RE: Gamma Spec

["Bradshaw, Keith" <Keith.Bradshaw@nnc.co.uk>]

> -----Original Message-----
> From:	dpharrison@aep.com [SMTP:dpharrison@aep.com]
> Sent:	Friday, March 03, 2000 1:19 PM
> To:	Multiple recipients of list
> Subject:	Gamma Spec
> 
> 
> 
> Question for gamma spec SMEs (which I am not):
> 
> You count a sample on a HPGe for a certain amount of time, but it doesn't
> meet a
> specific radionuclide LLD.  You calculate the new time where the LLD will
> be
> met.
> 
	Because of it's statistical nature, you can't really calculate this.
You can *estimate* the additional time only.  

>   Can you, instead of recounting the sample for the entire duration of the
> new calculated count time, start the count on top of the original spectrum
> and
> just count for the difference in time between the original count time and
> the
> calculated new time?
> 
	I'm pretty sure that at least Canberra (Genie) and EG and G software
will allow you to recall a spectrum and resume counting on top of it.  Be
careful of any 'decay correction during counting' options that may be
enabled.  I've not been into it, but apparently some software packages will
count until a preset LLD is met. 

	If you want to get deeper in the mire of estimating count times for
a certain LLD, see Health Physics vol 32 (Jan 1977) pp1-14: 'The statistical
interpretation of counting data from measurements of low-level
radioactivity' by Donn J J and Wolke R L.


	keith.bradshaw@nnc.co.uk




	END



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