the crimping of the tube the magnification in both photomicrographs is 250 x as can be seen in fig2 the self weld area is significantly smaller than in the tip off tube of fig3 this results in an increased wall thickness represented in each figure by the letter d the wall thickness d is measured from a point wherein crack closure becomes evident the self weld area extends from the point labeled d to the terminal end of the tip off tube in a direction to the left of d in fig2 and 3 as can be seen the self weld area has been increased by a factor of approximately three in the tip off tube of fig3 relative to the tip off tube of the prior art illustrated in fig2 in addition to this significant improvement in self welding of the tip off tube the tip off tube has been found to have a greater strength for example self welded copper tip off tubes of the prior art have been found to fail with a resulting loss of hermiticity with only a slight mechanical load on the end of the tube however a gold diffused alloyed tip off tube has been hammered repeatedly without loss of hermiticity thereby greatly improving the reliability and durability of a vacuum enclosure incorporating such a tip off tube furthermore the requirement of the prior art copper tip off tubes that a copper oxide coating be removed prior to pinch off has been eliminated inasmuch as the nobility of the surfaces resists the formation of such an.