Tritium Dose Conversion Factor Confusion -Reply

[FRAMEP@ORAU.GOV]

Gene Carbaugh's response is right on the money, a rel nice job. Let me
have a little fun and use this as an excuse to calculate the dose
conversion factor and ALI from basic principles. Sometimes this can
provide a little insight.

The cumulated activity (the number of tritium decays in the body because
of the intake of 1 Bq) is:

                     A (cumulated) = 1.44 T A (intake)

where T is the effective half life, which for tritium is determined by the
biological half life of 10 days (240 hrs). 1.44 T is simply the inverse of the
effective removal/decay constant. The equation assumes that integration
is perfomed over an infinite time. Since all the tritium is gone after 50
years, this assumption is reasonable.

          A (cumulated) = 1.44 x 240 x 1  = 345.6 Bq-hrs
               
This is equivalent to 1.244 E6 decays (345.6 Bq-hrs x 3600 s/hr)

Each decay averages 5700 eV  of beta energy therefore an intake of 1
Bq leads to the deposition of 7.0917 E9 ev or 1.13467E-9 J.  This energy
is deposited in reference man's 63 kg of soft tissue (ICRP doesn't use the
whole body here)

The answer:   1.13467E-9 J/63 kg  becomes 1.8E-11 J/kg or Gy or Sv
due to the intake (total intake from any combination of inhalation/skin
absorption/ingestion) EXACTLY the same as listed by ICRP 68.  

Dividing this into 0.05 Sv and rounding off (all ALIs are whole numbers)
gives an ALI of 3 E9, the same as reported in ICRP 30.

Fun stuff!!

Paul Frame
Professional Training Programs
ORISE
framep@orau.gov