Use of Fission to produce radioisotopes

Another, less common radiographic source, cesium-137 (Cs-137), is produced by a completely different means known as fission. In 1938, an Italian physicist Enrico Fermi along with a group of other scientists discovered nuclear fission. They found that when an atomic nucleus of uranium-235 is struck by a neutron, it splits into two nuclei of approximately equal mass. Nuclear fission has been defined as the splitting of an atomic nucleus into two smaller nuclei of roughly equal mass, known as intermediates. Heavy elements with atomic numbers greater than 90 are fissionable. As a result of fission, we can produce energy for electricity, produce neutrons for production of radioisotopes, and produce fission products. The latter being a stable element from an unstable nucleus.

During the fission reaction of uranium-235, the nucleus is bombarded with neutrons, which results in the fission fragments of barium-141 nucleus, and krypton-92 nucleus. In addition three neutrons are released (the original bullet neutron, and two neutrons from the U-235 nucleus) along with an energy.

This process may be represented by the following nuclear equation:

It is this process of fission that is important to the production Cs-137 as a radioisotope. Let's look specifically at the reaction and describe what is taking place. The reaction may be represented as:

The two fission fragments are the previously mentioned smaller atoms into which the U-235 has been split. It has been determined that the majority of fission fragments are close to a mass of 95 and or 140. A chemical treatment is required to extract the cesium from the uranium. Normally it is recovered as a chemical form, cesium chloride (CsCl). The product is then converted to a ceramic or glass form for encapsulation purposes to be utilized as a radiographic source.


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