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Re: More on VDTs
Shouldn't I get four choices? Anyway, the answer is b) electrostatic
attraction of radon daughters. The late Phil Perdue published a letter
about this in Health Physics in the early 1980's. You can verify this
through a number of experiments including looking at the alpha response
using a ZnS probe, covering the VDTs in plastic and recounting them after a
few hours' decay time, etc.
Bill Goldsmith
Radian Remediation Services
865.220.8265
bill_goldsmith@urscorp.com
"Algutifan, To: Multiple recipients of list
Elizabeth K. (ELB) <radsafe@romulus.ehs.uiuc.edu>
" cc:
<elb@bechteljacobs Subject: More on VDTs
.org>
Sent by:
radsafe@romulus.eh
s.uiuc.edu
07/31/2000 11:28
Please respond to
radsafe
Radsafers,
I wasn't going to bore you any more with this subject, but the more I dig,
the more questions arise. Hopefully this issue is worth dredging up again,
because I feel that what I have learned sheds a new light on the subject.
To summarize, I have access to a number of release surveys of computer
monitors showing direct beta-gamma readings (with a pancake G-M probe) of
2,000 - 3,000 dpm/100 cm^2. These computer monitors were surveyed while
turned off. I work at a DOE site, and although these levels are below the
DOE 5400.5 criteria, they are high enough to be of concern to management,
particularly in light of the latest DOE ruling on recycling of scrap metals
and how that moratorium may extend in the future to other items.
The Question is: Where are these counts originating from?
I have searched the Radsafe archives and numerous websites (including NRC,
FDA/CDRH, phosphor manufacturers, and computer technology companies) on
this
issue, and have spoken to a number of individuals. I have boiled all the
information down to three potential sources/opinions:
a) soft x-rays generated by the CRT
b) radon daughters electrostatically attracted to the screen and plastic
case
c) the phosphor coating on the CRT has trace amounts of NORM because cerium
or other rare earth metals used in the phosphors are extracted from
monazite
sands and are accompanied by thorium oxide
It seems that, with the rapid advances in computer technology - see
especially item c) -, new research is needed in this area. Based on what I
have seen and read, the only points of discussion in the more recent
literature are (1) soft x-rays, which are referred to as a non-issue now
because of better circuitry and shielding (through the use of leaded glass)
than what was available in the 60s with the old television receivers; (2)
low frequency electromagnetic radiation, which is the big issue the public
and activists have latched on to recently; and (3) environmental concerns
with the lead leaching out of the glass in the screens.
Has anyone looked into this issue lately? Can anyone provide current
references (say, later than 1996) that discuss this issue? Any new dose
estimates, survey data, comparisons between monitors coming from controlled
vs. uncontrolled areas, lists of substances and their activities that might
show up in these optical coatings, etc.? Has anything appeared in the
Health
Physics Journal about this since 1984?
Thanks,
Elizabeth Algutifan, CHP
Bechtel Jacobs Company LLC
East Tennessee Technology Park
Oak Ridge, TN
algutifane@bechteljacobs.org
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