Technetium

Technetium is a radioactive chemical element with atomic number 43 and no stable isotopes. It occurs naturally in trace amounts but is produced mainly in nuclear reactors.

Atomic number: The number of protons in an atom's nucleus, which defines its chemical element. Technetium's 43 protons distinguish it from molybdenum and ruthenium.
Technetium-99m: A metastable nuclear isomer of technetium-99 that emits gamma rays and has a half-life of about six hours. Its short half-life and useful gamma emissions make it the workhorse medical isotope.
Periodic table: A tabular arrangement of chemical elements by atomic number and recurring chemical properties. Technetium filled the long-predicted gap at atomic number 43.
Stable isotope: An isotope whose nucleus does not undergo radioactive decay. Unlike nearly every naturally abundant element, technetium has no stable isotope.
Isotope: One of two or more atoms of the same element with different numbers of neutrons. Technetium has no stable isotopes, and its isotope determines its decay and uses.
Nuclear medicine: The use of radioactive substances to diagnose, monitor, or treat disease. Technetium-99m is the most widely used radionuclide for diagnostic nuclear imaging.
Dmitri Mendeleev: A Russian chemist who formulated an influential periodic table and predicted undiscovered elements. His periodic system anticipated an element between molybdenum and ruthenium.
Promethium: A radioactive rare-earth element with atomic number 61 and no stable isotopes. Promethium is the other element between bismuth and uranium with no stable isotopes.
Radioactive decay: The spontaneous transformation of an unstable atomic nucleus, often accompanied by radiation. Every technetium isotope decays, setting its lifetime and radiation output.
Single-photon emission computed tomography: A medical imaging technique that reconstructs three-dimensional images from detected gamma rays. SPECT cameras commonly detect gamma rays from technetium-99m tracers.

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