Astatine

Astatine is the rarest naturally occurring element on Earth, a radioactive halogen so unstable that it exists only fleetingly, as a short-lived step in the decay chains of heavier radioactive elements like uranium and thorium. It's so scarce and so quick to decay that scientists have never gathered a visible sample of it — everything known about astatine comes from studying vanishingly small, artificially produced quantities.

Group · Period: 17 · 6
At room temp: solid
Melts at: 575 K
Density: 7 g/cm³
Discovered: 1940

Uses

Astatine has essentially no established industrial or commercial applications — it’s simply too rare and too short-lived to produce, store, or use at any meaningful scale. Its main relevance today is in scientific research, particularly in nuclear chemistry, where studying its behavior helps scientists better understand the broader halogen group and radioactive decay processes. The most promising area of active research is medical: astatine-211 is being investigated as a component of targeted alpha therapy, an experimental approach to cancer treatment where a radioactive atom is attached to a molecule designed to seek out and bind to cancer cells, delivering radiation precisely to the tumor while limiting damage to healthy tissue. This remains a research-stage technique, not a standard treatment available to patients.

History

Astatine was produced and identified in 1940 by Dale Corson, Kenneth MacKenzie, and Emilio Segrè at the University of California, Berkeley, who created it by bombarding bismuth with alpha particles in a particle accelerator. It was one of the last naturally occurring elements to be identified, and confirming its existence took a different approach than most earlier element discoveries, since natural astatine is present in such vanishingly small and short-lived amounts that no one could have isolated it directly. The name astatine, from the Greek word for “unstable,” reflects both how the element was found and its defining property.

Fun facts

At any given moment, scientists estimate only a few grams of astatine exist naturally across the entire Earth's crust, making it the rarest naturally occurring element.
Astatine's name comes from the Greek word astatos, meaning 'unstable' — a fitting name, since its longest-lived isotope has a half-life of only about eight hours.
No one has ever seen a visible piece of pure astatine, because any sample large enough to see would generate enough radioactive heat and decay to destroy itself almost instantly.

Frequently asked questions

Why is astatine so much rarer than other radioactive elements like radium?

Astatine only forms briefly as one step in the decay chains of heavier elements, and its own isotopes decay away extremely fast — the most stable known isotope lasts only hours. Because it's constantly forming and disappearing at such a tiny, fleeting scale, the total amount present in the Earth's crust at any one time is estimated at just a few grams worldwide.

Does astatine have any real-world use?

Not yet in routine medical practice, but it's an active area of research. One isotope, astatine-211, is being studied as a way to deliver targeted radiation directly to cancer cells in a technique called targeted alpha therapy, since it emits a strong, short-range form of radiation. This remains experimental and is not yet an established treatment.

How do scientists study an element this rare and short-lived?

Astatine used for research is made artificially, typically by bombarding a target material with charged particles in a particle accelerator, producing tiny numbers of atoms at a time. Scientists then have to study its chemistry very quickly, often using specialized techniques designed for working with minuscule, fast-decaying quantities of material.

Isotopes

39 known isotopes

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Isotope	Natural abundance	Half-life	Decay mode	Mass excess	Binding energy / nucleon	Decay width
At-209	—	5.42 h	Electron capture / beta-plus decay (95.9%), Alpha decay (4.1%)	-12,883.77 keV	7,814.78 keV	2.34 × 10-20 eV
At-210	—	8.1 h	Electron capture / beta-plus decay (99.825%), Alpha decay (0.175%)	-11,972.1 keV	7,811.66 keV	1.56 × 10-20 eV
At-211	—	7.214 h	Electron capture (58.2%), Alpha decay (41.8%)	-11,647.19 keV	7,811.35 keV	1.76 × 10-20 eV

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At-191	—	1.7 ms	Alpha decay (100%)	3,863.91 keV	7,702.92 keV	2.68 × 10-13 eV
At-192	—	88 ms	Alpha decay (100%)	2,925.74 keV	7,709.73 keV	5.18 × 10-15 eV
At-193	—	28 ms	Alpha decay (100%)	-67.32 keV	7,727.11 keV	1.63 × 10-14 eV
At-194	—	286 ms	Alpha decay (100%), SF+EC+B+ (0.8%), Electron capture / beta-plus decay	-716.49 keV	7,732.23 keV	1.60 × 10-15 eV
At-195	—	290 ms	Alpha decay (100%)	-3,470.3 keV	7,748.09 keV	1.57 × 10-15 eV
At-196	—	0.388 s	Alpha decay (95.1%), Electron capture / beta-plus decay (4.9%)	-3,913.18 keV	7,752 keV	1.18 × 10-15 eV
At-197	—	0.388 s	Alpha decay (96.1%), Electron capture / beta-plus decay (3.9%)	-6,355.26 keV	7,766.02 keV	1.18 × 10-15 eV
At-198	—	4.2 s	Alpha decay (90%), Electron capture / beta-plus decay (10%)	-6,708.75 keV	7,769.34 keV	1.09 × 10-16 eV
At-199	—	7.03 s	Alpha decay (90%), Electron capture / beta-plus decay (10%)	-8,823.38 keV	7,781.49 keV	6.49 × 10-17 eV
At-200	—	43 s	Alpha decay (52%), Electron capture / beta-plus decay (48%)	-8,987.89 keV	7,783.76 keV	1.06 × 10-17 eV
At-201	—	87.6 s	Alpha decay (71%), Electron capture / beta-plus decay (29%)	-10,789.44 keV	7,794.15 keV	5.21 × 10-18 eV
At-202	—	184 s	Electron capture / beta-plus decay (63%), Alpha decay (37%)	-10,595.11 keV	7,794.56 keV	2.48 × 10-18 eV
At-203	—	7.4 m	Electron capture / beta-plus decay (69%), Alpha decay (31%)	-12,162.61 keV	7,803.65 keV	1.03 × 10-18 eV
At-204	—	9.12 m	Electron capture / beta-plus decay (96.09%), Alpha decay (3.91%)	-11,875.25 keV	7,803.55 keV	8.34 × 10-19 eV
At-205	—	26.9 m	Electron capture / beta-plus decay (90%), Alpha decay (10%)	-12,984.52 keV	7,810.27 keV	2.83 × 10-19 eV
At-206	—	30.6 m	Electron capture / beta-plus decay (99.1%), Alpha decay (0.9%)	-12,439.39 keV	7,808.89 keV	2.48 × 10-19 eV
At-207	—	1.81 h	Electron capture / beta-plus decay (91.4%), Alpha decay (8.6%)	-13,227.48 keV	7,813.97 keV	7.00 × 10-20 eV
At-208	—	1.63 h	Electron capture / beta-plus decay (99.45%), Alpha decay (0.55%)	-12,469.9 keV	7,811.56 keV	7.78 × 10-20 eV
At-212	—	0.314 s	Alpha decay (100%)	-8,628.15 keV	7,798.34 keV	1.45 × 10-15 eV
At-213	—	125 ns	Alpha decay (100%)	-6,579.52 keV	7,790 keV	3.65 × 10-9 eV
At-214	—	558 ns	Alpha decay (100%)	-3,379.15 keV	7,776.36 keV	8.18 × 10-10 eV
At-215	—	0.10 ms	Alpha decay (100%)	-1,256.58 keV	7,767.86 keV	4.56 × 10-12 eV
At-216	—	0.30 ms	Alpha decay (100%), Beta-minus decay (0.006%), Electron capture (3e-7%)	2,256.68 keV	7,753 keV	1.52 × 10-12 eV
At-217	—	32.6 ms	Alpha decay (99.993%), Beta-minus decay (0.007%)	4,394.6 keV	7,744.62 keV	1.40 × 10-14 eV
At-218	—	1.28 s	Alpha decay (99.95%), Beta-minus decay (0.05%)	8,100.22 keV	7,729.12 keV	3.56 × 10-16 eV
At-219	—	56 s	Alpha decay (93.6%), Beta-minus decay (6.4%)	10,396.02 keV	7,720.2 keV	8.15 × 10-18 eV
At-220	—	3.71 m	Beta-minus decay (92%), Alpha decay (8%)	14,375.75 keV	7,703.7 keV	2.05 × 10-18 eV
At-221	—	2.3 m	Beta-minus decay (100%)	16,782.73 keV	7,694.48 keV	3.31 × 10-18 eV
At-222	—	54 s	Beta-minus decay (100%)	20,953.03 keV	7,677.39 keV	8.45 × 10-18 eV
At-223	—	50 s	Beta-minus decay (100%)	23,428.01 keV	7,668.06 keV	9.12 × 10-18 eV
At-224	—	1.3 m	Beta-minus decay	27,711.02 keV	7,650.74 keV	5.85 × 10-18 eV
At-225	—	300 ns	Beta-minus decay	30,300 keV	7,641 keV	1.52 × 10-9 eV
At-226	—	300 ns	Beta-minus decay	34,660 keV	7,624 keV	1.52 × 10-9 eV
At-227	—	300 ns	Beta-minus decay, Beta-minus, neutron emission	37,430 keV	7,613 keV	1.52 × 10-9 eV
At-228	—	300 ns	Beta-minus decay	41,880 keV	7,596 keV	1.52 × 10-9 eV
At-229	—	300 ns	Beta-minus, neutron emission, Beta-minus decay	44,890 keV	7,585 keV	1.52 × 10-9 eV