The coloring of the diamond by radium radiation

Abstract

1. 1. Diamond is not colored by the penetrating (beta and gamma) radiation from radium salt in glass tubes 0.5 to 1 mm. thick. 2. 2. Diamond is always colored green by direct radiation, either from high-grade radium salts or from the gas, radium emanation. No exceptions were met in more than thirty specimens. 3. 3. The green color is apparently light-permanent, but can be removed by heating to a dull red. 4. 4. Yellow and brown diamonds are also colored green, but are restored by heating to their original colors. In the case of large deep brown stones the color masking by green was not complete. 5. 5. Recutting the crystal after coloring removes the green color. This is possibly a heat effect during cutting, and does not prove that the coloring is merely a surface effect. 6. 6. The depth of penetration of the color zone could not be determined. If it is an alpha-ray effect, it would be limited by the range of alpha rays in diamond, about 0.001 inch. But reflection of green light from the highly polished surface interferes with optical observations. 7. 7. Radiation by emanation is more effective than by salts, owing to the greater absorption of alpha rays by the salt itself. 8. 8. In some cases in emanation, but never in salt, the radiation resulted in the production of “carbon spots” in the interior of the crystal. The black spots are probably a form of carbon, the nature of which was not definitely determined. They can be removed by prolonged heating in a blast flame. 9. 9. The “carbon spots” are undoubtedly beyond the range of alpha rays in the crystals, which suggests that the color may be penetrating also and that both are produced by some form of secondary radiation more penetrating than alpha rays.