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

412 CHAPTER 8
when rounded to one significant figure. It should be noted that the rounding to
one significant figure is for listing the final value only, not for carrying out the
successive calculations. If the numbers rounded to one significant figure were to be
used successively, rounding errors would accumulate and might lead to erroneous
final results.
Particle Size and DAC
Safety standards for radioactive aerosols that are listed in 10 CFR 20 are based on
ICRP 30 criteria for occupational inhalation. That is, they are for particles of 1-μm
AMAD and σg ≤ 4.5. For particles whose AMAD differs from 1 μm, adjustment of the
published DAC may be made according to the following relationship, given in ICRP
30, between the dose from the ith particle size and the dose from 1-μm particles:
H50(i)
H50(1μm)
where
= fNP
DNP(i)
DNP(1μm)
+ fTB
DTB(i)
DTB(1μm)
+ fP
DP(i)
, (8.56)
DP(1μm)
H50 = committed dose equivalents from the 1-μm and ith-μm
AMAD particles;
fNP, fTB, and fP = fractions of the committed dose equivalent due to
deposition in the NP, TB, and P respiratory compartments
(these values are listed in the supplements to Parts 1 and
2 of ICRP 30. Values can also be found in Table 8.8); and
DNP, DTB, and DP = deposition fractions in the respective respiratory
compartments for a given particle size.
W Example 8.8
The AMAD of UO2 particles in one of the production departments of a uraniumprocessing
facility was found to be 9.6 μm. The DAC given in 10 CFR 20 for class Y
(UO2 is a class Y compound) for 1-μm AMAD particles is 2 × 10 −11 μCi/mL (and
7 × 10 −1 Bq/m 3 in ICRP 30). What is the DAC corrected for the particle size?
Solution
We will calculate the size-corrected DAC with the aid of Eq. (8.56). The regional
deposition probabilities for the two different size distributions, which are found in
Figure 8-4, are listed below:
AMAD DNP DTB DP
1.0 0.30 0.08 0.25
9.6 0.87 0.08 0.05