Текст 2. Isotope separation

l. Today much work is devoted to the improvement of existing isotope separation techniques and the discovery of new ones. The demand for some isotopes is sufficient to overcome difficulties in implementing а separation process. This is true for hydrogen isotopes: industrial processes are established. Demand for other isotopes is often not strong enough to lead to widespread use of enriched materials. Such is the case for elements in the middle mass range.

2. The most scientifically and technologically demanding separation and purification process is isotope separation. Many effects in physics and chemistry result from а difference in neutron number. However, the observation of such an effect does not constitute an isotope separation technique, nor does the observation that such an effect leads to а small separation of isotope components of а mixture constitute а workable isotope separation process. Each isotope separation method should and can be developed by five steps. The first stage requires theoretical and experimental measurement of potential classic or quantum isotope effects. The latter are revealed in isotope shift of atomic and molecular spectra. The second stage involves either measurement of the single-stage separation factor of а suitable separation device or the measurement of the equilibrium constant between two phases. А third stage is the amplification of the single-stage isotope fractionation by suitable cascade or column design. This can be carried out оп а laboratory scale. The fourth step requires technological and economic assessment of large-scale production processes. Finally in the fifth step the evaluation and comparison of the growing risk of the process should be considered.

3. Isotope separation is at once both very simple and very complex. It is simple in that аall physical and chemical effects are affected by nuclear structure and may lead to small separation factors. It is complex because very few of these effects have been researched and developed to the point where they constitute valid isotope separation schemes. This secondary effort is only wisely undertaken once strong demand for an enriched isotope has been indentified. The majority of publications in this field refer to separation of the isotopes of uranium and hydrogen elements. A large variety of isotope applications occur in non-nuclear fields, especially in those of medical, biological and environmental sciences. There would also be а market for certain separated stable isotopes for use in the construction of nuclear reactors provided separation costs were not prohibitive. Dewitt indentifies а large variety of stable, stable activable and radioactive isotopes which would be required in gram to ton quantities to fulfill these applications. Thus, the separation and use of isotopes of elements in the middle mass range, unlike those of uranium and hydrogen, is still а developing field. Industrial production has been achieved for the isotopes of carbon, oxygen, nitrogen and sulphur. Most of the other stable isotopes (lithium to lead) may be obtained from electromagnetic separators. Indeed, all stable isotopes have been separated by such machines, although costs are high and production rates are generally low.