening of Xe level by intense laser field. The dependencies of VUV intensity on Xe pressure and two dye laser intensities were also investigated in this experiment.     

氪灯发光总功率和氙灯发光总能量检测设备

根据氪灯、氙灯发光的工作原理,介绍了氪灯发光总功率和氙灯发光总能量检测系统。该系统可以对氪灯发光总功率和氙灯发光总能量进行批量检验,使用户能在相关激光产品的生产和装配过程中对其进行质量控制,从而提高了激光产品的合格率,缩短了生产时间。在连续氪灯和脉冲氙灯的入厂检验中,氪灯发光总功率和氙灯发光总能量是需要检测的主要技术指标。新型氪灯、氙灯性能综合检测系统是通过采用积分球、功率计以及能量计来检测氪灯的发光总功率和氙灯的发光总能量的。设备由:积分球、功率计、能量计、氪灯和氙灯支架及冷却系统、氪灯和氙灯电源等五部分组成。