Radium (Ra, atomic number 88) and Polonium (Po, atomic number 84) are significant radioactive elements discovered in the late 19th century. Their utility in both historical and modern applications stems from their unstable nature, which causes them to continuously emit ionizing radiation. These unique emissions allow them to be used for targeted cancer treatment and eliminating static electricity in industrial settings. The distinct physical properties of each element determine its specific function in science and commerce.
Radium’s Historical and Therapeutic Applications
Radium’s discovery quickly led to its widespread adoption, especially for its luminescent properties. The isotope Radium-226 was mixed with zinc sulfide to create a self-luminous paint for watch dials, clock faces, and aircraft gauges, allowing them to glow in the dark without an external light source. This historical use resulted in severe health consequences for the workers due to the ingestion and accumulation of radium in their bones.
The element was also historically incorporated into various consumer products and so-called “health tonics” based on the mistaken belief that its radiation offered curative properties. Early medical applications, often termed “Curie therapy,” involved placing radium sources directly near or inside tumors, marking the beginning of internal radiation therapy for cancer. This technique was initially very crude, leading to unpredictable and often hazardous results.
Modern medicine has largely replaced the use of long-lived Radium-226 sources with safer, shorter-lived radioisotopes like Cobalt-60 or Iridium-192. However, a specific isotope, Radium-223 dichloride (Xofigo), represents a precise therapeutic application today. This drug is used to treat prostate cancer that has metastasized to the bone.
Radium-223 is an alpha-emitting isotope that chemically mimics calcium, allowing it to target areas of high bone turnover, such as bone metastases. Once delivered, the alpha particles precisely damage the tumor cells while minimizing harm to surrounding healthy tissues. This systemic internal radiation approach is a controlled evolution of radium’s initial therapeutic potential.
Polonium’s Specialized Industrial and Scientific Functions
Polonium, primarily the isotope Polonium-210, is used for applications that require a steady, intense source of alpha particles. The most common industrial use is in static eliminators, which are essential devices in manufacturing processes where static electricity is problematic. These eliminators are used in settings such as textile mills, paper production, and film processing to prevent materials from sticking together or attracting dust.
The Polonium-210 source releases alpha particles that ionize the surrounding air, creating a conductive path for the static charge to neutralize. The isotope is typically encased in a foil or ceramic matrix to prevent its ingestion, as alpha particles cannot penetrate the protective cage or even human skin. However, the short half-life of Polonium-210 (about 138 days) means that these static eliminator devices must be replaced periodically.
In scientific and nuclear contexts, Polonium-210 serves as a lightweight and compact heat source. A single gram of Polonium-210 generates approximately 140 watts of thermal power due to its rapid decay. This intense, predictable heat has been used in radioisotope thermoelectric generators (RTGs) to power satellites and space probes.
Polonium-210 is also combined with light elements, most often beryllium, to create neutron sources. The alpha particles from the polonium bombard the beryllium, knocking neutrons out of its nucleus in a reaction known as an alpha-neutron reaction. These compact neutron sources are utilized for research, instrument calibration, and historically, as initiators in nuclear weapons.
Understanding the Radioactive Properties That Make Them Useful
The utility of Radium and Polonium is rooted in the distinct types of radiation they emit upon decay.
Radium’s Mixed Emissions
Radium-226 and its decay products emit a mix of alpha, beta, and gamma radiation. Gamma rays are highly penetrating, similar to high-energy X-rays. This penetrating energy was historically valued for its ability to reach deep-seated tumors in brachytherapy.
The Power of Alpha Particles
Modern therapeutic uses of Radium, such as Radium-223, exploit the destructive, yet highly localized, nature of alpha particles. Alpha particles are relatively large and heavy, causing intense damage. They travel only a few cell diameters (less than 0.1 millimeter) before losing all their energy. This allows for precise, high-dose radiation delivery directly to targeted cells.
Polonium-210 is an almost pure alpha emitter, which defines its application in static elimination. The alpha particles efficiently ionize air molecules over a short distance, creating the necessary charged particles to dissipate static buildup. Since the alpha particles cannot escape the device’s casing or travel far from the source, the external radiation hazard during normal use is minimal.