Astatine

Astatine is a rare and highly radioactive element belonging to the halogen group in the periodic table, with the symbol At and atomic number 85. It is positioned below iodine in Group 17, sharing several chemical properties with the other halogens, yet differing significantly due to its radioactivity and scarcity. Owing to its extreme rarity in nature—estimated to exist in less than a gram in the Earth’s crust at any time—astatine remains one of the least studied naturally occurring elements. Despite these limitations, it holds scientific and potential practical interest, particularly in the fields of nuclear medicine and radiochemistry.

Discovery and Occurrence

Astatine was first synthesised in 1940 by Dale R. Corson, Kenneth Ross MacKenzie, and Emilio G. Segrè at the University of California, Berkeley. Its name derives from the Greek word astatos, meaning “unstable,” an apt description of its radioactive nature. Although earlier attempts had claimed its discovery under different names, the Berkeley team’s synthesis of astatine-211 through the bombardment of bismuth with alpha particles marked the first confirmed creation of the element.
In nature, astatine occurs only as a decay product in the radioactive decay chains of heavier elements such as uranium and thorium. Due to its short half-life—ranging from 125 nanoseconds to 8.1 hours, depending on the isotope—natural astatine exists only momentarily before transforming into other elements. The most stable isotope, astatine-210, has a half-life of about 8.1 hours, which makes laboratory study highly challenging.

Physical and Chemical Properties

Astatine’s physical characteristics are difficult to measure directly because of its radioactivity and scarcity. It is presumed to be a solid at room temperature, possibly exhibiting a metallic or semi-metallic lustre, and is thought to have a density higher than iodine. The element is less volatile than iodine and may display metallic conduction properties.
Chemically, astatine behaves similarly to other halogens, capable of forming compounds with hydrogen (hydrogen astatide, HAt) and metals (metal astatides such as sodium astatide, NaAt). However, its reactivity is somewhat less pronounced than that of iodine. Its compounds often display a mixed halogen–metallic character, bridging the chemistry of halogens and metals.

Medical and Everyday Research Applications

Although astatine has no direct everyday applications due to its extreme radioactivity and scarcity, it has significant potential in medical research, especially in the treatment of cancer. The isotope astatine-211 is particularly valuable for targeted alpha-particle therapy (TAT), a form of radiotherapy aimed at destroying malignant cells with minimal damage to surrounding tissues.
Key medical uses and research areas include:

• Targeted alpha therapy: Astatine-211 emits alpha particles that have high linear energy transfer (LET), causing localised destruction of cancer cells.
• Radiopharmaceuticals: It is used in experimental radiolabelled compounds that can target specific types of tumours or metastases.
• Diagnostic imaging: While less common, astatine-labelled compounds are also being investigated for use in imaging certain biological processes.

The element’s short half-life makes it ideal for clinical use, as it minimises prolonged radiation exposure to patients. However, its limited availability and the difficulty of handling it safely restrict its widespread adoption.

Industrial and Economic Context

From an industrial and economic perspective, astatine has no significant role in large-scale production or commercial applications. The cost of producing astatine is exceptionally high due to the complexity of its synthesis. It is produced artificially in particle accelerators, typically by bombarding bismuth-209 with alpha particles, which yields small quantities of astatine-211.
Economic aspects of astatine can be summarised as follows:

• Production Cost: The synthesis process is expensive and energy-intensive, involving advanced nuclear facilities.
• Limited Market: Because of its short half-life, astatine cannot be stored or transported easily; it must be used almost immediately after production.
• Scientific Value: Its economic significance lies primarily in research grants and specialised medical applications, rather than in industrial or consumer markets.

In practical terms, the market for astatine is confined to a handful of nuclear research laboratories and medical institutions specialising in radiopharmaceutical research.

Environmental and Safety Considerations

Astatine’s radioactivity poses considerable safety challenges. Although quantities used in laboratories are minute, handling requires strict radiation safety protocols, including the use of remote manipulation tools, shielded enclosures, and controlled ventilation systems. The isotopes of astatine decay into other radioactive elements, which can contribute to short-lived but intense localised radiation hazards.
From an environmental standpoint, astatine’s natural occurrence is negligible; hence, it poses no significant ecological risk. Nonetheless, artificial production necessitates the management of radioactive waste, demanding adherence to international radiation safety standards.

Scientific Importance and Future Prospects

Despite its limited practical use, astatine holds scientific importance as a transitional element bridging non-metals and metals within the halogen group. Its unique combination of halogen-like chemistry and metallic properties provides valuable insight into trends in the periodic table.
Future research directions include:

• Enhanced radiotherapy methods, particularly the use of astatine-211 in precision oncology.
• Theoretical chemistry and quantum modelling, to better predict astatine’s behaviour and interactions.
• Development of more efficient synthesis and isolation techniques, to increase availability for medical research.

With ongoing advances in nuclear chemistry and radiopharmaceutical technology, astatine may gain a stronger role in next-generation cancer therapies. Its economic viability, however, will remain limited by its production complexity and short-lived isotopes.