This material may be considered to be not contaminated and an instrument survey is
not necessary according to the DOE standard, Radiological Control, Ch. 1. (DOE,
2004). A material history release form should be used to document the release of
material that is known to be free of contamination by its history of use. If the material
history release form cannot be completed, or if the history of the material is
unknown, an instrument survey must be made of the material. Material released from
RBAs around Contamination Areas, High Contamination Areas, or Airborne
Radioactivity Areas should also be evaluated using an instrument survey.
The material evaluation process should also consider the nuclides to which the
material was potentially exposed. If the material was exposed to significant quantities
of nuclides that are difficult to detect, including tritium, 14C, 125I, or 129I, an
appropriate survey methodology should be applied.
4.2.6 Plutonium Contamination Detection
The detection and measurement of plutonium contamination is necessary to ensure
control of contamination and compliance with DOE requirements. Typically,
detection of plutonium contamination has been performed using survey instruments
that detect the alpha activity. Routinely used health physics instruments (i.e., alpha
survey instruments) may not be adequate for some D&D operations. Self-absorption
of plutonium alpha particles within the source or in an irregular surface area may
require the use of special X-ray and low energy photon instruments (e.g., a NaI
detector). The NaI detector should also be used to detect plutonium contamination
that has been painted over.
Discussions of methods used to detect plutonium contamination for past D&D
operations can be found in publications by Umbarger (1982) and West et al. (1991).
Umbarger reported on nondestructive assay techniques (including portable field
instrumentation and laboratory-based methods) for sorting waste in low-level (class
A) and TRU waste. Portable field instruments included the field FIDLER (i.e., thin
NaI detector), phoswich detector (i.e., thin NaI detector coupled with a thicker CsI
detector), ZnS alpha scintillation detector, a portable multichannel analyzer, and a
hand-held gamma-ray spectrometer gun. The advantage of a phoswich detector over
a NaI detector is its lower operating background. In the field, the phoswich detector
has a detection limit of <1 nCi/g. The ZnS scintillation detector had a detection limit
of 25 pCi/g for gross alpha counting. Laboratory-based systems include active and
passive gamma-ray spectroscopy, passive neutron detection, and pulsed portable
neutron generator interrogation.