Astatine-217

Astatine-217 was first produced artificially in the mid-20th century, as astatine has no stable isotopes and occurs naturally only in trace amounts as a decay product of heavier elements. It is typically synthesized by bombarding bismuth-209 with alpha particles in a cyclotron, a method that also yields other astatine isotopes. In nuclear reactors, it can appear as a short-lived intermediate in the decay chains of neptunium and plutonium isotopes, though its fleeting existence makes direct observation challenging.

Astatine-217 decays primarily by alpha emission, with a half-life on the order of tens of milliseconds, making it one of the shorter-lived astatine isotopes. Its decay chain leads to bismuth-213, which itself is an alpha emitter used in targeted alpha therapy for cancer treatment. The precise half-life and decay energies have been measured in accelerator experiments, contributing to nuclear data tables used in astrophysical models of the r-process.

Because astatine-217 sits near the predicted island of stability, it has been used as a projectile or target in attempts to synthesize superheavy elements. For instance, fusion reactions involving astatine-217 have been proposed to create elements with atomic numbers around 120, though such experiments remain highly challenging due to the low production rates and short half-life. Studies of its mass and decay properties help refine theoretical models of nuclear shell structure.

Astatine-217 is notable for its role in the neptunium decay series, where it appears as a daughter of francium-221. Its alpha decay leads to bismuth-213, which has found medical applications in alpha-particle radiotherapy, making astatine-217 an indirect precursor in a clinically relevant chain. Additionally, the isotope's short half-life means it has no practical industrial uses, but its study has provided insights into nuclear isomerism and the behavior of neutron-rich nuclei.

Alpha decay

A type of radioactive decay in which an atomic nucleus emits an alpha particle (two protons and two neutrons).

Half-life

The time required for half of a radioactive substance to decay.

Island of stability

A predicted region of the periodic table where superheavy elements may have relatively long half-lives.