Caesium isotopes

A further method for the determination of caesium isotopes in saline waters [60] is based on the high selectivity of ammonium cobalt ferrocyanide for caesium. The sample (100-500 ml) is made 1 M in hydrochloric acid and 0.5 M in hydrofluoric acid, then stirred for 5-10 min with 100 mg of the ferrocyanide. When the material has settled, it is collected on a filter (pore size 0.45 im), washed with water, drained dried under an infrared lamp, covered with plastic film and / -counted for 137caesium. If 131caesium is also present, the y-spectrometric method of Yamamoto [61] must be used. Caesium can be determined at levels down to 10 pCi/1. 

The major problem, apart from local radioactivity, in this and the other accidents, was that large amounts of volatile fission products were widely distributed high in the atmosphere. These subsequently polluted large land areas. The main volatile elements released at Chernobyl were the noble gases (especially krypton, Kr, and xenon, Xe), iodine, I, and caesium, Cs. The caesium isotopes, caesium-134 and caesium-137, posed a particular problem. The half-life of caesium-134 is 2.06 years. 

In order to reveal specific causes of the anomalous event, a program of studies was developed. This program envisaged sampling and analysis of impurities in the deposits over the CGP walls and in the primary sodium, measurement of caesium isotope activity in the reactor, studies on the impurities behaviour under conditions of experimental facilities etc. 

The mixed bed demineraliser in service can be supplemented by intermittent use of the cation bed demineraliser for additional purification in the event of fuel defects. In this case, the cation resin removes mostly lithium and caesium isotopes. The cation bed demineraliser has sufficient cqiacity to maintain the cesium-136 concentration at acceptable levels with the assumed level of Design Basis fuel defects. Each mixed bed and the cation bed demineraliser is sized to accept the maximum purification flow. Filters are provided downstream of the demineralisers to collect particulates and resin fines. 

In aqueous solution this exchange has been studied, in the absence of oxygen, in chloride and sulphate media. The isotope Sn was used as the indicator and the separation of Sn(IV) and Sn(II) was achieved by the formation of the insoluble salts caesium hexachlorostannate(IV) and stannous oxalate . 

High-energy radiation may be classified into photon and particulate radiation. Gamma radiation is utilized for fundamental studies and for low-dose rate irradiations with deep penetration. Radioactive isotopes, particularly cobalt-60, produced by neutron irradiation of naturally occurring cobalt-59 in a nuclear reactor, and caesium-137, which is a fission product of uranium-235, are the main sources of gamma radiation. X-radiation, of lower energy, is produced by electron bombardment of suitable metal targets with electron beams, or in a... 

Crystallisation was one of the earliest methods used for separation of radioactive microcomponents from a mass of inert material. Uranium X, a thorium isotope, is readily concentrated in good yield in the mother liquors of crystallisation of uranyl nitrate (11), (33), (108). A similar method has been used to separate sulphur-35 [produced by the (n, p) reaction on chlorine-35] from pile irradiated sodium ot potassium chloride (54), (133). Advantage is taken of the low solubility of the target materials in concentrated ice-cold hydrochloric acid, when the sulphur-35 as sulphate remains in the mother-liquors. Subsequent purification of the sulphur-35 from small amounts of phosphorus-32 produced by the (n, a) reaction on the chlorine is, of course, required. Other examples are the precipitation of barium chloride containing barium-1 from concentrated hydrochloric acid solution, leaving the daughter product, carrier-free caesium-131, in solution (21) and a similar separation of calcium-45 from added barium carrier has been used (60). 

This useful technique has made many contributions to radio- and nuclear chemistry, although primarily for investigational purposes rather than those of separation for its own ends. Thode and his co-workers have made many investigations into the inert gases produced in fission and it was by these means that the fine structure of fission was first discovered (79), (121). Since then several other elements, the rare-earths, strontium, caesium, zirconium, and molybdenum (35), (50), (132) have been investigated, and the isotopic ratios obtained provide relative values of fission-yields which are more accurate than can be obtained by standard radiochemical means. The latter technique, however, requires rather less heavily irradiated material than the former. 

Wiles, D. R., B. W. Smith, R. Horsley and H. G. Thode Fission Yields of the Stable and Longlived Isotopes of Caesium, Rubidium, and Strontium, and Nuclear Shell Structure. Canad. J. Physics 31, 419 (1953). 

F. W. Aston 60 has shown that the positive ray spectrum of lithium shows the existence of two isotopes of at. wt. 6 and 7 sodium shows no isotope potassium shows two isotopes with at. wt. 39 and 41 rubidium shows two isotopes of at. wt. 85 and 87 and caesium has possibly two isotopes. 

The determination of caesium in soil by multi-element analysis is discussed in Sect. 2.55 (isotope dilution analysis). 

GC isotope ratio mass spectrometry [7] and GC using a caesium bromide thermionic detector [8] have been used to determine, respectively, carboxylic ethers in apples and tetraethyl pyrophosphate in chloroform-acetone extracts of crops in amounts down to 0.01 ppm. 

In a recent study [175] of the methoxide ion catalysed tritium exchange in methanol of weakly acidic fluorinated bicycloalkanes (pIT ca. 20), comparison of the rates of exchange for six compounds, with ion-pair pK values determined in cyclohexylamine containing caesium ions, gave a Bronsted plot with slope (a) within experimental error of unity. The isotope effects for proton compared with deuteron transfer (feH/feD = 1.2) are similar to those observed with chloroform. The charge on these polyfluorocarbanions may also be localized on carbon [175]. 

In order to use geochemical anomalies for tracing particular source compositions, it is necessary to establish normal behavior first. Throughout the 1980s, Hofmann, Jochum, and co-workers noticed a series of trace-element ratios that are globally more or less uniform in both MORBs and OIBs. For example, the elements barium, rubidium, and caesium, which vary by about three orders of magnitude in absolute abundances, have remarkably uniform relative abundances in many MORBs and OIBs (Hofmann and White, 1983). This became clear only when sufficiently high analytical precision (isotope dilution at the time) was applied to fresh... 

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