Promethium is one of the rarest elements on Earth and belongs to the group of lanthanides, also known as rare earth elements. With the atomic number 61, it occupies a unique position on the periodic table as the only lanthanide that is radioactive but has no stable isotopes. Because it is both rare and unstable, naturally occurring promethium is nearly nonexistent. As a result, scientists must produce promethium through nuclear reactions in specialized facilities. The process of making promethium involves nuclear reactors, isotope separation, and careful handling due to its radioactive nature.
What Is Promethium?
Promethium (symbol Pm) is a chemical element discovered in the mid-20th century. Although traces of it were suspected earlier, it was officially identified and isolated in 1945. It is a soft, silvery metal that glows faintly in the dark due to its radioactivity. Promethium has several isotopes, but the most common and useful one is promethium-147. This isotope has a half-life of about 2.6 years and is used in certain types of batteries and luminous devices.
Characteristics of Promethium
- Atomic number: 61
- Symbol: Pm
- Group: Lanthanides (rare earth metals)
- Radioactive: Yes, no stable isotopes
- Uses: Atomic batteries, glow-in-the-dark materials, scientific research
Why Promethium Must Be Made
Unlike many other elements, promethium is not found in significant quantities in nature. It is occasionally produced through the natural decay of uranium or other elements, but these amounts are incredibly small. Therefore, in order to obtain usable quantities of promethium, it must be manufactured in a laboratory or reactor environment using nuclear technology.
Naturally Occurring Promethium
Though it can technically be found in uranium ores and during the decay of europium-151, the quantities are too small to be mined or collected. For practical and industrial purposes, promethium must be synthesized.
How Is Promethium Made?
The most common method for making promethium involves the irradiation of neodymium or uranium in nuclear reactors. These processes are complex and require strict control of conditions, shielding, and waste management due to the radiation involved.
Method 1: Neutron Irradiation of Neodymium-146
This is one of the primary methods used to produce promethium-147. The process includes the following steps:
- Neutron capture: Neodymium-146 is exposed to a neutron source, typically inside a nuclear reactor.
- Formation of Neodymium-147: The neutron is absorbed, forming neodymium-147.
- Beta decay: Neodymium-147 undergoes beta decay to produce promethium-147.
This reaction occurs as follows:
Nd-146 + n → Nd-147 → Pm-147 + β⁻
The resulting promethium-147 is then chemically separated from the other materials using solvent extraction or ion-exchange chromatography.
Method 2: Uranium Fission Products
Another major source of promethium is as a byproduct of uranium fission in nuclear reactors. When uranium-235 undergoes fission, it produces a variety of isotopes, including promethium-147 among the hundreds of fission fragments.
The steps include:
- Uranium fission: Uranium-235 is bombarded with neutrons and splits into smaller atoms, including promethium isotopes.
- Fuel reprocessing: The spent nuclear fuel is chemically treated to extract useful isotopes.
- Promethium separation: Promethium is separated from the other fission products through advanced chemical processing.
This method yields small but usable quantities of promethium-147 for commercial or research purposes.
Handling and Safety Considerations
Because promethium is radioactive, it must be handled with extreme care. Facilities that produce or use promethium are equipped with shielding, radiation monitoring, and specialized equipment to prevent exposure. Promethium-147 primarily emits beta ptopics, which are less penetrating than gamma rays but still require protection.
Storage and Transportation
- Stored in sealed containers, often shielded with metal
- Monitored for radiation leakage
- Transported in accordance with strict nuclear regulatory standards
Health and Environmental Concerns
If promethium is ingested or inhaled, it can pose health risks, particularly to bone marrow where radioactive ptopics may accumulate. Proper disposal of promethium waste is also essential to avoid contamination of the environment.
Uses of Promethium
Despite its scarcity and the complexity of its production, promethium has some valuable applications:
- Atomic batteries: Promethium-147 is used in betavoltaic batteries, which convert beta radiation into electrical energy. These are used in pacemakers and space probes where long-term power is needed without replacement.
- Luminous paints: It is used in glow-in-the-dark materials for dials, instruments, and signage, especially in military or aerospace contexts.
- Scientific research: Promethium is used in experiments involving radioactive decay and atomic behavior.
Although these applications are limited, they demonstrate the unique niche promethium fills due to its radioactivity and electrical properties.
Availability and Production Scale
Promethium is not produced on a large scale. Only specialized laboratories and nuclear facilities are authorized and equipped to manufacture and handle it. Global production is measured in grams rather than kilograms, which underscores how rare and controlled its use is.
Countries Producing Promethium
- United States (via Oak Ridge National Laboratory and other nuclear facilities)
- Russia
- Some European Union countries with advanced nuclear programs
Because of its limited use and radioactive nature, promethium is not commercially available to the general public. It is distributed under controlled conditions to specific industries and research institutions.
Promethium is a fascinating yet elusive element that cannot be easily sourced from nature. It is primarily made through nuclear reactions involving either neodymium irradiation or uranium fission. Once produced, promethium must be carefully extracted, purified, and handled due to its radioactive properties. Although its uses are specialized, it plays a critical role in applications requiring long-lasting, compact energy sources and luminous materials. The production of promethium highlights the intersection of nuclear science, chemistry, and technological innovation in creating elements that do not naturally exist in useful quantities on Earth.