In Vitro Analysis

DOE-STD-1136-2004

Guide of Good Practices for Occupational Radiological Protection in Uranium Facilities

When direct bioassay is used, the detection system should be calibrated for the radionuclides to be

measured in the appropriate organs. All calibration procedures, calibration records, and quality control

data should be maintained.

A uranium facility should have the capability to detect and assess depositions of uranium in the

lungs of affected workers. The major objective of lung counting is to provide measurements of

suspected intakes triggered by workplace monitoring results. Lung measurements should be made to

provide an early estimate of the magnitude of the intake and resulting lung deposition.

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.

For natural and enriched uranium, the energy most commonly used for in vivo monitoring is the 185-

keV gamma that is emitted with 54% abundance from the decay of 235U (ANSI/HPS 1995; Gerber and

Thomas 1992). For natural uranium, approximately 50% of the activity is due to decay of 234U. For

enriched uranium, 234U is the major contributor to total activity. Thus, one must be aware that in vivo

monitoring for uranium is based on detection and measurement of a uranium isotope that contributes very

little to the dose (ANSI/HPS 1995). To calculate dose, one needs to know the total uranium activity and

the isotopic distribution of the material.

For natural or depleted uranium, detection of the 92.4-keV and 92.8-keV K x-rays emitted by the

234

Th daughter product are most commonly used (ANSI/HPS 1995; Gerber and Thomas 1992). This

monitoring method would not be appropria te for freshly separated uranium as the 234Th will not be in

equilibrium with the 238U and would potentially result in an underestimate or overestimate of the actual

internal burden.

Measurement equipment to detect and measure uranium contamination in wounds should be available

at all uranium facilities. Instrumentation used for this purpose may include thin-crystal NaI(Tl), intrinsic

germanium, or Si(Li) detectors. 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 uranium in

wounds.

Estimates of the depth of uranium 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

uranium. 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.

Urinalysis. Urine sampling provides useful information about the amount of uranium excreted

following an intake. After chemical isolation, the uranium in urine samples may be determined by alpha

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