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RE: A Question for Power Reactor Types and others with portal monitors.



I assume that you meant that the Mo-99 would have an

activity of 357 nCi after one week.  Again, 0.15

uCi/mCi(Tc-99m) X 30 mCi(Tc-99m) = 4.5 uCi With a half

life of 2.75 days, the activity of Mo-99 would be 0.77

uCi.  Of course, you are also in transient equilibrium

with Tc-99m.  The combined activity would be 0.77

uCi-Mo-99 + (0.89)(0.770 uCi)-Tc-99m = 1.46 uCi. 

However, manufactures  are reporting Mo-99

breakthrough of only 0.03 uCi Mo-99/1 mCi Tc-99m, so

the values may be only 1/5 as great

http://www.nuclearonline.org/PI/Nycomed%20Mo%2099-Tc%2099m%20Genera.pdf

 



Most of the experience I have had in medical HP work

has never involved studing activities in the nCi

level.  The exception is for contamination smears.  I

guess that is why people in the medical fields do not

appreciate the problems with detection of

radionuclides, either at nuclear power plants or with

homeland insecutiry operations.





--- "Ayers, Rex G" <Rexg.Ayers@TycoHealthcare.com>

wrote:

> You always have a small amount of Mo-99 present. The

> capability to measure

> it with 4-5 orders of magnitude more Tc-99m is

> nearly impossible. At the

> limit 0.15 uCi/mCi, and we are never there, you

> would still have 357 uCi of

> Mo-99 after one week. Many portals, such as the NNC

> Gamma 60, can be tweaked

> to have a sensitivity as low as 20 nCi (mid-line

> with no self-shielding),

> for a radionuclide with energies in a range of

> Cs-137 where Mo-99 resides.

> This causes a Tc-99m test, depending upon compound,

> to cause portal alarms

> for several weeks.

> 

> The big issue is always Tl-201 as the Tl-202 stays

> around for several months

> with a 12.2 day half-life. The Tl-204 is negligible

> due to the small number

> of atoms produced and the much longer half-life. A

> person with a heart study

> using Tl-201 can set off the portal for 4-5 weeks.

> During manufacture, the

> biggest issue is the dose rate from Tl-200.

> 

> Rex Ayers, CHP

> Tyco Healthcare/Mallinckrodt

> 

> -----Original Message-----

> From: Stabin, Michael

> [mailto:michael.g.stabin@vanderbilt.edu] 

> Sent: Thursday, April 08, 2004 1:36 PM

> To: Sewell, Linda; Peter.Vernig@MED.VA.GOV;

> Radsafe@list.vanderbilt.edu

> Subject: RE: A Question for Power Reactor Types and

> others with portal

> monitors.

> 

> 

> >We have found that Tc-99 alarms our portals for 1-3

> weeks.  I think it

> really depends on how much Mo-99 there is as a

> contaminant.  

> 

> I agree with John J - first, I know you meant

> Tc-99m, but mostly I am

> surprised that any place would have enough Moly

> breakthrough to be so

> noticeable. This is supposed to be a major QA point.

> You are right about

> the 10 half-life rule, that just gets you to

> (1/2^10), not zero, and if

> you are set to a sensitive level, this may still be

> measureable, but

> Tc-99m has a 6 hour half-life, a typical

> administration is perhaps 500

> MBq (depends on the compound), so you are down to

> 1-2 Bq in a week. So I

> am also skeptical that Tc-99m would alarm for more

> than a week, even

> with a sensitive detector, and we are back to the

> Moly hypothesis.

> 

> Mike

> 

> 

> Michael G. Stabin, PhD, CHP

> Assistant Professor of Radiology and Radiological

> Sciences 

> Department of Radiology and Radiological Sciences 

> Vanderbilt University 

> 1161 21st Avenue South

> Nashville, TN 37232-2675 

> Phone (615) 343-0068

> Fax   (615) 322-3764

> Pager (615) 835-5153

> e-mail     michael.g.stabin@vanderbilt.edu 

> internet   www.doseinfo-radar.com

> 

>  

>

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-- John

John Jacobus, MS

Certified Health Physicist

e-mail:  crispy_bird@yahoo.com



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