Any of the above-mentioned isotope effects can be used to separate the isotopes. Distillation, gas diffusion, centrifugation, electromagnetic separation, electrolysis, and chemical isotope exchange are widely used methods for isotope separation. A newer, novel method of doing this is laser isotope separation (LIS).

The LIS technique was originally developed in the 1970s as a cost-effective, environmentally friendly way of supplying enriched uranium. The method is based on the fact that different isotopes of the same element absorb different wavelengths of laser light. Therefore, a laser can be precisely tuned to ionize only atoms of the desired isotope, which are then drawn to electrically charged collector plates.

The isotope separation is characterized by the separation factor. In a two- component system, the separation factor (a) is defined as:

Xf(1 ~ X0) = R, (1 — Xi)Xo Ro

where X0 and X, are the molar fraction of one of the isotopes before and after sepa­ration, respectively.

In addition, 1 — a is called the enrichment factor.

Since the degree of the isotope effects is usually small, one separation step is frequently not enough to reach a high enough enrichment. In this case, a multistage process in cascade can be applied. The enrichment factor of a separation cascade (A) is proportional to the number of stages (n):

A = an = —1 (3.42)

R0

By increasing n, the enrichment increases proportionally.

The enriched isotopes are used for the production of fuels and moderators of nuclear reactors and nuclear weapons, for analytical purposes (e. g., NMR, Mossbauer spectroscopy), and for the preparation of targets in the production of radioactive isotopes. In Table 3.5, the most important enriched isotopes are listed. Beside enrichment, the depletion of the isotopes can be important for special applications. Depleted 64Zn is used in nuclear industry. The addition of zinc to the cooling water inhibits the corrosion and the formation of 60Co (discussed in Section 7.3) from the steel of the reactor, decreasing the workers’ radiation expo­sure. Natural zinc contains 48% 64Zn; however, the gamma emitter 65Zn isotope is produced by (n, y) nuclear reaction of 64Zn (discussed in Section 6.3). To avoid the production of 65Zn, depleted MZn (<1%) is produced by centrifugation and applied in nuclear reactors.