Radium (Ra) and Polonium (Po) are highly radioactive elements found in the natural decay chain of uranium. Although chemically and physically distinct—Radium (atomic number 88) is an alkaline earth metal, and Polonium (atomic number 84) is a metalloid—their shared discovery linked them historically. Understanding their different properties is important for grasping the differences in their hazards and historical uses. This article explores the unique characteristics of Radium and Polonium, their contrasting applications, and the distinct ways they present dangers to human health.
The Shared History of Discovery
The connection between Radium and Polonium lies in their co-discovery from the same ore material. In 1898, Marie and Pierre Curie focused on pitchblende, a uranium-rich mineral whose radioactivity exceeded what its uranium content suggested. Marie Curie hypothesized the ore contained unknown, highly radioactive elements.
The Curies chemically separated the components of pitchblende residue, leading to the isolation of two new radioactive fractions. They first announced Polonium in July 1898, named after Marie’s native Poland, which chemically resembled bismuth. Five months later, they announced Radium, named from the Latin word for ray, which behaved chemically like barium.
The elements posed different challenges due to their half-lives. Radium-226 has a long half-life of approximately 1,600 years, allowing it to be isolated in macroscopic quantities. Polonium-210, however, has a short half-life of only about 138 days, meaning it decays rapidly, which made isolating Polonium in bulk difficult.
Radium: Characteristics and Applications
Radium is a silvery-white alkaline earth metal, chemically similar to calcium and barium. When Radium enters the body, it is treated like calcium and preferentially accumulates in the bones, making it a “bone-seeker.” This accumulation, combined with its long half-life, creates a chronic internal hazard.
Radium’s intense radioactivity causes its salts to exhibit a faint blue-green glow known as radioluminescence. This unique light led to its widespread use in the early 20th century in self-luminous paints for watch dials and aircraft instruments. The tragic health consequences for the workers who painted these dials, known as the “Radium Girls,” highlighted the element’s severe toxicity.
Historically, Radium was also employed in medicine for early cancer treatment, known as brachytherapy. Radium-226 decays into the gaseous element Radon-222. The continuous production of this radioactive gas is an environmental concern, as Radon can accumulate in enclosed spaces like basements, presenting a long-term health risk.
Polonium: Characteristics and Unique Dangers
Polonium is a rare metalloid found near the dividing line between metals and nonmetals. Its most significant isotope, Polonium-210, has a half-life of just 138 days, making it scarce and highly volatile. This rapid decay rate translates into a high power density, causing Polonium-210 samples to generate significant heat and sometimes glow blue due to air ionization.
This high power density allows for specialized applications, such as a lightweight heat source for thermoelectric generators in space probes. Polonium is also used in anti-static brushes, where its radiation neutralizes static electricity.
The danger of Polonium is unique because it is an almost pure alpha-particle emitter. Polonium-210 is considered one of the most radiotoxic substances known. This extreme hazard is realized only if the element enters the body through inhalation or ingestion. Once absorbed, it concentrates in soft tissues, including the liver, kidneys, and spleen, where its intense internal alpha radiation quickly destroys cellular structures.
Comparing Radiation Profiles and Health Risks
The health hazards posed by Radium and Polonium differ fundamentally due to the types of radiation they emit and their behavior inside the human body. Radium-226 emits alpha, beta, and gamma radiation, making it a multi-faceted external and internal threat. Radium’s gamma rays are highly penetrating and can damage tissues even from a distance, requiring dense shielding.
When ingested, Radium is incorporated directly into the bone structure due to its chemical similarity to calcium. Its long half-life ensures chronic exposure to the surrounding bone marrow and cells, which is the mechanism behind the bone cancers seen historically. Radium’s decay chain also continually produces Radon gas, which can irradiate the lungs and other soft tissues.
Polonium-210 is primarily a pure alpha-particle emitter. Its radiation is non-penetrating externally, making sealed sources safe to handle, but dramatically dangerous if internalized. Once inside, the high-energy alpha particles have a very short range, depositing all their destructive energy in a small, localized area. This results in massive cellular damage to the soft organs where Polonium concentrates, leading to rapid organ failure following acute exposure.