Introduction to Health Physics: Fourth Edition - Ruang Baca FMIPA UB

RADIATION DOSIMETRY 263
and MIRD Pamphlet No. 11 gives the S(body ← body) value for 137 Cs together with
its very short-lived daughter 137m Ba as 1.4 × 10 −5 rad/μCi-day (3.8 × 10 −6 Gy/MBqday).
The mean residence time τ 1 in compartment 1 is calculated as follows:
τ1 = 1.44 × 2 days = 2.88 days.
Since compartment 1 contained 10% of the activity, the cumulated activity in compartment
1 is
Ã1 = 0.1 × 1 MBq × 2.88 d = 0.288 MBq · d.
The dose due to compartment 1 is calculated with Eq. (6.97):
D1 = 0.288 MBq · d × 3.8 × 10 −6 Gy/ MBq · d = 1.09 × 10 −6 Gy.
For compartment 2, the mean residence time, τ 2, is
τ2 = 1.44 × 110 days = 158.4 days
and
Ã2 = 0.9 × 1 MBq × 158.4 days = 142.6 MBq · d.
The dose from the radiocesium in compartment 2 is
D2 = 142.6 MBq · d × 3.8 × 10 −6 Gy/ MBq · d = 5.42 × 10 −4 Gy.
The total dose is the sum of the doses from the two compartments:
D = D1 + D2 = 1.09 × 10 −6 Gy + 5.42 × 10 −4 Gy = 5.43 × 10 −4 Gy
ICRP Methodology
= 0.543 mGy (54.3 mrads).
The MIRD methodology was developed to calculate doses from radionuclides that
are administered for medical purposes. The ICRP methodology was developed to
calculate doses from internally deposited radionuclides for health physics purposes.
Since the objective for both methods is the same, namely to calculate a dose from
an internal emitter, it is not surprising that the two methods are essentially the
same. However, although they come to the same end point, the two computational
methodologies use different terminology in constructing their formulations. Another
difference between the two, which in most cases is trivial, is that the MIRD
formulation calculates the dose in gray by integrating the dose rate over an infinitely
long time after intake of the radionuclide, while the ICRP formulation calculates the
equivalent dose in sievert (or rems when the traditional units are used) accumulated
during 50 years after the intake.