Optical rotation bismuth

The first researchers to point the way to the present successful precision measurements in heavy atoms were the Bouchiats [13]. The showed that PNC transitions in atoms with atomic number Z were enhanced by a factor of Z. In heavy atoms this factor leads to an enhancement of PNC transitions of several orders of magnitude, and while still very small, these transitions or the related effect of optical rotation have been seen in several different heavy atoms, specifically cesium [Z = 55) [5], [14], thallium Z — 81) [15],[16], lead Z = 82) [17], and bismuth (z = 83)... 

Figure 16. Laser polarimeter used for detecting PNC optical rotation in atomic bismuth.

To illustrate the procedures and problems encountered in optical rotation PNC experiments, we will discuss the University of Washington experiments in some detail. These experiments have yielded measurements of PNC in atomic bismuth and, more recently, in atomic lead. 

Of great importance in the optical rotation experiments is the laser source. The laser must be tunable, and should be highly monochromatic, stable in intensity, and emit a beam of good optical quality. Tunable dye lasers satisfying all these criteria operated well at the 648-nm bismuth line in 1974 when work began in several places. The groups at Oxford and Novosibirsk and later at Moscow have all used such lasers to measure the effect on this line. 

The extraordinary quality of the experiment at Oxford can be seen in Fig. 10.4 which shows the optical rotation spectrum for the 8757 A line in atomic bismuth. The dispersion shaped profiles are centred on the positions of the hyperfine components (indicated by arrows). The curve shows the theoretical expectations in the SM and is in amazing agreement with the data. Note that the spectrum would be flat and featureless without the parity violation. (For the latest data see Macpherson et al., 1991.)... 

Fig. 10.4. Optical rotation spectrum for the 8757 A line in atomic bismuth, in the current Oxford experiment of Macpherson, Zetie, Hoare, Stacey and Warrington (courtesy of Dr D. N. Stacey). See text for explanation.

An experimental set-up similar to the one used in polarization spectroscopy is employed in experiments testing atomic manifestations of parity violation in the electro-wealc interaction. [9.359-9.361]. The experiments are important for testing the Standard Model hi elementary particle physics. Right-left asymmetries in atomic physics are of the order of 1 10 . A small optical rotation detectable using crossed polarizers is induced by interference between neutral weak and electromagnetic interactions in atoms. The most accurate experiments deal with heavy elements such as mercury, thalhum, lead and bismuth [9.362, 9.363]. Another way of probing the parity violation is to observe the strength of certain forbidden transitions, notably the 7 —... 

A homologous aliphatic acid, methyl 3,4-dicarboxy-3-hydroxy-19-oxoeicosanoate (43), has been isolated from Usnea meridensis 210). The structure of this compound followed from the spectroscopic and chemical properties, by comparison with the properties of caperatic acid (41) and by sodium bismuthate oxidation to methyl 3,19-dioxoeicosanoate (44) 210). Caperatic acid (41) and methyl 3,4-dicarboxy-3-hydroxy-19-oxoeico-sanoate (43) have similar optical rotations but the absolute configuration of these acids remains to be determined. 

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