Atomic-Beam Magnetic Resonance

In many spectroscopic techniques, e.g. in ABMR, atomic beams are employed [7.1]. Such beams are generated in a vacuum system by evaporation 

The first atomic beam experiments were performed between 1910 and 1920. In 1922 O. Stern and W. Gerlach performed their famous experiment, in which they showed that a beam of silver atoms was divided up into two components in an inhomogeneous magnetic field [7.4]. This was the first direct experimental demonstration of space quantization. In order to explain the results of this experiment we will first consider an electric dipole placed in an inhomogeneous electric field, as illustrated in Fig.7.3. The dipole is influenced by the force 

Corresponding expressions are obtained for the y and z components. The electric dipole moment is defined as P = edr and thus 

An analogous expression is valid for a magnetic dipole in an inhomogeneous magnetic field B 

If /i is the dipole moment /xj of an atom, only the force component in the direction of the field will yield a net effect due to the precessional motion. 

In many spectroscopic techniques, e.g. in ABMR, atomic beams are employed [7.1]. Such beams are generated in a vacuum system by evaporation of atoms. Vacuum techniques are discu ed in [7.2, 7.3]. The energy of the atoms will be of the order of kT, normally corresponding to thermal velocities of a few himdred m/s. The temperatm e needed to produce an atomic beam is determined by the vapour pressure of the element [7.4, 7.5] (typically a value of 10 torr is used in the evaporating oven). In Fig. 7.2 vapour pressure data for different elements are given. 

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The transeinsteinium actinides, fermium (Fm), mendelevium (Md), nobelium (No), and lawrencium (Lr), are not available in weighable (> ng) quantities, so these elements are unknown in the condensed bulk phase and only a few studies of their physicochemical behavior have been reported. Neutral atoms of Fm have been studied by atomic beam magnetic resonance 47). Thermochromatography on titanium and molybdenum columns has been employed to characterize some metallic state properties of Fm and Md 61). This article will not deal with the preparation of these transeinsteinium metals. 

The discovery of fermium (also einsteinium) was not the result of very carefully planned experiments, as in the cases of the other trans uranium elements, bill fermiuni and einsteinium were found in Ihe debris of an atomic weapon lest in the Pacific in November 1952. Researchers, using the Oak Ridge High Flux Isotope Reactor (HFIR) which produced 3.2-hour " Fm. determined ihe magnetic moment of the atomic ground state of the neutral fermium atom with a modified atomic beam magnetic resonance... 

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. 

Thermal atomic beams have been used extensively to determine nuclear spins and moments by investigations of the atomic hyperfine structure. The atomic-beam magnetic resonance (ABMR) method has already become classical [2]. More recent efforts include laser spectroscopy in a crossed-beam geometry, in which a large supression of the Doppler width is obtained by collimation of the atomic beam. 

This is due to the fact that at longer time intervals, the caesium atomic beam magnetic resonance clock is more accurate. For example, modem commercial Cs clocks have reported stabilities of about 3 parts in lo at 10 days (9 x 10 s) [5],... 

Millimeter wave spectroscopy with a free space cell such as a Broida oven is more sensitive than lower frequency microwave spectroscopy. However, the higher J transitions monitored by millimeter wave spectroscopy often do not show the effects of hyperfine structure. In the case of CaOH and SrOH, the proton hyperfine structure was measured in beautiful pump-probe microwave optical double resonance experiments in the Steimle group [24,68], They adapted the classic atomic beam magnetic resonance experiments to work with a pulsed laser vaporization source and replaced the microwave fields in the A and C regions by optical fields (Fig. 15). These sensitive, high-precision measurements yielded a very small value for the proton Fermi contact parameter (bF), consistent with ionic bonding and a... 

W. Ertmer, B. Hofer, Zeiofield hyperfine structure measurements of the metastable states 3d 4s F3/29/2 of SC using laser-fluorescence-atomic beam magnetic resonance technique. Z. Phys. A 276,9 (1976)... 

Flguic 1. Apparatus for atomic beam magnetic resonance. 

Recent Developments and Results of the Atomic-Beam Magnetic-Resonance Method Siegfried Penselin... 

Fig.7.5. Atomic-beam magnetic-resonance apparatus (flop-in arrangement)... 

S. Biittgenbach, G. Meisel, S. Penselin, K.H. Schneider A new method for the production of atomic beams of highly refractory elements and first atomic beam magnetic resonances in Ta i. Z. Physik 230, 329 (1970)... 

S. Penselin Recent developments and results of the atomic beam magnetic resonance method, in Progress in Atomic Spectroscopy, Pt.A, ed. by W. Hanle, H. Kleinpoppen (Plenum, New York 1979) p.463... 

Briefly explain the Atomic Beam Magnetic Resonance (ABMR) technique according to Rabi. Why can only certain types of magnetic resonance transitions be seen What deteimiines the linewidth of the transitions ... 

Comparison of the magnetic moments for alkali metal cations purely surrounded by water molecules with the results of atomic beam magnetic resonance experiments yields the shielding of nuclei by water molecules around the ions. This shielding, which for instance for ions is worth -0.1052 x 10 , is a nearly linear function of the atomic number (62). 

Fig,10.16, Schematic diagram of atomic beam magnetic resonance method using optical pumping and probing with lasers [10.27e]... 

Figure 10.16 shows a block diagram of the whole apparatus, used by PEN-SELIN and his group for atomic beam magnetic resonance spectroscopy detected by laser-induced fluorescence [10.27e]. The pump laser beam crosses the atomic beam several times to assure high pumping efficiency. The rf tran-... 

W. Zeiske, G. Meisel, H. Gebauer, B. Hofer, W. Ertmer Hyperfine structure of cw dye-laser populated high lying levels of Sc by atomic-beam magnetic-resonance. Phys. Lett. 55A, 405 (1976)... 

Using the atomic-beam magnetic-resonance (ABMR) method, Buttgenbach et al. [1] have measured the Zeeman effect In the even Isotope ° Ru and derived the electronic g factors... 

The ground state 4d 5s Fg/2 has been established independently by Sommer [1] and by Meggers and Laporte [2]. Its g value, determined from optical spectra as 1.329 [3], has now been measured by the atomic-beam magnetic-resonance (ABMR) method to be g = 1.33253(3) [4]. 

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