纳秒激光诱导C_(60)分子碎裂中轻碎片离子C_n~+(n<30)的产生机理研究

采用飞行时间质谱计测量了纳秒激光诱导C60分子碎裂中轻碎片离子Cn+(n≤11)的初始平均动能,结果显示轻碎片离子具有相同的初始平均动能(约为0.34 eV),并且该动能在一定范围内不随激光通量的变化而明显改变.结合前人的实验结果,对纳秒激光诱导C60分子碎裂中轻碎片离子Cn+(n<30)的主要产生模式作了新的阐述,即C60分子级联发射15个C2分子和一个电子形成自身不稳定的C3+0离子,在皮秒时间尺度内C3+0离子的笼形结构塌陷,进而轻碎片离子产生.

~(129)Xe~(30+)轰击Ni表面激发靶原子偶极跃迁和禁戒(M1和E2)跃迁的特征光谱线

报道了用高电荷态离子1 2 9Xe30 + (15 0keV)轰击金属Ni表面 ,激发的 2 0 0— 10 0 0nmNiⅠ和NiⅡ的特征光谱线的实验结果 .实验结果表明 :用电荷态足够高的离子作光谱激发源 ,无需很强的束流强度 (nA量级 ) ,便可有效地产生原子和离子的复杂组态间跃迁所形成的可见光波段的特征谱线 ,特别是NiⅠ和NiⅡ偶极禁戒的电四极跃迁E2和磁偶极跃迁M1的特征光谱线 .通过分析发现 ,在禁戒跃迁的谱线中 ,有些是电子组态相同而原子态不同的偶极禁戒跃迁光谱线而且NiⅡ的 6 84 84nm谱线较强

30 MeV/u~(40)Ar+~(nat)Ag反应中类弹碎片发射的时-空演化

报道了 ３０ＭｅＶ／ ｕ(４０)Ａｒ＋(ｎａｔ)Ａｇ反应中中等质量碎片（ＩＭＦ）发射时间（τ）随发射源空间大小的演化规律，并对类弹碎片的发射时空进行了讨论．结果表明，ＩＭＦ的发射时标与中等质量碎片关联函数以及发射源的核物质密度（ρ）有关，而与发射源的质量数的关系不大．对于能量较高的类弹碎片来说，在较小的核物质密度下提取的发射时间也较小，因此，在正常核物质密度参数下提取出的发射时间值可作为碎片实际发射时间的上限值．中速碎片的发射时间随密度大小的变化非常缓慢，提取出的发射时间值即可作为实际的发射时间。

High negative ion production yield in 30 keV F2+ + adenine (C5H5N5) collisions

In collisions between slow F2+ ions (30 keV) and molecular targets, adenine, scattered particle production yields have been measured directly by simultaneous detection of neutrals, positive and negative ions. The relative cross-section for a negative ion formation channel was measured to be 1%. Despite a slight decrease compared to a larger target, the fullerene C-60, the measured negative ion formation cross section is still at least one order of magnitude larger than the yield in ion-atom interactions.

Isolated sub-30-as pulse generation of an He+ ion by an intense few-cycle chirped laser and its high-order harmonic pulses

We present an efficient method to generate a ultrashort attosecond (as) pulse when a model He+ ion is exposed to the combination of an intense few-cycle chirped laser pulse and its 27th harmonics. By solving the time-dependent Schroumldinger equation, we found that high-order harmonic generation (HHG) from He+ ion is enhanced by seven orders of magnitude due to the presence of the harmonic pulse. After optimizing the chirp of the fundamental pulse, we show that the cut-off energy of the generated harmonics is extended effectively to I-p+25.5U(p). As a result, an isolated 26-as pulse with a bandwidth of 170.5 eV can be obtained directly from the supercontinuum around the cut-off of HHG. To better understand the physical origin of HHG enhancement and attosecond pulse emission, we perform semiclassical simulations and analyze the time-frequency characteristics of attosecond pulse.

纳秒激光诱导C60分子碎裂中轻碎片离子C+n(n＜30)的产生机理研究

The time of flight mass spectrometric technique was used to determine the initial mean kinetic energy of small fragment ions C-n(+) (n <= 11) produced from C-60 excited by 532 nm nanosecond laser pulses. The measured kinetic energy shows little variation with the fragment mass and the laser fluence in a broad range. Based on the assumption that C-30(+) is produced predominantly by a single electron emission followed by successive C-2 evaporation from hot C-60 in the nanosecond laser field, the formation of small fragments is interpreted as the complete breakup of the unstable C-30(+) cage structure. The interpretation is consistent with the previously observed results.

Molybdenum L-shell X-ray production by 350-600 keV Xeq+ (q=25-30) ions

Molybdenum L-shell X-rays were produced by Xeq+ (q = 25-30) bombardment at low energies from 2.65 to 4.55 keV/amu (350-600 keV). We observed a kinetic energy threshold of Mo L-shell ionization down to 2.65-3.03 keV/amu (350-400 keV). The charge state effect of the incident ions was not observed which shows that the ions were neutralized, reaching an equilibrium charge state and losing their initial charge state memory before production of L-shell vacancies resulted in X-ray production. The experimental ionization cross sections were compared with those from Binary Encounter Approximation theory. Taking into account projectile deflection in the target nuclear Coulomb field, the ionization cross section of Mo L-shell near the kinetic energy threshold was well described. (C) 2010 Published by Elsevier B.V.

EXPERIMENTAL INVESTIGATION OF THE STELLAR REACTION S-30(p, gamma)(31) Cl VIA COULOMB DISSOCIATION

The Coulomb dissociation of the proton-rich nuclei Cl-31 was studied experimentally using Cl-31 beams at 58 MeV/nucleon with a lead target. The relative energy between the reaction products, S-30 and proton, was obtained. The first excited state in Cl-31 was observed which is relevant to the resonant capture of stellar S-30(p, gamma)Cl-31 reaction

30,35MeV/u 36,40Ar＋112,124Sn反应中热核性质同位旋效应的实验研究

针对①中能反应中同位旋自由度是否达到平衡，②同位旋自由度对几中不同方法测量的核温度是否有影响 这两个基本问题，设计了用30和35MeV/u ~(36,40)Ar轰击~(112,124)Sn反应的实验方案。得到如下结果：对于前角5°处的耗散弹核碎裂产物，丰中子同位素与稳定核的产额比随产物出射动能的增加而减小，而丰质子子同位素与稳定核的产额比随动能的增加而增加，呈现明显的剪刀差分布特性。随耗散时间的增大，产物的平均中质比逐渐由弹核的平均中质比向系统的平均中质比过渡。这个结果说明在该反应中，同位旋自由度没有达到完全平衡。而对于20°处的DIC产物，上述剪刀差分布特性变得更不明显，这是同位旋自由度由非平衡向平衡过渡的表现。后角轻粒子的能谱分析表明，初始热核的同位旋会影响斜率核温度的提取，由于丰中子轻粒子~6He在~(40)Ar + ~(112)Sn系统中的蒸发被抑制，相比~(40)Ar + ~(112)Sn而言，其蒸发比较容易发生在衰变链早期，因此提取的温度偏高，同样，丰质子轻粒子~3He的温度在~(40)Ar + ~(112)Sn中略高。但中后角的同位素产额分析表明，反应系统的同位旋对双同位素比核温度几乎没有影响。核温度作为热核的热力学量，是独立于测量方法的，这种不同的方法得出的差异主要来源于同位旋对衰变机制的影响。作为一个尝试，将中高能反应中的熵的提取推广到这个能区，发现两个系统的熵几乎一致。在量子统计模型框架下，考察核温度与熵的关系发现，~(40)Ar + ~(112)Sn反应的挤出时刻密度略高于~(40)Ar + ~(112)Sn。

Cyclopropanation on a highly active heterogeneous catalyst: CuO/TiO2-Al2O3

Some heterogeneous catalysts, cupric oxide supported on different supports, were prepared and employed to catalyze the cyclopropanation of styrene and 2,5-dimethyl-2,4-hexadiene with ethyl diazoacetate (EDA). The catalytic performance for cyclopropanation strongly depends on the nature of the support. A novel catalyst, CUO/TiO2-Al2O3, in which Al2O3 is modified with a monolayer TiO2, is found to be most active and selective for the cyclopropanation reaction. The yields of 93 and 94% cyclopropanes are obtained for styrene and 2,5-dimethyl-2,4-hexadiene at 40 degreesC as the substrates, respectively. The activity and selectivity in cyclopropanes are optimized with a monolayer dispersion of cupric oxide on the corresponding supports. (C) 2002 Elsevier Science B.V. All rights reserved.

科尔沁碱化草地改良配套技术研究

为探讨科尔沁地区碱化草地改良的有效途径,提高牧草产量和品质,采用翻耙、补播沙打旺以及施用酸性肥料(NH4)2SO4等技术对典型碱化草场进行了改良试验。试验结果表明,翻耙补播技术可提高草地产草量1.18~3.66倍;在此基础上施用(NH4)2SO475~225kg.hm-2可使重度碱化草场继续增产11.0%~41.2%。经过翻耙后草地土壤综合生产性能得到显著提高,土壤理化性质明显改善,土壤脲酶、磷酸单酯酶、多酚氧化酶和蔗糖酶的活性均大幅度提高。这些方法可以在科尔沁地区推广应用,对其他类似的半干旱地区草地改良也具有一定的参考价值和指导意义。

岷江上游地区近30年森林生态系统水源涵养量与价值变化

根据岷江上游地区自然地理环境条件的差别,将该区森林植被划分为暗针叶林、其它针叶林、阔叶林和灌木林等4个类型,利用年降雨量、林冠截流量数据、径流系数以及“影子价格”等方法,计算和评述了该区森林生态系统水源涵养效益;并利用遥感4期影像分析了岷江上游地区森林生态系统水源涵养量的变化原因。结果表明:2000年岷江上游森林生态系统年水源涵养量最高,为1·3892×1010m3,经济价值为93·07亿元。去除降雨量的影响后,在各时期年降雨量为705mm的情况下,岷江上游地区1986年的水源涵养量最高,为1·3348×1010m3,经济价值为89·43亿元;1995年水源涵养量下降,为1·2320×1010m3,经济价值为82·54亿元;2000年水源涵养量及经济价值与1995年基本持平。造成这一现象的主要原因是20世纪90年代岷江上游森林景观受到人为的严重破坏,而随后实施的“天然林保护工程”与“退耕还林还草”政策,加强了人工植被恢复建设,改善了森林生态系统,使森林生态系统水源涵养量有所恢复。