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
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.
18.104.22.168 In Vitro Analysis
The two most common forms of in vitro analysis are urinalysis and fecal analysis.