Spectroscopy ISOLDE

Hyperfine structure measurements using on-line atomic-beam techniques are of great importance in the systematic study of spins and moments of nuclei far from beta-stability. We will discuss the atomic-beam magnetic resonance (ABMR) method, and laser spectroscopy methods based on crossed-beam geometry with a collimated thermal atomic-beam and collinear geometry with a fast atomic-beam. Selected results from the extensive measurements at the ISOLDE facility at CERN will be presented. 

Most data on ground state properties of nuclei far from stability have been obtained at the on-line mass separator ISOLDE at CERN, where the isotopes of over 60 elements are available with high yields (up to 10 atoms per sec and mass number) and half lives down to 10 sec. [CER85]. Fig. 1 shows the chart of nuclei and indicates those regions where optical spectroscopy has been performed in long isotopic chains. Similar systematics of mass measurements have been restricted until now to the isotopes of the alkaline elements [AUD84]. 

Several groups at ISOLDE are planning further improvements of their techniques. For each element the most appropriate experimental scheme has to be found. Today, collinear laser spectroscopy is the most general high-resolution and sensitive method for optical spectroscopy on radioactive beams delivered by on-line mass separators. Its sensitivity ranges from 10 - 10 atoms/s depending on the strength and multiplicity of the optical transitions. 

TABLE 1 On-line techniques for Optical Spectroscopy at ISOLDE... 

The rest of the apparatus is the same as when operated at the Proton Synchrotron. First tested on cesium [ HUB 78 ], [ THI 81 ] the apparatus was used to uncover the resonance lines of francium for which no optical transition had ever been observed. The CERN on line mass separator, Isolde, makes available a source of more than 10 atoms/sec of chemically and isotopically pure 213 Fr isotope. Such an amount is more than needed for a laser atomic beam spectroscopy. The first step is obviously to locate the resonance line at low resolution, using a broad band laser excitation. In a second step, once the line is located, a high resolution study is undertaken, [ LIB 80] and [ BEN 84]. The observed signal is displayed (fig 3a) at low resolution and(3 b)at high resolution. 

When working on line with a mass separator, such as Isolde, the collinear laser spectroscopy is a method fully adapted. In a collaboration Orsay - Mainz, the second members of the principal series in francium have been located and studied at high resolution with this method. In table 1 the measured wavenumbers of the four lines are given. 

The schematic view of the Mainz apparatus for collinear laser spectroscopy, installed at Isolde is given in fig 4. The 60 keV ion beam is set collinear with the laser beam, then accelerated (or decelerated) and finally neutralized in charge exchange cell. By Doppler tuning the atomic absorption is set resonnant with the stabilized laser frequency, and the fluorescence emitted is detected. 

A considerable extension of the ABMR measurements in the alkali elements, discussed above, was obtained by the introduction of the atomic-beam laser experiments at ISOLDE. With this method the nuclear quadrupole moments could be reached by studying the hfs of the excited state, as well as the IS in the isotopic sequences studied. A number of nuclear spins and magnetic dipole moments was also added. Of particular importance was the discovery of the Dj optical line in francium which opened the way to hfs and IS measurements in this element. The atomic-beam laser spectroscopy works at ISOLDE on the alkali elements 3,Rb, 55CS and Fr have been presented in Refs. [20-25]. 

Among the odd-proton rare-earths, the element europium (Z = 63) has been thoroughly investigated at ISOLDE by coUinear fast-beam laser spectroscopy in the range Eu [47]. The ABMR works include spin measurements in ... 

The isotopic sequence of die heaviest alkali element, francium, has been extensively studied at ISOLDE by the three atomic-beam techniques ABMR, atomic-beam laser spectroscopy and collinear fast-beam laser spectroscopy. 

It may be surprising to find the most extensive application of collinear laser fast-beam spectroscopy in a field that a priori has little connection with the special features of this technique. Neither the Doppler shift nor the accessibility of ionic spectra plays a decisive role for the on-line experiments on radioactive isotopes from nuclear reactions. However, most of the problems encountered in the preparation of a sample of free atoms (cf. Part B, Chapter 17 by H.-J. Kluge) are solved by a combination of the fast-beam technique with the well-established concept of on-line isotope separation. The isotope separators (with ISOLDE at CERN as an outstanding example) provide the unstable species in the form of ion beams whose phase-space volume is well matched to the requirements of collinear spectroscopy. 

Figure 10. Essential components of the ISOLDE setup for collinear fast-beam laser spectroscopy. The postacceleration and scanning...

Abstract In this tutorial we describe the basic principles of the ion implantation technique and we demonstrate that emission Mossbauer spectroscopy is an extremely powerful technique to investigate the atomic and electronic configuration around implanted atoms. The physics of dilute atoms in materials, the final lattice sites and their chemical state as well as diffusion phenomena can be studied. We focus on the latest developments of implantation Mossbauer spectroscopy, where three accelerator facilities, i.e., Hahn-Meitner Institute Berlin, ISOLDE-CERN and RIKEN, have intensively been used for materials research in in-beam and on-line Mossbauer experiments immediately after implantation of the nuclear probes. 

On-line Mn/ Fe Implantation Mossbauer Spectroscopy at ISOLDE, CERN... 

The main lines of research at ISOLDE are nuclear structure physics, nuclear astrophysics, atomic physics, solid state physics, life sciences and fundamental interactions. A laboratory portrait been published as a special volume of Hyperfine Interactions [35]. In this volume a complete chapter is devoted to Mossbauer Spectroscopy at ISOLDE [36]. A schematic view of the set-up is shown in Fig. 6.22. 

Fedoseyev, V. N., Fedorov, D. V., Horn, R., Huber, G., Koster, U., Lassen, J., Mishin, V. L, Seliverstov, M. D., Weisman, L., Wendt, K., and the ISOLDE Collaboration (2003). Atomic spectroscopy studies of short-lived isotopes and nuclear isomer separation with ISOLDE RILIS. Nuclear Instruments and Methods in Physical Research B, 204, 353—358. 

Mueller, E.W. Otten, C, Ekstrom, J. Heinemeier, ISOLDE, Fast-Beam Laser Spectroscopy of Neutron-Rich Barium Isotopes, Hyperfine Inter. 9 151 (1981) R.E. Silverans, G. Borghs, J.-M. 

W. Otten, ISOLDE, The Isotope Shift of the Radioactive Cd-Iso-topes (102 < A < 120) Determined by On-Line Laser Spectroscopy, Hyperfine Inter. 9 165 (1981) (b) R. Wenz, A. Timmer-... 

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