Re: Spurious TLD results

["Mike Malaxos" <rss@arach.net.au>]

Sandy asked . What level of dose do I recall.

The doses recorded worked out to be from around 0.1 to 1 mrem/h. However
the total does was measured over a few days. The lowest dose of around 0.1
mrem/h would be around ten time background.  This rate should be easily
detected with a low energy x-ray probe (1 mm Na I xtal and Be window). 
Typical 26 cm picture tubes run at around 24 kV. Bremsstrahlung generated
in the steel mask would normally be absorbed by the thickened face of the
tube. Test I have carried out in modern sets have detected a trace of
photon radiation from the glass (?? K40) when the set has been switched
off. (this was checked to ensure it was not due to radon daughter dust
attracted by the electrostatic charge).

Earlier picture tubes (1960) may have had thin fronts which transmitted
some Bremsstrahlung when the EHT increased above 26 kV. I believe the
source of the x-ray emissions  from the colour sets  in the early 60's was
due to radiation generated in a faulty designed shunt regulator valve. When
the cathode went low emission the full HT was dropped across the anode
cathode gap. The anode did not fully enclose the cathode allowing 26 kVp
x-rays to be emitted through the thin glass wall of the valve..
  

Best Regards
M.Malaxos
Radiation Safety Services
69-71 Robinson Avenue Belmont
Western Australia.  6104 
Fax 61 89 475 0165
P 61 89 475 0099  a/h 089 255 1214
email  rss@arach.net.au
email  radiation safety.com.au  

----------
> From: Sandy Perle <sandyfl@earthlink.net>
> To: Multiple recipients of list <radsafe@romulus.ehs.uiuc.edu>
> Subject: Re: Spurious TLD results
> Date: Saturday, 12 September 1998 9:03
> 
> Mike Malaxos said:
> 
> > I remember a situation about 12 years ago where a 
> > significant dose was said to be recorded over a period 
> > of about a week using  TLD's attached to
> > the front of the picture tube of modern television receivers by some
> > researchers in Bombay. 
> 
> I am not familiar with the above situation.I wonder if this TV had an 
> x-ray tube and it was generating enough high voltage to produce a 
> dose? In past days there was a limit 0 0.5 mR/hr at the face of a 
> TV picture tube. Of course at this rate, there would be no 
> significant dose. Mike, what level dose do you recall?
> ------------------
> Sandy Perle
> Technical Director
> ICN Dosimetry Division
> Costa Mesa, CA 92626
> Office: (800) 548-5100 x2306 
> Fax:    (714) 668-3149
>   
> sandyfl@earthlink.net
> sperle@icnpharm.com
> 
> Personal Website: http://www.geocities.com/CapeCanaveral/1205
>         
> ICN Dosimetry Website: http://www.dosimetry.com
> 
> "The object of opening the mind, as of opening 
> the mouth, is to close it again on something solid"
>               - G. K. Chesterton -
> 
> The opinions expressed are solely, absolutely, positively, definitely
those of the author, and NOT my employer
> 
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