TU-B-224-01: Impact of the National Institute of Standards and Technology (NIST) on Radiation Dosimetry in Medical Physics

This paper describes a 10 V Josephson Voltage Standard (JVS) direct comparison between the National Institute of Standards and Technology (NIST) and the Instituto Nacional de Metrologia, Normalizacao e Qualidade Industrial (Inmetro) using automatic data acquisition. The results were in agreement to within 1.1 nV and the mean difference between the two JVSs at 10 V is 0.54 nV with a pooled combined standard uncertainty of 1.48 nV. Considering a recent JVS comparison between NIST and the Bureau International des Poids et Mesures (BIPM) [1], the difference between Inmetro and the BIPM thus was found to be −0.26 nV with a standard uncertainty of 1.76 nV.

This paper describes a 10 V Josephson Voltage Standard (JVS) direct comparison between the National Institute of Standards and Technology (NIST) and the Instituto Nacional de Metrologia, Normalização e Qualidade Industrial (INMETRO) using automatic data acquisition. The results were in agreement to within 1.1 nV and the mean difference between the two JVSs at 10 V is 0.54 nV with a pooled combined standard uncertainty of 1.48 nV. Considering a recent JVS comparison between NIST and the Bureau International des Poids et Mesures (BIPM), the difference between INMETRO and the BIPM thus was found to be -0.26 nV with a standard uncertainty of 1.76 nV. INMETRO JVS improvements since the 2006 INMETRO-BIPM comparison are also described.

ABSTRACTThe National Institute of Standards and Technology (NIST) has developed a dynamic and on-going educational outreach program designed to support middle school science teachers and increase their understanding of the science they teach with applications to the real world and connections to the latest NIST research. In the NIST Summer Institute for Middle School Science Teachers, science topics are taken from NIST research pertinent to the middle school curriculum, and the research is translated for use in the classroom. During the two-week summer program teachers from around the country are given the opportunity to focus on NIST research as it relates to the middle school classroom by participating in a combination of hands-on activities, lectures, tours, and visits with scientists and engineers in their laboratories. The NIST Summer Institute is designed to increase teacher understanding of the subjects they teach, provide inquiry activities for the classroom, rekindle teachers’ enthusiasm for science, provide increased understanding of how scientific research is performed, create a learning community of teachers and scientists, and provide role models for the teachers. Teachers finish the NIST Summer Institute with a wealth of knowledge about core topics in introductory biology, chemistry, physics, and materials to integrate these topics into their existing curriculum.The NIST Summer Institute has spawned additional related outreach activities, including “Science Afternoons at NIST,” in which teachers are invited back to NIST during the school year for events in which the focus is on a single topic such as designing buildings to resist earthquakes, infrared energy, and nanomagnetism. Based on continued requests from participants in the NIST Summer Institute, an additional program, the NIST Research Experience for Teachers program, was begun in 2011 with teachers performing research at NIST under the guidance of NIST scientists and engineers, and designing ways to take their research experience back into the classroom to share with their students. This proceeding will give examples of topics covered and activities developed in past Summer Institutes, as well as ways similar Institutes are being implemented at other locations. While not a teaching institution but a research institute focused on meeting the measurement science needs of the nation, NIST has a wealth of resources for the education community. The NIST Summer Institute for Middle School Science Teachers is one way of sharing these resources and building partnerships between middle school science teachers and their students and NIST scientists and engineers.

In early 1998, three transfer ionization chambers were used to compare the air-kerma and absorbed-dose-to-water calibration factors measured by the National Research Council of Canada (NRCC) and the National Institute of Standards and Technology (NIST). The ratios between the NRCC and NIST calibration factors are 0.9950 and 1.0061 in the case of the absorbed-dose-to-water and air-kerma standards, respectively. In the case of the standard of absorbed dose to water, the combined uncertainty of the ratio between the standards of the two laboratories is about 0.6% and consequently, the observed difference of 0.5% is not significant at the one sigma level. In the case of the standard of air kerma, the combined uncertainty of the ratio between the standards of the two laboratories is about 0.4%, and so the observed difference of 0.61% is significant at the one sigma level. However, this discrepancy is due to the known differences in the methods of assessing the wall correction factor at the two laboratories. Taking into account changes implemented in the standards that form the basis of the calibrations, the present results are consistent with those of the previous comparison done in 1990/91. As a direct result of these differences in the calibration factors, changing from an air-kerma based protocol following TG-21 to an absorbed-dose-to-water based protocol following TG-51, would alter the relationship between clinical dosimetry in Canada and the United States by about 1%. For clinical reference dosimetry, the change from TG-21 to TG-51 could result in an increase of up to 2% depending upon the ion chamber used, the details of the protocol followed and the source of traceability, either NRCC or NIST.

The air-kerma standards used for the measurement of medium-energy x rays were compared at the National Institute of Standards and Technology (NIST) and at the Bureau International des Poids et Mesures (BIPM). 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 standards. Reference beam 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 %.

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The reciprocity technique has long served as a method for pressure calibration of microphones. It is a primary method, which determines microphone sensitivities from first principles and does not require a previously calibrated acoustic transfer standard. For calibrations of laboratory standard microphones, this method is standardized and utilized at national measurement institutes worldwide. Standard microphones calibrated by reciprocity are in turn used to calibrate additional microphones and sound calibrators, which apply known sound pressures to calibrate acoustical measuring devices and systems. Reciprocity calibrations done at the National Institute of Standards and Technology (NIST), which is the national measurement institute for the U.S., provide its customers with accurate results traceable to the International System of Units (SI). These customers and organizations that utilize their services perform large numbers of secondary and further calibrations and measurements concerned with hearing conservation and testing, aircraft noise, noise regulation enforcement, acoustical test and measurement equipment, and auditory research. An overview of the reciprocity technique is presented along with a few examples of how customers of the NIST acoustical calibration services make use of their calibrated devices and calibration data.

The aim of the book is to provide a summary of the various facets of mass measurement, and it is aimed at the highest level of mass metrology as well as industrial and commercial users. The book is a mix of the general principles of mass metrology as summarized by the authors and a collection of specific experimental work carried out in some cases by the authors and in some cases lifted almost directly from the work of others (in all cases the sources of the original work are referenced). The eclectic nature of the book makes it quite difficult to read as a continuous text but it is an invaluable collection of data, some of which was not previously available, the rest only being available in individual published papers.Chapter 1 provides an introduction to the field of mass metrology. Despite getting off to a poor start, misquoting the date of the first CIPM meeting (which should be 1889 not 1899) and identifying the Pavillon de Breteuil (the home of the Kilogram) rather loosely as`a building at BIPM', the chapter provides a useful introduction with some interesting historical detail.Chapters 2 to 4 deal with the maintenance and dissemination of the unit of mass and consist mostly of a summary of data previously published by NIST (National Institute of Standards and Technology, USA) and the BIPM (Bureau International des Poids et Mesures).Chapters 5 to 27 deal with various aspects of balanceconstruction and usage and the calibration of mass standards.The information given again has a strong bias towards theprocedures used by NIST. Most relevant areas of the massmeasurement process are addressed but more detail in certainareas would have been welcome. In particular, a great deal ofresearch has been done into the areas of weight cleaning andstorage, and thermal effects and magnetic interaction between balances and weights, little of which is referenced in this book.Areas such as the density of water and air are covered in detailand the uncertainty analysis of the equation to calculate thedensity of air is particularly detailed and useful.The book concludes with details of some research into specific applications of mass measurement, which are interesting and give a flavour of the more esoteric research that goes on in the mass metrology field. I would have liked to see some mention of the various projects being undertaken to redefine the unit of mass (the Avogadro, Watt balance and ion accumulation projects), as these will become important to the field over the next 10 to 20 years.Overall the book gives a good introduction to the field of mass metrology albeit with a distinctly American slant. It covers allthe major areas necessary for the calibration of mass standardsin both an industrial and a research environment and, given thepaucity of publications in this field, it is to be commended. Incomparison with the only other text in the area, Comprehensive Mass Metrology edited by Kochsiek and Glaser(Wiley), this book does not have the depth of detail in theresearch areas and perhaps gives a more basic introduction for the industrial user, particularly for the American market.Stuart Davidson

For over sixty years, the Bureau International des Poids et Mesures (BIPM) has maintained the results of international comparisons of luminous intensity and luminous flux as "world-mean" values, in the form of groups of lamps. It was recently decided that this is no longer a satisfactory and reliable means of maintaining the photometric units of the International System of Units (SI). To maintain the luminous-flux unit, an attempt was made at the BIPM to use the Absolute Integrating-Sphere Method developed at the National Institute of Standards and Technology (NIST). A new technique (ac/dc) employing a chopper for the external source, which allows simultaneous measurement of the internal and external sources, has been developed to overcome an unexpected problem with the characteristics of the BIPM sphere, in that the heat from the lamp affected the sphere coating. The ac/dc technique allows absolute calibration of the integrating sphere while the internal lamp is operating and being measured. Having implemented this technique and replaced the sphere coating, experiments on the derivation of the unit are in progress at the BIPM and the NIST, the preliminary results of which are reported.

A comparison of the dosimetry for accelerator photon beams was carried out between the National Institute of Standards and Technology (NIST) and the Bureau International des Poids et Mesures (BIPM) in September and October 2010. The comparison was based on the determination of absorbed dose to water for two radiation qualities at NIST. The comparison result, reported as a ratio of the NIST and the BIPM evaluations, is 1.004 at 6 MV and 0.996 at 18 MV, each with a combined standard uncertainty of 6 parts in 103. This result is the third in the on-going BIPM.RI(I)-K6 series of comparisons.Main text.To reach the main text of this paper, click on Final Report. Note that this text is that which appears in Appendix B of the BIPM key comparison database kcdb.bipm.org/.The final report has been peer-reviewed and approved for publication by the CCRI, according to the provisions of the CIPM Mutual Recognition Arrangement (CIPM MRA).

National measurement institutes (NMIs) participate in international key comparisons organized by the Bureau International des Poids et Mesures (BIPM), the Regional Metrology Organizations (RMOs) or the Consultative Committees of the Comité International des Poids et Mesures (CIPM) in order to provide evidence of equivalent reference standards and measurement capabilities. The US National Institute of Standards and Technology (NIST) and the National Measurement Institute of Australia (NMIA) have recently examined power loading and several other influences on the value of precision transportable 1 Ω resistors that can increase the uncertainty of key comparisons. We have studied the effects of temperature, barometric pressure, humidity, power loading and heat dissipation in oil on transportable wire-wound 1 Ω resistance standards that are based on different alloys and construction principles. This work focuses on standards manufactured from 1970 through 2000 by the NMIA made of Evanohm alloy and on Thomas-type resistors designed in the 1930s and made of Manganin alloy. We show that the relative standard uncertainty related to transport can be less than 0.01 μΩ Ω−1 when using certain resistors of these two types that are characterized and selected for stability. We describe the characterization process, and relate the environmental influences to the physical design, as well as to the mechanical properties and condition of the standards.

The National Aeronautics and Space Administration (NASA) Kennedy Space Center (KSC) requires accurate gas mixtures containing argon (Ar), helium (He), hydrogen (H(2)), and oxygen (O(2)) in a balance of nitrogen (N(2)) to calibrate mass spectrometer-based sensors used around their manned and unmanned space vehicles. This also includes space shuttle monitoring around the launch area and inside the shuttle cabin. NASA was in need of these gas mixtures to ensure the safety of the shuttle cabin and the launch system. In 1993, the National Institute of Standards and Technology (NIST) was contracted by NASA to develop a suite of primary standard mixtures (PSMs) containing helium, hydrogen, argon, and oxygen in a balance gas of nitrogen. NIST proceeded to develop a suite of 20 new gravimetric primary PSMs. At the same time NIST contracted Scott Specialty Gases (Plumsteadville, PA) to prepare 18 cylinder gas mixtures which were then sent to NIST. NIST used their newly prepared PSMs to assign concentration values ranging from 100 to 10,000 micromol/mol with relative expanded uncertainties (95% confidence interval) of 0.8-10% to the 18 Scott Specialty Gases prepared mixtures. A total of 12 of the mixtures were sent to NASA as NIST traceable standards for calibration of their mass spectrometers. The remaining 6 AIRGAS mixtures were retained at NIST. In 2006, these original 12 gas standards at NASA had become low in pressure and additionally NASA needed a lower concentration level; therefore, NIST was contracted to certify three new sets of gas standards. NIST prepared a new suite of 22 PSMs with weighing uncertainties of <0.1%. These 22 PSMs were compared to some of the original 20 PSMs developed in 1993 and with the NIST valued assigned Scott Specialty Gas mixtures that NIST had retained. Results between the two suites of primary standards and the 1993 NASA mixtures agreed, verifying their stability. At the same time, NASA contracted AIRGAS (Chicago, Illinois) to prepare 45 cylinder gas mixtures which were then sent to NIST. Each of the 3 sets of standards contained 15 cylinder gas mixtures: set no. 1, He at 12,000 micromol/mol, H(2) at 600 micromol/mol, Ar at 100 micromol/mol, and O(2) at 600 micromol/mol; set no. 2, He at 15 000 micromol/mol, H(2) at 5000 micromol/mol, Ar at 1000 micromol/mol, O(2) at 5000 micromol/mol; and set no. 3, He at 50 micromol/mol, H(2), Ar, and O(2) each at 25 micromol/mol with a balance gas of N(2). NIST used their newly prepared primary standards to assign concentration values to each component in these three new mixture sets to relative expanded uncertainties of 0.5-2.2%. The NIST certified AIRGAS prepared mixtures were then sent to NASA to use as "working standards" to calibrate their mass spectrometers (MSs).

We report on a 2012 comparison of gravity used to determine the Planck constant by the National Institute of Standards and Technology (NIST) and the National Research Council Canada (NRC) watt balances. The results provide verification of the gravity values used in recently published discrepant Planck constant determinations that play a vital role in the redefinition effort of the International System of Units (SI) and set an upper limit of 10 parts in 109 on the relative uncertainty contribution of gravity observations to future Planck constant determinations by the NIST and NRC watt balances.

The use of liquid-in-glass (LIG) thermometers is described in many documentary standards in the fields of environmental testing, material testing, and material transfer. Many national metrology institutes, including the National Institute of Standards and Technology (NIST) and the National Research Council of Canada (NRC), list calibration services for these thermometers among the Calibration Measurement Capabilities of Appendix C of the BIPM Key Comparison Database. NIST and NRC arranged a bilateral comparison of a set of total-immersion ASTM-type LIG thermometers to validate their uncertainty claims. Two each of ASTM thermometer types 62C through 69C were calibrated at NIST and at NRC at four temperatures distributed over the range appropriate to each thermometer, in addition to the ice point. Collectively, the thermometers span a temperature range of − 38 °C to 305 °C. In total, 160 measurements (80 pairs) comprise the comparison data set. Pair-wise differences (TNIST–TNRC) were formed for each thermometer at each temperature. For 8 of the 80 pairs (10 %), the differences exceed the k = 2 combined uncertainties. These results support the claimed capabilities of NIST and NRC for the calibration of LIG thermometers.

A comparison was made between the National Institute of Standards and Technology (NIST) and Ente per le Nuove Tecnologie l’Energia e l’Ambiente (ENEA) air kerma standards for medium energy x rays and 60Co gamma rays. The comparison took place at ENEA in June 1994. Two different transfer chambers from NIST were used for the comparison. The measurements were made at radiation qualities similar to those used at the Bureau International des Poids et Mesures (BIPM) (generating voltages of 100 kV, 135 kV, 180 kV and 250 kV, respectively) and with 60Co gamma radiation. The transfer chamber calibration factors obtained at the NIST and at the ENEA agreed with one another to 0.03 % for 60Co gamma radiation and between 0.1 % to 0.8 % for the medium energy x-ray beam codes.