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

260 CHAPTER 6
is listed in the output data as 0.058 MeV. A 0.279-MeV gamma ray is emitted after
each beta transformation. The gamma ray, however, is internally converted in 18.3%
of the transformations, thus leading to conversion electrons from the K, L, or M
energy levels and, therefore, effective gamma-ray emission occurs in only 81.7% of
the transformations.
Table 6-9 lists the absorbed dose per unit cumulated 203 Hg activity. For the kidneys
as the source, S (kidneys ← kidneys) = 8.1 × 10 −4 rad/μCi · h, and for the total
body as the source, the dose to the kidney, S (kidneys ← total body) = 6.1 × 10 −6
rad/μCi · h. The total dose to the kidneys is the sum of the doses due to the 203 Hg
deposited in the kidneys, and also of the radiomercury in the rest of the body. If
0.5 MBq (13.5 μCi) in the kidneys represents 8% body burden of Hg, then the total
activity in the body is
0.5 MBq
0.08
= 6.25 MBq (168.9 μCi).
Since 0.5 MBq is in the kidneys, the amount of 203 Hg distributed throughout the
rest of the body is 6.25 − 0.5 = 5.75 MBq.
Of the 6.25 MBq deposited in the body, 95%, or 5.938 MBq, will be eliminated
with an effective half-life, TE, from Eq. (6.54):
TE = TR × TB
=
TR + TB
47 days × 40 days
= 21.6 days,
47 days + 40 days
and the remaining 5% of the deposited 203 Hg will have an effective half-life of
47 days. The corresponding effective clearance rate constants are
and
λ1 = 0.693
21.61 days = 3.2 × 10−2 d −1
λ2 = 0.693
47 days = 1.47 × 10−2 d −1 .
The cumulated activity in the kidney is given by extending Eq. (6.90) to several
compartments, c1, c2, ...,cn, within an organ or a tissue is given as
à =
Ac1 (0)
+ Ac2 (0)
λE1
λE2
Acn (0)
+····+ . (6.99)
λEn
From Table 6-9, we find S (kidneys ← kidneys) to be 8.1 × 10 −4 rad/μCi · h.
To convert rad/μCi · htoGy/Bq · d:
Gy rad 1Gy
= ×
Bq · d μCi · h 100 rad ×
1 μCi
3.7 × 10 4 Bq
× 24 h
d
Gy rad
=
Bq · d μCi · h × 6.5 × 10−6 . (6.100)
Using the conversion factor in Eq. (6.100) we find that