What Is Radium?

Radium is a naturally occurring radioactive element with atomic number 88 and chemical symbol Ra, belonging to the alkaline earth metal group of the periodic table. It is produced in nature through the decay chain of uranium-238 and is found in trace quantities in uranium ores such as pitchblende. All 33 known isotopes of radium are radioactive, with radium-226 being the most stable, carrying a half-life of approximately 1,600 years. Its discovery marked a foundational moment in the history of nuclear science and established the modern understanding of radioactivity as an atomic, rather than chemical, phenomenon.

Radium was isolated in 1898 by Marie and Pierre Curie through the painstaking processing of several tonnes of pitchblende ore. The Nobel Prize committee recognized this work with the Physics Prize in 1903 and a second Nobel Prize in Chemistry in 1911, awarded to Marie Curie alone for isolating pure radium metal. Marie Curie also coined the term "radioactivity" during this period, and the unit of radioactivity, the curie (Ci), was subsequently named in honor of the Curies and defined as the activity produced by one gram of radium-226.

Physical and Chemical Properties

Radium is a silvery-white metal that tarnishes rapidly on exposure to air, forming a black surface oxide. Its chemical behavior closely resembles that of calcium and barium, both neighboring alkaline earth metals, and this similarity means the body treats ingested radium as it does calcium, concentrating it preferentially in bone tissue. Radium-226 emits alpha particles, gamma rays, and beta radiation as it decays, and its immediate decay product is radon-222, a radioactive gas that itself poses health risks. Radium salts are luminescent, producing a faint blue-green glow from the continuous ionization of surrounding air molecules.

Radioactive Decay and Radiation Emission

The decay of radium-226 initiates a chain of successive daughter nuclides before terminating at stable lead-206. This chain passes through radon-222, polonium-218, bismuth-214, and several other isotopes, each contributing its own radiation signature. The alpha particles emitted by radium and its progeny have energies in the 4 to 7 MeV range, enough to cause direct ionization damage to biological tissue at close range. The EPA's radiation protection guidelines address exposure to radium and its progeny as part of broader natural background radiation management, given that radium occurs in soils and groundwater globally.

Medical and Scientific Applications

Early twentieth-century medicine used radium as a radiation source for cancer treatment, inserting radium needles directly into tumors in a technique called brachytherapy. While radium has largely been replaced by safer artificial isotopes such as iridium-192 in modern brachytherapy, a specific isotope, radium-223 (marketed as Xofigo), remains a clinically approved targeted alpha therapy for bone metastases from prostate cancer. According to research published in PMC on radium's enduring medical legacy, radium-223 selectively accumulates in bone lesions and delivers highly localized cytotoxic alpha doses while minimizing damage to surrounding healthy tissue. In the laboratory, the curie unit and the broader framework of radioisotope chemistry that radium's study established remain foundational to nuclear science and radiation protection worldwide.

Applications

Radium has applications in a range of scientific and technical domains, including:

• Targeted alpha therapy for bone-seeking cancers, particularly prostate cancer metastases
• Historical brachytherapy, where radium needles were used for localized tumor irradiation
• Calibration and reference standards in early nuclear physics instrumentation
• Geological dating, through the uranium-radium decay series used to age ancient rocks and minerals
• Neutron source production, when mixed with beryllium to create portable neutron generators for industrial radiography