Believable Statements of Uncertainty and Believable Science.

Nearly fifty years ago, two landmark papers appeared that should have cured the problem of ambiguous uncertainty statements in published data. Eisenhart's paper in Science called for statistically meaningful numbers, and Currie's Analytical Chemistry paper revealed the wide range in common definitions of detection limit. Confusion and worse can result when uncertainties are misinterpreted or ignored. The recent stories of cold fusion, variable radioactive decay, and piezonuclear reactions provide cautionary examples in which prior probability has been neglected. We show examples from our laboratory and others to illustrate the fact that uncertainty depends on both statistical and scientific judgment.

A second-generation low-background gamma-ray spectrometer.

For the ultimate sensitivity in trace radiochemical analysis, the radiation detector must have high efficiency and low background. A low-background gamma-ray spectrometer in regular use at NIST for over twenty years is being supplemented by a new system, improved in several ways. The new detector is much larger, a shield of iron reduces cosmic neutron background compared with lead, large plastic scintillators reduce the muon continuum background, and a digital data acquisition system gives new opportunities for optimization.

Accurate and precise measurement of selenium by instrumental neutron activation analysis.

An accurate and precise measurement of selenium in Standard Reference Material (SRM) 3149, a primary calibration standard for the quantitative determination of selenium, has been accomplished by instrumental neutron activation analysis (INAA) in order to resolve a question arising during the certification process of the standard. Each limiting factor of the uncertainty in the activation analysis, including the sample preparation, irradiation, and γ-ray spectrometry steps, has been carefully monitored to minimize the uncertainty in the determined mass fraction. Neutron and γ-ray self-shielding within the elemental selenium INAA standards contributed most significantly to the uncertainty of the measurement. An empirical model compensating for neutron self-shielding and reducing the self-shielding uncertainty was successfully applied to these selenium standards. The mass fraction of selenium in the new lot of SRM 3149 was determined with a relative standard uncertainty of 0.6%.

Preparation and characterization of standard reference material 1849 infant/adult nutritional formula.

Standard Reference Material (SRM) 1849 Infant/Adult Nutritional Formula has been issued by the National Institute of Standards and Technology (NIST) as a replacement for SRM 1846 Infant Formula, issued in 1996. Extraction characteristics of SRM 1846 have changed over time, as have NIST's analytical capabilities. While certified mass fraction values were provided for five constituents in SRM 1846 (four vitamins plus iodine), certified mass fraction values for 43 constituents are provided in SRM 1849 (fatty acids, elements, and vitamins) and reference mass fraction values are provided for an additional 43 constituents including amino acids and nucleotides, making it the most extensively characterized food-matrix SRM available from NIST.

Endogenous lithium and boron red cell-plasma ratios: normal subjects versus bipolar patients not on lithium therapy.

This study was undertaken to compare endogenous lithium concentrations in human blood and its components from normal donors versus bipolar patients. The patients were not on lithium therapy at the time that the blood samples were donated and had not received any lithium therapy for at least 2 yr. Blood components were separated by centrifugation. The analytical method for lithium as developed in this laboratory consists of thermal-neutron activation of freeze-dried samples. 3H is produced via the reaction 6Li + n = 3H + 4He, and high-sensitivity rare gas mass spectrometry is used to measure 3He formed from beta-decay of 3H. Boron measurements are made concurrently using 4He from the reaction 10B + n = 4He + 7Li. Seven normal donors and seven patients with a diagnosis of bipolar disorder participated in this study. Measurements of lithium and boron were made in whole blood, plasma, and red cells. Red cell-plasma ratios R(Li) and R(B) were calculated after corrections were made for trapped plasma in the red cells. The results show that bipolar patients may have higher concentrations of lithium in blood, plasma, and red cells (p = 0.08, 0.02, and 0.02, respectively) and may have higher R(Li) values than normal donors (p = 0.01). No evidence was found for bipolar-normal differences in these four parameters for boron. Although our sample size is admittedly very small, the results clearly show that the endogenous red cell ratio R(Li) and plasma or red cell lithium concentrations may become useful diagnostic indicators for bipolar illness if the analytical methods are further developed.

Binding of lithium and boron to human plasma proteins II: results for a bipolar patient not on lithium therapy.

We report further measurements of lithium and boron bound to human plasma proteins using the techniques of gel chromatography, thermal-neutron activation, and high-sensitivity helium isotope mass spectrometry. The plasma sample was donated by a bipolar patient who had never been on lithium therapy. The plasma lithium-binding pattern for the bipolar patient is distinctly different from that previously observed in this laboratory for plasma donated by a normal individual. In the bipolar case, virtually all of the lithium is bound to low-molecular-weight proteins (approx 1000 amu), whereas in the normal case, most of the lithium eluted from the gel column was bound to five high-molecular-weight proteins (approx 50,000 amu to approx 1,000,000 amu). The gel elution profiles for boron were roughly similar for the normal and bipolar cases. The lithium results are in agreement with our previous speculation that lithium-binding plasma proteins are missing or exist in very low concentrations in some individuals suffering from affective disorders.

Prompt-Gamma Activation Analysis.

A permanent, full-time instrument for prompt-gamma activation analysis is nearing completion as part of the Cold Neutron Research Facility (CNRF). The design of the analytical system has been optimized for high gamma detection efficiency and low background, particularly for hydrogen. Because of the purity of the neutron beam, shielding requirements are modest and the scatter-capture background is low. As a result of a compact sample-detector geometry, the sensitivity (counting rate per gram of analyte) is a factor of four better than the existing Maryland-NIST thermal-neutron instrument at this reactor. Hydrogen backgrounds of a few micrograms have already been achieved, which promises to be of value in numerous applications where quantitative nondestructive analysis of small quantities of hydrogen in materials is necessary.