Comparison of the NIST and BIPM medium-energy x-ray air-kerma measurements.The air-kerma standards used for the measurement of medium-energy x rays were compared at the National Institute of Standards and Technology National Institute of Standards and Technology, governmental agency within the U.S. Dept. of Commerce with the mission of "working with industry to develop and apply technology, measurements, and standards" in the national interest. (NIST (National Institute of Standards & Technology, Washington, DC, www.nist.gov) The standards-defining agency of the U.S. government, formerly the National Bureau of Standards. It is one of three agencies that fall under the Technology Administration (www.technology. ) and at the Bureau International des Poids et Mesures (body, standard) Bureau International des Poids et Mesures - (BIPM) The standards body that ensures world-wide uniformity of measurements and their traceability to the International System of Units (SI). (BIPM BIPM - Bureau International des Poids et Mesures ). The comparison involved a series of measurements at the BIPM and the NIST using the air-kerma standards and two NIST reference-class transfer ionization ionization: see ion. ionization Process by which electrically neutral atoms or molecules are converted to electrically charged atoms or molecules (ions) by the removal or addition of negatively charged electrons. standards. Reference beam A reference beam is a laser beam used to read and write holograms. It is one of two laser beams used to create a hologram. In order to read a hologram out, some aspects of the reference beam (namely its angle of incidence, beam profile and wavelength) must be reproduced exactly as qualities in the range from 60 kV to 300 kV were used. The results show the standards to be in agreement within the combined standard uncertainty of the comparison of 0.35%. Keywords: air kerma; free-air ionization chamber; primary standard; reference radiation qualities; medium-energy x rays; x-ray X-ray Electromagnetic radiation of extremely short wavelength (100 nanometres to 0.001 nanometre) produced by the deceleration of charged particles or the transitions of electrons in atoms. calibration calibration /cal·i·bra·tion/ (kal?i-bra´shun) determination of the accuracy of an instrument, usually by measurement of its variation from a standard, to ascertain necessary correction factors. . [J. Res. Natl. Inst. Stand. Technol. 108, 383-389 (2003)] 1. Introduction An indirect comparison was made between the air-kerma primary standards for medium-energy x rays at the National Institute of Standards and Technology (NIST) and at the Bureau International des Poids et Mesures (BIPM). The measurements were conducted in March of 1991 at the BIPM and at the NIST. The measurements at the NIST were made using tungsten tungsten (tŭng`stən) [Swed.,=heavy stone], metallic chemical element; symbol W; at. no. 74; at. wt. 183.85; m.p. about 3,410°C;; b.p. 5,660°C;; sp. gr. 19.3 at 20°C;; valence +2, +3, +4, +5, or +6. reference radiation qualities in the range from 60 kV to 300 kV. The reference radiation qualities used at the BIPM are those in the range from 100 kV to 250 kV recommended by the Consultative Committee for Ionizing Radiation i·on·i·zing radiation n. High-energy radiation capable of producing ionization in substances through which it passes. Ionizing radiation (CCEMRI) [1]. Two NIST reference-class ionization chambers were shipped to the BIPM for the comparison. 2. Determination of the Air-Kerma Rate For a free-air ionization chamber standard with measuring volume V, the air-kerma rate is determined by the relation K = [I/[[[rho].sub.air]V]][[W.sub.air]/e][1/[1 - [g.sub.air]]][Product.i] [k.sub.i], (1) where I/[[rho].sub.air] V is the mass ionization current measured by the standard, [W.sub.air] is the mean energy expended ex·pend tr.v. ex·pend·ed, ex·pend·ing, ex·pends 1. To lay out; spend: expending tax revenues on government operations. See Synonyms at spend. 2. by an electron of charge e to produce an ion pair in dry air, [g.sub.air] is the fraction of the initial electron energy lost by bremsstrahlung bremsstrahlung (brĕm`shträ'ləng): see X ray. bremsstrahlung (German; “braking radiation”) production in air, and [PI]ki is the product of the correction factors to be applied to the standard. The values for the physical constants used in the determination of the air-kerma rate are given in Table 1. 3. Characteristics of Chambers 3.1 Description of Air-Kerma Standards Both air-kerma standard chambers used in the comparison are parallel-plate free-air ionization chambers. The measuring volume V is defined by the diameter of the chamber aperture An orifice. It often refers to an opening in which light is allowed to pass in optical systems such as cameras and lasers. See f-stop and numerical aperture. and the length of the collecting plate. The BIPM air-kerma standard is described in Refs. [2] and [3]. The NIST Wyckoff-Attix chamber is described in Refs. [4] and [5]. The main dimensions, the measuring volume, and the polarizing voltage for each chamber are given in Table 2. 3.2 Description of Transfer Ionization Chambers Two NIST transfer chambers (NIST-T1 and NIST-T2, serial numbers 2022 and 2023 respectively) were used for the comparison. Both of the NIST transfer standards are spherical spher·i·cal adj. Having the shape of or approximating a sphere; globular. and constructed with a wall of air-equivalent plastic. Each has a nominal volume of 3.6 c[m.sup.3], an external diameter of 1.9 cm, and a wall thickness of 0.25 mm. A collecting voltage of 300 V was applied to the NIST transfer standards. A negative polarity (1) The direction of charged particles, which may determine the binary status of a bit. (2) In micrographics, the change in the light to dark relationship of an image when copies are made. was used at NIST and both polarities were used at the BIPM. Both of the NIST transfer chambers were calibrated cal·i·brate tr.v. cal·i·brat·ed, cal·i·brat·ing, cal·i·brates 1. To check, adjust, or determine by comparison with a standard (the graduations of a quantitative measuring instrument): using the NIST and the BIPM standards. The calibration factors for both chambers were determined at the NIST before and after the calibrations at the BIPM. 4. Comparison Details 4.1 Irradiation irradiation /ir·ra·di·a·tion/ (i-ra?de-a´shun) 1. radiotherapy. 2. the dispersion of nervous impulse beyond the normal path of conduction. 3. Facilities and Reference Beam Qualities The BIPM portion of the comparison was conducted at the BIPM medium-energy x-ray laboratory, which houses a constant-potential generator generator, in electricity, machine used to change mechanical energy into electrical energy. It operates on the principle of electromagnetic induction, discovered (1831) by Michael Faraday. (maximum usable USable is a special idea contest to transfer US American ideas into practice in Germany. USable is initiated by the German Körber-Stiftung (foundation Körber). It is doted with 150,000 Euro and awarded every two years. generating potential 250 kV) and a tungsten-anode x-ray tube X-ray tube An electronic device used for the generation of x-rays. X-rays are produced in the x-ray tube by accelerating electrons to a high velocity by an electrostatic field and then suddenly stopping them by collision with a solid body, the so-called with an inherent filtration filtration: see sewerage; water supply. Filtration The separation of solid particles from a fluidsolids suspension of which they are a part by passage of most of the fluid through a septum or membrane that retains most of the solids of around 2.3 mm of aluminium. Both the generating potential and the tube current are stabilized sta·bi·lize v. sta·bi·lized, sta·bi·liz·ing, sta·bi·liz·es v.tr. 1. To make stable or steadfast. 2. using feedback systems constructed at the BIPM, resulting in high stability, eliminating the need for a transmission current monitor. For a well-behaved transfer instrument, the variation in the measured ionization current over the duration of a comparison is typically less than 0.04%. The BIPM radiation qualities, which range in energy between 100 kV and 250 kV, are recommended by CCEMRI [1] and are given in Table 3. The NIST portion of the comparison was accomplished through the use of the Wyckoff-Attix chamber in the NIST 300 kV calibration facility. The x-ray source at the time of the comparison was a 320 kV x-ray generator with a metal-ceramic x-ray tube, both supplied by Seifert (1). The x-ray generator was a high-frequency (500 Hz), highly stabilized voltage source A voltage source is any device or system that produces an electromotive force between its terminals OR derives a secondary voltage from a primary source of the electromotive force. with an x-ray output variation of no more than [+ or -] 0.5% in 1 h. The x-ray tube had a beryllium beryllium (bərĭl`ēəm) [from beryl ], metallic chemical element; symbol Be; at. no. 4; at. wt. 9.01218; m.p. about 1,278°C;; b.p. 2,970°C; (estimated); sp. gr. 1.85 at 20°C;; valence +2. window of thickness 3 mm and a projected focal spot focal spot, n See spot, focal. focal spot the area on the target of the x-ray tube which the electron stream strikes and from which x-rays are emitted. Called also focus. size of 5 m[m.sup.2]. The materials used for the filtration and for the measurement of half-value layer half-value layer (HVL), n the thickness of a specified material (usually aluminum, copper, or lead) required to decrease the dosage rate of a beam of radiograph at a point of interest to half its initial value. (HVL HVL, n See half-value layer. HVL half-value layer. ) were 99.99% pure with thicknesses known to within [+ or -]0.01 mm. Output stability was monitored using a transmission ionization chamber. The measured currents were normalized to account for fluctuations. Used in this relative way, the absolute response of the transmission monitor does not change calibration results. The reference radiation qualities used at NIST were generated between 60 kV to 300 kV and are listed in Table 3. 4.2 Correction Factors Although free-air chambers are designed to minimize or eliminate corrections to the measured ionization current, certain corrections are unavoidable. The correction factors applied to each free-air chamber and the associated uncertainties are listed in Tables 4 and 5 by radiation quality. A correction must be made for the attenuation Loss of signal power in a transmission. Attenuation The reduction in level of a transmitted quantity as a function of a parameter, usually distance. It is applied mainly to acoustic or electromagnetic waves and is expressed as the ratio of power densities. of the x-ray fluence Flu´ence n. 1. Fluency. along the air path L between the reference plane and the center of the collecting volume. The correction factor [k.sub.a] is calculated using the measured or calculated air-attenuation coefficients [[mu].sub.air], according to according to prep. 1. As stated or indicated by; on the authority of: according to historians. 2. In keeping with: according to instructions. 3. [k.sub.a] = exp exp abbr. 1. exponent 2. exponential ([[mu].sub.air] L) (2) The effective attenuation path L varies with the temperature and pressure of the air in the chamber. The values for [k.sub.a] are corrected for this effect. All ionization measurements are also corrected for the temperature and pressure of the ambient Surrounding. For example, ambient temperature and humidity are atmospheric conditions that exist at the moment. See ambient lighting. air between the radiation source and the reference plane. All measured ionization currents using the free-air chamber standards are corrected for ion recombination recombination, process of "shuffling" of genes by which new combinations can be generated. In recombination through sexual reproduction, the offspring's complete set of genes differs from that of either parent, being rather a combination of genes from both parents. , [k.sub.s]. The ionization currents measured with the transfer standards are not corrected for ion recombination. Since the air-kerma rates used at both facilities are low, minimal volume recombination occurs in the transfer chambers. It is assumed that the difference in the recombination effect, produced at each facility, is negligible  This article or section is written like a personal reflection or and may require .Please [ improve this article] by rewriting this article or section in an . . The standard chambers are corrected for the humidity humidity, moisture content of the atmosphere, a primary element of climate. Humidity measurements include absolute humidity, the mass of water vapor per unit volume of natural air; relative humidity (usually meant when the term humidity effect [k.sub.h] which is taken as 0.998 for both standards and all radiation qualities. 4.3 Chamber Positioning and Measurement Procedure At the NIST and at the BIPM the transfer ionization chambers and each standard chamber remain fixed in position throughout the comparison measurements. All calibrations of the transfer chambers were preceded by measurements using the standard free-air chambers. At both laboratories alignment on the beam axis was measured to around 0.1 mm and this position was reproducible re·pro·duce v. re·pro·duced, re·pro·duc·ing, re·pro·duc·es v.tr. 1. To produce a counterpart, image, or copy of. 2. Biology To generate (offspring) by sexual or asexual means. to better than 0.01 mm, as observed by an alignment telescope telescope, traditionally, a system of lenses, mirrors, or both, used to gather light from a distant object and form an image of it. Traditional optical telescopes, which are the subject of this article, also are used to magnify objects on earth and in astronomy; . No correction is applied for the radial radial /ra·di·al/ (ra´de-al) 1. pertaining to the radius of the arm or to the radial (lateral) aspect of the arm as opposed to the ulnar (medial) aspect; pertaining to a radius. 2. non-uniformity of each beam. The reference plane for each chamber was positioned at 1000 mm from the radiation source at the NIST and 1200 mm at BIPM. This distance was measured to 0.03 mm and was reproducible to better than 0.01 mm. The beam diameter The beam diameter of an electromagnetic beam is the diameter along any specified line that is perpendicular to the beam axis and intersects it. For this purpose, the diameter is often defined as the distance between the two diametrically opposite points at which the irradiance is a in the reference plane was 35 mm at the NIST and 105 mm at the BIPM. The leakage LEAKAGE. The waste which has taken place in liquids, by their escaping out of the casks or vessels in which they were kept. By the act of March 2, 1799, s. 59, 1 Story's L. U. S, 625, it is provided that there be an allowance of two per cent for leakage, on the quantity which shall appear current was measured before and after each series of ionization current measurements and a correction made based on the mean of these leakage measurements. For all measurements the leakage current was less than 1[0.sup.-4] of the ionization current. For all chambers at the NIST, six sets of two to six charge measurements were made. Each charge measurement had an integration time of 60 s. The statistical standard uncertainty of the current measurements was typically less than 0.02% for the NIST standard and transfer chambers. At the BIPM each calibration factor was obtained from a total of 80 measurements of around 30 s performed with the BIPM standard and each transfer chamber. The statistical standard uncertainty of each calibration factor is less than 0.01%. The polarity correction for the transfer chambers was measured at the BIPM to be only 1.0003 for both transfer chambers. Only negative polarity was used for each transfer chamber during the calibrations at the NIST. A component of 0.03% is included in the uncertainty of the current measurement at the NIST to account for the polarity effect. All transfer ionization chamber current measurements were normalized to 293.15 K and 101 325 Pa. The transfer chamber currents are not adjusted for humidity. The humidity is monitored and recorded at both facilities. The BIPM laboratory humidity is maintained at 50%. The NIST laboratory average humidity is 30%. 5. Measurement Uncertainties The uncertainties associated with the primary standards are given in Table 6. The NIST uncertainties were evaluated according to Ref. [6]. The uncertainties associated with the calibration of the transfer ionization chambers at the NIST and at the BIPM are listed in Table 7. Table 8 list the uncertainty of the comparison results, [R.sub.K], which are the ratios of the calibration coefficients [N.sub.K] for each chamber as a function of HVL. The uncertainties of the ratios [N.sub.K,NIST]/[N.sub.K,BIPM] take into account correlations due to common Type B uncertainties associated with the physical constants and the humidity correction. There is also significant correlation in the values used for [k.sub.sc] and [k.sub.e]. This has been accounted for in an approximate way by halving these uncertainty components. 6. Results and Discussion The results for the transfer ionization chamber calibrations at both laboratories are shown in Table 9 and in Figs. 1 and 2. Since the HVL's at the NIST and the BIPM are very different, a quartic quar·tic adj. Mathematics Of or relating to the fourth degree. [Latin qu  rtus, fourth; see quart + -ic. fit
was used for each transfer chamber to interpolate See interpolation. the NIST data in terms
of HVL in order to derive comparison results [R.sub.K] at the HVL values
which correspond to the BIPM radiation qualities;[R.sub.K] = [Value of fit [N.sub.K,NIST](HVL) at BIPM HVL]/[N.sub.K,BIPM] A second fit using a rational function was also made. The agreement between the two fits is close, at worst 0.07%, and an uncertainty component of 0.04% is included in the comparison results to account for the interpolation interpolation In mathematics, estimation of a value between two known data points. A simple example is calculating the mean (see mean, median, and mode) of two population counts made 10 years apart to estimate the population in the fifth year. procedure. The results, [R.sub.K], of this analysis based on the quartic fits are shown in Table 10. The agreement between the two standards is within the combined standard uncertainty of the comparison of 0.35%. [FIGURE 1 OMITTED] This report was not published at the completion of the analysis in June of 1992 because it was thought to be unnecessary as the findings were similar to those of the previous indirect comparison. It is now accepted practice to publish all direct and indirect comparisons at both the NIST and the BIPM. In February of 2003, a similar indirect comparison began between the BIPM and the NIST. Upon completion of the 2003 comparison, it is the intention of the authors to publish the results. [FIGURE 2 OMITTED]
Table 1. Physical constants used in the determination of the air-kerma
rate
Physical Value Relative standard
constant uncertainty
(%)
[[rho].sub.air] (a) 1.293 kg [m.sup.-3] 0.01
[W.sub.air]/e 33.97 J [C.sup.-1] 0.15
(a) Density of dry air at 273.15 K and 101 325 Pa
Table 2. Main characteristics of the primary standards used in the
comparison
Characteristic NIST BIPM
Air-path length (cm) 30.8 28.15
Plate separation (cm) 20.0 18.0
Collecting plate length (cm) 10.08 6.0004
Aperture diameter (cm) 0.9999 0.9939
Measuring volume (c[m.sup.3]) 7.92 4.6554
Polarizing voltage (V) -5000 4000
Table 3. Characteristics of the reference radiation qualities used for
the comparison
Reference Generating Additional filtration
radiation potential
kV mm A1 mm Cu mm Sn
BIPM 100 kV 100 1.2032
BIPM 135 kV 135 0.2321
BIPM 180 kV 180 0.4847
BIPM 250 kV 250 1.5701
NIST M60 60 1.51
NIST M100 100 5.0
NIST M150 150 5.0 0.25
NIST M200 200 4.1 1.12
NIST M250 250 5.0 3.2
NIST M300 300 4.0 6.5
Reference Half-value layer Air-kerma
radiation (HVL) rate
mm A1 mm Cu mGy [s.sup.-1]
BIPM 100 kV 4.027 0.148 0.21
BIPM 135 kV 0.494 0.21
BIPM 180 kV 0.990 0.30
BIPM 250 kV 2.500 0.39
NIST M60 1.68 0.052 0.58
NIST M100 5.0 0.20 0.59
NIST M150 10.2 0.67 0.78
NIST M200 14.9 1.69 0.87
NIST M250 18.5 3.2 0.80
NIST M300 22 5.3 0.32
Table 4. Correction factors used in the comparison for the NIST
Wyckoff-Attix standard
Correction factor Generating potential (kV)
60 100 150
Air attenuation [k.sub.a] (a) 1.0203 1.0097 1.0068
Scattered radiation [k.sub.sc] 0.9923 0.9940 0.9960
Electron loss [k.sub.e] 1.000 1.000 1.0015
Ion recombination [k.sub.s] 1.0011 1.0011 1.0012
Aperture transmission [k.sub.l] 1.0000 1.0000 1.0000
(b)
Field distortion [k.sub.d] 1.0015 1.0015 1.0015
Polarity effect [k.sub.pol] 1.000 1.000 1.000
Wall transmission [k.sub.p] (b) 1.0000 1.0000 1.0000
Bremsstrahlung 1 - [g.sub.air] 1.0000 1.0000 1.0000
Correction factor Generating
potential (kV)
200 250
Air attenuation [k.sub.a] (a) 1.0055 1.0045
Scattered radiation [k.sub.sc] 0.9961 0.9964
Electron loss [k.sub.e] 1.004 1.005
Ion recombination [k.sub.s] 1.0013 1.0012
Aperture transmission [k.sub.l] 1.0000 1.0000
(b)
Field distortion [k.sub.d] 1.0015 1.0015
Polarity effect [k.sub.pol] 1.000 1.000
Wall transmission [k.sub.p] (b) 1.0000 1.0000
Bremsstrahlung 1 - [g.sub.air] 1.0000 1.0000
Correction factor Generating Relative standard
potential uncertainty (%)
(kV)
300 Type A Type B
Air attenuation [k.sub.a] (a) 1.0039 0.07
Scattered radiation [k.sub.sc] 0.9968 0.07
Electron loss [k.sub.e] 1.006 0.1
Ion recombination [k.sub.s] 1.0009 0.1
Aperture transmission [k.sub.l] 1.0000 0.04
(b)
Field distortion [k.sub.d] 1.0015 0.2
Polarity effect [k.sub.pol] 1.000 0.03 0.1
Wall transmission [k.sub.p] (b) 1.0000 0.01
Bremsstrahlung 1 - [g.sub.air] 1.0000 0.01
(a) These are nominal values for T = 293.15 K and p = 100 000 Pa. Each
measurement is corrected using the air temperature and pressure measured
at the time.
(b) The uncertainties in aperture transmission [k.sub.l] and wall
transmission [k.sub.p] are negligible.
Table 5. Correction factors used in the comparison for the BIPM standard
Correction factor Generating potential (kV)
100 135 180 250
Air attenuation [k.sub.a] (a) 1.0102 1.0067 1.0057 1.0049
Scattered radiation [k.sub.sc] 0.9948 0.9962 0.9967 0.9969
Electron loss [k.sub.e] 1.0000 1.0023 1.0052 1.0078
Ion recombination [k.sub.s] 1.0004 1.0005 1.0005 1.0003
Field distortion [k.sub.d] 1.0000 1.0000 1.0000 1.0000
Aperture transmission 0.9999 0.9998 0.9997 0.9996
[k.sub.l]
Wall transmission [k.sub.p] 1.0000 0.9999 0.9998 0.9985
Bremsstrahlung 1 - [g.sub.air] 0.9999 0.9999 0.9998 0.9997
Correction factor Relative standard
uncertainty (%)
Type A Type B
Air attenuation [k.sub.a] (a) 0.03 0.01
Scattered radiation[k.sub.sc] 0.07
Electron loss [k.sub.e] 0.10
Ion recombination [k.sub.s] 0.02 0.01
Field distortion [k.sub.d] 0.07
Aperture transmission 0.01
[k.sub.l]
Wall transmission [k.sub.p] 0.01
Bremsstrahlung 1 - [g.sub.air] 0.01
(a) These are nominal values for T = 293.15 K and p = 100 000 Pa. Each
measurement is corrected using the air temperature and pressure measured
at the time.
(b) The uncertainties in aperture transmission [k.sub.l] and wall
transmission [k.sub.p] are negligible.
Table 6. Relative standard uncertainties (in %) associated with the
standards.
NIST BIPM
Source of uncertainty Type A Type B Type A Type B
Ionization current 0.02 0.13 0.03 0.02
Volume 0.04 0.01 0.01 0.05
Positioning 0.01 0.01 0.01
Correction factors (excl. [k.sub.h]) 0.03 0.29 0.04 0.14
Humidity [k.sub.h] 0.10 0.03
Physical constants 0.15 0.15
[K.sub.LAB] 0.05 0.36 0.05 0.21
Table 7. Relative standard uncertainties (in %) associated with the
calibration of the transfer ionization chambers
NIST BIPM
Source of Type A Type B Type A Type B
uncertainty
Air kerma rate 0.05 0.36 0.05 0.21
Ionization current 0.02 0.13 0.04 0.02
Positioning 0.01 0.01 0.01
[N.sub.K,LAB] 0.05 0.38 0.07 0.21
Table 8. Relative standard uncertainties (in %) associated with the
comparison results [R.sub.K]. Correlations arising from the physical
constants, the humidity correction and the correction factors
[k.sub.sc] and [k.sub.e] are removed. A type B component of 0.04% is
included to account for the use of different radiation qualities for
the NIST and BIPM calibrations
Source of uncertainty Type A Type B
0.09 0.3
[R.sub.K] 0.35
Table 9. Measured results for the calibration of the NIST transfer
chambers at both laboratories
Reference radiation Half-value layer NIST transfer chambers
Calibration factors
(1[0.sup.6] Gy [C.sup.-1])
mm Al mm Cu NIST-T1 NIST-T2
BIPM Measurements
BIPM 100 kV 4.027 0.148 8.374 8.472
BIPM 135 kV 0.494 8.481 8.551
BIPM 180 kV 0.990 8.607 8.666
BIPM 250 kV 2.500 8.744 8.793
NIST Measurements
NIST M60 1.68 0.052 8.517 8.635
NIST M100 5 0.2 8.343 8.425
NIST M150 10.2 0.67 8.500 8.549
NIST M200 14.9 1.69 8.644 8.681
NIST M250 18.5 3.2 8.714 8.737
NIST M300 22 5.3 8.717 8.741
Table 10. Results RK of the comparison of the NIST and BIPM airkerma
standards
Generating potential Half-value layer [R.sub.K]
(kV) (mm Cu) (1991)
100 0.148 0.9952
135 0.494 0.9953
180 0.990 0.9942
250 2.500 0.9930
Accepted: November 5, 2003 Available online: http://www.nist.gov/jres (1) Certain commercial equipment, instruments, or materials are identified in this paper to foster understanding. Such identification does not imply recommendation or endorsement, nor does it imply that the equipment identified are necessarily the best available for the purpose. 7. References [1] BIPM, Qualites de rayonnements, Consultative Committee for Ionizing Radiation (CCEMRI) (Section I), 1972, 2, R15. [2] M. Boutillon, Mesure de l'exposition au BIPM dans le domaine des rayons X de 100 a 250 kV, Rapport The former name of device management software from Wyse Technology, San Jose, CA (www.wyse.com) that is designed to centrally control up to 100,000+ devices, including Wyse thin clients (see Winterm), Palm, PocketPC and other mobile devices. BIPM-78/3, 1978. [3] M. Boutillon, Measuring Conditions Used for the Calibration of Ionization Chambers at the BIPM, Rapport BIPM-96/1, 1996. [4] H. O. Wyckoff and F. H. Attix, Design of free-air ionization chambers, National Bureau Standards Handbook
This article is about reference works. For the subnotebook computer, see .
[5] P. J. Lamperti and M. O'Brien, Calibration of X-Ray and Gamma-Ray Measuring Instruments, NIST Special Publication 250-58 (2001). [6] B. N. Taylor and C. E. Kuyatt, Guidelines guidelines, n.pl a set of standards, criteria, or specifications to be used or followed in the performance of certain tasks. for Evaluating and Expressing the Uncertainty of NIST Measurement Results, 1994 Edition, NIST Technical Note 1297, September 1994. D. T. Burns Tom Burns spent more than thirty years at the University of Edinburgh, retiring in 1981 as Professor of Sociology. His early interests were in urban sociology, and he worked with the West Midland Group on Post-War Reconstruction and Planning. Bureau International des Poids et Mesures, F-92312 Sevres Cedex, France M. O'Brien National Institute of Standards and Technology, Gaithersburg, MD 20899 USA michelle.obrien@nist.gov P. Lamperti National Institute of Standards and Technology, Gaithersburg, MD 20899 USA and M. Boutillon Bureau International des Poids et Mesures, F-92312 Sevres Cedex, France About the authors: Michelle O'Brien is a physicist in the Ionizing Radiation Division, Dosimetry dosimetry /do·sim·e·try/ (do-sim´e-tre) scientific determination of amount, rate, and distribution of radiation emitted from a source of ionizing radiation, in biological d. and Interactions Group of the NIST Physics Laboratory. David Burns David Burns may refer to:
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