Applicatons of Nuclear Reactions

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Nuclear reactions are used to produce new nuclides or elements, release energy, and produce subatomic particles. These features can be applied to

scientific investigations,
engineering projects,
medical diagnosis and treatments,
and biological experiments.

Let your imagination stretch and apply nuclear reactions to benefit you and your society. In the past, nuclear reactions have been applied to solve some scientific puzzles, and further research and development have made many beneficial applications. The following applications are based on nuclide productions.

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:

\[\ce{^{96}Mo + ^2D \rightarrow ^{97}Tc + ^1n}\]

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,

\[\ce{^{42}Mo + ^1n \rightarrow ^{42}Tc + _{-1}\beta}\]

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. \(^{99m}Tc\) 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
\[^{99}Mo \rightarrow ^{99m}Tc + \gamma\]
and washed out by a saline solution.

For thyroid scanning, \(^{99m}Tc\) 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).

The Synthesis of Astatine, At

A portion of the periodic table.
Sn	Sb	Te	I	Xe
Pb	Bi	Po	__	Rn

The element below iodine and between Po and Rn was unknown until D.R. Corson, K.R. Mackenzie and E. Segr‚ synthesized it. They irradiated bismuth sheets by a particles hoping to increase the atomic number by 2. They assumed the element be similar to iodine from its position on the periodic table. Thus, they heat the bismuth sheet and the isotopes of astatine sublimated, and condensed on a cold surface.

\[\ce{^{209}_{83}Bi +^4_2He \rightarrow ^{213-x}_{85}At} + x ^1_0n\]

The reaction releases \(x\) = 1, 2, or 3 number of neutrons. In 1940, they made the missing element and called it astatine, At, after the Greek word astatos meaning unstable. Knowing the properties of some astatine isotopes enable the detection of natural astatine isotopes. To date, almost 20 astatine isotopes have discovered with \(\ce{^{210}At}\) having the longest half-life of 8.3 h.

Neutron Activation Analysis (NAA)

Neutron Activation Analysis (NAA) is an important application of of nuclear reactions that is a multi-, major-, minor-, and trace-element analytical method for the accurate and precise determination of elemental concentrations in a materials. Sensitivity for certain elements are below nglevel. The method is based on the detection and measurement of characteristic gamma rays emitted from radioactive isotopes produced in the sample upon irradiation with neutrons. High resolution germanium semiconductor detector gives specific information about elements. Some 60 elements are routinely analyzed by the NAA center in Cornell University. It analyzed samples from agriculture, geology, medicine, to oceanography, serving various discipline and industries. There are other centers carrying out routine NAA services for their clients too.

Contributors and Attributions

Chung (Peter) Chieh (Professor Emeritus, Chemistry @ University of Waterloo)