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

RADIATION SAFETY GUIDES 389
The bb compartments are irradiated by the activity deposited there plus the activity
brought up from the compartments in the AI region. Activity transferred from a
given compartment is equal to the activity initially deposited there minus the sum
of the dissolved activity plus the decayed activity:
Activity transferred = deposited activity − (dissolved + decayed) activity. (8.34)
For long-lived activity, such as in 14 C, decay may be neglected. The slow dissolution
rate (Table 8-13) is 0.0001 per day. For the half-day mean retention time, an insignificant
amount will have dissolved, and we can ignore the decrease in activity by
solution. Therefore, the number of disintegrations in bb1 due to activity transferred
from AI1 to bb1 (AI1 → bb1), that contribute to the dose to bb1 is
0.0159 Bq × 1dps
Bq
s
× 86,400 × 0.499975 d = 687 disintegrations.
d
Similar calculations for transfers to bb1 from AI2 and AI3 plus the activity initially
deposited there, yield a total of 2,318 disintegrations in compartment bb1. In the bb2
compartment, we calculate 15,788 and in bbseq, 659 disintegrations. The number of
disintegrations in each compartment that contribute to the regional dose, which was
calculated by multiplying the activity in the source by the mean retention time from
Table 8-16, is listed in Table 8-17.
The radiosensitive target cells within the HRT are irradiated from several different
sources of radioactive particles that are located in several different parts of the respiratory
system. In the ET regions, for example, the radiation sources are particles that
lie directly on the surface of the skin, by particles sequestered by macrophages that
are concentrated in the subepithelial tissue of the airway wall, and by radionuclides
chemically bound to the epithelium.
Target cells in the BB and bb regions are irradiated by radioactive particles that are
being transported by the fast-moving mucous and by the slow-moving mucous within
the airways of the upper respiratory tract, by particles sequestered in macrophages,
by radioactivity chemically bound to the airway wall, and by particles that are within
the alveolar-interstitium. The AI region is irradiated by radioactive particles within
the alveoli and by particles in the bb and BB regions. The fractions of the energy
emitted from the several sources that are absorbed by the radiosensitive target cells,
AF(T←S), are listed in ICRP 66 Tables H.1 to H.5. Absorbed fractions for three beta
emitters: tritium, Ē = 0.0056 MeV; 14 C, Ē = 0.0498 MeV; and 32 P, Ē = 0.6918 MeV,
which are taken from ICRP 66 Table H.5, are shown in Table 8-18.
To calculate the dose to the lung, we will
(1) calculate the regional equivalent dose, HR,
(2) multiply the regional doses by the appropriate fraction, A, of the tissue weighting
factor, w T, for the lung (from Tables 8-3 and 8-14), and
(3) sum the products HR × A to calculate the equivalent dose to the lungs.
H lungs = (HR × A) Sv (or rem). (8.35)