Laser spectroscopy of Radioactive Isotopes

原子核的性质，如大小和磁场强度，会轻微地改变或扰动原子电子的轨道，这些改变很小，并且在电子结合能的百万分之一的水平上。它们可以通过使用可调谐激光的各种技术以极高的精度进行测量，可以以十亿分之一的精度进行控制。当激光被调谐到与电子跃迁频率精确匹配时，它会共振激发所选元素的同位素。受激发的原子随着荧光的发射而迅速衰变，所述荧光可以被对单光子敏感的光电倍增管检测到。以这种方式，可以通过实验测量激光谐振的频率。通过对同位素系列共振频率的分析，我们可以推断出原子核大小随中子数的变化。这是可能的，以检测质子分布的变化所造成的一个单一的中子。同样的数据可以清楚地表明，当中子增加或减少时，原子核的形状是否发生了变化。原子核周围的磁场强度，也是在这些实验中测量的，是由质子和中子的运动产生的。磁场理论已经很好地理解了，关于质子和中子所占据的核子轨道也可以得出明确的结论。因此，激光方法提供了关于核的基本性质的基本信息-大小，形状，磁性，核“自旋”角动量-这有助于改进我们的理论方法来解释观察到的性质，并预测我们还不能在实验室合成的核的性质。这些理论的预测能力非常重要。许多在地球上无法研究的原子核都参与了超新星的过程。如果不首先了解所涉及的原子核，我们就不能开始了解这些过程。激光技术，我们

Nuclear properties such as the size and magnetic field strength slightly shift or perturb the orbits of the atomic electrons.These shifts are small and at the level of a part per million of the electron binding energies. They can be measured with great precision by a variety of techniques using tunable laser light, which can be controlled with part per billion precision. When the laser light is tuned to exactly match an electronic transition frequency, it resonantly excites an isotope of the selected element. The excited atom quickly decays with the emission of fluorescence light which may be detected by photomultipliers sensitive to single photons. In this way the frequency of the laser resonance can be measured experimentally. The analysis of the resonant frequencies across an isotope series allows us to deduce the change in nuclear size as a function of neutron number. It is possible to detect the change of the proton distribution caused by the removal of a single neutron. The same data can show in a clear way whether the nucleus is changing its shape as neutrons are added or subtracted. The magnetic field strength around the nucleus, also measured in these experiments, is produced by the motion of both protons and neutrons. The theory of the magnetic field is well understood and clear conclusions can be drawn about the nucleon orbits occupied by the protons and neutrons. Thus the laser method provides fundamental information on basic properties of the nucleus - size, shape, magnetic properties, nuclear 'spin' angular momentum - which helps to refine our theoretical approaches to explain observed properties, and predict properties of nuclei we can not yet synthesize in the laboratory. The predictive power of these theories is very important. Many of the nuclei unavailable for study on Earth are involved in supernova processes. We cannot begin to understand the processes without first having an understanding of the nuclei involved. The laser techniques we