[ RadSafe ] IAEA DACs

[JGinniver at aol.com]

Joel,
I assuming (perhaps rashly) that you are refering to the DAC values given  in 
Table A-II of the annexe to IAEA Safety Standards Series No. RS-G-1.2  
(Assessment of Occupational Exposure due to Intakes of Radionuclides) see: 
_http://www-pub.iaea.org/MTCD/publications/PDF/P077_scr.pdf_ 
(http://www-pub.iaea.org/MTCD/publications/PDF/P077_scr.pdf) 
 
I belive the key differences which have resulted in the different(in some  
cases much lower) values for DACs are:
1) New tissue weighting factors introduced in ICRP60, for example the  
weighting factor for bone surfaces drops from 0.03 to 0.01.
2) The model for the respiratory tractin ICRP30 has been replaced with  a 
more complex physiologically based model.  this is described in ICRP66,  and 
summaries are given in ICRP68 and ICRP78.  Where ICRP30 only  allowed the 
calculation of the average dose to the lungs, the model given  in ICRP66 allows 
calculation of doses to specific tissues in the respiratory  tract.  In addition, 
for many of the more important radionuclides the  ICRP have developed new 
systemic models and these are described in ICRP56,  ICRP67 and ICRP69.
3) The current value now recommended by the ICRP for the  activity median 
aerodynamic diameter (AMAD) is now 5 micron,  as opposed to the 1 micron value 
recommended in ICRP 30.
 
Finally it should be noted that, as you mentioned, the effective dose  limt 
has been reduced to 20 milliSv, consequently the limiting factor for  all 
intakes will now be the stochastic effects.
 
I hope this helps,
                Julian