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

Thu May 11 10:58:29 CDT 2006

A pancake will detect alphas but is not very efficient; it is certainly
not the instrument of choice for performing alpha surveys, especially at
or near typical release limits for transuranics, or when there is a
mixture of alpha and beta emitters present.  Remember that in the case
of U-238, what is really being counted is the hard beta from Pa-234m.

Glenn Marshall, CHP

-----Original Message-----
From: NIXON, Grant [mailto:Grant.NIXON at mdsinc.com] 
Sent: Thursday, May 11, 2006 11:04 AM
To: Haleem, Mahmoud S.
Cc: Ron Reif; radsafe at radlab.nl
Subject: RE: [ RadSafe ] Measuring alphas with GM? Re: Survey MDAs vs.
ScanMDAs

Hi Mahmoud:

For a Bicron Surveyor 2000 portable survey meter equipped with a PGM
pancake probe, the following conversion factors are typical:

872 CPM=185 Bq (5nCi) of Co-60 
1474 CPM=185 Bq (5nCi) of Cs-137
2797 CPM=185 Bq (5nCi) of U-238

These figures are for scenarios approximating full 2 Pi geometry (i.e.,
pancake probe directly over the contaminated surface at zero height
above surface. Because 185 Bq (5nCi) corresponds with 11100 DPM, only
5550 DPM would be detectable for the given geometry. 

The PGM's mica window material thickness is between 1.4-2.0 mg/cm2, the
area is 15.5 cm2. 

Ron, the PGM quoted should be compatible with any +900V count rate
meter.

Best regards,

Grant

Grant I. Nixon, Ph. D., P. Phys.
Radiation Physicist
Engineering
MDS Nordion
Tel: (613) 592 3400 ext. 2869
Fax:( 613) 592 7423

-----Original Message-----
From: Haleem, Mahmoud S. [mailto:HALEEM at cua.edu] 
Sent: Thursday, May 11, 2006 8:34 AM
To: NIXON, Grant
Subject: RE: [ RadSafe ] Measuring alphas with GM? Re: Survey MDAs vs.
ScanMDAs

I wonder what is the efficiency for such a system?

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf Of NIXON, Grant
Sent: Wednesday, May 10, 2006 5:22 PM
To: Emil; radsafe at radlab.nl
Cc: Ron Reif
Subject: RE: [ RadSafe ] Measuring alphas with GM? Re: Survey MDAs vs.
ScanMDAs

No joke Emil. Some GM detectors, equipped with a thin mica window, would
be able to measure high-energy alphas. For example, a pancake probe that
is typically used for detecting contamination (e.g., betas from Co-60)
can also detect alphas from uranium.

Grant

-----Original Message-----
From: radsafe-bounces at radlab.nl [mailto:radsafe-bounces at radlab.nl] On
Behalf Of Emil
Sent: Wednesday, May 10, 2006 5:03 PM
To: radsafe at radlab.nl
Cc: Ron Reif
Subject: [ RadSafe ] Measuring alphas with GM? Re: Survey MDAs vs. Scan
MDAs

Ron,

Is it a joke?

Not to offend anybody but I am wondering how do you measure alphas
with GM detector???
The GM window thickness makes it impossible.

Regards,

Emil.

@radlab.nl>
Cc: 'John Andrews' <jandrews at whoi.edu>, 'steven pike'
	<spike at whoi.edu>,	'Mary McGeoghegan' <Dear Radsafe list:

 I'm trying to determine the Minimum Detectable Activity (MDA) for 
gross
alpha measurements using a GM detector coupled to a rate meter.  Some
colleagues have pointed me to NUREG-1757, which I have reviewed.  
NUREG-1757
refers to NUREG-1507, "Minimum Detectable Concentrations with Typical
Radiation Survey Instruments for Various Contaminants and Field 
Conditions",
June 1998.  However, I cannot locate this document on NRC's web site.
Apparently, they do not keep 'older' documents on their web site.  
Does
anyone have the proper MDA equations for evaluating (a priori) the
sensitivity of a rate meter?  It is my understanding that the 
standard MDA
equation for integrated measurements (scaler mode) does not apply to 
rate
meters.  A link to NUREG-1507 would also be appreciated.  

Please reply directly to me.  Thank you.

-----

Ron Reif, P.E.,CHP,CIH

EH&S Manager

Woods Hole Oceanographic Institution

http://ehs.whoi.edu

p:508-289-3788

f:508-457-2015

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