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Contaminated Wounds - doe-std-1128-98_ch10151
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DOE Standard Guide of Good Practices for Occupational Radiological Protection In Plutonium Facilities
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Table 6.1. Effective Depth of Tissue for Various Organs - doe-std-1128-98_ch10154


DOE-STD-1128-98
6.0
EXTERNAL DOSE CONTROL
The purpose of an external dose control program is to protect the individual radiation
worker by minimizing dose to levels as low as reasonably achievable (ALARA) and
preventing exposures above prescribed limits. This also implies minimizing the collective
dose by summing all the individual total effective dose equivalents in a specified
population. This section discusses methods to minimize exposures by characterizing the
radiations emitted by plutonium and effective methods to shield or otherwise reduce
exposures.
The Department of Energy provides a detailed explanation of the recommendations for
external dosimetry in the Implementation Guide, External Dosimetry Program (DOE,
1999e). Specific applicable documents for external dosimetry are listed in the reference list
of that Implementation Guide. Because the requirements and recommendations are
explicitly given in these documents, they will not be discussed in any great detail in this
section. Rather, the emphasis will be given to items that are unique to plutonium facilities
and the radiological aspects for safe handling of plutonium.
Measuring the external radiation exposure and the resultant dose for personnel handling
plutonium is a difficult task because of the many radiations involved. Examples of the
radioactive decay schemes and radiations emitted were presented in Section 2.0 for the
various plutonium isotopes and radioactive progeny. Plutonium has a wide distribution of
gamma energies; literally hundreds of different photon energies are present. Fortunately,
plutonium emits few high-energy photons, so photon dose rates are low. But plutonium also
emits highly penetrating neutrons from spontaneous fission and alpha-neutron reactions
from compounds and alloys.
In the past, most of the dose in plutonium facilities was the result of plutonium production
and fabrication operations. Most of these operations involved physical contact with freshly
separated plutonium in glove boxes during fabrication and assembly operations. With the
reduction in weapons production, emphasis has shifted to dismantlement and storage
operations and to D&D of plutonium facilities. Much of the material in these facilities is
low-exposure plutonium containing 6% 240Pu that is at least 20-years-old, so a significant
fraction of the 241Pu has decayed into 241Am. The radioactive progeny have increased
gamma dose rates, making dismantlement of plutonium facilities more difficult. Although
many of the examples in this section involve higher-exposure plutonium, it is expected that
most dosage in plutonium facilities will originate from clean-up and storage of weapons-
grade plutonium.
6.1
DOSE LIMITS
Limits of interest used for control of external radiations are specified at various depths by
10 CFR 835 (DOE, 1998a) as well as the ICRP and the National Council on Radiation
Protection and Measurements (NCRP). The limits are given in Table 6.1 for the appropriate
depths in tissue for the whole body, lens of the eye, "unlimited areas of skin," forearms,
and hands and feet.
6-1


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