Example 4.5. Potential Technology Shortfall for Breathing Zone Air Sampling of High Specific

DOE-STD-1121-98

Example 4.5. Potential Technology Shortfall for Breathing Zone Air Sampling of High Specific

Activity Alpha Emitting Nuclides

For high specific activity alpha emitters, a single large particle on an air sampler filter may

give erroneous results, a phenomenon that can be described as the "countable number of particles

problem." In facilities where 238Pu is processed, it may be difficult to use BZ or personal air

monitoring to control intakes near the level of 2% of a NALI. Using the methods in ICRP Publication

66, and a density of 11 g/cm3 for plutonium oxide (ICRP 1994a and p. 1.7 of Faust et al. 1988), the

table below was calculated. The equivalent physical diameter also accounts for slip correction and

thermodynamic effects, both important at small particle sizes. The table shows that one particle with

an aerodynamic diameter of 5 :m is approximately 2% of a NALI.

With Monte Carlo analysis, Scott et al. (1997) show that calculated average intake of high specific

activity alpha emitters, in DAC-h, is not an operationally useful quantity. They used a light activity

breathing rate of 1.5 m3h-1, a density of 10.0 g cm-3, an AMAD of 5:m, and a GSD of 2.5 and

calculated the intakes of 10,000 workers exposed. In an 8 DAC-h exposure, 9,831 had no intake, 4

had intakes greater than one ALI (that is, 2,000 DAC-h or 600 Bq of 238Pu), and 165 had intakes

ranging from a fraction of a DAC-h to nearly 2,000. All intakes resulted from inhaling a single

particle of 239PuO2. Thus, the average intake computed for the group of workers, would both

overestimate the intakes of the vast majority of individuals and seriously underestimate intakes of the

more highly exposed individuals.

Aerodynamic Equivalent

Number of Number of

physical Volume Mass per Activity per particles per particles per

diameter

(:m) dia. (:m)

(cm3) particle (g) particle (Bq)

NALI 0.02 NALI

0.1

1.2E-02 8.1E-19

8.9E-18

5.0E-06

1.5E+08

2.9E+06

0.2

2.9E-02 1.2E-17

1.3E-16

7.5E-05

9.6E+06

192,551

0.3

5.0E-02 6.7E-17

7.3E-16

4.1E-04

1.8E+06

35,224

0.5

1.0E-01 5.6E-16

6.2E-15

3.5E-03

207,805

4,156

0.7

1.6E-01 2.1E-15

2.4E-14

1.3E-02

54,698

1,094

2.5E-01 8.1E-15

8.9E-14

5.0E-02

14,530

291

5.5E-01 8.6E-14

9.5E-13

5.3E-01

1,361

8.5E-01 3.2E-13

3.5E-12

2.0E+00

367

7.3

5 1.4E+00 1.6E-12

1.8E-11

9.8E+00

1.5

7 2.1E+00 4.5E-12

5.0E-11

2.8E+01

0.52

10 3.0E+00 1.4E-11

1.5E-10

8.3E+01

8.7

0.17

20 6.0E+00 1.1E-10

1.2E-09

6.8E+02

1.05

0.021

30 9.0E+00 3.8E-10

4.2E-09

2.3E+03

0.31

0.0062

50 1.5E+01 1.8E-09

2.0E-08

1.1E+04

0.066

0.0013

70 2.1E+01 4.9E-09

5.4E-08

3.0E+04

0.024

0.00048

100 3.0E+01 1.4E-08

1.6E-07

8.8E+04

0.0082

0.00016

200 6.0E+01 1.1E-07

1.3E-06

7.0E+05

0.0010

0.00002

300 9.0E+01 3.9E-07

4.3E-06

2.4E+06

0.00030

6.1E-06