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DOE-STD-1136-2004
Guide of Good Practices for Occupational Radiation Protection in Uranium Facilities
6.4 PERSONNEL DOSIMETRY
It is important to verify and document that personnel dosimetry systems provide accurate
measurements and records of the occupational radiation doses received by workers in uranium facilities. To
provide a level of confidence in dosimetry services in DOE facilities, the DOELAP accreditation program
has been established. 10 CFR 835 requires participation in the DOELAP program (or specific exceptions or
other approvals) by all DOE facilitie s that are subject to the individual external dose monitoring
requirements. Previously, the National Institute of Standards and Technology (NIST) established the
National Voluntary Laboratory Accreditation Program (NVLAP) for testing and accreditation of dosimeter
processors serving the commercial nuclear power industry and medical facilities. The DOELAP standard
includes some tests that differ from those in ANSI N13.11 (ANSI 1983a), on which the NVLAP program is
based. Both DOELAP and NVLAP accreditation programs use performance tests that evaluate the accuracy
and precision of personnel dosimetry measurements. The accuracy is determined by comparing the
measured dose equivalent to the "conventionally true dose equivalent" derived from calibration standards
directly traceable to NIST in carefully controlled conditions.
DOE G 441.1-4, External Dosimetry Program Guide, provides detailed guidance for developing
and implementing an external dosimetry program that will comply with the requirements of 10 CFR 835.
This section will focus on dosimetry problem areas specific to uranium facilities and possible solutions.
Personnel dosimeters produce the data that become the formal or "legal" record of personnel
exposure. However, these detectors experience many of the same energy dependence and angular
response problems encountered by survey instruments. The most difficult problem is relating badge
results to the shallow or skin dose.
Thermoluminescent dosimeters (TLDs), currently the dosimeter of choice in most DOE uranium
facilities, provide the most accurate and precise means of measuring doses received by workers. Film
badges and nuclear track detectors are other types of dosimeters. Although the following discussion focuses
on the more widely used TLD detector systems, the basic principles apply to film badges, with the added
uncertainties associated with the increased susceptibility of film to environmental influences, such as
temperature, humidity, pressure, etc. Great care is necessary to ensure that the shallow and deep doses are
accurately discriminated and measured.
An ideal dosimeter would directly measure doses at 7, 1000, and perhaps 300 mg/cm2 (shallow,
deep, and lens of eye doses). In practice, the dose at such depths in tissue must be inferred from a
combination of measurements with different filters. TLD and film elements are mounted in a badge
arrangement, which is covered by at least 10 to 30 mg/cm2 of Mylar, paper, or other covering for
mechanical and/or protective reasons.
6.4.1 Energy Dependence
Personnel dosimeters are beta energy-dependent for the same reason that survey instruments are
beta energy-dependent. That is, the reading obtained from the dosimeter is proportional to the average rate
of energy deposition through the "sensitive volume" or body of the element. If this average energy
deposition is less than the deposition at 7 mg/cm2, then the dosimeter will under-respond.
6-18


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