Laboratory scale isotope separation

A number of special processes have been developed for difficult separations, such as the separation of the stable isotopes of uranium and those of other elements (see Nuclear reactors Uraniumand uranium compounds). Two of these processes, gaseous diffusion and gas centrifugation, are used by several nations on a multibillion doUar scale to separate partially the uranium isotopes and to produce a much more valuable fuel for nuclear power reactors. Because separation in these special processes depends upon the different rates of diffusion of the components, the processes are often referred to collectively as diffusion separation methods. There is also a thermal diffusion process used on a modest scale for the separation of heflum-group gases (qv) and on a laboratory scale for the separation of various other materials. Thermal diffusion is not discussed herein. 

T nterest in the separation of isotopes started as a scientific curiosity. The question arose as to whether it was indeed at all feasible or possible to separate isotopes. After this question was answered in the affirmative (24), it became of interest to separate isotopes on a laboratory scale for use in scientific research. A few examples show the range of utility of separated isotopes. Deuterium has attained widespread use as a biochemical and chemical tracer. It is now abundantly available and is used as freely as any cheap chemical reagent. He has opened up an entirely new field of research in low temperature physics and has important applications in the production of temperatures below 1°K. with a thermal neutron cross section of 4,000 barns, has found wide use in nuclear particle detectors—neutron proportional counters. still finds use as a tracer, but in recent years its most frequent use has been in electron spin and nuclear magnetic resonance spectroscopy. occupies a unique position as the only usable tracer for nitrogen. finds application as a... 

The thermal diffusion method requires large quantities of power and is therefore primarily of interest for preparation of laboratory scale samples. As such, it has been developed by Clusius among others, and is a very effective separation process. Overall separations as high as 10,000,000 have been achieved by the Clusius group. A summary of the evolution of the thermal diffusion column in Clusius laboratory is given in Table III (JO). Of particular note is the enrichment of Ar, a middle isotope, from a natural abundance of 0.064% to a final isotopic purity of 99.984%. 

The present work has been the first application of extraction chromatography to isotope separation. This technique proved to be a simple and convenient laboratory-scale method for studying lithium isotope separation by liquid-liquid extraction. The method may have even more interesting possibilities for isotopes of elements which form a variety of complexes which are soluble in organic solvents. 

Isotopes separated. Table 14.24 gives examples of some of the highest reported concentrations of separated isotopes that have been obtained by thermal diffusion. Most of these separations were on a small laboratory scale. The high purity to which scarce isotopes such as C, N, and 0 have been concentrated is a notable feature of these examples of thermal diffusion. The feasibility of concentrating rare isotopes of intermediate mass, such as Ne and A, by thermal diffusion is also noteworthy. These separations are facilitated by the large number of stages obtainable from a single thermal diffusion column. 

Invention of the laser provided the intense, monochromatic, tunable light source needed to make (diotochemical isotope separation apfdicabie to all elements, at least on a laboratory scale. The promise of this method was recognized as early as 1965 by Robieux and Audair [Rl], who were issued the first patent on it. Since the pioneering experiments of Tiffany et al. [Tl] on bromine isotopes in 1966, an enormous amount of work has been done with lasers, with small-scale separation reported for most elements. 

The foregoing discussion fairly well demonstrates that on a small scale any desired Isotope can be separated either by the electromagnetic or the thermal diffusion method. In contrast to these laboratory-scale processes, the separations of the heavier Isotope D, of the lightest element, hydrogen, and of the lighter Isotope 235u, of the heaviest natural element uranium, are carried out on a literally enormous Industrial scale. 

O Equations (15.4) andO (15.5) show that the deflections of the ions of the lighter isotope are greater than those of the heavier isotope, provided that their velocities and charges are the same. The isotope analysis by mass spectrometry and the electromagnetic isotope separation method using large-scale mass spectrometers, called Calutrons because of their early development at the University of California Cyclotron Laboratory, are based on these effects. 

Calutrons are electromagnetic isotope separators that operate like analytical mass spectrometers. The term calutron is a tribute to the work of E. O. Lawrence and his team of scientists who developed the process at their University of California cyclotron laboratory and assisted in its transformation to a production-scale process at the electromagnetic plant located at the Y-12 site in Oak Ridge, Tennessee. The Y-12 calutron process was replaced shortly after the end of World War II by the gaseous diffusion process located at the K-25 plant (also in Oak Ridge). The gaseous diffusion operation had much larger production capabilities and was far less labor intensive. 

The classical methods of isotope separation on a large, technical scale, such as thermal diffusion, or gas centrifuge techniques are expensive because they demand costly equipment or consume much energy [14.11], New techniques based on a combination of laser spectroscopy with photochemistry may considerably reduce the costs. Up to now several methods have been proposed and some of them already proved their feasibility in laboratory experiments. The extension to an industrial scale, however, demands still more efforts and many improvements. ... 

Although thermal diffusion equipment is simple in construction and operation, the thermal requirements are so high that this method of separation is useful only for laboratory investigations or for recovery of isotopes on a small scale, which is being done currently. 

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