Caesium emission

The considerable influence of the potassium content on rubidium and caesium emission is not eliminated in the method described, (the calibration curves do not pass through the zero point), but since it is kept at a constant... 

All the cations of Group I produce a characteristic colour in a flame (lithium, red sodium, yellow potassium, violet rubidium, dark red caesium, blue). The test may be applied quantitatively by atomising an aqueous solution containing Group I cations into a flame and determining the intensities of emission over the visible spectrum with a spectrophotometer Jlame photometry). 

Atomic absorption spectroscopy is highly specific and there are very few cases of interference due to the similar emission lines from different elements. General interference effects, such as anionic and matrix effects, are very similar to those described under flame emission photometry and generally result in reduced absorbance values being recorded. Similarly, the use of high temperature flames may result in reduced absorbance values due to ionization effects. However, ionization of a test element can often be minimized by incorporating an excess of an ionizable metal, e.g. potassium or caesium, in both the standards and samples. This will suppress the ionization of the test element and in effect increase the number of test atoms in the flame. 

After Bunsen had detected and isolated caesium, spectroscopy was taken up with great enthusiasm by William Crookes, and this led to his detection and isolation of thallium in 1861.191 Crookes letters to Charles Hanson Greville Williams, who was also working with the spectroscope, and who felt he deserved some of the credit for the discovery of thallium, have been published.192 The use of spectrochemistry in the search for hitherto unknown chemical elements in Britain over the period 1860-1869 has been described. It was perceived that, like Crookes, a scientist could make his reputation by discovering a new element. This resulted in several claims for the existence of new elements that later proved to be unfounded.193 Once Kirchhoff had established beyond doubt that the dark Fraunhofer lines were caused by the same element that caused emission lines of identical wavelengths, the way was open for the chemical analysis of the atmosphere of the sun and stars. This was a process which had been declared to be an impossibility by Auguste Comte less than 30 years previously.194... 

Sodium is still often determined by flame photometry, measuring the emission intensity of the doublet at around 589 nm, but care is necessary to make sure that excess calcium does not cause spectral interference (from molecular emission). This is unlikely to be a problem if AES is used, with a narrow spectral band-pass, and the intensity of emission at 589.0 nm from an air-acetylene flame is measured. However, at low determinant concentrations it is then advisable to add 2-5 mg ml 1 potassium or caesium as an ionization buffer. This is even more true if a nitrous oxide-acetylene flame is used for FES, although its use is rarely justified in environmental analyses because the additional sensitivity gained is rarely necessary. 

The most sensitive flame spectrometric procedure for the determination of strontium is FES, the emission intensity at 460.7 nm being measured from a nitrous oxide-acetylene flame. A detection limit of 1 ng ml-1 or better is generally readily attainable, although the element has a low ionization potential and addition of potassium or caesium at a final concentration of 2-5 mg ml 1 is essential as an ionization buffer. Chemical interference from phosphate, silicate and aluminium is reduced dramatically in this flame. 

Definite layers, more than one molecule thick, can however be obtained on metals under certain special conditions. Instances of these are the monatomic layer of caesium on top of a monatomic layer of oxygen, and the similar layers of alternate oxygen and barium atoms, which are of such importance for thermionic emission (Chap. VIII, 4). 

The first report of a highly structured luminescence from a carbanion deals with absorption and fluorescence from the caesium salt of the 1,1,2,3,3-penta-cyanopropenide anion. Fluorescence and emission characteristics of... 

The quenching of tyrosyl emission by acrylamide has been studied and compared with the effects of caesium ions/ The photochemistries of tyrosine and its derivatives in solid polymer films have also been investigated. ... 

It is perhaps significant that distinct 4 p 1j2 and 4 p3/2 energies are found (139) in X-ray spectra of silver (/ = 55.9 and 62.6 eV), caesium (161.6 and 172.3 eV) and barium, but not in the interval (Z between 48 and 54) where the value given seems to refer to 4 p3 2. This situation suggests that the lack of definition of a sharp energy of the ionized system lacking a 4p 1j2 electron also occurs in the final states of X-ray emission where, for instance, a 4p electron jumps down in a vacant 1 s or 3 d position. 

Armed with the empirical knowledge that each element in the periodic table has a characteristic spectmm, and that heating materials to a sufficiently high temperature dismpts all interatomic interactions, Bunsen and Kirchoff invented the spectroscope, an instrument that atomizes substances in a flame and then records their emission spectmm. Using this instmment, the elemental composition of several compounds and minerals were deduced by measuring the wavelength of radiation that they emit. In addition, this new science led to the discovery of elements, notably caesium and mbidium. 

The absorption and emission spectra of metals such as copper, lithium, caesium, calcium and potassium involve lines at different wavelengths to those observed in the sodium spectrum. As with sodium, a few lines in each spectrum dominate the colours of compounds of these metals in the gas flame. This is the basis of the flame tests which are used to indicate the presence of compounds of these metals (see page 195). 

One of the reasons why physical properties of rare-earth mixtures sometimes looked confusing was that some measured quantities are not at aU proportional to the concentration of the individual constituents. Sir William Crookes was a most extraordinary scientist, who also discovered thallium by flame emission spectra (as Bunsen and Kirchhoff did in the case of rubidium and caesium), but for our purposes Iris main... 

Two elements, caesium and rubidium, were discovered by Robert Bunsen in 1860 and 1861 after studying atomic emission spectra of this type. They are named after the presence of a pair of brightly coloured lines in their spectra—caesium from the Latin caesius meaning bluish grey and rubidium from the Latin rubidus meaning red. 

Flame atomic emission spectrometry Basic information on FAES is presented elsewhere in this encyclopedia. Sodium measurements are performed at 590 nm with the use of a propane flame (1925°C). Physiological samples for sodium determination are highly diluted before measurement. The diluent and the calibrator solution contain the same concentration of lithium ions so as to balance flame instability by a concomitant measurement of lithium in the reference beam (the so-called lithium guideHne). At the same time, lithium ions inhibit the ionization of sodium atoms. This procedure cannot be used in the case of therapy with lithium salts. That is why some authors prefer the concomitant measurement of caesium to that of lithium. Dilution adjusts the viscosity of the sample to that of the calibrator solution to produce identical aspiration rate and drop size on nebulization. As other electrolytes interfere with sodium measurement, their concentration in the caH-brator solution must be similar to their concentration in the sample. For the measurement of sodium in urine, calibrator solutions different from those for serum measurement are needed as the electrolyte concentrations in urine samples are quite different from those in serum and their relations are very variable. As the concentration of the electrolytes in serum is rather constant, calibrator solutions for serum measurements can fulfill their function better than those for urine in other words, urine determinations are usually less accurate. FAES proved to be sufficiently reliable to be used as the basic principle of the sodium reference measurement procedure. In routine use, however, FAES is less accurate. Its application is given up by most clinical laboratories in favor of potentiometric measurements... 

Gnaser, H., Oechsner, H. (1994) Emission of MCs secondary ions from semiconductors by caesium bombardment. Surface and Interface Analysis, 21,257-260. 

Thorium-coated tungsten filaments have a high thermionic emissivity and, like caesium-coated tungsten filaments, have been widely studied (45,24,1,22). It is possible to prepare filaments of tungsten with thoria incorporated, and it is with... 

Frank (28) measured the changes in photoelectric emissivity of tungstic oxide (p. 358), as caesium in measured quantity was deposited, and then allowed to diffuse away. He found that at high temperatures the deposit decayed more slowly, but this result was due in some way to the caesium which liad collected below the surface by migration, during the deposition, or in earlier experiments. 

The method of Brattain and Becker (p. 351) has been used to show that migration of barium and caesium can occur. When barium (or caesium) was deposited on one side of the tungsten strip, which was then raised to 1000°K., the thermionic emissions from the front and back slowly became equal. The value of / = on the front was initially 0-80, while after the flashing at 1000° K., the flnal value of / on both back and front was 0 4. 

Caesium iodide can also be used without an activator but at the expense of a much reduced relative conversion efficiency - 4—6% compared to 45 % and 85 % for the doped materials. The emission maximum at 315 nm means that better output would be obtained when using quartz-windowed photomultipliers. 

---