Instrumental Neutron Activation Analysis for Certification of Ion-Implanted Arsenic in Silicon

Standard reference material (SRM) 2134 Arsenic Implant in Silicon was produced at the National Institute of Standards and Technology (NIST) as a calibrant for secondary ion mass spectrometry. Instrumental neutron activation analysis was used as a primary method for certification of the arsenic implanted dose. A complete evaluation of all sources of uncertainty yielded an expanded relative uncertainty for the mean value of this SRM to be 0.38% at approximately the 95% level of confidence. No evidence indicating significant heterogeneity among samples was observed.     

Investigating the role of the outer-coordination sphere in [Ni(P(Ph)2N(Ph‑R)2)2]2+ hydrogenase mimics

A series of dipeptide substituted nickel complexes with the general formula, [Ni(P(Ph)(2)N(NNA-amino acid/ester)(2))(2)](BF(4))(2), have been synthesized and characterized (P(2)N(2) = 1,5-diaza-3,7-diphosphacyclooctane, and the dipeptide consists of the non-natural amino acid, 3-(4-aminophenyl)propionic acid (NNA), coupled to amino acid/esters = glutamic acid, alanine, lysine, and aspartic acid). Each of these complexes is an active electrocatalyst for H(2) production. The effects of the outer-coordination sphere on the catalytic activity for the production of H(2) were investigated; specifically, the impact of sterics, the ability of the side chain or backbone to protonate and the pK(a) values of the amino acid side chains were studied by varying the amino acids in the dipeptide. The catalytic rates of the different dipeptide substituted nickel complexes varied by over an order of magnitude. The amino acid derivatives display the fastest rates, while esterification of the terminal carboxylic acids and side chains resulted in a decrease in the catalytic rate by 50-70%, implicating a significant role of protonated sites in the outer-coordination sphere on catalytic activity. For both the amino acid and ester derivatives, the complexes with the largest substituents display the fastest rates, indicating that catalytic activity is not hindered by steric bulk. These studies demonstrate the significant contribution that the outer-coordination sphere can have in tuning the catalytic activity of small molecule hydrogenase mimics.     

Effectiveness of a Mathematics Methods Course in Reducing Math Anxiety of Preservice Elementary Teachers

In an attempt to find ways of reducing the mathematical anxiety of preservice elementary teachers, three cases were investigated. The first was a section of mathematics for elementary teachers taught in a very traditional manner, and the second was the same course taught in a manner consistent with the recent recommendations of the National Council of Teachers of Mathematics. The third case included two sections of a methods course which covered the same mathematical content, as well as addressing how it should be taught to children. The Mathematics Anxiety Rating Scale for Adults was administered before and after the courses. No significant reduction of anxiety was measured in either mathematics section, but both sections of the methods course showed a significant reduction.     

The half-life of 111mPd

As a contribution toward improving the accuracy of neutron activation analysis, the half-life of ^111mPd was measured by gamma-ray spectrometry. The uncertainty of this parameter is greater than desired for accurate work, largely because ^111mPd represents a small part of the total activity of palladium exposed to neutrons. In this work, several irradiated samples of pure palladium were counted continually with high-resolution Ge gamma detectors through about ten half-lives. The 172 keV photopeak was integrated with a region-of-interest procedure, and each datum corrected for rate-related losses before fitting to an exponential function by a nonlinear least-squares procedure. The half-life found is 5.580 ± 0.032 h, where the uncertainty is an estimate of the 95 % confidence level, a substantial improvement over published values.     

Toolkits for nuclear science: Data and spreadsheets

Summary In the past decade, the combination of readily accessible, reliable data in electronic form with well-tested spreadsheet programs has changed the approach to experiment planning and computation of results. This has led to a flowering of software applications based on spreadsheets, mostly written by scientists, not by professional programmers trained in numerical methods. Formal quality systems increasingly call for verified computational methods and reference data as part of the analytical process, a demand that is difficult to meet with most spreadsheets. Examples are given of utilities used in our laboratory, with suggestions for verification and quality maintenance.     

Accuracy and uncertainty in radioactivity measurement for NAA

The basic assumptions of activation analysis are that the induced radioactivity is proportional to the amount of analyte, and that the quantity of radioactivity can be related simply to the number of counts observed. Quantitative measurement of activity (and of its uncertainty) is not always simple, especially when accuracy better than a few percent is sought. Recent work with ⁷⁷Ge and ⁷⁶As has demonstrated that the accuracy of half-lives in the literature is sometimes insufficient. Despite these and other problems, quantitative understanding and documentation of uncertainties can be accomplished, providing demonstrable quality assurance and supporting claims of traceability to the Système International.     

The half-life of 76As

In the course of making high-accuracy measurements of arsenic, we found that the most recently published and compiled half-life of ⁷⁶As did not agree with our data as well as the earlier accepted value. To redetermine this parameter, ⁷⁶As sources were measured on four Ge gamma detector systems, and an exponential function was fitted to the decay data by two different nonlinear least-squares methods. We obtained T _1/2 = 1.09379 days with a standard uncertainty of 0.00045 days. This result is 1.5% higher than the most recent value, but is in agreement with the older, less precise, consensus value.     

An Improved Preparation of Ethyl 2-Oxo-3-Pyrrolidinecarboxylate

The title 3-substituted pyrrolidinone is a useful building block that has been prepared via base-catalyzed additions of diethyl malonate to 1-benzene-sulfonylaziridine (3 steps, 43% overall yield),¹ 1-iodo-2-azidoethane with subsequent reduction and cyclization (49% yield for 5 steps from commercially available materials),² or chloroacetonitrile with a subsequent Raney Ni reduction (15% overall yield).³ We now wish to report a simple two step process that gives good yields of the title compound.     

Errors,PGAA, and metrology

Analytical chemists are scientific scavengers, using any available physical phenomenon to determine the composition of materials. Accuracy, unlike mere reproducibility, depends on understanding the measurement process, most usefully by stressing it until it bends. The use of neutron capture gamma rays for analysis involves some issues not encountered in conventional neutron activation analysis which, when understood, extend the utility and reinforce the value of nuclear methods of elemental analysis. These methods are being increasingly recognized as tools for SI-traceable metrology.