Cesium isotopes

NatuiaUy occuiiing cesium and cesium mineials consist only of the stable isotope Cs. The radioactive cesium isotopes such as Cs are generated in fuel rods in nuclear power plants (38). 

Cesium isotopes can be recovered from fission products by digestion in nitric acid, and after filtration of waste the radioactive cesium phosphotungstate is precipitated using phosphotungstic acid. This technique can be used to prepare radioactive cesium metal or compounds. Various processes for removal of Cs isotopes from radioactive waste have been developed including solvent extraction using macrocycHc polyethers (62) or crown ethers (63) and coprecipitation with sodium tetraphenylboron (64). 

Cesium fluoride, 21 234, 235, 237, 247 Cesium hexahalogenopolonite, 4 218 Cesium hydrogen phosphate, 4 14 Cesium ion, in crown ether synthesis, 21 24 Cesium isotope, halWife determination, 2 325-326... 

Only one stable isotope is known to exist, Cs. All the other cesium isotopes are radioactive, the most well-known being which has a half-life of 30.1 years. Less well-known is Cs, which is produced... 

Additions of stable cesium to the environment as a result of human activities are few in number, and are also very improbable due to the low technical importance of cesium and the very low cesium content of fuels. Consequently, contamination of the atmosphere, waste waters or sewage sludges by stable cesium isotopes are largely unknown. The situation differs, however, in the case of radioactive isotopes of cesium (see Section 1.5.8), as nuclear plants - and especially those in which uranium is regained - may in exceptional circumstances cause massive pollution of the air, soil and water. 

Most cesium compounds are water-soluble, and this enables plants to absorb almost all radiocesium from the soil (Zhu and Smolders, 2000). The cesium isotopes are transported and stored in plants much in the way that potassium ions are stored, and this results in total radiocesium contamination of the plant tissues that in turn are eaten by animals (Zhu and Shaw,... 

Cesium, isotope of mass 134 Cesium, isotope of mass 137... 

Additional examples of functionalized magnetic materials described in the literature for specific appHcations are summarized in this section. Magnetic microparticles with embedded silicotitanate have shown excellent adsorption ability for radioactive cesium isotope ( Cs) from HEDPA (l-hydroxyethane-l,l-diphosphonic acid), although dissolution of magnetite in acidic solutions in the regeneration step leads to a decrease in magnetic susceptibility (Kaminski and Nunez, 2002). 

The cleaning of radionuclides from the soil is a very important practical problem. This problem has become particularly relevant after the accident at the Chernobyl nuclear power plant in 1986 (Fig. 5.6). As a result of the accident, land in the vast territory of Ukraine, Belarus, Russia, and some neighboring states were contaminated with radionuclides ( Cs, Sr, 239,240p. tables 5.S-5.5). Cesium isotopes were the main polluter after the accident. Some data on contaminated land by Cs in... 

Some radionuclides are physiologically similar to their nonradioactive, stable isotopes for example, tritium behaves like stable hydrogen, and follows C pathways. Actually, both tritium and are used to stutfy the physiological pathways of their stable isotopes. This isotopic substitution tends to work for all radionuclides, although there is often a shght discrimination because of differences in molecular weight. In addition, some elements with similar characteristics in the periodic table often behave similarly. For example, cesium (e.g., Cs) and potassium have similar chemical characteristics, so that often cesium isotopes follow potassium pathways. This similarity also occurs within animals, most notably when radium (e.g., Ra) follows calcium pathways and is deposited in bone. 

To enhance the sensitivity, the probe beam can again be split into two parts. One beam passes the region of the sample that is saturated by the pump beam, and the other passes the sample cell at an unsaturated region (Fig. 7.10). The difference between the two probe-beam outputs monitored with the detectors D1 and D2 yields the saturation signal if this difference has been set to zero with the pump beam off. The pump-beam intensity measured by D3 can be used for normalization of the saturation signal. Figure 7.11 shows as an example the saturation spectrum of a mixture of different cesium isotopes... 

Higher fuel temperatures effect a pronounced transport of cesium from the pellet center to the outer regions. This can be seen from Fig. 3.23., representing measurements performed on a fuel pellet which, after a bumup of about 20 MWd/kg U, was subjected to a power ramp with a terminal power of 404 W/cm (corresponding to a fuel centerline temperature of about 1970 K) for about 48 hours subsequently, irradiation was continued at the lower, normal power level to a final bumup of about 22 MWd/kg U. The depletion of radioactivity in the central region is particularly pronounced for Cs, again reflecting the differences in the production mechanisms for both cesium isotopes. 

The activity concentrations of the longer-lived cesium isotopes s and Cs exhibit a spiking behavior during reactor shutdown which is virtually identical to that of the iodine isotopes this applies to PWRs as well as to BWRs. 

When failed fuel rods are present in the reactor core, fission product cesium isotopes will also appear in the primary coolant in significant activity concentrations. The high solubility of the cesium compounds deposited in the gap of the fuel rod facilitates the transport to the coolant which, however, is only possible via the liquid phase. This means that under constant-load operating conditions a significant cesium transport will only occur when such fuel rod failures are present in the core that allow a direct contact between fuel and liquid coolant in addition, the shutdown spiking results in a considerable cesium transport to the coolant with almost all types of fuel rod defects. The comparatively low cesium retention on the primary circuit purification resins which are saturated with LiOH occasionally leads to the buildup of activity concentrations of cesium isotopes in the coolant on the same order of magnitude as that of the iodine isotopes 1 and 1, even at comparatively low cesium source strengths or those which are not constant over time. 

The major cesium isotope in the coolant (like in the fuel) is Cs, accompanied by Cs, which is produced from the stable fission product Cs by neutron capture (thermal neutron cross section 3 10 cm ) therefore, this radionuclide is of greater significance the higher the bumup level of the failed fuel rod. In addition to these two main isotopes, the very long-lived pure P" emitter Cs appears in the coolant as well as produced from it by neutron capture (thermal neutron cross section 8 10" cm ) their activity concentrations in the coolant also depend on the bumup of the defective fuel rods. Finally, the short-lived Cs has to be mentioned from the dependence of its source strength on the decay constant (see Fig. 4.3.) it can be concluded that this isotope is not released itself from the fuel rod, but that it is generated in the coolant by decay of its precursor Xe. Cesium isotopes with mass numbers beyond 138 are usually not detected in the coolant apparently, because of their short halflives they decay completely on the way from the fuel rod to the coolant. 

It can be assumed that the radioactive cesium isotopes are present in the coolant as Cs" ions, but as yet there is no direct experimental proof of this assumption. Very low cesium activities which are occasionally detected in filtered suspended corrosion products are probably attached by occlusion or by adsorption at the surfaces of the solids. Since cesium is not able to form insoluble compounds in the primary coolant, it does not participate noticeably in the contamination buildup on the primary circuit surfaces. 

The behavior of the cesium isotopes on the cation exchangers of the primary circuit purification system is complex. A newly inserted ion exchanger bed shows a certain retention efficiency for cesium isotopes which decreases to a purification... 

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