In Vitro Analysis - doe-std-1128-98

DOE-STD-1128-98

The americium-tracer method has the advantage of better detection capability for

some mixtures of plutonium. The typical MDA for 241Am lung counting is 0.1 to 0.2

nCi. The americium-tracer method depends on the plutonium/americium ratio, which

must be independently determined or estimated for each intake. The detection level

for this method with a plutonium/americium ratio of 15 is typically 2-nCi plutonium

in the lung. The americium-tracer method also has the advantage of being less

affected by attenuation in the chest wall or by variations in the muscle/fat ratio.

However, it has the disadvantage of requiring an estimate of the

plutonium/americium ratio, both initially and at long times post intake. This ratio

may change over time because of ingrowth of 241Am as the decay product of 241Pu or

because americium may naturally clear from the lungs and translocate among internal

organs at a rate different than that for plutonium.

The most widely used systems for lung counting are high-purity germanium

detectors, thin sodium-iodide detectors, phoswich detectors, and proportional

counters. Multiple high-purity germanium detectors have advantages over the other

detector systems because of their good resolution, allowing better identification of

the radionuclide, better detectability, and better background prediction capability.

The main disadvantages of germanium detector arrays are their higher cost relative to

other types of in vivo detectors and their lower reliability. Germanium detectors also

must be continuously cooled with liquid nitrogen.

Measurement equipment to detect and measure plutonium contamination in wounds

should be available at all plutonium facilities. Instrumentation used for this purpose

may include thin-crystal NaI(Tl), intrinsic germanium, or Si(Li) detectors. The

detection level for plutonium wound measurements is typically 0.1 nCi for 239Pu.

Correction for depth due to absorption of photons in the overlying tissues should be

considered. Collimated detectors are useful for determining the location of the

plutonium in wounds.

Estimates of the depth of plutonium contamination in a wound may be made using

solid-state germanium or Si(Li) detectors to measure the relative absorption of the

low-energy X-rays emitted by plutonium. Information about depth is important for

determining whether tissue excision is necessary to remove the contamination.

5.3.3.2 In Vitro Analysis

The two most common forms of in vitro analysis are urinalysis and fecal analysis.

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