~(15)N原子核共振反应及Pd中的氢剖析

用~(15)N ~1H→~(12)C ~4He 4.43MeV(γ射线)的共振核反应测量超导体Pd H中氢的浓度与深度之间关系,是较精确的方法。因为1)深度分辨率高;2)γ射线能透过低温和真空系统而易于探测;3)反应共振能量为6.385MeV,为孤立共振,共振宽度很窄(6keV),易于分开;4)有大的反应截面(0.45b),灵敏度高。本文讨论了这种方法的原理、实验装置和不同制备条件下Pd(H)超导体中氢分布、并与压力荷电样品的结果相比较,对氢在这类超导体中的行为提出一些新的不同的看法。     

Ti/4H-SiC肖特基势垒二极管抗辐射特性的研究

本文采用γ射线、高能电子和中子对Ti/4H-SiC肖特基势垒二极管(SBD)的抗辐射特性进行了研究.研究发现对于γ射线和1 MeV电子辐照,-30 V辐照偏压对器件的辐照效应没有明显的影响.经过1 Mrad(Si)的γ射线或者1×l0¹³ n/cm²的中子辐照后,Ti/4H-SiC肖特基接触都没有明显退化;经过3.43×10¹⁴ e/cm²的1 MeV电子辐照后Ti/4H-SiC的势垒高度比辐照前轻微下降,这是由于高能 关键词： 碳化硅 肖特基 辐照 偏压     

大气中Pd-H(D)系中H(D)的释放及其表面附近H的分布

将经过950℃热处理后缓慢冷却及淬火处理的Pd样品,分别作为阴极在重水(D₂O)和轻水(H₂O)中进行150h电解,以引入H和D。用X射线衍射方法测量Pd-H(D)系存放于大气中经过不同时间后的衍射图及β相晶格常数的变化,并用¹H(¹⁹F,αγ)¹⁶O核反应测量H在各Pd-H(D)系表面层中的分布。淬火Pd与退火Pd相对比,在电解吸H(D)后,前者初始含H(D)百分比较高而H(D)的释放速度较快。H的浓度在Pd-H合金的表面处达到极大值而在离表面深度为数百埃处达到极小值。 关键词：     

现代物理信息

 1.D_?⁺的新衰变道.第一次观测到D_?⁺→ηρ⁺,η¹ρ⁺,确定了D_?⁺→φρ⁺.这些衰变方式的分支比,比D_?⁺→φπ⁺要大.（CLEO collaboration,No.9）2.新的质子放射同位素.用300MeV的⁵³Ni离子轰击¹⁰⁶Cd靶,经质量分离而得最重的放射质子同位素¹⁶⁰Re与¹⁵⁶Ta.测到放出质子的能量、总寿命和质子分支比,对¹⁶⁰Re是1261±6KeV、790±160μs和（91±10）%,对¹⁵⁶Ta是1022±13KeV、165_-55⁺¹⁶⁵ms和～100%.（R.D.Page et al.,No.9）3.飞秒激光产生MeV级能量的X射线0.5TW、120fs Ti:兰宝石激光照射到固体靶上,当聚焦达10¹⁸W/cm²时,产生的等离子体会放出能量超过1MeV的X射线.产额随入射激光功率的3/2而上升.40mJ激光打靶,X射线能量在20Key以上的能量转换达0.3%,X射线的能谱符合1/E分布.     

用于GaAs太阳能电池的NaYF4中Tb3+-Er3+耦合对的光谱转换

观测到一种以Tb³⁺-Er³⁺进行光谱转换的量子剪裁现象。一个高能紫外光子(Tb³⁺的⁷F₆→⁵L₁)被量子剪裁成两个低能光子:一个是近红外光子(Er³⁺的⁴I_9/2→⁴I_15/2),另一个是蓝色光子(Tb³⁺的⁵D₄→⁷F₆),它们两个 都可以被GaAs太阳能电池有效地吸收。量子剪裁效率高达188%,接近理论极限的200%。从Tb³⁺(⁵L₁→ ⁵D₄) 到Er³⁺(⁴I_15/2→⁴I_9/2)的能量传递的能量失配是237 cm^-1,比NaYF₄中的声子能400 cm^-1小,能量传递是近共振的。Tb³⁺施主间的能量迁移可以近似地用扩散模型处理, 从Tb³⁺-Er³⁺对之间能量传递的初始过程发现,偶极-偶极相互作用占主导地位。     

Double-heavy tetraquark states with heavy diquark-antiquark symmetry

We calculate the masses of the QQqq(Q=c,b:q=u,d,s)tetraquark states with the aid of heavy diquark-antiquark symmetry(HDAS)and the chromomagnetic interaction(CMI)model.The masses of the highestspin(J=2)tetraquarks that have only the(QQ)(3):(qq)₃.color structure are related with those of conventional hadrons using HDAS.Thereafter,the masses of their partner states are determined with the mass splittings in the CMI model.Our numerical results reveal that(i)the lightest ccnn(n=u,d)is an I(J^P)=0(1⁺)state around 3929 MeV(53 MeV above the DD^* threshold),and none of the double-charm tetraquarks are stable;(ii)the stable double-bottom tetraquarks are the lowest 0(1⁺)bbin around 10488 MeV(≈116 MeV below the BB^*threshold)and the lowest 1/2(1⁺)bbns around 10671 MeV(≈20 MeV below the BB_s^*/B_sB^*threshold);and(iii)the two lowest bcnn tetraquarks,namely the lowest 0(0⁺)around 7167 MeV and the lowest 0(1)around 7223 MeV,are in the nearthreshold states.Moreover,we discuss the constraints on the masses of double-heavy hadrons.Specifically,for the lowest nonstrange tetraquarks,we obtain T_cc<3965 MeV,T_bb<10627 MeV,and T_bc<7199 MeV.     

SrZn2(PO4)2:Sn2+,Mn2+荧光粉的发光性质及其能量传递机理

采用高温固相法制备了SrZn₂(PO₄)₂:Sn²⁺(SZ₂P:Sn²⁺), SrZn₂(PO₄)₂:Mn²⁺(SZ₂P:Mn²⁺), SrZn₂ (PO₄)₂:Sn²⁺, Mn²⁺(SZ₂P:Sn²⁺, Mn²⁺) 荧光粉. 通过X射线衍射、激发和发射光谱详细研究了荧光粉的物相和发光性质. 在SrZn₂(PO₄)₂ 基质中, Sn²⁺离子发射光谱是峰值位于461 nm宽带谱, 归属于Sn²⁺离子的³P₁→¹S₀能级跃迁, SZ₂P:Mn²⁺激发光谱由基质吸收带(200–300 nm)和位于352, 373, 419, 431和466 nm的一系列激发峰组成, 分别对应Mn²⁺离子的⁶A₁(⁶S)→⁴E(⁴D), ⁶A₁(⁶S)→⁴T₂(⁴D), ⁶A₁(⁶S)→[⁴A₁(⁴G), ⁴E(⁴G)], ⁶A₁(⁶S)→⁴T₂(⁴G)和⁶A₁(⁶S)→⁴T₁(⁴G)能级跃迁, 因此, SZ₂P:Sn²⁺ 的发射光谱与SZ₂P:Mn²⁺的激发光谱有较大范围的重叠. 结果表明Sn²⁺对Mn²⁺发光有明显的敏化作用. 基于Dexter电多极相互作用能量传递公式和Reisfeld近似原理分析, 荧光粉SZ₂P:Sn²⁺, Mn²⁺中Sn²⁺-Mn²⁺离子之间的能量传递机理属于电四极-电四极相互作用引起的共振能量传递, 并计算出Sn²⁺-Mn²⁺离子之间能量传递临界距离R_c ≈ 1.78 nm. 通过改变Sn²⁺, Mn²⁺离子掺杂浓度, 实现了荧光粉发光颜色的调节, 在254 nm短波紫外激发下荧光粉发出较强的蓝白光. 研究结果表明SZ₂P:Sn²⁺, Mn²⁺荧光粉有望应用于紧凑型节能灯照明领域, 随着半导体紫外芯片技术的发展, 有潜力应用于未来的白光发光二极管照明领域.     

离子注入超导体PdCu中的氢分布和超导临界温度

制造超导体钯铜合金的新方法是把铜注入钯,然后在室温下电解,将Pd-Cu合金再在液氮温度下注入氢,这样所得到的超导结构H/Pd₅₅Cu₄₅≈0.7可以达到最高的超导临界温度为17K。由于氢的浓度对该系统超导性的存在是关键,因此,我们仍用¹⁵N的共振核反应法研究这类合金中氢分布及其对超导临界温度的影响和作用。从而对探索这类超导体新方法提供有意义的信息。 关键词：     

多壁碳纳米管束储氢机理的X射线吸收谱研究

采用X射线吸收精细结构光谱探索性地研究了多壁碳纳米管束.在多壁碳纳米管束不同入射角的X射线吸收精细结构光谱中，观察到C—H σ^*共振峰强度随入射角的变化而发生变化.在常温常压下出现C—H键可能与多壁碳纳米管束中存在缺陷有关，缺陷数量越大C—H σ^*共振峰的强度越大.光谱中C—C π^*和C—C σ^*共振峰强度的变化趋势都不同于C—H σ^*共振峰，这有力地证明了在常温常压条件下氢原子是吸附在多壁碳纳米 关键词： X射线吸收精细结构光谱 碳纳米管 储氢 化学吸附     

表面等离子共振金/钯复合膜氢敏传感器

提出了一种新颖的钯(Pd)/金(Au)复合膜表面等离子共振氢敏结构,与单一Pd膜氢敏传感器相比,具有可靠性好、灵敏度高和响应度大等特点。利用表面等离子共振理论建立了Au/Pd复合膜氢敏传感器的数学模型,并对Au/Pd复合膜氢敏传感器的灵敏度进行了数值模拟。数值模拟结果表明:基于Au(2nm)/Pd(20nm)复合膜氢敏传感器所获得的最佳灵敏度比单一Pd(20nm)膜氢敏传感器提高了49 4%。     

F离子弹性反冲法分析固体中H的深度分布

本文报道7—8MeVl⁴⁺离子弹性反冲法(ERD)分析固体中H的深度分布。实验和理论分析表明,近表面处的深度分辨率为200—300?。探讨了散射几何条件和入射能量等的最佳化问题。比较了同一样品用F离子ERD法与6.4MeV¹H(¹⁹F,αγ)¹⁶O核反应法(NRA)的测试结果。表明F离子ERD法是快速(5—10min)、低辐照(5—10μC)、深度分辨和灵敏度较好的分析固体中H的深度分布的一种方法。 关键词：     

Band structures of Se and Se

Band structures of ⁷⁶Se and ⁷⁸Se have been studied with the ^74,76Ge(, 2nγ)^76,78Se reactions by using a variety of in-beam γ-techniques : γ-ray singles spectra, γ-ray excitation functions, γ-γ-t coincidences, γ-ray angular distributions and γ-ray linear polarizations.

Spins and parities have been assigned uniquely for many new levels in ⁷⁶Se and ⁷⁸Se and four bands have been identified in both nuclei: (i) the ground-state band, (ii) a positive-parity ΔJ = 1 band built on the second 2⁺ state (γ-vibrational band), (iii) a negative-parity Δ J = 2 band built on the 3⁻ state (octupole band) and (iv) a ΔJ = 2 band built on the high-lying J = 4 state. In addition, the second 8 ⁺ and 10⁺ states, which are possibly the lowest members of a band, have been found in both nuclei.

Systematics of the band structures obtained are discussed. Level energies of the band members and B(E2) ratios for some of the inter-band transitions between γ- and ground-state bands have been calculated with the proton-neutron interacting boson model IBM-2 and a reasonable agreement with the present data has been obtained.     

High-spin study of Xe

High-spin states have been populated in ₅₄¹¹⁹Xe via the ⁹⁶Mo(²⁷Al,p3n) reaction at 133 MeV, using the γ-ray spectrometer to record triple γ-ray coincidences. The known level scheme has been significantly extended and several band crossings identified. In particular, the νh_11/2 yrast band has been extended to I^π = (83/2⁻) and shows features which are consistent with those of smooth band termination at high spin. Theoretical results for ¹¹⁹Xe at high spin are discussed within the framework of cranked Nilsson-Strutinsky calculations, together with results for ¹¹⁷Xe.     

The surface structure of catalysts activated with hydrogen donors as elucidated by multinuclear solid-state NMR

¹H, ²⁷Al and ³¹P MAS, and ¹³C and ²⁹Si CP/MAS NMR spectroscopies, were used to characterize catalysts of Pd supported on various solids including SiO₂, AlPO₄ and Mg₃(PO₄)₂ that were activated with the chiral hydrogen-donor limonene. The above-mentioned techniques were used to check for the formation of an organopalladium complex between Pd²⁺ atoms and the olefin bonds in the limonene molecule on the catalyst surface. The results are compared with those obtained for catalysts activated in a hydrogen stream.     

吩噻嗪-1,4萘醌-乙二醇体系光化学过程的时间分辨ESR研究

用时间分辨ESR方法研究了吩噻嗪(PTH)-1,4-萘醌(NQ)-乙二醇(RH)体系中的光化学过程.只观察到萘醌的中性半醌自由基NQH^*的全发射极化的CIDEP(化学诱导动态极化)信号,并未观察到极化的萘醌负离子NQ·^-*的CIDEP信号,表明RH与三重态NQ间的质子转移反应远比PTH与NQ间的电子转移反应为快.NQH·^*的CIDEP信号随pH值的变化表明体系中同时有极化自由基NQH·^*与NQH·₂^+*存在,并且其间有质子交换.     

分子影像新技术——氘代谢波谱及成像的综述与展望

目前常用的分子影像技术主要有正电子发射型断层显像（PET）、质子磁共振波谱（¹H MRS）及成像（¹H MRSI）、化学交换饱和转移（CEST）、超极化¹³C MRSI等.近4年来,氘代谢波谱（DMS）及成像（DMI）作为一种新兴的分子影像技术获得了越来越多的关注,其通过采集注射或口服氘代葡萄糖后的目标组织与正常组织间氘代谢产物的磁共振信号进行组织区分.相比于其他分子影像方法,该影像技术具有无辐射、稳定性好、扫描操作相对简单等优点.本文综述了近年来DMS/DMI技术的研究进展及其意义,归纳总结了其临床应用价值,并对该技术未来的发展和改进方向,以及应用前景进行了展望.     

Hydrogen distribution in oxynitride/oxide structures

Silicon oxynitride films with five different O/N ratios were deposited with low pressure chemical vapor deposition on a silicon substrate covered with an oxide. The films were subjected to subsequent post-deposition anneals in N₂ and H₂ at 1000°C, and a H plasma at 300°C to obtain information about the hydrogen chemistry. The overall film compositions were determined with elastic recoil detection. The resonant reaction ¹⁵N(¹H, γ)¹²C was used to obtain hydrogen depth profiles. The hydrogen depth profiles are characterized by a value for the bulk concentration and width of the interfacial region. We found that the stability of the hydrogen in the bulk has a maximum for O/N ≈ 0.32. From the measured interfacial widths we deduced that for low values of O/N the stability of hydrogen in the interfacial region is relatively large. For intermediate values of O/N the stability of the hydrogen in the bulk and the interfacial region do not differ significantly, while for high O/N a relatively low stability of the interfacial hydrogen is observed. The O/N dependence of the stability of the interfacial hydrogen is consistent with the bulk stability if we assume that the interfacial oxynitride is oxygen enriched as compared to the bulk oxygen concentration.     

A multinuclear magnetic resonance study of intramolecular hydrogen bonding in some Schiff and Schiff-Mannich bases in solution and in the solid state

Two Schiff bases; N, N′-bis(5-bromosalicylidene)-1,2-diaminoethane, BS, and 7-[(1-{5-bromo-2-hydroxyphenyl} methylidene)amino]-4-methylcoumarin, Sc, and two appropriate Schiff–Mannich bases, N, N′-bis{5-bromo-3-[(diethylamino)methyl]salicylidene}-1,2-diaminoethane, BSM, and 7-[(1-{5-bromo-3-[(diethylamino)methyl]-2-hydroxyphenyl} methylidene)amino]-4-methylcoumarin, SMc, capable of intramolecular hydrogen bonding have been investigated by multinuclear magnetic resonance methods in both solid and liquid phases. In all of the compounds under investigation tautomeric equilibrium involving an intramolecular hydrogen bond has been found. The Schiff–Mannich bases, which can form two different kinds of H bonds at room temperature, form relatively weak H bonds with the imino nitrogen atoms. At low temperatures the tautomeric proton exchange becomes slow on the NMR time scale and both hydrogen-bonded forms can be observed by ¹H, ¹³C, and ¹⁵N NMR methods. In the solid state the tautomeric process is frozen and only one H-bonded form is present. On the basis of 13C and ¹⁵N CPMAS NMR spectra this is identified as the form with hydrogen bonds involving the imino groups. This conclusion is in good agreement with previous results obtained by X-ray diffraction methods.

The investigated Schiff bases (BS and Sc) form relatively weak H bonds. The proton position in the hydrogen bridge, estimated from ¹⁵N and ¹³C chemical shifts, is very similar in both the solution and solid phases. In chloroform solution the observed tautomeric equilibria are almost insensitive to a temperature change within the range 223 to 303 K.     

A Detailed Study of Pre-scission γ Emission as a Probe of Nuclear Dissipation

Using a Langevin equation coupled with a statistical model, we calculate pre-scission giant dipole resonance （GDR） γ-ray multiplicity of nuclei 194 pb, 200Pb, 206Pb, and 200 Os. It is demonstrated that with increasing the isospin asymmetry of these fissioning nuclei the sensitivity of the emitted γ multiplicity to the nuclear viscosity coefficient is decreased significantly. For 200Os nuc/eus, this γ-ray emission is no longer sensitive to the magnitude of the viscosity coefficient. In addition, the effect of the isospin asymmetry on the γ rays as a probe of nuclear dissipation is reduced with increasing angular momentum. These results suggest that to obtain a more accurate information of the viscosity coemfficient by the measurement of pre-scission GDR γ-ray multiplicity it is better to choose those compound systems with small isospin asymmetry and low spin.