Radium Chloride
Properties
| State | Solid |
| Color | White to pale yellow (darkens with self-radiolysis) |
| Solubility | Soluble in water; slightly soluble in concentrated HCl |
| Melting Point | 900 °C (approximate) |
| Boiling Point | 1500 °C (approximate) |
About Radium Chloride
Radium chloride is a white-to-pale-yellow crystalline salt (RaCl2, 296.9 g/mol) and the first radium compound ever isolated in pure form. Marie and Pierre Curie spent four years processing several tons of pitchblende residue from the Jachymov mine in a leaky shed on the rue Lhomond in Paris, exploiting the slightly lower solubility of RaCl2 versus BaCl2 through thousands of sequential fractional crystallizations to get to about 0.1 g of pure material, announced in 1902. That isolation established radium as a new element and earned Marie Curie her second Nobel Prize, in Chemistry, in 1911. RaCl2 is isomorphous with BaCl2 in the PbCl2-type orthorhombic structure, which fits the periodic-table expectation for the heaviest stable Group 2 metal. Through the early 20th century RaCl2 became the standard commercial radium form for radium-dial paint, intracavitary brachytherapy needles, and laboratory research, with prices peaking near $100,000 per gram in 1920s dollars. Radium therapy was a frontline cancer treatment from roughly 1910 until the 1950s, when cobalt-60 and cesium-137 sources displaced it. The well-documented health collapse of dial painters and early radium therapists is what gave us the first quantitative dose-response data for internal alpha emitters and is the reason modern radiation-protection limits exist at all.
Where you'll encounter it
If you've ever toured the Curie Museum in Paris or the Marie Curie laboratory at the Institut du Radium, the notebooks, doorknobs, and lab benches are still measurably radioactive a century later — Marie Curie's lab notebooks live in lead-lined boxes at the Bibliotheque Nationale and require protective gear to consult. The same chemistry that lets the Curies separate RaCl2 from BaCl2 by fractional recrystallization runs in reverse in environmental remediation today: contaminated groundwater near uranium mining sites is treated by co-precipitating Ra2+ with BaSO4. In modern oncology the brachytherapy lineage that started with RaCl2 needles continues with Ir-192 and I-125 seeds, and the dose calculations for prostate brachytherapy still cite Curie-era radium dosimetry as the historical baseline. NIST in Gaithersburg still maintains a small RaCl2 reference standard sealed in a quartz ampoule for calibrating gamma spectrometers.
Common Uses
- Historical feedstock for radium-needle brachytherapy and skin cancer treatment
- Historical dopant for ZnS:Cu radioluminescent dial paint
- Historical neutron source when mixed with Be powder (~15 n/s per mg Ra)
- Reference material for early actinide and heavy alkaline-earth chemistry
- Starting material for Ra-226/Rn-222 generator research
Safety Information
EXTREMELY RADIOTOXIC. Ra-226 emits alpha particles and decays through a chain that includes gaseous Rn-222 — the same radon that contaminates uranium-mining-region basements and is a major lung-cancer risk class. Stored RaCl2 accumulates Rn-222 inside the container over a few weeks, and opening an aged ampoule releases a radon bolus that must be captured by lab exhaust. Ra2+ substitutes chemically for Ca2+ in bone hydroxyapatite at microgram body burdens, delivering lifelong alpha dose to bone-marrow stem cells. GHS: Carcinogen Category 1A from radioactivity. NRC-licensed material only in the US. Annual intake limits are in the nanocurie range. Legacy radium-dial sites remain EPA Superfund priorities.
This safety summary is for educational reference only and may not be complete. It is not a substitute for Safety Data Sheets (SDS), medical advice, or professional chemical safety guidance. Always consult appropriate SDS and qualified professionals before handling chemicals.