Re: 40w globe lightbulb = safe plasma ball?

["Tesla list" <tesla-at-pupman-dot-com>]

Original poster: "David Speck by way of Terry Fritz <twftesla-at-qwest-dot-net>" <dave-at-davidspeckmd-dot-org>

The getter was a narrow trough of conductive metal channel filled with 
metallic barium, strontium, or other reactive alkali metal.  The channel 
was part of a circular conductive ring that could be heated to 
incandescence by an inductive loop heater.  When so heated under vacuum, 
the metal would evaporate and vapor plate on a selected spot on the 
glass tube wall.  This silvery spot of reactive metal would grab any 
oxygen that happened to bump into it and lock it up as an oxide, thus 
preventing it from attacking the filaments.  As long as there is some 
silvery material left in the getter patch, then the tube should have a 
good vacuum in it.  I've heard of some people refiring the getters to 
pump down a marginally operating tube that had become "gassy."

Tungsten filament lamps will also plate some of their filament material 
on the glass envelope walls with time, causing darkening of the 
envelope.  Halogen lamps were designed to prevent this, making the bulb 
brighter for a longer time.  Though not as chemically reactive as a 
formal getter, this plating can trap gas molecules and cause the gas 
pressure in the lamp to drop, possibly to a level that would produce 
X-rays.  

It was my understanding that if you are seeing green fluorescence in the 
glass, then you are seeing the results of X-ray production.  The 
biological significance of the X-rays depends on the voltage that 
creates them.  Below 10-12 KV, they are not very penetrating.  30 KV 
x-rays, as from a color CRT, are biologically significant.  My brother's 
dental X-ray units use 72 kV to penetrate teeth and bone.  I would think 
that most TCs would easily have voltages well above those ranges, so do 
your lamp experiments with all appropriate caution.
Dave

> typically
>	leaving a silvery spot.  This was called
>	'gettering'.  IIR, one of the normal electrodes had
>	an additional electrode called a 'getter', of
>	no function in normal operation (being out of the
>	electron path) but useful here.
>