Re: Tl-201

[Mike Lantz <mlantz33@CYBERTRAILS.COM>]

Matt is absolutely correct.  I just saw two messages that implied

that we were wrong in telling Kurt Geber that Tl-202 is the cause of the

portal monitor alarms.  They reasoned that Tl-202 was less than 5%

of the original activity.  In fact, it is usually less than 2% in

the MANY cases I have seen  -- ON DAY 1.

However, at day 60, it is 99% of what the individual has in them.  This is simple decay of two radionuclides, one with a short half-life and one with a slightly longer half-life.

We happen to have portal monitors AND whole body counters at our site.  So, it is very simple to evaluate a portal monitor alarm and show the Tl-202 begin to dominate over time.  Therefore, when workers still irradiate their TLDs from the inside out, alarm portal monitors, and make the assessment of other internal radionuclides difficult to separate (past 30 days, as was the original question), it isn't because of the Tl-201 that, yes, was 95% of the mix on day 1, it is because of the Tl-202.

Mike Lantz, CHP

willim01@mskcc.org wrote:

     Kurt,

     It is not excessive and someone hit it right on.  It is the impurity
     (Tl202, T1/2 12.2 d) that's hanging around still alarming the portals;
     4 to 5 weeks sounds about right.

     Obtain a copy of HPS Vol. 61. No.3 pp. 427-430, 1991, Michael Stabin
     and Audrey Schlafke-Stelson for other nuclides and contaminants of
     interest.
 

     Matt Williamson
     Memorial Sloan-Kettering Cancer Center
     New York, NY  10021

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