Decay and ingrowth equations

[stabinmg <michael.g.stabin@vanderbilt.edu>]

The following post from Lew Helgeson, please direct responses there. Thanks.



From: "Lew Helgeson" <lewhelgeson@wwc.com>

To: "Radsafe" <radsafe@list.vanderbilt.edu>

Subject: Decay and ingrowth equations

Date: Fri, 20 Jul 2001 15:42:35 -0700



Fellow Health Physicists,



I need a refresher course on the growth of daughter products from a =

parent. Normally, I would have it at my fingertips in my office, but I =

am staying at the hospital where my wife is recovering from right hip =

prosthesis replacement and I must rely on memory for many things.



In particular, I am looking for the amount of Tl-208 present in a =

30-year old 1 gram plated Th-232 source. I recognize that some of the =

Rn-220 can escape from the palted metal surface, but a calculation =

should put me in the ballpark.



As I recall, the equations has the form:



N(daughter) =3D N(Parent)*[1 - exp(-ln(2)*t(now)/t(half-life of =

parent)]*[exp(-ln(2)*t(now)/t(half-life of daughter)].



(Note to John Andrews, this is the source you gave me in 1967 or 68.)



Lew Helgeson



PS: because the nursing staff doesn't want me to tie up yhe telephone =

lines, I am using a Ricochet wireless modem (fantastically fast - 115 =

kbps, I love it). That requires me to use a different e-mail address for =

sending only. Responses may be sent directly to me at my usual address:



lewhelgeson@helge.com



or at the Richochet address



lewhelgeson@wwc.com



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