Buzz
(Homeland) - This particular element is so rare that scientists still lack fundamental information about it, such as its visual appearance.
As of now, humans have documented a total of 118 elements in the periodic table of chemistry. Interestingly, not everyone has the opportunity to encounter all these mentioned elements. Instead, the likelihood of someone coming into contact with a mere 5 elements is nine times higher than the remaining 113 elements.
The reason is quite simple: Among the dozens of elements found in the Earth's crust, five elements including oxygen, silicon, aluminum, iron, and calcium constitute over 92%. In fact, nearly half of the atoms we encounter daily are oxygen, making it the most prevalent element on the planet.
On the flip side, humans have also acknowledged the existence of astatine - considered the rarest natural element on Earth at present. According to estimates, there are only about 25 grams of astatine across the entire surface of the Earth. This rare element is so precious that scientists still lack basic information about it, such as its visual appearance.
Astatine is named after the Greek word meaning 'unstable'. This name is considered the most accurate description of the element's characteristics. It exhibits extremely high radioactivity, with a half-life of just over eight hours even in its most stable form, known as astatine-210. This means that even if you are fortunate enough to find a certain amount of astatine, you will only retain about 1/8 of that amount after approximately 24 hours. The rest will decay into bismuth-206 or polonium-210.
With its unstable isotope form, astatine undergoes a decay cycle of a second or less. In elemental form, it's even more prone to vaporize: its radioactivity is so high that, if visible to the naked eye, it would literally evaporate under its own heat.
While scientists can handle this element directly, they can only do so artificially, usually through nuclear reactions – often by bombarding bismuth-209 with alpha particles.
Therefore, most of what we know about this element comes from theory rather than practical experiments. For instance, scientists speculate that astatine might resemble a black solid, as it belongs to the halogen group on the periodic table. Halogens get darker as they get heavier: fluorine is basically colorless, chlorine is yellow-green, bromine is reddish-brown, and iodine is dark gray-purple. So, logically, this element should be even darker.
However, this speculation also leads to much debate about astatine, such as whether it is a metal or a halogen. This is considered a divisive question for chemists, as astatine also lies diagonally along a row in the periodic table containing metalloids like boron and silicon. In chemical reactions, it sometimes behaves like a halogen, while at other times, it acts like a metal, making even seasoned chemists struggle to classify.
Although rare to the point of almost nonexistence – and puzzling to the extent that we essentially know nothing for sure about it – astatine turns out to have some potentially significant real-world applications. When this element decays, it emits alpha particles, i.e., radiation particles formed from the combination of two protons and two neutrons. For various reasons, they are actually effective in targeting cancer cells in radiation therapy treatments.
'Astatine is the Goldilocks of alpha emitters,' Mehran Makvandi, a radiology specialist at the University of Pennsylvania Medical School (USA), comments on astatine.
Goldilocks here is a concept named after a character in the children's story 'The Three Bears.' When tasting three different bowls of porridge, Goldilocks prefers it not too hot or too cold, but just the right temperature.
In simple terms, astatine here possesses a 'power' that is just sufficient. It emits fewer α particles than other isotopes like actinium-225. This makes astatine less potent, but in return, it has an advantage in terms of radiation amount.
Astatine has an extremely short half-life, meaning it won't exist for a long time. Importantly, it only emits α particles – the least harmful type among various radiation types.
If scientists can attach astatine isotopes to target molecules in cancer cells, they could create a cancer treatment method that can penetrate through the cancer cell's DNA, leaving the surrounding tissues relatively normal. Thus, no other potential cancer treatment method can achieve a similar targeted effectiveness if astatine is used, according to expert Makvandi.
Of course, this method still has many barriers to overcome. Firstly, researchers need the opportunity to directly study astatine. This is considered a challenging task as astatine is very rare and unstable.
This might be the reason why this element is officially listed as having no biological or functional role other than serving research purposes.
From a different perspective, the lack of comprehensive understanding about astatine in humans could be considered a positive aspect. After all, if we truly knew its significance, perhaps we would need more than 25 grams of astatine currently existing on Earth.
Reference: IFL Science
