Re: More on VDTs

[Franz Schoenhofer <schoenho@via.at>]

At 10:28 31.07.2000 -0500, you wrote:


>Radsafers,
>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.

When did you find these readings? Just after having turned the monitors off
or a long time after? I have just for fun made some experiments a few years
ago, taking smear samples from computer screens at different times - before
turning them on, during operation and after turning off - and subjected
these smears to liquid scintillation spectrometry. It was fascinating to
see the radon daughters in the LS spectra and how they decayed. I have not
published it, because it did not seem to me to be scientific enough..... So
radon daughters may be a good candidate for your countrates.

>
>a) soft x-rays generated by the CRT

This is rather unlikely concerning new techniques

>b) radon daughters electrostatically attracted to the screen and plastic
>case

a good candidate (see above)

>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 

in my feeling this contribution cannot be very big, though your reasoning
is reasonable

Finally do not forget that all glass contains K-40, whether this would
contribute significantly to the countrate I cannot judge.

Hope this is a small bit of the puzzle you have to put together!

Franz


Franz Schoenhofer
Habicherg. 31/7
A-1160 Vienna
Austria
Tel.: +43-1-495 53 08
Fax.: same number
mobile phone: +43-664-338 0 333
e-mail: schoenho@via.at


Office:
Ministerialrat Dr. Franz Schoenhofer
Federal Ministry of Agriculture, Forestry, Environment and Water Management
Radiation Protection Department (BMLFUW I/8 U)
Radetzkystr. 2
A-1031 Vienna
AUSTRIA

phone: -43-1-71172-4458
fax: -43-1-7122331

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