Reporting Measurement Uncertainty Research Articles

Measurement variability associated with KXRF bone lead measurement in young adults.

In vivo bone lead measurement using K X-ray fluorescence (KXRF) has been used to estimate long-term lead exposure, especially in adults. Relatively few studies have been conducted on young subjects with this technique. To explore the measurement variability of KXRF bone lead measurements in young subjects, the tibiae of two male cadavers from Boston, Massachusetts, 17 and 20 years of age, were obtained for repeated bone lead measurements. Bone lead concentrations were measured using a grid of nine locations, 1 cm apart, centered at the midpoint of the tibia. Each location was sampled using five 60-min measurements. Measured concentrations ranged from < 0 to 11.8 microg Pb/g bone mineral across a tibia with mean concentrations for the midpoint locations of 0.8 microg Pb/g bone mineral SD = 2.5 and 2.0 microg Pb/g bone mineral (SD = 1.9) for the left and right legs of the younger subject and 3.6 microg Pb/g bone mineral (SD = 2.6) and 6.0 microg Pb/g bone mineral (SD = 3.3) for the left and right legs of the older subject. Although bone lead concentrations did not vary significantly by measurement location in an individual leg, reported measurement uncertainty increased significantly at locations that were 1 cm from the center of the tibia horizontally (p < 0.0001). Symmetry in bone lead concentration between legs was observed for the 17-year-old subject. Potential asymmetry between the left and right legs was suggested for the 20-year-old subject (p = 0.06). These data describe the degree of variability that may be associated with bone lead measurements of young subjects with low bone lead concentrations using a standard spot-source KXRF instrument. Because of the importance of conducting additional research on adolescent lead toxicity, further improvements to the precision of KXRF measurement are needed.

Elements of an Approach to the Assessment of Systematic Uncertainty in Transient Measurements

Although there has been an increasing interest in experimental research investigating time-dependent fluid phenomena, accepted methods for assessing and reporting measurement uncertainty, i.e., those contained in ANSI/ASME PTC 1991-1998. do not consider issues pertaining specifically to the assessment of uncertainty in transient measurements. Complementing the author’s previous work which presented a method for assessing the random component of uncertainty in transient measurements, this paper presents a method for assessing the systematic component of uncertainty in transient measurements.

Description of Critical Experiments in Spherical Geometry Containing UO2F2 Solution

Hundreds of criticality experiments were performed at Oak Ridge National Laboratory in the 1950s. Several sets of these experiments were used to determine the critical properties of 233U and 235U. Here, four sets are analyzed to provide benchmark descriptions for validation of computational tools used by nuclear criticality specialists. All four sets were performed in water-reflected spherical geometry and contained a highly enriched uranyl fluoride solution (93.18% 235U) with the hydrogen-to-fissile ratio of measurements ranging from 35.8 to 1272. The scope of these experiments spans the minimum values of the subcritical mass limit curve. One experiment was never reported in the open literature, and three experiments were performed at elevated temperatures. An uncertainty in the experimental keff was found by sensitivity studies on reported measurement uncertainties, inconsistencies, and omissions in experimental parameters. To be useful for all computer codes, one-dimensional benchmark configurations were determined for all sets of experiments. The descriptions can be used to find bias values for a code/cross-section package. The keff values for similar configurations can then be corrected using the bias values. The sensitivity analysis of the experiments was performed using ONEDANT with 27-group ENDF/B-IV cross sections and MCNP with continuous-energy ENDF/B-V cross-section data. The keff values for both one- and three-dimensional configurations were found using MCNP with ENDF/B-V and ENDF/B-VI cross-section data. The values for keff for the one-dimensional configuration were also found by using ONEDANT and KENO V.a with Hansen-Roach and 27-group ENDF/B-IV cross sections.

In vivo bone lead measurement in suburban teenagers.

Bone represents a biologically active long-term storage site for lead, and bone lead data on teenagers are limited. Therefore, this study was designed to identify the distribution of bone lead in a teenage population and to explore the environmental and demographic factors associated with bone lead concentrations in young, nonoccupationally exposed subjects. A cross-sectional study of bone lead levels in high school students. A total of 168 students at a suburban Boston high school. Subjects (90 boys, 78 girls) ranged in age from 13.5 to 19 years and included 40% nonwhite minorities. Of the 168 subjects, 45 lived in homes constructed before 1960. None of the participants reported a history of lead poisoning. Tibial bone lead concentrations were measured in vivo for 60 minutes using K x-ray fluorescence. Lead exposure information was obtained by self-administered questionnaire. Point estimates of bone lead levels ranged from -7.15 to 14.23 microg lead/g bone mineral (microg/g), (mean, 4.0 microg/g; standard deviation, 4.4 microg/g). The reported measurement uncertainties accompanying each of the point estimates ranged from 2.56 to 9.01 microg/g (mean, 3.9 microg/g; standard deviation, 1.0 microg/g). Bone lead levels were not associated with the demographic factors of age, sex, or race. Additionally, current home conditions (housing age, traffic level) were not predictive of bone lead levels, even though these factors were predictive of in-home lead concentrations. These results demonstrate that although bone lead levels are measurable in this age group, the common predictors of blood and bone lead concentrations are not explanatory for bone lead levels.

Descriptions of High and Low Enriched U 235 Critical Experiments in 174-1 Spheres

A wide variety of criticality experiments, using different geometries and solutions, was performed at Oak Ridge National Laboratory in the 1950s. Two sets performed in 174-1 spheres are analyzed to provide benchmark descriptions for validation of computational tools used by nuclear criticality specialists. One set was performed in an unreflected sphere and contained a highly enriched uranyl nitrate solution (93.18% U 235). Three of the four measurements from this set were poisoned with boron. The second set consists of one unreflected and two water-reflected measurements and used low-enriched uranyl fluoride solutions (4.9% U 235). One of these experiments was critical with the sphere 83% full. An uncertainty in the experimental k eff was found by sensitivity studies on reported measurement uncertainties, inconsistencies, and omissions in experimental parameters. Benchmark configurations were found for all experiments. To be functional for all computer codes, one-dimensional configurations were used when possible. The sensitivity study of the experiments was performed using ONEDANT with 27-Group ENDF/B-IV cross sections and MCNP with continuous energy ENDF/B-V cross section data. K eff values for the benchmark configurations were found using MCNP with ENDF/B-V and ENDF/B-VI cross section data, ONEDANT and KENO-Va with Hansen-Roach and 27-group ENDF/B-IV cross sections. © 1997 Elsevier Science Ltd.

Validation of K-XRF bone lead measurement in young adults.

K-X-ray fluorescence (K-XRF) is a useful tool for assessing environmental exposure to lead in occupationally exposed individuals and older adults. This study explores the possibility of using this technique on young adults with low environmental lead exposure. Twenty-three college students, aged 18-21 years, were recruited for 2 hr of bone lead measurement. Bone lead measurements were taken from the mid-shaft tibia for periods of 30 or 60 min. In the analysis, 30-min measurements were combined so that each subject had the equivalent of two 60-min measurements. The average concentration of two bone lead measurements in this population ranged from -1.5 to 8.2 micrograms Pb/g bone mineral, with a mean of 3.0 micrograms Pb/g bone mineral. In a one sample t-test, this mean was significantly different from 0 (p < 0.0001). A linear trend with age was detected despite the small age range of our population. By doubling the sampling time, the reported measurement uncertainty decreased by a factor of 1.5, resulting in uncertainty estimates below the mean bone lead estimates. Power calculations using the observed variance estimates suggest that with 80% power, differences in bone lead concentration of 2-3 micrograms Pb/g bone mineral can be identified in groups of 100 or smaller. Due to the large within-person variation in young adults, K-XRF may not yet be a useful diagnostic tool for individual subjects, but it may be of great use to environmental scientists trying to characterize long-term lead exposure and dose in the general population or specific subpopulations.

Validation of K-XRF Bone Lead Measurement in Young Adults

K-X-ray fluorescence (K-XRF) is a useful tool for assessing environmental exposure to lead in occupationally exposed individuals and older adults. This study explores the possibility of using this technique on young adults with low environmental lead exposure. Twenty-three college students, aged 18-21 years, were recruited for 2 hr of bone lead measurement. Bone lead measurements were taken from the mid-shaft tibia for periods of 30 or 60 min. In the analysis, 30-min measurements were combined so that each subject had the equivalent of two 60-min measurements. The average concentration of two bone lead measurements in this population ranged from -1.5 to 8.2 micrograms Pb/g bone mineral, with a mean of 3.0 micrograms Pb/g bone mineral. In a one sample t-test, this mean was significantly different from 0 (p &lt; 0.0001). A linear trend with age was detected despite the small age range of our population. By doubling the sampling time, the reported measurement uncertainty decreased by a factor of 1.5, resulting in uncertainty estimates below the mean bone lead estimates. Power calculations using the observed variance estimates suggest that with 80% power, differences in bone lead concentration of 2-3 micrograms Pb/g bone mineral can be identified in groups of 100 or smaller. Due to the large within-person variation in young adults, K-XRF may not yet be a useful diagnostic tool for individual subjects, but it may be of great use to environmental scientists trying to characterize long-term lead exposure and dose in the general population or specific subpopulations.