Neodymium half-life

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. 

ISOTOPES There are 47 isotopes of neodymium, seven of which are considered stable. Together the stable isotopes make up the total abundance in the Earth s crust. Two of these are radioactive but have such long half-lives that they are considered stable because they still exist on Earth. They are Nd-144 (half-life of 2.29x10+ years) and Nd-150 (half-life of 6.8x10+ years). All the other isotopes are synthetic and have half-lives ranging from 300 nanoseconds to 3.37 days. 

All the possible mass numbers between 142 and 150 are already taken by neod)Tnium (Z = 60) and samarium (Z = 62), so that no stable isotope is expected for element 61. They would all be radioactive, just as in the case of technetium (Z = 43). The Mattauch rule however was not capable of ascribing these radioactive isotopes a certain half-life. A number of uranium and thorium isotopes are also radioactive, but their half-lives are great enough so that one can still find them in nature. During that same year, in 1934, the American physicist and future Noble Prize winner, Willard Libby (1908-1980), discovered that neodymium is a (3 emitter (Libby, 1934). According to Soddy s displacement laws, this should imply that when neodymium decays, isotopes of element 61 should be formed. 

Unfortunately, the produced amoimt of element 61 was too small to study its properties. Pool and Quill were nevertheless convinced that they had s)mthesized an isotope of element 61 with mass number 144 and half-life of 12.5 h. More isotopes of element 61, with mass number 144,147, and 149, were produced two years later in collaboration with Kurbatov, Law and MacDonald (Kurbatov et al., 1942 Law et al., 1941). Pool and his team decided to name the element cyclonium (symbol Cy) in honor of the cyclotron in which all artificial elements had been formed. Most chemists however questioned the validity of their assertions, and doubted that the neodymium targets had been entirely pure. Every presence of impurities... 

Neodymium are known. The most stable of these are the naturally occurring Nd (half-life of 2.29 x 10 years) and °Nd (half-life of 7 x 10 years). The remaining radioactive isotopes have half-lives that are less than 11 days (Table 3.6). 

As if trying to restore the honour of American science after its setback in 1926 two physicists from the University of Ohio conducted the first experiment on artificial synthesis of element 61 in 1938. They bombarded a neodymium target with fast deutrons (the nuclei of heavy hydrogen). They believed that the resulting nuclear reaction Nd d- -- 61 -1- ra gave rise to an isotope of element 61. Their results were inconclusive but nevertheless they thought that they obtained an isotope of the new element with the mass number of 144 and the half-life of 12.5 hours. 

Its half-life is 1.06 10 years. On decay the stable neodymium isotope Nd is formed. The reaction is used to determine the age of minerals and rocks, as described in Chapter 4 Geochemistry. 

Note Promethium, effectively, does not occur in nature. It is a fission product of uranium and may be made, for example, by neutron bombardment of neodymium to give an isotope with a half-life of just under 4 years. 

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