Re: another reaction to the Pittsburg TMI "study"

[Ted de Castro <tdc@XRAYTED.COM>]

Yes - that is what I was commenting on as well.  While a x-ray tube is

glass and has a vacuum as well - it usually has a small thinner section

as a window or even other material like Be for these lower energies. 

Beyond that x-ray tubes tend to be an inherently stronger cylindrical

design.  CRT's on the other hand have a very large flat face which

requires considerable thickness to support the vacuum and even more so

to hold the face flat and to do so against a disadvantageous geometry.



I would invite you to check the most definitive article I have seen on

the subject:



"Low-background Radiation Measurements on Video Display Terminals"

Health Physics VOl 46 no 2 pp 413 - 417, 1984.



There is really nothing in that article that does not apply to today's

CRT's.



Stephen Mecca wrote:

> 

> Thanks for this information, Ted and Bjorn:

> I was not thinking of the power supplies as the source but rather the

> Bremsstrahlung produced as the electrons are decelerated by the screen

> materials.  The glass is strong enough to hold a vacuum, but so is an

> x-ray tube's glass strong enough to support a vacuum.  I know that the

> manufacturers are not using the high lead glass.  While I'm quite sure

> you are right about the fact that the dose is low, I'm curious as to

> what the level might be.  I'm wondering if it has been measured.

> Thanks for your help on this.

> ..Steve Mecca

> Ted de Castro wrote:

> 

> > You can't get that much from a TV or CRT - except a projection CRT.

> > These devices haven't put out significant x-rays since they went to

> > solid state high voltage power supplies many many years ago.

> > As for x-rays from the face ... the materials the beam can strike

> > does

> > not have a high cross section for x-ray production and the thickness

> > of

> > the glass required to stand the forces of the vacuum is more than

> > enough

> > shielding.

> > It just doesn't happen!

> > This was one of those bad cases to use a film badge - in this energy

> > region it over responds.

> > Bjorn Cedervall wrote:

> >

> >> My friend "Steve" (professor and physicist - not on Radsafers) -

> >> sent me the

> >> question below. Please help Steve with relevant information:

> >> smecca@providence.edu

> >> Thanks in advance,

> >> Bjorn Cedervall   bcradsafers@hotmail.com

> >> -----------------------------------------

> >> I have a question you might be able to help me with. Do you have

> >> any

> >> information as to risks of somatic or genetic effects of X-Rays

> >> from TV or

> >> Computer monitors. The breaking radiation from the face of a

> >> monitor will

> >> have maximum energy X-Rays in the 20-25 KeV region. An old friend

> >> of mine,

> >> with whom I've lost contact, some years ago put an X-Ray film on a

> >> monitor

> >> screen and determined that in order to get 100 mR per week (the

> >> allowable

> >> limit) one would have to wrap oneself around the monitor and be in

> >> co

> >> ntact

> >> with it. Nevertheless, I have this sense that, with the low prices

> >> of LCD

> >> screens, it might be worthwhile for schools such as ours to

> >> consider orderly

> >> replacements of the older tube monitors. Any thoughts, references

> >> or wisdom

> >> on this?

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