Hi John:
> Are you sure that you can get appreciable X-radiation at 8 kV? In the
> days of monochrome TV with 9 and 12 inch tubes running at 8 kV, we never
> bothered about X rays, but projection sets running at 25 kV were known
> as a radiation hazard. Maybe tolerance levels have been reduced greatly
> over 50 years? 8 kV seems high for 1 inch tubes, anyway. The 1CP1 used
> to require less than 1 kV, IIRC.
X-radiation is generated whenever an electron strikes
a target. Some target materials are more efficient
at generating x-radiation than others, given the same
electron energy. In a crt, the space inside the crt
is filled with x-radiation resulting from the bombardment
of the screen (or the shadow mask) by the electron beam.
The faceplate and funnel glass are x-radiation-attenuating
glass. For conventional crts operating at 15 kV or less,
the thickness of ordinary glass necessary for the
structure also provides adequate x-radiation attenuation.
Above 15 kV, the glass usually needs to include some
specific x-radiation-absorbing materials such as lead or
boron. (Lead glass is subject to x-ray browning so it is
not used for faceplate glass.)
The x-radiation frequency and magnitude is a function
of the target material and the electron beam energy,
keV.
As a general rule, x-radiation energies from electrons
at less than 5 keV cannot penetrate paper. So, they
cannot escape the glass envelope of the crt. However,
because x-radiation energy (for a given target material)
is a power function of the voltage (as high as 20), the
increase of x-radiation with increase of voltage can be
dramatic.
Assuming a 1-inch crt is relatively thin glass, 8 kV
*may* be enough to produce measurable x-radiation at
the crt faceplate (rather than the standard 50 mm).
Since the device is in the form of a goggle, and since
the eye is much closer to the crt than 50 mm, one would
want to measure the x-radiation at the crt faceplate.
(X-radiation drops as a function of the square of the
distance from the source, assuming a point source.)
No, I am not sure that there would be measurable
x-radiation at the faceplate of an 8 kV 1-inch crt.
But, based on the above technical facts, I think it
would be prudent to consider the possibility of such
x-radiation. The crt manufacturer should be able to
provide an isoexposure curve for the crt.
Best regards,
Rich
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