Samarium-147 dating

The fourth chapter gives a comprehensive review about catalyzed hydroamina-tions of carbon carbon multiple bond systems from the beginning of this century to the state-of-the-art today. As was mentioned above, the direct - and whenever possible stereoselective - addition of amines to unsaturated hydrocarbons is one of the shortest routes to produce (chiral) amines. Provided that a catalyst of sufficient activity and stabihty can be found, this heterofunctionalization reaction could compete with classical substitution chemistry and is of high industrial interest. As the authors J. J. Bmnet and D. Neibecker show in their contribution, almost any transition metal salt has been subjected to this reaction and numerous reaction conditions were tested. However, although considerable progress has been made and enantios-electivites of 95% could be reached, all catalytic systems known to date suffer from low activity (TOP < 500 h ) or/and low stability. The most effective systems are represented by some iridium phosphine or cyclopentadienyl samarium complexes. 

We were quite elated, and it appeared that it was a rich field. Now, fifty years later, I must say that it wasn t as rich as we thought. But we have over the years discovered half a dozen natural radioactive elements, and two of these, the samarium-147 with its decay to neodymium-143 and rhenium-187 with its decay to osmium-187, prove to be of use in Nuclear Dating. The importance of rhenium is that it is iron soluble while the other radioactivities are insoluble in metallic iron. In fact, the best half life we have for rhenium-187 was obtained by measuring the osmium-187 to rhenium-187 ratio in iron meteorites which had been dated by other methods. This work was started many years ago by Dr. Herr and others in Germany. The half life is 43,000,000,000 years. 

Chesley, J.T., A.N , Halliday, and R.C. Scrivener Samarium-Neodymium Direct Dating of Fluorite Mineralization," Science. 949 (May 17, 1991)... 

As was found in early transition metal and actinide chemistry, the CsMes ligand has allowed the isolation of complexes difficult to obtain by other means. More importantly, however, following the principle of steric oversaturation, the CsMes ligand has provided access to some of the most highly reactive organolanthanide complexes known to date. In addition, as demonstrated by the samarium and lutetium complexes [(C5Mes)2LnH]2,... 

Isochron age calculations are commonly made for the Rb-Sr (rubidium-strontium], Sm-Nd (samarium-neodymium], and U-Pb (uranium-lead] radioactive systems. They are most commonly applied to whole-rock systems, that is, a suite of samples thought to have formed at the same time, such as an igneous plu-ton or a suite of lavas. Isochron age calculations may also be made for a suite of minerals in a rock, in which case they date the time at which the minerals lost isotopic contact with each other, that is, became closed systems. This approach can be useful in dating metamorphism. 

A single attempt has been made to induce asymmetry in the intermolecular cross coupling reaction by employing a chiral ligand for the samarium ketyl [56]. Utilizing 2,2 -bis(diphenylphosphinyl)-l,l -binaphthyl (BINAPO) as a chiral ligand, a modest start has been made to develop an enantioselective process. However, in the examples reported to date the method is plagued by low yields and/or moderate stereoselectivities. 

The Cocks Formation contains a porphyritic pillow lava that was dated by RoweU et al. (1993) by means of the samarium-neodymium (Sm-Nd) method (Appendix 3.6.6). The rock yielded a Sm-Nd model date of700-800 Ma, which indicates that the flow was extruded during the Neoproterozoic Era The metamorphic grade of the Cocks Formation also increases in a northerly direction. 

To date our applications have been to kinetic studies of aqueous samarium sulfate (7), silver thiosulfate (8), and a variety of macrocyclic systems (9). It can be persuasively argued that the same systems could have been studied as effectively by other ultrasonic techniques, particularly the pulse method (10), Our response would be that the "looking at sound" experiment lends itself particularly well to minicomputerization and the latter greatly speeds the data taking process (by a factor of more than ten) and at the same time significantly reduces imprecision in the experimental data. 

The decays of " Sm (Samarium) to " Nd (Neodymium), Lu (Lutetium) to Hf (Hafnium), and Re (Rhenium) to Os (Osmium) all have long parental half-lives and very low natiual abimdances of the parent isotopes which means that the radiogenic daughter isotopes accumulate very slowly. Before about 1980 these decay schemes were of little value as radiometric dating methods. However, improvements in analytical techniques have permitted geochronologists to apply these three dating methods to certain types of problems. 

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