Isotope separation via atom optics in the Bragg regime

We study the resonant interaction of a beam of mono-velocity two-level atoms with a standing-wave light field in the Bragg regime. The atomic beam consists of two different isotopes, and the density is sufficiently small so that at most one atom is inside the cavity at a time. The momentum transfer between the atoms and photons in the process significantly effects the center-of-mass motion of the atoms, thus separating the isotopes in different directions.     

通过极化原子束的磁偏转实现激光同位素浓缩

本文描述一种通过极化原子束的磁偏转实现同位素和同质异能素浓缩的新方法。用具有不同频率和偏振的激光进行选择性光抽运,使束中两同位素的原子分别反向高度极化,然后使这些反向极化的原子在经过自旋选态磁铁后沿不同方向偏转,从而实现同位素浓缩。推算了此法的选择性和产量,与其他方法相比,讨论了其优缺点和可能的应用前景。提出了用锂或钾进行实验的方案。 关键词：     

Optical pumping experiments using a cw dye laser with a narrow spectral output

An optical pumping experiment on the Na atoms of an atomic beam by means of a continuous wave dye laser is described. The atoms interact at two different regions with the laser beam. In the first region the atoms are optically pumped so that a Zeeman coherence in their substates is produced. In the second light beam the coherence is probed. Any changes in the phase of the eigenfunction of the atom through interaction in a magnetic field, or through collisions, or other effects occuring in the light free section can thus be sensitively detected. The possible applications of the set-up are discussed.     

Laser traps for radioactive isotopes

The techniques of laser cooling and trapping now make it possible to observe large samples of stable atoms in a small volume at low temperature. This capability was recently extended to radioactive isotopes. This opens up new opportunities for the investigation of fundamental symmetries through measurements using radioactive atoms. In this paper we will discuss several fundamental measurements in atomic systems and how the ability to trap radioactive atoms will play an important role in improving the precision of such measurements. Measurements of the effects of the weak interaction are of particular note since they are becoming quite precise. In particular, we will describe in detail the system developed at Stony Brook to trap radioactive alkali atoms and measure weak interaction effects in francium isotopes.     

Frequency locking of a 399-nm laser referenced to fluorescence spectrum of an ytterbium atomic beam

The laser cooling of ytterbium(Yb) atoms needs a 399-nm laser which operates on the strong1S0-1P1 transition and can be locked at the desired frequencies for different Yb isotopes.We demonstrate a frequency locking method using the fluorescence spectrum of an Yb atomic beam as a frequency reference.For unresolved fluorescence peaks,we make the spectrum of the even isotopes vanish by using the strong angular-dependence of the fluorescence radiations;the remained closely-spaced peaks are thus clearly resolved and able to serve as accurate frequency references.A computer-controlled servo system is used to lock the laser frequency to a single fluorescence peak of interest,and a frequency stability of 304 kHz is achieved.This frequency-locked laser enables us to realize stable blue magneto-optic-traps(MOT) for all abundant Yb isotopes.     

Magneto-Optical Trapping of Ytterbium Atoms with a 398.9nm Laser

We report the realization of ytterbium magneto-optical trap （MOT） operating on the dipole-allowed ^1S0 - ^1P1 transition at 398.9nm. The MOT is loaded by a slowed atomic beam produced by a Zeeman slower. All seven stable isotopes of Yb atoms could be trapped separately at different laser detuning values. Over 10^7 174 Yb atoms are collected in the MOT, whereas the atom number of fermionic isotope ^171Yb is roughly 2.3 × 10^6 due to a lower abundance. Without the Zeeman slower the trapped atom numbers are one order of magnitude lower. Both the even and odd isotopes are recognized as excellent candidates of optical clock transition, so the cooling and trapping of ytterbium atoms by the blue MOT is an important step for building an optical clock.     

Bohr–Weisskopf effect: influence of the distributed nuclear magnetization on hfs

Nuclear magnetic moments provide a sensitive test of nuclear wave functions, in particular those of neutrons, which are not readily obtainable from other nuclear data. These are taking added importance by recent proposals to study parity non-conservation (PNC) effects in alkali atoms in isotopic series. By taking ratios of the PNC effects in pairs of isotopes, uncertainties in the atomic wave functions are largely cancelled out at the cost of knowledge of the change in the neutron wave function. The Bohr–Weisskopf effect (B–W) in the hyperfine structure interaction of atoms measures the influence of the spatial distribution of the nuclear magnetization, and thereby provides an additional constraint on the determination of the neutron wave function. The added great importance of B–W in the determination of QED effects from the hfs in hydrogen-like ions of heavy elements, as measured recently at GSI, is noted. The B–W experiments require precision measurements of the hfs interactions and, independently, of the nuclear magnetic moments. A novel atomic beam magnetic resonance (ABMR) method, combining rf and laser excitation, has been developed for a systematic study and initially applied to stable isotopes. Difficulties in adapting the experiment to the ISOLDE radioactive ion beam, which have now been surmounted, are discussed. A first radioactive beam measurement for this study, the precision hfs of ¹²⁶Cs, has been obtained recently. The result is 3629.515(∼0.001) MHz. The ability of ABMR to determine with high precision nuclear magnetic moments in free atoms is a desideratum for the extraction of QED effects from the hfs of the hydrogen-like ions. We also point out manifestations of B–W in condensed matter and atomic physics. This revised version was published online in July 2006 with corrections to the Cover Date.     

量子模型分析激光驻波原子透镜的像差

采用量子模型对近共振激光驻波原子透镜会聚Cr原子束、形成纳米量级光栅结构的物理过程进行数值模拟。为提高原子透镜的成像质量,对各种像差,如衍射像差、球差、色差、及原子束发散角、原子磁支能级、原子同位素等因素引起的像差进行了理论分析。模拟结果表明,相比粒子光学模型,量子模型能更加精确地描述原子会聚结果,且能解释原子在驻波光场中的衍射现象。在各种像差中,原子束发散角是最主要的因素,其影响大于衍射像差、球差、色差。原子的磁支能级、同位素等因素对像差影响很小,可以忽略不计。激光冷却准直原子束的方法可以减小束发散角引起的像差,压缩原子速度Vz分布范围的方法可以减小色差。     

Fundamental symmetries studies with cold trapped francium atoms at ISAC

Francium combines a heavy nucleus (Z = 87) with the simple atomic structure of alkalis and is a very promising candidate for precision tests of fundamental symmetries such as atomic parity non-conservation measurements. Fr has no stable isotopes, and the ISAC radioactive beam facility at TRIUMF, equipped with an actinide target, promises to provide record quantities of Fr atoms, up to 10¹⁰/s for some isotopes. We discuss our plans for a Fr on-line laser trapping facility at ISAC and experiments with samples of cold Fr atoms. We outline our plans for a measurement of the nuclear anapole moment – a parity non-conserving, time-reversal conserving moment that arises from weak interactions between nucleons – in a chain of Fr isotopes. Its measurement is a unique probe for neutral weak interactions inside the nucleus.      

Rydberg hydrogen atom in the presence of uniform magnetic and quadrupolar electric fields

Laser cooling and trapping offers the possibility of confining a sample of radioactive atoms in free space. Here, we address the question of how best to take advantage of cold atom properties to perform the observation of as highly forbidden a line as the 6S-7S Cs transition for achieving, in the longer term, atomic parity violation (APV) measurements in radioactive alkali isotopes. Another point at issue is whether one might do better with stable, cold atoms than with thermal atoms. To compensate for the large drawback of the small number of atoms available in a trap, one must take advantage of their low velocity. To lengthen the time of interaction with the excitation laser, we suggest choosing a geometry where the laser beam exciting the transition is colinear to a slow, cold atomic beam, either extracted from a trap or prepared by Zeeman slowing. We also suggest a new observable physical quantity manifesting APV, which presents several advantages: specificity, efficiency of detection, possibility of direct calibration by a parity conserving quantity of a similar nature. It is well adapted to a configuration where the cold atomic beam passes through two regions of transverse, crossed electric fields, leading both to differential measurements and to strong reduction of the contributions from the M₁-Stark interference signals, potential sources of systematics in APV measurements. Our evaluation of signal-to-noise ratios shows that with available techniques, measurements of transition amplitudes, important as required tests of atomic theory, should be possible in ¹³³Cs with a statistical precision of 10^-3 and probably also in Fr isotopes for production rates of Fr atoms s^-1. For APV measurements to become realistic, some practical realization of the collimation of the atomic beam as well as multiple passages of the excitation beam matching the atomic beam looks essential.Received: 5 March 2003, Published online: 17 July 2003PACS: 32.80.Ys Weak-interaction effects in atoms - 32.70.Cs Oscillator strengths, lifetimes, transition moments - 32.80.Pj Optical cooling of atoms; trapping - 39.90.+d Other instrumentation and techniques for atomic and molecular physicsS. Sanguinetti: Also at E. Fermi Physics Dept., Pisa Univ., Pisa, Italy.     

Nuclear physics using unstable nuclear beams

As an application of the projectile fragmentation in high-energy heavy-ion collisions, use of the unstable nuclei as secondary nuclear beams is discussed. Results of the test experiment of secondary beam line at the Bevalac (LBL, Berkeley) is described. Clean beams of He and Li isotopes were produced with reasonable intensity. A plan of a proposed experiment, which uses the unstable nuclear beam to determine radii of unstable nuclear isotopes through a measurement of interaction cross sections, is shown.     

Isotope separation of Potassium with a magneto–optical combined method

Due to the similar physical and chemical properties, isotopes are usually hard to separate. On the other hand, the isotope shifts are very well separated in a high-resolution spectrum, making them possible to be addressed individually by lasers, thus separated. Here we report such an isotope separation experiment with Potassium atoms. The isotopes are independently optical pumped to the desired spin states, and then separated with a Stern–Gerlach scheme. A micro-capillary oven is used to collimate the atomic beam, and a Halbach-type magnet array is used to deflect the desired atoms. Finally, the ⁴⁰K is enriched by two orders of magnitude. This magneto–optical combined method provides an effective way to separate isotopes and can be extended to other elements if the relevant optical pumping scheme is feasible.     

Multifrequency radiation pressure laser,isotope separation

Isotope separation by laser deflection of an atomic beam is limited in its efficiency by the accumulation of atoms in metastable states. This restriction can be removed with the use of lasers which excite metastable atoms to states from which spontaneous decay to the ground state is allowed. This is demonstrated in the separation of barium isotopes, where efficiency was improved from a lower limit of 70% to at least 83% using a second laser. Efficiency approaching 100% can be achieved in barium with a second laser but the required wavelength is not available.     

On the feasibility of in-beam PAC studies

A pulsed particle beam can be used for PAC studies at probe atoms with lifetimes of the mother activity between microseconds and several minutes. The experimental realization of this In-Beam method is discussed and a list of suitable isotopes is given. Preliminary results in the system GeZn and InCd prove the feasibility of this modified PAC technique.     

Isotope separation by laser deflection of an atomic beam

Separation of isotopes of barium has been accomplished by laser deflection of a single isotopic component of an atomic beam. With a tunable narrow linewidth dye laser, small differences in absorption frequency of different barium isotopes on the 6s^{2 1}S₀₋ 6s6p¹P₁ 5536 Å resonance were exploited to deflect atoms of a single isotopic component of an atomic beam through an angle large enough to physically separate them from the atomic beam. It is shown that the principal limitation on separation efficiency, the fraction of the desired isotopic component which can be separated, is determined by the branching ratio from the excited state into metastable states. In barium, repeated absorptions and emissions on the 5536 Å transition eventually result in decay from the 6s6p¹P₁ state to the metastable 6s5d¹D₂ state. This was observed to occur for all but 3% of the¹³⁸Ba atoms. As a result, the efficiency of separation was about 0.7 for the 8 mrad atomic beam divergence employed. (Throughput was nearly 1 mg/day. No attempt was made to maximize this value.) The isotopic purity of the separated atoms was measured to be in excess of 0.9, limited only by instrumental uncertainty. The effects of near resonant atomic scattering and excitation exchange on isotopic purity are considered. Work performed under the auspices of the U.S. Energy Research & Development Administration.     

Entanglement evolution of a two-qubit system with decay beyond the rotating-wave approximation

The entanglement property of two identical atoms, initially entangled in Bell states, coupled to a single-mode cavity is considered. Based on the reduced non-perturbative quantum master equation method, the entanglement evolution of the two atoms with decay is investigated beyond the conventional rotating-wave approximation. We show that the counter-rotating wave terms, usually neglected, have a great influence on the disentanglement behaviour of the system. The phenomena of entanglement sudden death and entanglement sudden birth will occur. In addition, we show that the entanglement can be strengthened by introducing the dipole--dipole interaction of the two atoms.     

Atomic probes of electromagnetic and weak interactions with trapped radioactive atoms

The alkali element francium has a simple electronic structure, and copious amounts of a wide range of isotopes can be produced in present and future rare isotope facilities. The atomic parity violating weak interaction in Fr is 18 times larger than in Cs, which makes it one of the best candidates to search for the effects of the weak interaction and its isotopic dependence. Atomic trapping methods now offer new ways to study these atoms with precision, and we will discuss some of our recent measurements with trapped Fr atoms. Future measurements of the spin-independent weak interaction can be used to test the standard model, but advances in atomic theory and improved understanding of the neutron distribution in nuclei are needed to make progress. We have made precise hyperfine-anomaly measurements in Fr and have shown that they are sensitive to the radial distribution of the neutron magnetization. Measurements of this type can help to constrain the neutron distributions. Future measurements of the spin-dependent weak interaction should allow extraction of the nuclear anapole moments for a sequence of isotopes, and allow separation of the neutron and proton weak interactions between hadrons. Received: 1 May 2001 / Accepted: 4 December 2001     

X-ray spectroscopy at PSI

Crystal spectroscopy of the X-rays of exotic atoms started with a series of experiments using transmission spectrometers. Experiments at lower energies were made possible by the development of reflection spectroscopy. The progress made is illustrated with a measurement of the pion mass and the determination of strong interaction effects in pionic hydrogen isotopes. Modern developments aim at a determination of the strong interaction width on the level of %. The way to reach this goal is presented and the limits of the method and possible future experiments are discussed. This revised version was published online in August 2006 with corrections to the Cover Date.     

Murrell-Sorbie势下He-HCl碰撞体系微分散射截面的研究

根据在CCSD(T)/aug-cc-pVQZ理论水平下计算的He-HCl相互作用能数据,作者采用Murrell-Sorbie势函数形式拟合了He原子与HCl分子相互作用的各向异性势,并与其它势模型进行了比较;然后采用公认的精确度较高的CC近似方法计算了He-HCl碰撞体系的微分散射截面,总结了非弹性微分散射截面的变化规律.研究表明:采用拟合的各向异性势计算的微分散射截面与实验结果符合得很好.拟合势不但表达形式简洁,而且较好地描述了He-HCl系统相互作用的各向异性特征;利用碰撞体系分子间势的量子化学从头计算结果,可解决势能参数难以确定的问题.对进一步研究原子与分子相互作用的机制有一定的参考价值.     

Emission anomalous optical magnetic resonances in a mixture of even neon isotopes

Unusual resonances have been detected in the dependence of the discharge glow in neon on the longitudinal magnetic field. The resonances appear in fairly high magnetic fields and are observed only at low gas pressures and exclusively in a mixture of ²⁰Ne and ²²Ne isotopes. This phenomenon is an evidence of collective resonant radiation processes involving atoms of different neon isotopes.