Production of highly polarized slow radioactive nuclear beams and their application

为了对不稳定原子核的电磁矩进行系统的测量，从而大大扩展核结构研究的实验范围，我们开发了在放射性原子核中产生自旋极化的实验方法，并对一些轻质量富中子的原子核进行了β-NMR测量。为了实现多种核的高度极化，我们采用了一种基于原子束技术的极化方法。这种方法成功应用于放射性核的关键是实现在一些薄的停止材料中有效地停止抛射碎片反应产生的高能反应产物，因为这种反应已知是放射性束的最强大的生产方法。在对几种不同的停止方法的性能进行了一些测试实验和计算机模拟工作之后，我们决定将原子核停止在高压、大体积的氦气中，用一组电极将它们的带电状态收集到一个小体积中，中和它们，然后在载气流中从喷嘴喷出。设计并制作了停止气室、电极和拉瓦尔型喷嘴。从RIKEN的放射性束流线RIPS中获得的放射性原子核^<17>N束被引入气室，并通过计算^<17>N活动释放的β射线来研究^<17>N原子核的停止和喷射。因此，我们证实，电场分布在喷嘴位置的强度呈指数增长，允许在喷嘴位置收集40%或更高的停止放射性活动。我们还证实从喷嘴中提取了^<17>N原子。设计了Laval型喷嘴，以实现尖锐的前向气体喷射，并构建了一个激光装置来研究气体射流的形状和从喷嘴喷出的原子的速度。目前，该装置正在进行改进，并正在制造六重磁体自旋分析仪。我们还通过弹丸破片反应，用常规极化法测量了富中子核^<17>C和^<15>C的磁矩和^<17>B的四极矩。这样，我们的方法产生自旋极化放射性光束的基础已经建立，整个装置从放射性原子源到自旋分析仪将很快进行测试。然后，我们将继续开发剩余的rf跃迁-自旋分析部分，在RIKEN完成新的放射性束流设施RIBF三年后，我们将把目前的方法应用于远离稳定核的广泛区域的核矩测量。少

In order to carry out a systematic measurement of electromagnetic moments for unstable nuclei and thereby to drastically extend the experimental reach of nuclear structure studies, we developed experimental methods to produce spin polarization in radioactive nuclei and did β-NMR measurements on some light-mass neutron-rich nuclei.To achieve high degrees of polarization for a wide variety of nuclei, we took a polarization method that is based on the atomic beam technique. The key to a successful application of this method to radioactive nuclei is the realization of an efficient stopping of high-energy reaction products from the projectile fragmentation reaction in some thin stopping material, since this reaction is known to provide the most powerful production method for radioactive beams. After some test experiments and computer simulation works on the performance of a few different stopping methods, we decided to stop nuclei in a high-pressure, large-volume helium gas, collect them in … More their charged state into a mall volume by using a set of electrodes, neutralize them, and then spout them out from a nozzle in a flow of the carrier gas. A stopping gas chamber, electrodes, and a Laval type nozzle were designed and fabricated. A beam of radioactive nuclei ^<17>N, obtained from the radioactive beam line RIPS at RIKEN, was introduced in the gas chamber and the stopping and spouting of the ^<17>N nuclei were investigated by counting the β-rays emitted from ^<17>N activities. We thus confirmed that an electric field profile with an exponentially growing strength towards the nozzle position allowed the collection of 40 % or higher of the stopped radioactivities at the nozzle position. We also confirmed an extraction of ^<17>N atoms from the nozzle. The Laval type nozzle was designed to implement a sharp forward-directed jet of gas, and a setup with a laser was constructed to investigate the shape of the gas jet and the velocities of the atoms spouting from the nozzle. The setup is now under an improvement, and a spin analyzer sextuple magnet under fabrication. We also carried out measurements of magnetic moments for neutron-rich nuclei ^<17>C and ^<15>C and quadrupole moment for ^<17>B by means of the conventional polarization method through the projectile fragmentation reaction.Thus, a basis for our method to produce spin-polarized radioactive beams has been established, and a whole setup from the radioactive atom sources upto the spin analyzer will soon be tested. We will then proceed to the development of the remaining rf transition-spin analysis section, and after three years when the completion of a new radioactive beam facility RIBF at RIKEN, we will apply the present method to measurements of nuclear moments for wide regions of nuclei far from stability. Less