Radium Bromide
Properties
| State | Solid (darkens on storage from self-radiolysis) |
| Color | White to cream initially, darkens to yellow-brown over days |
| Solubility | Very soluble in water; soluble in ethanol |
| Melting Point | 728 °C |
| Boiling Point | 900 °C (approximate, decomposes) |
About Radium Bromide
Radium bromide is a white-to-cream orthorhombic salt (RaBr2, 385.81 g/mol) that visibly darkens to yellow and then deep brown within days of preparation as its own alpha decay shreds the crystal lattice. It was prepared shortly after the Curies' 1902 isolation of RaCl2 and quickly became the preferred commercial form of radium because it fractionates more cleanly than RaCl2 from the BaBr2 that comes along with it during pitchblende processing. RaBr2 is isomorphous with BaBr2 in the PbCl2-type orthorhombic structure, which is what you'd expect for the heaviest Group 2 cation. Between roughly 1910 and 1940 the entire commercial output of the compound — never more than tens of grams worldwide — was being mixed with ZnS:Cu phosphor and gum arabic and painted onto wristwatch faces, aircraft instruments, and gun sights. The alpha particles from Ra-226 excited the zinc sulfide and produced the green-yellow glow that defined a generation of dial paint. The young women who painted those dials at U.S. Radium in Orange, New Jersey, and at Radium Dial in Ottawa, Illinois, were taught to lip-point their brushes between strokes, and the resulting microgram-level radium ingestion produced the osteosarcoma and jaw necrosis that gave us the modern occupational radiation framework.
Where you'll encounter it
If you've ever seen a vintage 1930s aircraft cockpit panel in a museum and noticed the dial markers are an off-white or pale brown rather than the original luminous green, you're looking at the visible end-state of RaBr2 self-radiolysis — the radium is still there, still emitting, but the ZnS:Cu phosphor that did the glowing is long since destroyed by alpha damage. Radiation safety officers at aviation museums routinely run a Geiger counter over WWII-era instruments and find them still hot eight decades later. Antique dealers occasionally turn up old radium-paint pots in estate sales — sealed jars that have been accumulating Rn-222 daughter gas the entire time, and that need to be opened only inside a fume hood by someone with a state radiation license. The Orange, NJ and Ottawa, IL dial-painting sites remain on the EPA Superfund priority list almost a century after the factories closed.
Common Uses
- Historical radioluminescent paint for aircraft instruments and watch dials, 1910s-1950s
- Historical commercial radium source for medical brachytherapy needles
- Research feedstock for Ra-226/Rn-222 radon-generator systems
- Reference phase for early actinide and heavy Group 2 chemistry studies
- Calibration source for legacy alpha and gamma radiation-detection instruments
Safety Information
EXTREMELY RADIOTOXIC. Aged RaBr2 should be assumed to contain a significant Rn-222 inventory that releases the moment the container is opened — handling requires a fume hood with HEPA filtration and full radiation PPE. Ingested or inhaled radium bioaccumulates in bone hydroxyapatite at microgram body burdens because Ra2+ chemically mimics Ca2+, and delivers alpha doses to bone-marrow stem cells for the rest of the person's life (Ra-226 biological half-life in bone is roughly 2800 days). GHS: Carcinogen Category 1A from radioactivity, Acute toxicity by ingestion. NRC- or IAEA-licensed material only; possession outside a licensed facility is a federal offense in the US. Legacy dial-paint manufacturing 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.