7 Apr
2012
7 Apr
'12
11:42 a.m.
I've got to do some reading--I remember that
"aluminized" screens
started to be included in the 1950s. I wonder if that had to do with
X-rays.
I don't see how it can do.
X=ray emission occurs when the electron is decelerated -- when it hits
the screen, basically. Now, you need the electrons to hit the phosphor
(in front of the aluminium layer) to excite it, so you actually get a
visible glow. That means the X-rays would be produced in front of the
aluminium layer...
Aluminising had 2 main purposes :
1) Althoguh the electrons could get throug it to hit the phosphor,
heavier ions could not. This protected the phospohr from damage, and
stopped a problem called 'ion burn' where you got a dark spot or X in the
middle fo the screen. Before that, the normal way to prevent ion burn was
to have a bent electron gun with a small external magnet to dedirec the
electron beam along the CRT axis. THe ions were not much effected by this
magnetic field and so they ended up hitting one of the gun electrodes or
the wall of the CRT. The magnet assembly was known (at least over here)
as the 'ion trap', and if it was not properly postioned you coudl end up
with no image on the screen at all.
2) It acts as a light reflector, so most of the light emitted by the
phosphor comes out of the front of the CRT. No point in easting it by
illumninating the inside of the set :-)
I _think_ almost all electromagnetlcally-deflected CRTs used in classic
computers, certainly the onses used in DEC termninals, etc, will be
aluminised.
-tony