Resonant X-ray scattering from a rotating medium: The Nuclear Lighthouse Effect

A coherently excited nuclear state is carried with a rotating sample so that its radiative decay is redirected by the rotation angle that has developed during its lifetime. As a result, the time spectrum of the nuclear decay is mapped to an angular scale. This effect has been observed in nuclear resonant scattering of synchrotron radiation from a rotating ⁵⁷Fe metal foil. Applications with respect to elastic and inelastic nuclear resonant scattering are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Lifetime of a Nuclear Excited State in Cascade Decay

It is shown that the lifetime of a nuclear excited state in the region of femtoseconds could be accurately measured by a precision measurement facility of a flat crystal spectrometer, if the angular correlation of two successive γ-rays in cascade decay is taken into account in the Doppler shift attenuation method.     

分子角动量定向布居的制备探测和它的碰撞弛豫

利用受激Ｒａｍａｎ泵浦,使线性分子Ｃ２Ｈ２选择性地制备振动态角动量定向布居参数Ａσ（１）达到０．７～０．８。并测定了角动量定向布居碰撞诱导的弛豫速率常数,采用园偏振的紫外激光诱导荧光方法,可表征分子角动量定向布居的制备和它的碰撞弛豫过程。     

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.     

Decay of a prepared state treated as a doorway phenomenon

We consider a doorway state phenomenon: Via a selective process, likey γ-decay, a highly excited nuclear state of simple structure is prepared. We investigate its decay with particular emphasis on the compound nucleus modes. The formulae may be applied to radiationless decays in muonic atoms or to the decay of the residual nucleus after a (e, 'ep) or (p, 2p) reaction.     

超精细结构效应对辐射光谱圆极化特性的影响

在相对论多组态Dirac-Fock方法和密度矩阵理论的基础上,利用发展的全相对论扭曲波程序,系统研究了超精细结构效应对纵向极化电子碰撞激发过程以及退激发辐射光谱圆极化特性的影响.计算得到了类氦Sc~(19+)和~(205)Tl~(79+)离子1s~2 ~1S_0→1s2p ~3P_2超精细结构层次上M_F能级的碰撞强度,考察了辐射衰变过程中发出特征光子的极化特性,并分析了E1-M2量子干涉效应以及电子-电子间相互作用的相对论修正对退激发辐射光子圆极化度的影响.     

Bimodality as a signal of a liquid-gas phase transition in nuclei?

We use the heavy-ion phase-space exploration model to discuss the origin of the bimodality in charge asymmetry observed in nuclear reactions around the Fermi energy. We show that it may be related to the important angular momentum (spin) transferred into the quasiprojectile before secondary decay. As the spin overcomes the critical value, a sudden opening of decay channels is induced and leads to a bimodal distribution for the charge asymmetry. In the model, it is not assigned to a liquid-gas phase transition but to specific instabilities in nuclei with high spin. Therefore, we propose to use these reactions to study instabilities in rotating nuclear droplets.     

低振动激发HeI2分子振动预离解寿命和终转动态分布

用含时黄金规则波包法，对ＨｅＩ２分子在低初始振动激发（ｖ＜１２）态下振动预离解动力学作了全维量子力学计算。所预言的总衰变宽度和寿命与谱线宽和皮秒时间分解的实时态－态测量外推数据符合得相当好。计算的总衰变宽度对初始振动态ｖ是敏感的并呈现一种非线性关系。结果表明低振动激发ＨｅＩ２分子衰变模式仍应是量子力学的。除终态相互作用对决定终转动分布有重要作用以外，首次发现，低振动激发态的初始特性也能显著影响终转动态分布。用Ｉ２的转动常数对ｖ的关系合理地解释了这个独特现象     

A General Formula Used to Deduct the Effect of Excited State to Base State Was Deduced in Measurement of Cross Section of Nuclear Reaction

According to the regulation of growing and decay of artificial radioactive nuclide, a general formula used to deduct the effect of excited state to ground state was deduced. Therefore, the problem of effect of excited state to ground state was solved in the measurement of cross section of nuclear reaction.     

核反应截面测量中扣除激发态对基态影响的计算公式

根据人工放射性的生长与衰变规律，推导出了一个扣除激发态对基态影响的普遍计算公式，解决了在实际的核反应截面测量中激发态对基态的影响问题.     

Two-proton correlations in the decay of 45Fe

The decay of extremely neutron-deficient 45Fe has been studied in detail by means of a novel type of a gaseous detector employing digital imaging to record tracks of charged particles. The two-proton radioactivity channel was clearly identified. For the first time, the angular and energy correlations between two protons emitted from the nuclear ground state were determined, indicating the genuine three-body character of this decay. The half-life of 45Fe was found to be 2.6+/-0.2 ms and the observed 2p decay branching ratio is 70+/-4%.     

Femtosecond to nanosecond relaxation time scales in electronically excited tetrakis(dimethylamino)ethylene: identification of the intermediates

In the TDMAE molecule (title molecule), the time evolution has been analyzed from the very initial excitation step down to a fluorescent state, over widely different time scales. Pump probe measurements have been performed at 3 different excitation wavelengths 400, 266 and 200 nm. The decay has been followed over the femtosecond and subnanosecond ranges with this method and the decay of the final charge transfer state has been detected by its fluorescence emission. This allows an overview of the complete decay mechanism. The initial relaxation pathway is interpreted in a similar way to ethylenic molecules, where the initial wavepacket is quickly trapped in a doubly excited state Z with charge transfer character. Then the Z state decays slowly (10-100 picoseconds) into the final state. In difference to monoalkenes the final stage of this evolution is a charge transfer state. The decay of transient Z state to the charge transfer state is a further assessment of the partial ionic character of the Z state. This type of molecule with low ionization potential can be viewed as a demonstrative example of the interrelation between the charge induced forces and the deformations in excited state reaction dynamics. Received 17 January 2001 and Received in final form 23 February 2001     

Effects of vacuum fluctuation suppression on atomic decay rates

The use of atomic decay rates as a probe of sub-vacuum phenomena will be studied. Because electromagnetic vacuum fluctuations are essential for radiative decay of excited atomic states, decay rates can serve as a measure of the suppression of vacuum fluctuations in non-classical states, such as squeezed vacua. In such states, the renormalized expectation value of the square of the electric field or the energy density can be periodically negative, representing suppression of vacuum fluctuations. We explore the extent to which atomic decays can be used to measure the mean squared electric field or energy density. We consider a scheme in which atoms in an excited state transit a closed cavity whose lowest mode contains photons in a non-classical state. A crucial feature of our analysis is that we do not employ the rotating wave approximation. The change in the decay probability of the atom in the cavity due to the non-classical state can, under certain circumstances, serve as a measure of the mean squared electric field or energy density in the cavity. We make some estimates of the magnitude of this effect, which indicate that an experimental test might be possible, although very challenging.     

Studies of the alpha decay of U

The decay of ²³³U through the first and second excited states of ²²⁹Th has been studied using a uranium oxide source. The half-life of the first excited state of ²²⁹Th was found to be less than 1.9 nsec; it decays by an almost pure M1 transition. The half-life of the second excited state of ²²⁹Th was found to be 0.5±0.2nsec; this level de-excites by E2 cross-over radiation in 96% of events. Contrary to expectations, an anisotropic alpha-gamma angular correlation was not found, and the probable reason for this is discussed.     

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.     

Effects of magnetic monopoles on nuclear wave functions and possible catalysis of nuclear beta decay and spontaneous fission

Mixing effects in nuclear wave functions by the strong magnetic field of a magnetic monopole are estimated. A monopole at a distance of 10 fm from a deuteron mixes the single and triplet spin levels with a strength comparable to the deuteron binding energy. Forbidden nuclear beta decay transitions can be enhanced bymixing nuclear wave functions with other states for which the beta decay transition is less inhibited. Particularly suitable candidates have nearby excited states connected by magnetic dipole transitions to the ground state. Magnetic mixing can also strongly enhance spontaneous fission.     

Microscopic structure of nuclei from scattering through isobaric analogue resonances

Microscopic nuclear structure information that can be reached by proton scattering through isobaric analogue resonances (IAR) is discussed, mainly within the framework of weak-coupling. The concept of isospin for unbound states is examined. A critical evaluation of the methods for extracting nuclear structure information from the experimental results (such as excitation functions, angular distributions, etc.) is given. The mass regions that are studied in detail are the Pb-region and the N = 82 neutron single-closed shell nuclei. Attention is given to the comparison between weak-coupling calculations and experimental results supporting this concept in many nuclei. Level schemes as well as proton partial decay widths and angular distributions have been calculated and compared with the existing data concerning the proton decay of IAR. The concept of generalized neutron particle-hole (GNPH) state is introduced and its occurence extensively discussed within the Pb-region and N = 82 nuclei.     

An exotic type of nuclear isomeric transition

A new type of nuclear isomeric transition similar to double beta decay, the β^-? process, is proposed. Under the full ionization of atoms, this process can compete with ordinary types of nuclear isomeric transitions in which the excited metastable state is deexcited via a gamma transition.     

分子聚集体中激子-激子湮灭过程

分子的激发能量转移和电荷转移是提高光伏电池和发光二极管效率的关键问题,其中分子聚集体中的激子-激子湮灭过程是影响分子激发能量转移的重要方面,细致研究激子-激子湮灭的动力学过程并与相关的瞬间吸收谱信号对比对相关的理论和实验都有重要意义.本文在分子间弱耦合近似下,用经典的率方程,应用方酸分子的基本参数对激子-激子湮灭过程做...