Atomic-beam technique

Furthermore, LandS s theory only represents a first-order approximation, and the L and S quantum numbers only behave as good quantum numbers when spin-orbit coupling is neglected. It is interesting to note that the most modem method for establishing the atomic ground state and its configuration is neither chemical nor spectroscopic in the usual sense of the word but makes use of atomic beam techniques (38). 

Spins and Moments Determined by On-Line Atomic-Beam Techniques... 

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. 

Astatine-197, decay scheme, 260f Atomic-beam spectroscopy, schematic view, 360f Atomic-beam technique, 358-363... 

For the experienced practitioner of atomic physics there appears to be an enigma right at this point. What does nonlinear chaos theory have to do with linear quantum mechanics, so successful in the classification of atomic states and the description of atomic dynamics The answer, interestingly, is the enormous advances in atomic physics itself. Modern day experiments are able to control essentially isolated atoms and molecules to unprecedented precision at very high quantum numbers. Key elements here are the development of atomic beam techniques and the revolutionary effect of lasers. Given the high quantum numbers, Bohr s correspondence principle tells us that atoms are best understood on the basis of classical mechanics. The classical counterpart of most atoms and molecules, however, is chaotic. Hence the importance of understanding chaos in atomic physics. 

SPINS AND MOMENTS OF NUCLEI FAR FROM STABILITY DETERMINED BY ON-LINE ATOMIC-BEAM TECHNIQUES... 

Here, I will concentrate on the different on-line atomic-beam techniques used in hyperfine structure measurements at ISOLDE, and on selected experimental results showing the importance of systematic spin and moment measurements. 

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. 

Figure 7. Laser-atomic beam technique applied to the A554 nm transition of Bal. The input polarisation has been adjusted to reduce the contribution from the even isotopes ( Ba is 71 6J abundant).

The atomic beam technique is a very versatile one. Atomic beams can be produced for essentially any element, whereas conventional cell techniques are limited to a temperature interval up to about 1000° C. Besides reducing the Doppler width, collisional effects are significantly reduced with the atomic-beam technique compared with cells. The possibility of utilizing spatially separated interaction regions along the beam is also valuable in certain cases. We note that the most probable velocity v of a thermal atomic beam emerging from an oven is... 

C. El trom Spins and moments of nuclei far from stability determined by on-line atomic-beam techniques. Adv. Quantum Chem. 30, 361 (1998)... 

Figure 1 Schematic illustration of an atomic-beam technique to reduce Doppler broadening. Atomic vapour effuses from a small orifice of an oven. The angular divergence of atoms in the beam is limited to 6Q = Brr bldi by a slit whose aperture is 2d placed at a distance b from the orifice.

Thus, in addition to the extrapolation to zero intensity of the pumping light which must be made to eliminate systematic errors due to the light shifts discussed in section 17.9.7, a further extrapolation of the measured hyperfine resonance frequencies to zero buffer-gas density must be made. Zero-field hyperfine intervals measured by the optical pumping method are listed in Table 18.3, together with a selection of the results obtained by the atomic beam technique. Generally the optical pumping results are more precise than the older atomic beam results. The table... 

We can now understand how the atomic beam technique may be used to detect magnetic resonance transitions between ground-state hyperfine sub-levels. In the region labelled C in Fig.18.10 the atoms experience a uniform static field and in addition a radio frequency field which usually rotates in the perpendicular plane at the angular frequency (Oq. At resonance, magnetic dipole transitions are induced between the hyperfine sub-levels and the orientation of the magnetic moments of a substantial number of the atoms will have been altered before they leave the C-field region. 

Hyperfin structure investigations by the atomic beam technique... 

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