Recoil atom reaction yield

When comparing recoil atom reaction yields of (n,y) and (n,2n) reactions, there is a distinct difference in the thermal reaction yield, whereas little if any difference can be observed in the hot reaction yield. Note that an (n,2n) reaction provides recoil energy 10 -10 times larger than that an (n,y) reaction. Probably this result indicates a difference of thermal radical concentration in the cages formed along the track of the recoil atom. As hot reactions occur at the end of the recoil track after slowing down and is not affected by recoil energy so much. This is shown in Fig, 24,14 for the Br recoils produced by (n,y) and (n,2n) reactions (Cole et al. 1966). 

The relation between recoil energy and hot atom reaction yield is a question of fundamental importance in a solid system, but no answer had been given until Yoshihara and Kudo (1970) proposed use of (y,y) reaction in an indium complex in 1970. Controlling energy of y-rays from a linear electron accelerator, a separable yield of from a bulk of irradiated In-EDTA... 

Inorganic compounds may be more stable to radiation damage than organic compounds, and their decomposition products are less deleterious. Accordingly, a search was made for inorganic compounds which would contain these trivalent ions in a nonexchangeable state and, at the same time, allow recoil atoms ejected from their position in the structure to be separated. Szilard-Chalmers reactions have been reported for certain inorganic systems, for example clays ( ), but yields and enrichment factors were both low. 

Another example involves the soxurce of acetylene as a major product from the reaction of recoiling carbon atoms and cyclopropane (18). MacKay and Wolfgang attributed the formation of acetylene from carbon-atom reactions with alkanes to an insertion into a C—bond followed by fragmentation of the intermediate carbene (18). The hi yield of labeled acetylene from cyclopropane was in accord with this mechanism, since the intermediate cyclopropylmethylene was believed to cleave into two stable molecules ethylene in addition to acetylene. 

Formation of Allene from + CH2=CH2. Allene is formed in about 15% yield from the reactions of recoiling atoms with ethylene... 

Modeling of the recoil process provides a detailed rationale for the success of this important new approach to thermal kinetics. Initial work was designed to explore both the conditions under which best results might be obtained and the limitations anticipated as applications are broadened (42). Calculated results based on earlier methods for determining recoil reaction yields (25) and parameterized forms for cross-section functions (15,16) were used for this analysis. The cross sections used, while not precisely vahd for real chemical systems, were approximated representations for hydrogen atom abstraction and addition reac-... 

In well-designed experiments the mean hot atom lifetime is much shorter than the mean thermal reactive lifetime. The MNR technique thus oflFers good utility for precise equilibrium kinetics studies wdth the radioactive atoms and unstable radicals produced using nuclear recoil methods. Small residual nonthermal reaction yields are invariably observed in recoil experiments, but these have no direct bearing on the validity of the MNR equilibrium hypothesis. 

Direct interaction of recoil atoms or fragments, obtained in the C(y,n) C process with various Cg hydrocarbons, resulted in the formation of C-labelled methane, acetylene, ethane + ethylene, propane + propylene and l,3-butadiene Methane- and acetylene- have been produced in the radiochemical reaction between and liquid benzene, with the yield ratio (CH4/C2H2) being in the range of 0.02 to 0.03. 

The recoil chemistry of carbon-11 in liquid C5-C7 hydrocarbons has been investigated by Clark The recoil atoms have been produced in the (y,n) reaction. The study of the product yields of ethane, ethylene and acetylene (as well as of methane) from different target molecules has been the main concern in this work. Iodine affected the yields of all the volatile products except acetylene. Acetylene-the principal products in all the hydrocarbons investigated, is produced in hot reactions with naked atoms. Insertion of recoil fragments into C—H and C=C bonds leads to various C-labelled hydrocarbons. 

The recoil atoms produced by the reaction I(n,y) I distributed among CH3 I(54.4%), CH2r I(l%), and inorganic species 45%) when no moderator gas was added. Mixing of moderator gases Ne, Ar, or Kr changed the yield of to... 

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