Coloration of the Alkali Halides by X-rays

Coloration of alkali halides and other salts by x-rays.—(1) Hues produced. CsF, RbF, Ca${\mathrm{F}}_2$, CsCl, RbCl, KCl, NaCl, LiCl, AgCl, BaCl, BeCl, Ca${\mathrm{Cl}}_2$, CsBr, RbBr, KBr, KI, NaI, CdI, HgI and ${\mathrm{K}}_2$Si${\mathrm{O}}_3$ were colored, whereas KF, NaF, LiF, NaBr, RbI, ZnCl, N${\mathrm{H}}_4$Cl and about 20 other salts showed no coloration with 5 hours exposure to intense radiation. (2) Spectral absorption of colored halite and sylvite. Halite (NaCl), colored amber, has a broad absorption band from 0.3μ to 1.3μ with a maximum at 0.46μ. Sylvite (KCl), colored purple, has a similar absorption band with a maximum at 0.55μ. (3) Spectral fading of colored alkali chlorides. The colors fade logarithmically when exposed to daylight, the time varying from a few seconds to days. When exposed to the spectrum of a 500 watt Mazda Clamp, colored NaCl, KCl, RbCl and CsCl fade most rapidly at wave-lengths 0.51μ, 0.61μ, 0.68μ and 0.62μ respectively. When correction is made for the energy distribution, halite and sylvite are found to fade most rapidly at wave-lengths where their absorption increase due to their coloration is a maximum.