Re: dose conversion

[LIPTONW@detroitedison.com]

While useful, the "6CEN" rule of thumb applies ONLY to photons.  It does NOT 
apply to beta radiation.  To make an activity estimate, you would need to know 
the geometry of the source and the distance at which the 78 rad/sec value 
applies.  A rule of thumb for beta's, from the 1970, "Rad Health Handbook," 
page 204 is that: 
 
"For a point source of beta radiation )neglecting self- and air-absorption) of 
strength Ci curies, the dose rate at 1 ft is approximately equal to 300 Ci 
rads/hr.  The variation with energy is small over a wide range." 
 
Assuming the 78 rads/sec = 4.68 E3 rad/hr is at 1 foot and the source is a 
point source, and there's no absorption, this results in an activity of 
approximately 16 Ci.  Since the source has decayed through approximately 1 
half life, the present activity is approximately 8 Ci.  Since the Sr-90 A1 and 
A2 values are 5.41 and 2.70 Ci, respectively, this would NOT be an excepted 
quantity shipment.   
 
This is NOT a valid activity estimate, just an indication that a more detailed 
evaluation will be needed to ship this material.  The "78 rads/sec" reading 
does not indicate a distance, or whether it accounts for any absorption.  It's 
also unclear whether this dose is to air or tissue, and, if tissue, at what 
depth.  If no additional documentation is available, you will need to take a 
new survey and make some attempt to determine the source geometry.  Varskin 
may be useful for the activity calculation. 
 
The opinions expressed are strictly mine. 
Here's to a risk free world, and other fantasies. 
 
Bill Lipton 
liptonw@detroitedison.com

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• To: Multiple,recipients,of,list,radsafe@romulus.ehs.uiuc.edu
• Subject: Re: dose conversion
• From: "radsafe@romulus.ehs.uiuc.edu" <radsafe@romulus.ehs.uiuc.edu>
• Date: 24 Apr 97 23:23:03
• Reply-to: radsafe@romulus.ehs.uiuc.edu

At 03:31 PM 4/24/97 -0500, you wrote:
>I need to make a shipment of Sr-90, the only indicator of activity 
>that I have is an old calibration stating that the eye applicator 
>delivered 78 beta rads per second as of 12/17/65. 
>
>Anyone know how the dose rate was calculated and I can back calculate 
>into a reasonable estimate of the activity?
><><><><><><><><><><><><><><><><><>            
><>    Charles R. (Russ) Meyer                  <>
><> Email: cmeyer@brc1.tdh.state.tx.us           <> 
><>     Phone:(512)834-6688                       <>
><>        Fax:(512)834-6654                        <>
><><><><><><><><><><><><><><><><><>
>
>
Is the eye applicator an instrument? You should be able to ship it
"Excepted package-instruments or articles" 10-2 A2 value or "Excepted
package- limited quantity of material" 10 -3 A2 value and the package is
below .5 mr/hr contact on all six sides. Then fill out the exception
statement place it in or on the package. Mark the item or the package
radioactive and ship.  

If you can take a reading of the source you can use the 6CEN formula to
estimate the Curie amount.  C = D/E

Alan

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