Cesium neutron absorption

The elemental contribution to neutron absorption by fission products tends to follow the effective fission yield of the elements, but with exceptions for several individual elements. The rare earths neodymium, promethium, samarium, europium, and gadolinium, as well as xenon and cesium, are the important neutron-absorbing elements resulting from the high-mass fission-yield peak, and rhodium and its near neighbors are the important neutron absorbers from the low-mass peak. 

Techniques for the analysis of trace amounts of stable cesium include neutron activation analysis (NAA), and optical emission and atomic absorption spectroscopy (Iyengar et al., 1980). Often, the analysis of cesium in biological samples was only developed as a by-product of multielement NAA. Older analytical techniques include precipitation with potassiumiodobis mutha-te(III) or with K3[Fe(CN)6] in the presence of acetic acid. A more modem approach is that of precipitation with NH4Fe[Fe(CN)6] to the CsFe[Fe(CN)6], a reaction which is mainly used to minimize the intestinal absorption of radiocesium in farmed or wild animals (Jander and Blasius, 1989). 

Graphite compounds of rubidium and cesium seem to be more stable and to be formed easily. This is of technical importance since the absorption of the fission elements rubidium and cesium by graphite immersed in liquid sodium will be applied to remove them from the sodium coolant of a fast neutron reactor The formation of a lithium compound of this type has never been observed. 

The most common method of analytical determination of rubidium is atomic absorption spectroscopy (AAS) or neutron activation analysis (NAA). Chemical methods of analysis for the determination of rubidium are difficult because of the tedious procedures required to effect the separation from the other alkali metals. The beneficial effects of the addition of other alkali metals, particularly potassium, sodium, and cesium, added to interfere with the ionization of rubidium is detailed by many authors [39,53-55]. Recent evaluation of the benefits of these ions in the determination of rubidium in human erythrocytes has concluded that erythrocytes should be diluted 1 50 with potassium to give a final potassium concentration of 10000 ppm. Under these conditions, the sensitivity of absorbance was increased about threefold and rubidium concentrations could be determined in the range 0-60 ppm [56]. 

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