Patent ID: 8134289

Claim:
An electrode for cold cathode tube, comprising: a cylindrical sidewall portion; a bottom portion provided at one end of the cylindrical sidewall portion; and an opening portion provided at the other end of the cylindrical sidewall portion, wherein the electrode is formed of a sintered body of a simple substance of a metal selected from tungsten, niobium, tantalum, molybdenum and rhenium, or an alloy containing the metal; and wherein the electrode satisfies L≧6 (mm), d 2 >d 1 , R≧20 (mm), where L is an overall length of the electrode with respect to an axial direction of the cylindrical sidewall portion, d 1 is an inside diameter of the cylindrical sidewall portion at a portion of ½ of the overall length L d 2 is an inside diameter of the bottom portion, and R is a radius of curvature of an arc of an inner surface of the cylindrical sidewall portion connecting a portion of the inside diameter d 1 and a portion of the inside diameter d 2 .