The Synthesis of Technetium (Tc)

Technetium is the element with symbol Tc and atomic number 43; it is the element with the lowest atomic number in the periodic table that has no stable isotopes (i.e., all isotopes are radioactive). Nearly all technetium is produced synthetically, and only minute amounts are found in nature. In 1937, C. Perrier and E. Segr‚ increased the atomic number of Mo by bombarding it with cyclotron accelerated deuterium:

⁹⁷Tc has a half life of 2.6 million years; other long-lived isotopes include ⁹⁸Tc (4.2 million years) and ⁹⁹Tc (0.2 million years). In general, technetium isotopes are made by the reaction,

or from the fission products of uranium or plutonium. Some kilograms of ⁹⁹Tc have been isolated from processing nuclear fuels. Of particular importance is Technetium-99m, which is a metastable nuclear isomer (indicated by the "m" after its mass number 99). This means it is a decay product whose nucleus remains in an excited state that lasts much longer than is typical. The nucleus will eventually relax to its ground state through the emission of gamma rays which rearranges the nucleons without transmuting technetium into another element. 99mTc

is widely used in nuclear medicine for the following applications:

• The gamma emission has a suitable half-life of 6 hr and long beta half-life of ⁹⁹Tc means very low beta emission.
• Little energy of the gamma ray is absorbed by the patient, but sensitive detectors are available, making it a safe isotope to use.
• Radioactive technetium can be incorporated into many compounds that can concentrate in target area of patients. It can be produced by the decay of ⁹⁹Mo
  ⁹⁹Mo→99mTc+γ

and washed out by a saline solution.

For thyroid scanning, ⁹⁹mTc solution is injected into patients. After 20-40 minutes, ^99mTc is trapped in the thyroid, and images can be obtained. Oral taking of 123 or 131I requires 6 to 24 hours. Thyroid imaging is useful in evaluating the location, approximate size, anatomy, and functional status of the thyroid gland. This is especially helpful for thyroid nodules, multinodular goiter, thyroiditis, and possible ectopic thyroid tissue (eg, lingual or mediastinal).