Recoil yield

This experiment provides a spectrum of the particle (recoils) yield, Y Ed) (number of recoils detected with an energy between Ed-dkE/2 and Ed+ E/2 where AE is the energy width of the multichannel analyzer), versus Ed The depth resolution of this technique is 80 nm and the labelled diffusant can be followed to depths --SOO nm. 

As with RBS, the simplest and most precise measurement that ERS can provide is the absolute measure of total hydrogen content ( H and/or H) within a surface layer or film of thickness less than a few thousand angstroms. When the layer is thin, this is determined from the total number of events, or yield Ysummed over the elastic recoil spectral peak. The yield may be expressed as... 

Synthesis of ruthenocene from fission-product ruthenium isotopes was done by neutron irradiation ofU30g and FeCpj powder mixtures. It was shown that most of the ruthenocene found was actually produced by the decay of a precursor. Subsequent knowledge makes it apparent that the fission product recoils formed a rhodium dicyclopentadienide whose structure was preserved through the decay . The total yield of ruthenocene reached a value of 60% under some experimental conditions and was rarely less than 40%. 

Henrich and WolP have studied the formation of Mo(CO)5 by catching Mo and Mo recoils in Cr(CO)g. The Molybdenum isotopes were produced in several different reactions, so that the recoil energy varied over a wide range. It was found that the yields of Mo(CO)g with the two isotopes differed from each other, but varied only slightly as a function of initial recoil energy. These authors were also able to show that the isotope effect of about 8% is nearly insensitive to radiation received by the sample (and catcher) during the bombardment. They argued that there remains only one possible cause of this isotope effect, that is, differences in the de-excitation schemes of the product nuclei. 

The nature of the first type of thermal reactions is as yet only speculative. The two obvious possibilities seem to be (1) reaction of an incomplete molecule (radical) with an unbound nearby ligand, made available by recoil fragmentation, radiolysis, chemical dissociation, or the presence of an external atmosphere and (2) reaction of the moiety with a nearby molecule to abstract a ligand. The first type with an external source of CO has been clearly demonstrated for the case of the Group VI carbonyls which, when heated in an atmosphere of CO (up to 100 atm pressure) showed a marked increase in yield. A much smaller enhancement of yield in vacuo was attributed (99) to radiolytic dissociation, because of the influence of irradiation at various y-fluxes. The alternative possibility—that of equilibrium dissociation of Cr(CO)6 in the solid state—has not been investigated. 

The high atomic mass yields small recoil energies and thus a large recoU-free fraction even at room temperature (/300 0.95 for Ta metal [175]) this allows measurements of the resonance effect to be made over a wide temperature range up to about 2,300 K. 

Fig. 11. Displacement yield of 51Cr-/3-diketonate by recoil implantation as a function of mean implantation energy (MIE) [54]...

Astatohalobenzenes can be synthesized directly in At recoil (Table III) experiments either via hydrogen replacement by recoil astatine in monohalobenzenes or by halogen replacement in dihalo-benzenes. In the former, total yields range from 5 to 15%, with an almost statistical mixture of ortho-, meta, and para-astatohalobenzene products 145, 150). The production of AtC5H4F from the corresponding CIC6H4F isomers has been achieved with yields of 14% without noticeable isomerization of the products (19). 

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