AW: ...no subject...

[Navert Stephan <Stephan.Navert@hsk.psi.ch>]

> -----Ursprüngliche Nachricht-----
> Von:	maj_louie_tonry@ddeamc.smtplink.amedd.army.mil
> [SMTP:maj_louie_tonry@ddeamc.smtplink.amedd.army.mil]
> Gesendet am:	Mittwoch, 6. Januar 1999 14:09
> An:	Multiple recipients of list
> Betreff:	Re: ...no subject... 
> 
> 
>      Heir Feinhals;
>      
>      Evaluation of surface contamination for alpha can be done with a
> ZnS 
>      scintillator.  It has a selective response to alpha only and will
> not 
>      be disturbed by the gamma or beta component.  However with a
> direct 
>      reading device, you will not be able to distiguish between
> removable 
>      and non-removable contamination.  To accomplish this, smears will
> have 
>      to be performed.  As for the beta component, how about using a
> plastic 
>      scintillator.  The responce would be very low for the gammas 
	[Navert Stephan]  Generally spoken yes, but it can't be
neglected. And for a surface area of about 300 cm^2 at the given
doserate I would expect at least some 10E5 of photons / s  (just a rough
guess!!) of a quasi unknown energy distribution. And assuming an
efficiency of 0.01 for the gammas in the massive plastic I still end up
with a few 10E3 counts in my detector. And from this I have to separate
approx. 1200 counts according to the betas, also continuous and unknown
spectra. Very difficult!!

	An other possibility might be a very thin wire chamber (as it is
used in HEP-detectors) or a very thin plastic scintillator ( < 1 mm
thickness ). But up to my knowledge all these items are only used in
research (for discrimination purpose), and are not commercialy available
or even calibrated to a standard!

> and it 
>      wouldn't respond to the alphas.  Again, smears would be required
> for 
>      quantifing removable contamination.
>      
>      When performing the removable smears, liquid scintillation
> counting is 
>      probably your best option for the betas.  You didn't say what
> types of 
>      contamination you had on the casks.  
	[Navert Stephan]   Contamination is mainly Cs-137, Co-60 and
other fission or activation products...

> I would assume there is H-3 in 
>      which case you almost have to use LSC.  For the remander of the 
>      isotopes a good gas flow proportional counter with a thin window
> would 
>      give good results.
>      
>      I hope this helps.
>      
>      MAJ Tonry, US Army
>      
>           
>  
> ======================================================================
> 
>      + LOUIE TONRY, CHP
> + 
>      + MAJOR, MS
> + 
>      + Chief, Radiation Protection Division
> + 
>      +
> + 
>      + Eisenhower Army Medical Center
> + 
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> +
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> +
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> + 
>  
> ======================================================================
> 
> 
[Navert Stephan]  ---
Dr. Stephan Navert
Hauptabteilung fuer die Sicherheit der Kernanlagen
Sektion Radiologischer Arbeitsschutz
CH 5232 Villigen HSK

Tel:	+41 56 310 3858 	FAX: ++41 56 310 4905
e-mail:	navert@hsk.psi.ch
>  
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