Thanks again to all who responded and helped me understand.
For others who wanted to know, the answer (see question below) is of course that Po-210 has a much shorter physical and biological T½ -- only 138d & 50d respectively, versus the 50-year bio-T½ of both Pu-239 & Am-241. This was the main point in the replies. The ALI for Po-210 is 100x higher than those of Pu-239 & Am-241, implying that Po-210 is considered 100x less harmful than Pu-239 & Am-241.
Some also suggested its the progeny ingrowth over 50 years -- the fact that Po-210 turns to stable lead-206, whereas the two transuranics have radioactive progeny. My guess is that this is not such a big factor, since the ingrowth would be minute over 50y -- Pu-239 & Am-241 decay to U-235 & Np-237 (respectively, I think) both of which have multi-million-year T½.
Some replies also suggested that I should have been able to figure this out by myself -- which is true.
My confusion started when I read a publication which stated that "The International Commission on Radiological Protection calculates that polonium-210 is five to ten times more harmful than plutonium 239." This is evidently false. The problem is that it was written by a respected scientist - which made it hard for me to believe that it could possibly be wrong !
Oh well, live & learn.....
....its so easy to get mixed up in these things !
Cheers,
Jaro
-----Original Message-----
From: Franta, Jaroslav [mailto:frantaj@AECL.CA]
Sent: 18 June 2002 15:26
To: Radsafe (E-mail)
Subject: HP question - alpha sources[Scanned]
Dear Radsafers,
Would anyone be able to tell me why it is that the ALI (IC-W) for Po-210 is 100 times HIGHER (0.6 µCi) than for Pu-239 & Am-241 (both 0.006 µCi), even though the T½ for Po-210 is 1140-times shorter than that of Am-241, and 63570-times shorter than that of Pu-239 ? Can someone please enlighten me about the reasons for this ?
Thanks in advance.
Jaro