[ RadSafe ] Speaking of a de minimis regulatory level ....

Joseph Preisig jrpnj01 at gmail.com
Thu Dec 17 20:54:01 CST 2015

     Hmmmm.  Don't know much about television dose limits.  Older
televisions work something like as follows.  An electron
beam starts out at the back of a TV, via an electron gun, (febetron???).
The beam is shot towards the TV screen and sweeps horizontally across the
TV screen (rather quickly).  In some time step (also quickly) there is some
vertical stepping so the whole TV screen is scanned.  A phosphor on the TV
screen is activated at each TV pixel location, and you see the TV picture.
Newer TV's have LED or Liquid Crystal or other displays.  Of course, the TV
is receiving the signal via an antenna, cable system or whatever.

     I would believe, without specific knowledge, that the oscilloscope was
a precursor to the TV.  The television was developed by groups led by
Farnsworth (read about him on the internet) or Vladimir Zworykin (RCA
Laboratories USA).  My Dad also worked at RCA Labs (Princeton, New Jersey)
and he held a few patents and one patent on a portable color TV.  He worked
on vacuum tube technology and eventually solid state.  When RCA ended, the
TV division was absorbed by Thomson Electronics, the Solid State Division
was absorbed by General Electric and there were other pieces.  I think
there are still some TV's manufactured with the RCA name.

     So, in terms of health physics, what goes on with a television?  The
electron beam is accelerated (at some current) via some voltage towards the
TV screen, which is a fairly thick piece of glass.  The television tube is
under vacuum.  The electron beam isn't directed at one position at the TV
screen, but sweeps vertically and horizontally across the screen.  I don't
know the range of the electron beam in the glass, and I expect this number
varies by television model/brand.  I would hope not much electron  beam is
getting out of the TV glass, but if it does, it is being distributed all
across the room where people may be watching.  I suspect there are TV
regulations/safety regulations on the internet, or in paper or book form.
Not everything is on the internet.

     Have a good weekend.  Anyone stick their fingers into xray units
lately, or has anyone crawled into holes in radiation shielding and/or
defeated interlocks and gotten some large doses???  The demand at
Universities and/or research institutes must really be large these days
with various people doing xray diffraction and xray flourescence, with
people analyzing DNA samples etc. The NSLS II (the National Synchrotron
Light Source 2) is starting to run nowadays at Brookhaven Lab.  Brookhaven
now has a pretty fair assortment of physics toys with the exception of not
having a Large Hadron collider.  The NSLS2 is there, along with all the
accelerators associated with the Relativistic Heavy Ion Collider (200 GeV x
200 GeV protons and various Heavy Ions such as gold) --- a Cockroft-Walton
accelerator, a linac, a booster accelerator, the Alternating Gradient
Synchrotron, and RHIC itself.  There is also a NASA beamline for
radio-biology etc. studies and BLIP for accelerator production of
radioisotopes.  Many of the Health Physics technicians at Brookhaven have
Masters degrees.

     Joe Preisig

On Thu, Dec 17, 2015 at 8:38 PM, Ted de Castro <tdc at xrayted.com> wrote:

> Recently while doing some consulting for an analytical x-ray installation
> I explained the use of the HEW "Color TV limit" as a "bullet proof" leakage
> criteria without needing to go any lower.
> Thinking about that I realized that the HEW in declaring an acceptable
> emission limit for an entertainment device in the home and often attended
> by young children had in effect made a regulatory declaration of de minimis
> acceptable radiation levels.
> Never mind that few if any sets actually emitted this much, that the ones
> that did only emitted that much out the back, that it applies only to now
> obsolete technology and that it was stipulated under conditions that
> rendered the image unviewable - never the less - its out there, in federal
> law and effects to living rooms across the country!
> I wonder what dose consequences were assumed in arriving at that standard?
> Comments on this notion?
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