Example 4.2. Maximizing the Detection Sensitivity for Chronic Intakes of Tritium

DOE-STD-1121-98

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Use of this equation can help determine the optimum sampling frequency for radionuclides for which the

MDA is undesirably high. Example 4.2 shows this approach for tritium.

Example 4.2. Maximizing the Detection Sensitivity for Chronic Intakes of Tritium

To illustrate the dependence of the detection sensitivity on f, consider the IRFu(t) for 3H:

where k is a normalizing constant. Substituting 365/f for t and putting this in the )Amin equation, we

have

For the case of 3H, the sampling frequency that makes minimum demands on analytical

technology is

The solution to this is found by setting the term in parentheses to zero, giving

The interval between the samples is simply the average clearance time Jeff = 1/8eff = 14.4 days for 3H.

A plot of the 3H )Amin for a constant total annual missed dose as a function of sampling

frequency is shown in Figure 2. If sampling is done more often than once every Jeff, a lower )Amin

(better analytical lab capability) is needed to see intakes resulting in the AMDD.

While use of the second method for establishing DILs may provide assurance that there is no

possibility of missing intakes resulting in doses at or above the IL, it may be too complicated for practical

implementation.

It may be possible to apply the averaging techniques of Strom and McGuire (Strom and McGuire

1993) as detailed in NUREG 1400 (Hickey et al. 1993) to improve the counting statistics, and thus reduce

the MDA for a given bioassay technique, but this has been established only for air monitoring.