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

396 CHAPTER 8
Thus, for airborne 137 Cs, whose inhalation ALI is listed in ICRP 30 as 6 × 10 6 Bq,
the DAC is
DAC =
6 Bq
6 × 10
yr
2400 m3
yr
= 2.5 × 10
3 Bq
,
3
m
which is rounded off to 2 × 10 3 Bq/m 3 .
According to ICRP 60 criteria, the annual dose limit is 0.02 Sv/yr. For 5-μm
AMAD, class F 137 Cs particles, the DC is listed as 6.7 × 10 −9 Sv/Bq, the ALI is
calculated as
0.02 Sv
ALI =
= 3 × 10
−9 Sv
6.7 × 10
Bq
6 Bq,
and the DAC is
DAC = 3 × 106 Bq
Bq
= 1.3 × 103 3 2400 m m
Gaseous Radioactivity
3 .
Immersion in a cloud of radioactive gas leads to external exposure from the activity
in the surrounding air and to internal exposure due to the inhaled gas. For the case
of biochemically inert gases argon, krypton, and xenon, the external submersion
dose limits the atmospheric concentration, as shown by the calculations for 41 Ar in
the following paragraphs.
Argon-41, a biochemically inert gas, is transformed to 41 K by the emission of a
1.2-MeV beta particle and a 1.3-MeV gamma ray. The half-life of 41 Ar is 110 minutes,
or 0.076 days. For the case of submersion, it is assumed that a person is exposed
in an infinite hemisphere of the gas. For this exposure condition, ICRP 68 lists the
effective DC for 41 Ar as 5.3 × 10 −9 Sv/d/ per Bq/m 3 . The reference working year is
250 days of 8 hours each. For an effective annual dose of 0.02 Sv (2 rems), the mean
concentration of 41 Ar is calculated by
−9 Sv/d
Bq
0.02 Sv = 5.3 × 10 × 250 d × C
Bq/m3 m3 4 Bq
C = 1.5 × 10
m3
−7 μCi
4 × 10 .
mL
(8.39)
When a gas is inhaled, it may dissolve in the body fluids and fat after diffusion
across the capillary bed in the lung. In the case of an inert gas, absorption into
the body stops after the body fluids and fat are saturated with the dissolved gas.
The saturation quantity of dissolved 41 Ar in the body fluids due to inhalation of
contaminated air at the DAC, based on submersion, must be calculated in order
to determine the internal dose. The first step in this calculation is the determi-