Which radioisotope is frequently used in medical diagnostics and has a half-life of 6 hours?

Technetium-99m is the radioisotope commonly used in medical diagnostics due to its ideal characteristics for imaging. With a half-life of approximately 6 hours, it is suitable for procedures such as single-photon emission computed tomography (SPECT) scans. This relatively short half-life allows for a quick decay of radioactivity after the diagnostic procedure, reducing the patient's exposure to radiation while still providing sufficient time for the radioactive decay to emit detectable gamma rays.

In contrast, carbon-14, iodine-131, and uranium-238 have longer half-lives or are less commonly used in diagnostic applications. Carbon-14 is primarily used in dating and biological research. Iodine-131 has a half-life of about 8 days and is used for thyroid treatments rather than diagnostics in the same manner. Uranium-238 has an even longer half-life and is mainly utilized in nuclear power and weapons rather than in medical diagnostics. Therefore, technetium is the preferred choice in the context of this question.