The concept diagram illustrates the rare earth element promethium surrounded by organic ligands. Scientists at Oak Ridge National Laboratory (ORNL) have uncovered hidden properties of promethium, paving the way for research on other lanthanide elements. Image Source: Oak Ridge National Laboratory
BEIJING, May 24th (Xinhua) - According to a report in the journal Nature on the 22nd, scientists at the Oak Ridge National Laboratory (ORNL) in the United States have revealed a property of promethium for the first time. This rare earth element was also discovered by scientists at the laboratory about 80 years ago. Despite promethium being used in medical research and long-lasting nuclear batteries, some of its characteristics remain elusive. The latest discovery marks a significant advancement in rare earth research and may rewrite chemistry textbooks, opening up new pathways for exploring key elements in modern technology.
The ORNL research team prepared a chemical complex of promethium and characterized it in solution for the first time. Through a series of detailed experiments, they unveiled the secrets of this extremely rare lanthanide element with an atomic number of 61.
Researchers explained that most of the rare earth elements belong to the lanthanide series, consisting of 15 elements from lanthanum, the 57th element on the periodic table, to lutetium, the 71st element. Promethium is exceptionally rare, with only about a pound naturally occurring in the Earth's crust if one were to search every corner of the globe. Unlike other rare earth elements, promethium lacks stable isotopes. It is the last lanthanide element to be discovered and the most challenging to study.
The research team combined radioactive promethium with a special organic ligand molecule called diglycolamide and then used X-ray spectroscopy to determine the properties of the resulting complex, including the chemical bond lengths with neighboring atoms like plutonium.
In the experiment, the team produced the isotope promethium-147 with a half-life of 2.62 years. With sufficient quantity and high purity, it can be used to study its chemical properties.
Using research reactors, hot cells, and supercomputers, the team demonstrated for the first time the contraction of the entire lanthanide series (including promethium) in solution. Lanthanide contraction refers to the phenomenon where the atomic radius of lanthanide elements gradually decreases as the atomic number increases. Due to the same charge being confined in a smaller space, unique chemical and electronic properties are produced. The team obtained a clear signal from promethium, allowing them to better determine the trend shape of the entire series.
They found that this contraction accelerates along the atomic sequence but slows down significantly after promethium. This is an important milestone in understanding the chemical bonding properties of chemical elements and their structural changes across the periodic table.
Lanthanide and actinide elements have wide applications in cancer diagnosis and treatment, renewable energy technologies, and nuclear batteries for deep space exploration.
