Caesium fluoride - CsF

As with barium fluoride, there are few advantages of this material when compared to the more popular scintillators, except for the short lifetime of the light output. Although much longer than for barium fluoride, the 4.4 ns scintillation lifetime is considerably shorter than that of the fluorescence in more conventional materials. Yet again, the low light output means poor resolution. 

There are a number of new scintillator materials under development to add to the list of conventional materials. The properties of some of these, GSO, LSA and YAP, for example, are listed in Table 10.1. Many of these materials have specific applications in specific fields, such as 

The design of photomultipliers varies depending upon what they are to measure. For scintillation gamma-ray measurements, they are always of an end-window design with the photocathode deposited on the inside of the face of the tube. The whole structure is enclosed within an evacuated glass envelope and connections made via a multipin plug at the anode end. 

Not every photon received wiU produce a photoelectron. The energy of a typical scintillation photon in the blue region of the spectrum is about 3eV. The electrons excited by such photons must migrate to the surface of the photocathode and still have sufficient energy to overcome the work function which might be 1.5 to 2eV in the materials described. This places a limit on the thickness of the photocathode to a few tens of nanometres. At such thicknesses, the photocathode will only be semi-transparent, even to the scintillation light, by which this process further reduces the overall yield of photoelectrons. 

The quantum efficiency of a photocathode material, the number of photoelectrons emitted per incident photon, might be 20-30 % at the optimum photon energy. Now, in Nal(Tl), it takes about 26 eV of energy absorbed by the detector to produce one photon. Taking the quantum efficiency into account as well, this means that it takes 

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The reaction of 1 -trimethylsilylnaphthalene with pivaldehyde in the presence of 20 mol% Bu-P4 base proceeded smoothly at room temperature to give the alcohol in 91% yield. Other phosphazene bases with weaker basicities, such as Bu-P2 base and BEMP, showed no catalytic activity. As one of the conventional strong organic bases, DBU was found to be inactive. Caesium fluoride (CsF) was then examined as a fluoride anion donor, but no carbon-silicon bond cleavage was observed. Reactions with other aldehydes have been examined that with benzaldehyde was found to proceed somewhat slowly at room temperature. Other aryl aldehydes with electron-donating groups were also employed as electrophiles and the reactions proceeded smoothly at room temperature [57] (Table 5.5). 

Caesium Niobium Fluoride, CsF.NbFs or CsNbF6, is obtained in fine needles by repeated crystallisation of csesium niobium oxyfluoride, CSjNbOFj, from hydrofluoric acid.2 Another csesium niobium fluoride having the probable composition 7CsF.NbFs or Cs7NbF5 has been prepared by the action of a solution of caesium hydroxide in hydrofluoric add on niobic acid in the same solvent.3... 

Csesium fluorides.—Evaporation of a solution of caesium carbonate in hydrofluoric acid yields the primary fluoride, CsF,HF.6 When heated, this substance is converted into the normal fluoride, CsF, which crystallizes in cubes, melts at 684° C.,6 and boils at 1251° C.8 Its vapour-pressure in atmospheres corresponds with the expression 6... 

This dispersion could be related to the fact that caesium fluoride is very difficult to dry thoroughly (more than potassium fluoride). As a consequence, fluorination with CsF a 180°C is quite completely matched by the formation of oxygenated byproducts. 

Comparison between Tables 14 and 15 clearly demonstrates that caesium fluoride is far more effective than potassium fluoride towards 2,4-dichloronitrobenzene. As some papers reported about the addition of CsF as catalyst in the Halex reaction using KF (refs. 42 - 46), we quantified the behaviour of CsF-KF mixtures to look for some synergistic effect. 

Caesium fluoride Cesium fluoride Cesium fluoride (CsF) Cesium monofluoride Dicesium difluoride EINECS 236-487-3 NSC 84270 Tricesium trifluoride. Used in optics, catalysis, specialty glasses. Atomergic Chemetals Cerac Noah Cham. Spectrum Chem. Manufacturing. 

Three other types of reaction were studied with the newly available perfluoro-3-alkylbuta-l, 2-dienes, CFs CRfiCiCFs (Rf = CFs, CsFs, n-CsF , and i-CsF ). Methanol addition proceeds in ail cases by an initial nucleophilic attack at C-2, followed when Rp i-CsF mainly by protonation at C-3 (50—95%) the accompanying products arise by loss of fluoride from C-4 (effectively Ssl substitution) giving methoxydienes, a process which accounts for 98 % of starting material when Rf = i-CsF (see Scheme 41). Secondly, caesium fluoride-initiated rearrangement... 

CFaiN RfCOF + hvRr + COF Rr + CFjiN- -> RpN CFj. Extension of this to the bis-acyl fluorides FOC (CF2)3-COF and FOC-(CF2>4-COF, however, gives low yields of perfluoro-(Af-methylpyirolid-2-one) (15 %) and perfluoro-(A -methylplperidin-2-one) ca. 10%), respectively, instead of the imines CFg N-(CF2) N CF2 (a = 3 or 4), presumably via the sequence of events shown in Scheme 39. Fluoride-initiated (CsF) reactions between the formaldazine and these, and other, acyl fluorides leads to novel heterocyclic carbonyl compounds which suffer decarbonylation when irradiated with u.v. light (see Scheme 40). Carbonyl fluoride and oxalyl fluoride react with the formaldazine in the presence of caesium fluoride to yield the acylic and cyclic product (57) (70%) and (58) (ca. 55%), respectively the latter fragments to trifluoromethyl isocyanate when exposed to u.v. light. 

CsCl HgCl2=3 1, 2 1, 1 1, 2 3, 1 2, and 1 5 and five caesium antimonious fluorides where CsF SbF3=l 1, 3 4, 4 7, 1 2, and 1 3. According to I. Remsen s rale (1889) When a halide of any element combines with a halide of an alkali metal to form a double salt, the number of molecules of the alkali salt which are added to one molecule of the other halide is never greater, and is generally less than the number of halogen atoms contained in the latter—for instance, in the double fluoride of sodium and aluminium, where the negative halide has three fluorine atoms, no more than three molecules of sodium fluoride will be found united with one of aluminium fluoride. 

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