镜像核13N-13C 和15N-15O中的激发态晕或皮(英文)

用非线性相对论平均场对两对镜像核13N-13C 和15N-15O进行了研究. 发现无论在基态还是激发态， 用两套参数所得的结合能都跟实验值很接近. 计算结果显示13N的第一激发态（2s1/2）和第三激发态（1d5/2）各存在一个非束缚的质子晕， 而13C的第三激发态（1d5/2）存在一个弱束缚的中子皮. 另外研究表明, 在另一对镜像核15N-15O的第二激发态（2s1/2）和第一激发态（2s1/2）分别存在一个中子晕和质子皮. Properties of two pairs of mirror nuclei 13N-13C and15N-15O are investigated by using the nonlinear relativistic mean field theory. It is found that all the calculated binding energies with two different parameter sets are very close to the experimental ones for both the ground states and the excited states. The calculations show that the first excited state (2s1/2) and the third excited state (1d5/2) in 13N are both unbound resonances with proton halo structure, whereas the third excited state (1d5/2) in 13C is weakly bound with a neutron skin. It is also predicted that there has a proton halo in the second excited state (2s1/2) of 15N as well as a neutron skin in the first excited state (2s1/2) of 15O.     

Confirmation/Observation of Hindered E2 Strengths in-16,18C

The lifetime of the first excited 2~+ state in ~(18)C was measured using an upgraded recoil shadow method to determine the electric quadrupole transition.The measured mean lifetime is 18.9±0.9 (stat)±4.4 (syst) ps,which corresponds to a B(E2;2~+_1→0~+_(gs)) value of (4.3±0.2±1.0) e~2fm~4,or about 1.5 Weisskopf units.The mean lifetime of the first 2~+ state in ~(16)C was remeasured to be about 18 ps,about four times shorter than the value reported previously.This discrepancy was explained by incorporating the γ-ray angular distribution measured in this work into the previous measurement.The observed transition strengths in ~(16,18)C are hindered compared to the empirical transition strengths,indicating that the anomalous hindrance observed in ~(16)C persists in ~(18)C.     

原子核第一激发能的统计规律

原子核的第一激发态能级是所有激发态能级中最重要的一条能级,在一定程度上可直接反映该核素的稳定性。通过对2 125个核素的第一激发态能级纲图进行统计分析,发现传统幻数位置的第一激发能明显高于邻近核素的第一激发能,亦对应于同位素链、同中子素链上原子核第一激发能最大的核素。对于第一激发能较大且明显偏离传统幻数位置的少量核素,发现都具有同质异位素相似态或为裂变核的混合能级,这些给出的值是否是第一激发态,在理论和实验上仍存在一定的不确定性;而对于原子核第一激发能最大的核素,其自旋宇称为2+的最多（高达42%）。对于中重核区内的偶偶核,其第一激发能与价核子N_pN_n关系明显趋于指数的衰减形式。     

Resonant coherent excitation of Ar17+ ions taking into account a fine structure of energy levels

The effect of a fine structure of the orbital electron energy levels of an Ar¹⁷⁺ ion on the resonant coherent excitation under planar channeling has been investigated by computer simulation technique. The obtained resonance curves are characterized by two closely situated peaks due to the transitions of an electron from the ground to excited states corresponding to the different components of a fine structure of the first excited state which differ in the value of the total electron momentum (1/2 or 3/2).     

Revisit to Two-Proton Radioactivity of 19Mg and Observation of Two-Proton Decay of 30Ar

An experiment aimed to investigate the two-proton (2p) decay of the previously unknown nucleus 30Ar was performed at GSI: By tracking the decay products in-flight with silicon micro-strip detectors, the 2p decays of 30Ar were observed for the first time. For the calibration purpose, 2p decays of 19Mg were also remeasured by tracking the coincident 17Ne+p+p trajectories. By comparing the measured angular p-17Ne correlations with those obtained from the corresponding Monte Carlo simulations, the simultaneous 2p decay of 19Mg ground state and the sequential 2p emission of several known excited states of 19Mg were confirmed. One new excited state in 19Mg and two new excited states in 18Na were observed.     

Spectroscopic observation of resonant electric dipole-dipole interactions between cold Rydberg atoms

Resonant electric dipole-dipole interactions between cold Rydberg atoms were observed using microwave spectroscopy. Laser-cooled 85Rb atoms in a magneto-optical trap were optically excited to 45d(5/2) Rydberg states using a pulsed laser. A microwave pulse transferred a fraction of these Rydberg atoms to the 46p(3/2) state. A second microwave pulse then drove atoms in the 45d(5/2) state to the 46d(5/2) state, and was used as a probe of interatomic interactions. The spectral width of this two-photon probe transition was found to depend on the presence of the 46p(3/2) atoms, and is due to the resonant electric dipole-dipole interaction between 45d(5/2) and 46p(3/2) Rydberg atoms.     

类钠Ni~(17+)离子双电子复合过程理论研究

使用基于相对论多组态方法的FAC程序,研究了类钠Ni17+(3s)离子通过双激发态Ni16+(3pnl,3dnl)(Δn=0激发)的双电子复合过程,得到了态选择的双电子复合截面和速率系数,并与文献中的实验和理论数据进行了对比.结果发现,计算通过3p3/210l和3p1/211l共振态的双电子复合积分截面在实验误差范围内与实验测量很好地符合,并好于全相对论的多体微扰理论计算结果.结合量子亏损理论,发现包含高里德伯态的共振双激发态的辐射跃迁和自电离速率具有较好的标度关系,利用该关系给出了近激发阈值的所有共振态的双电子复合积分截面和速率系数.比较3pnl和3dnl两个系列,发现在低温(大约小于100eV)等离子体情况下前者速率系数比后者大,更高的温度后者大.     

超短脉冲激光场中间二氯苯的激发态动力学

利用飞秒时间分辨的飞行时间质谱技术研究了间二氯苯的激发态动力学.间二氯苯分子吸收一个200 nm或者267 nm的光子被抽运到激发态,随后再吸收多个800 nm的光子被电离.实验获得了电离产生的离子质谱信号及其随抽运探测激光延迟时间的变化曲线.在200 nm时,分子被抽运到激发态(π,π*),可观察到三个相互竞争的解离通道的寿命:内转换到排斥态(n,σ*)或者(π,σ*)并发生快速解离,其寿命约(0.15±0.01)ps;内转换到基态的高振动态,能量在基态"热"振动态间弛豫的寿命约为(4.94±0.08)ps;系间窜越到相邻的三重态从而发生预解离过程,其寿命约为(110.09±4.33)ps.在267 nm时,分子被抽运到第一激发态的低振动态,可观察到一个长寿命(约(1.06±0.05)ns)的系间窜越过程.除此之外,在碎片离子信号中还观察到了激发态与基态的高振动态之间的内转换过程.     

CaBa-铝酸盐玻璃中Cr4+谱线宽度随温度的变化

测量了15~300K温度范围内57.5%Al_1.5O-35%CaO-7.5%BaO玻璃中四价铬的发射光谱.这种材料中铬离子的能级处于Tanabe-Sugano图上弱场范围中,最低的激发态是³T₂,发射谱是一个宽带.按照单频近似理论拟合低温下的光谱,得到³T₂能级的零声子线位置E_zp=8400cm^-1,声子能量tω=320cm^-1,黄昆因子S=358.尽管单频近似能够较好地描述低温下的线形,发射光谱宽度随温度的变化却与单频近似理论的结果不符.讨论了这种差别的原因,认为可能的解释是与激发态耦合的声子能量大于与基态耦合的声子能量.     

Anisotropic x-ray emission from heliumlike Fe24+ ions aligned by resonant coherent excitation with a periodic crystal potential

We have measured deexcitation x rays emitted from the resonant coherently excited 2(1)P(1) state of heliumlike Fe24+ ions of 423 MeV/amu, planar channeling through a Si crystal. Large anisotropy in the angular distribution of deexcitation x-ray emission is observed: the x-ray emission in the direction parallel to the channeling plane is favored by a factor of 2 compared to the perpendicular direction. This anisotropy originates from the direction of the periodic crystal field, which populates specific m states in resonant coherent excitation and aligns the excited states.     

共掺杂Ce~(3+)调控β-NaLuF_4:Yb~(3+)/Ho~(3+)纳米晶体的上转换荧光发射

在980 nm近红外光激发下,通过共掺杂Ce~(3+)离子调控六方相NaLuF_4:Yb~(3+)/Ho~(3+)纳米晶体的上转换荧光发射.实验结果表明,当掺杂Ce~(3+)离子浓度从0增加到12.0%时,Ho~(3+)离子的上转换荧光发射实现了由绿光向红光的转变,其红绿比提高了近24倍.根据Ho~(3+)离子的能级结构发现,Ho~(3+)离子的红光发射源自~5F_5能级到5I8能级的辐射跃迁,因此要增强红光发射,必须提高该能级粒子数布居.Ho~(3+)与Ce~(3+)离子之间相近的能级差促使它们之间产生了共振交叉弛豫,从而有效地提高了Ho~(3+)离子~5F_5能级的粒子数布居,增强了红光发射.同时对Ho~(3+)离子的上转换调控机理进行讨论,并借助不同的激发策略,进一步证实了Ho~(3+)与Ce~(3+)离子之间相互作用的发生.     

Eu原子4f~76snlRydberg态的研究

利用三步双色共振激发技术和三步三色孤立实激发技术,系统地研究了铕原子在42250—44510 cm~(-1)能域内的光谱特性,提供了该能域内56个束缚高激发态的光谱信息.为了能确定这些态的光谱归属,进行了两方面的探索:第一,观察能否利用孤立实激发技术,把处于这些态上的铕原子进一步共振激发到自电离态,从而推断这些态属于单电子激发的束缚Rydberg态还是属于双电子激发的价态,并对Rydberg态的电子组态进行了光谱确认;第二,通过计算这些态相对于各个电离阈的量子亏损并观察它们分别收敛于哪个电离阈,以便获取其主量子数的信息.最后,设计并采用了三种不同的激发路径,分别将原子布居到同一高激发能域并探测它们在该能域的光电离光谱.通过比较这些光谱的异同并结合上述激发路径所对应的跃迁选择定则,便可惟一地确定这些高激发态的总角动量.研究发现:所探测到的高激发束缚态只有三个属于单电子激发的束缚Rydberg态,其余都是价态.本文确定了这三个Rydberg态的电子组态和原子状态.     

J~P assignments of Λ_c~+ baryons

The "good" diquark is employed to study Λ_c~+ baryons within a mass loaded flux tube model. The study indicates that all Λ_c~+ baryons candidates in the 2008 review by the Particle Data Group (PDG) are well described in the mass loaded flux model. The quantum numbers J~P of these Λ_c~+ candidates are assigned. If Λ_c(2765)~+ is an orbitally excited Λ_c~+, it is likely the J~P=3~+/2 one. If Λ_c(2765)~+ is an orbitally excited Σ_c, there ought to be another J~P = 3~+/2 Λ_c~+ with mass ≈ 2770 MeV. In the model, there exists no J~P = 1~+/2 Λ_c~+ (≈ 2700) predicted in existing literature. Λ_c(2940)~+ is very possible the orbitally excited baryon with J~P = 5~-/2.     

Finite-field calculation of electric quadrupole moments of ~2P_(3/2),~2D_(3/2,5/2),and ~2F_(5/2,7/2) states for Yb~+ ion

Electric quadrupole moments of low-lying excited states of Yb~+ are calculated by relativistic coupled-cluster theory with perturbations from external fields.The field-dependent energy differentiation provides accurate values of the electric quadrupole moments o f~2P_(3/2),~2D_(3/2,5/2),and~2F_(5/2,7/2) states which agree well with experimental values.The important role of the electronic correlation to the electric quadrupole moments is investigated.Our calculations indicate the early dispute of the electric quadrupole moment of the Yb~+(~2F_(7/2))state for which the measured and theoretical values have a large discrepancy.These electric quadrupole moment values can help us to determine the electric quadrupole shifts in start-of-the-art experiments of the Yb~+ ion.     

LiCaBO_3:Sm~(3+)材料的发光特性(英文)

以CaCO3(99.9%)、Li2CO3(99.9%)、Na2CO3(99.9%)K2CO3(99.9%)、H3BO3(99.9%)、Sm2O3(99.9%)为原料,按所设计的化学计量比称取以上原料,在玛瑙研钵中混合均匀并充分研磨,装入刚玉坩埚,采用固相法制备LiCaBO3:Sm3+材料;通过美国XRD6000型X射线衍射仪和日本岛津RF-540荧光分光光度计对材料的性能进行表征,所有测量均在室温条件下进行。LiCaBO3:Sm3+材料的发射光谱由三个橙红色发射峰组成,主峰位于561,602,651nm,分别对应Sm3+的4G5/2→6H5/2、4G5/2→6H7/2和4G5/2→6H9/2跃迁;监测602nm发射峰,得到其激发光谱由320～420nm的宽激发带组成。由激发和发射光谱看出,LiCaBO3:Sm3+能够有效地被紫外LED芯片激发,发射红色光。研究了Sm3+浓度(x)对LiCa1-xBO3:xSm3+材料发射强度的影响,结果表明:随Sm3+浓度的增大,发射强度先增强后减弱,Sm3+掺杂摩尔分数为3%时,发射强度最大,依据Dexter理论,计算得出其浓度猝灭机理为电偶极-偶极相互作用。掺入电荷补偿剂Li+、Na+和K+均提高了LiCaBO3:Sm3+材料的发射强度。     

Controlling isotopic effects in the resonance ionisation mass spectrometry of krypton

We have investigated and characterised possible sources of variation in measured isotope ratios in the resonance ionisation mass spectrometry of krypton using resonant transitions at 116.48 and 558.04 nm and ionisation at 1064 nm. Variation arises when the spectral width of the hyperfine structure of the odd isotopes is comparable to the laser bandwidth and from the alignment of the first excited state, which depends on the relative polarisations of the laser pulses exciting the resonant transitions.     

Application of electric field ionization method to detect the high-lying Rydberg states of Eu I

The 4f~76s(~9S)np 8 P J (J = 5/2, 7/2, 9/2) Rydberg series converging to the first ionization limit 4f 7 6s 9 S 4 of the Eu atom using the three-step laser excitation and electric-field-ionization (EFI) method are studied. First, the Eu atom is excited from the 4f 7 6s 2 8 S o 7/2 ground state to the 4f 7 6s7s 8 S o 7/2 state through the 4f 7 6s6p 10 P 9/2 state by the first two dye lasers. Next, it is populated to many higher-n members of the 4f 7 6s( 9 S)np 8 P J Rydberg series by the third dye laser whose wavelength is scanned within a certain range. Finally, the atom in these higher-n states is ionized by the external pulsed electric field. With the field strength up to 2 kV/cm, we can detect the atom in 4f 7 6s(9 S)np 8 P J states with n 40. With the given laser line width, the level energies of Rydberg states with n as high as 72 can be determined. We not only confirm the previous data on the 4f 7 6s(9 S) np 8 P J Rydberg series, but also extend the n-value assignment significantly by detecting more states.     

Borromean three-body heteroatomic resonances

We present an approach to analyze recent experimental evidences of Efimov resonant states in mixtures of ultracold gases, by considering two-species three-body atomic systems bound in a Borromean configuration, where all the two-body interactions are unbound. For such Borromean three-body systems, it is shown that a continuum three-body s-wave resonance emerges from an Efimov state as a scattering length or a three-body scale is moved. The energy and width of the resonant state are determined from a scaling function with arguments given by dimension-less energy ratios relating the two-body virtual state subsystem energies with the shallowest three-body bound state. The peculiar behavior of such resonances is that their peaks are expected to move to lower values of the scattering length, with increasing width, as one raises the temperature. For Borromean systems, two resonant peaks are expected in ultralow-temperature regimes, which will disappear at higher energies. It is shown how a Borromean-Efimov excited bound state turns out to a resonant state by tuning the virtual two-body subsystem energies or scattering lengths, with all energies written in units of the next deeper shallowest Efimov state energy. The resonance position and width for the decay into the continuum are obtained as universal scaling functions (limit cycle) of the dimensionless ratios of the two and three-body scales, which are calculated numerically within a zero-range renormalized three-body model.     

Recent results on nucleon resonance electrocouplings from the studies of π~+π~-p electroproduction with the CLAS detector

Recent results on nucleon resonance studies in π~+π~-p electro- production off protons with the CLAS detector are presented. The analysis of CLAS data allowed us to determine all essential contributing mechanisms, providing a credible separation between resonant and non-resonant parts of the cross sections in a wide kinematical area of invariant masses of the final hadronic system 1.3 < W < 1.8 GeV and photon virtualities 0.2 < Q~2 < 1.5 GeV~2. Electrocouplings of several excited proton states with masses less than 1.8 GeV were obtained for the first time from the analysis of π~+π~-p exclusive electroproduction channel.     

Selective population and neutron decay of an excited state of 23O

We have observed a resonance in neutron-fragment coincidence measurements that is presumably the first excited state of 23O at 2.8(1) MeV excitation energy which decays into the ground state of 22O. This interpretation is consistent with theory. The reaction mechanism supports the assignment of the observed state as the 5/2+ hole state. This assignment and the recently observed 3/2+ particle state advance the understanding of 23O.