[ RadSafe ] Measuring alphas with GM? Re: Survey MDAs vs. ScanMDAs

[John Jacobus]

Unless you put the material right up against the
screen, alpha surveying in the field is pretty poor. 
During a training exercise, I had a friend who had
problems surveying cacti in the desert.

--- "Glenn R. Marshall" <GRMarshall at philotechnics.com>
wrote:

> Ludlum also quotes 19% efficiency for Tc-99 (4-pi),
> and I've received
> pancakes from them with reported 4-pi efficiencies
> in excess of 20%.
> Everyone else gets 10-12%.  I called their tech
> support people once and
> asked about it.  The person on the other end of the
> phone said they put
> the source inside the recess of the probe, right up
> against the screen.
> Perhaps he was pulling my leg; if so, would somebody
> please tell me?  I
> don't put much stock in advertised efficiency.  In
> the field, under
> normal industrial conditions, alpha efficiency on a
> pancake is usually
> pretty crappy.
> 
>  
> 
> Glenn 
> 
>   _____  
> 
> From: JGinniver at aol.com [mailto:JGinniver at aol.com] 
> Sent: Thursday, May 11, 2006 3:26 PM
> To: Glenn R. Marshall; Grant.NIXON at mdsinc.com;
> HALEEM at cua.edu
> Cc: rreif at whoi.edu; radsafe at radlab.nl
> Subject: Re: [ RadSafe ] Measuring alphas with GM?
> Re: Survey MDAs vs.
> ScanMDAs
> 
>  
> 
> Hmmm,
> 
> pancake GMs are not as bad as many people think at
> detecting Alphas.
> 
>  
> 
> Thermo quote 0.9 cps per Bq per cm2 for Pu-238 for
> the 900EP15
> (contamination monitor)  see
>
http://www.thermo.com/com/cda/product/detail/1,1055,21854,00.html
> , this
> is generally fitted with an LND pancake GM e.g.
> 7311, 7312, 7313 or 7314
> (depending on the connectors required and operating
> voltage).
> 
>  
> 
> Ludlum quotes 15% (4pi) efficiency for Pu-239 for
> the 44-9, as this and
> other similar probes (e.g. Eberline HP260, Bicron
> PGM, Tech Assoc P15)
> all use a 15.5 cm2 pancake geiger similar to those
> listed above from LND
> (e.g. Canberra, St Gobain etc.) the performance for
> alpha monitoring
> will be broadly similar.
> 
>  
> 
> Regards,
> 
>     Julian
> 
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+++++++++++++++++++
"People will be shocked to see how safe it is to live in New York City."
ANDREW KARMEN, a sociology professor at John Jay College of Criminal Justice, on murder trends in the city.

-- John
John Jacobus, MS
Certified Health Physicist
e-mail:  crispy_bird at yahoo.com

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