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Although these criteria were developed by representatives of federally-owned calibration laboratories, they are not limited to application in the federal sector. Application in the state or private sectors is suitable also, and would result in achievement of a similar high level of performance by those laboratories. The National Institute of Standards and Technology (formerly the National Bureau of Standards) is actively supporting the development of a secondary level of calibration laboratories for ionizing radiation measurements. Such laboratories can provide a high-quality link between the physical measurement standards maintained by NIST and those who make routine measurements at the field level. Since the criteria contained in this publication represent a significant step in the development of a national system of secondary laboratories, NIST is pleased to make them generally available for use. v NOTE REGARDING UNITS It is the policy of NI ST to use the modern metric system of measurement units (International System of Units; abbreviated as SI) in all publications. Units used with the International System and units in use temporarily, as recognized in NIST Special Publication 330, are acceptable. Included in those two categories are the following units in this document: Unit Quantity Unit Name Symbol Value in SI units time hour h 1 h = 3600 seconds energy electronvolt eV 1 eV = = 1.602 x IO-1 9 joule (J) exposure roentgen R 1 R = 2.58 x 10-1+ coulomb/kilogram absorbed dose rad rad 1 rad = 10-2 g ray (Gy) dose equivalent rem rem 1 rem = 10-2 sievert (Sv) Although use of the roentgen, rad, and rem is temporarily acceptable, a timely transition to SI units is desirable. Therefore this document will show the SI equivalent in parentheses wherever feasible. The SI units indicated above will be shown for the quantities absorbed dose and dose equivalent. However, since the quantity exposure is being phased out, the SI unit coulomb/kilogram will not be shown in this document. It has no special name, it is inconvenient (especially for exposure rate), and its definition is not consistent with other physical quantities. The quantity exposure will be replaced with the quantity air kerma, which has the SI unit joule/kilogram (J/kg) with the special name gray (Gy): 1 Gy = 1 J/kg. Although the factor used for conversion from exposure in roentgens to air kerma in grays depends slightly on photon energy, that variation is insignificant for the purposes of this document and a single value will be used: air kerma (in grays) = 0.00878 times exposure (in roentgens) When a rounded value of exposure is given, the SI equivalent value of air kerma will be rounded also (e.g., 10 mR/h * 90 yGy/h). vi CRITERIA FOR THE OPERATION OF FEDERALLY-OWNED SECONDARY CALIBRATION LABORATORIES PART A-GENERAL CRITERIA 1.

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