U.S. flag

An official website of the United States government

Official websites use .gov
A .gov website belongs to an official government organization in the United States.

Secure .gov websites use HTTPS
A lock ( ) or https:// means you’ve safely connected to the .gov website. Share sensitive information only on official, secure websites.

Search Publications by: Richard Essex (Fed)

Search Title, Abstract, Conference, Citation, Keyword or Author
Displaying 1 - 11 of 11

Gravimetric deposition of microliter drops with radiometric confirmation

September 9, 2023
Author(s)
Denis E. Bergeron, Richard Essex, Svetlana Nour, Gordon A. Shaw, R. Michael Verkouteren, Ryan P. Fitzgerald
A manual gravimetric dispensing technique is demonstrated using a micropipettor modified for use with removeable microcapillaries. Liquid scintillation sources were prepared from a well-characterized 241Am reference solution, providing a radiometric check

Isotope Dilution Mass Spectrometry as an Independent Assessment for Mass Measurements of Milligram Quantities of Aqueous Solution

January 1, 2023
Author(s)
Richard Essex, Jacqueline L. Mann, Denis E. Bergeron, Ryan P. Fitzgerald, Svetlana Nour, Gordon A. Shaw, R. Michael Verkouteren
Isotope dilution mass spectrometry was used to independently assess the accuracy of mass measurement methods developed to quantitatively dispense milligram quantities of aqueous solution. Solutions of isotopically enriched 158Gd and enriched 155Gd were

Toward a New Primary Standardization of Radionuclide Massic Activity Using Microcalorimetry and Quantitative Milligram-Scale Samples

February 24, 2022
Author(s)
Ryan P. Fitzgerald, Bradley Alpert, Dan Becker, Denis E. Bergeron, Richard Essex, Kelsey Morgan, Svetlana Nour, Galen O'Neil, Dan Schmidt, Gordon A. Shaw, Daniel Swetz, R. Michael Verkouteren, Daikang Yan
We present a new paradigm for the primary standardization of radionuclide activity per mass of solution (Bq/g). Two key enabling capabilities are 4π decay-energy spectrometry using chip-scale sub-Kelvin microcalorimeters and direct realization of mass by

New reference materials for trace-levels of actinide elements in plutonium

January 27, 2022
Author(s)
Richard Essex, Lav Tandon, Amy Gaffney, Cole Hexel, Debbie Bostick, Lisa Colletti, Diana Decker, Casey Finstad, Joseph Giaquinito, Elmer Lujan, John Partridge, Benjamin Roach, John Rolinson, Kyle Samperton, Alice Slemmons, Khalil Spencer, Floyd Stanley, Lisa Townsend, Kerri Treinen, Ross Williams, Christopher Worley
Two plutonium oxides were prepared as unique reference materials for actinides occurring as trace constituents in Pu. Each reference material unit is approximately 200 mg of PuO2 in a quartz glass vial. Characterized attributes of the oxides included mass

REFERENCE MATERIALS FOR TRACE ACTINIDE CONTENT IN PLUTONIUM OXIDE

October 1, 2021
Author(s)
Richard Essex, Lav Tandon, Cole Hexel, Amy Gaffney
Nuclear forensic analyses of plutonium (Pu) materials encountered outside nuclear safeguards control can include chemical composition, isotopic composition, and the concentration of various contaminants. Results from these measurements provide insights

A Highly-enriched 244Pu Reference Material for Nuclear Safeguards and Nuclear Forensic Measurements

January 26, 2021
Author(s)
Richard Essex, Ross W. Williams, Kerri C. Treinen, Amelie Hubert, Marc A. Humphrey, Jeremy D. Inglis, William S. Kinman, Joel Maassen, Maxim V. Penkin, Robert E. Steiner
A highly-enriched 244Pu isotope dilution reference material has been prepared and characterized for metrologically traceable measurements of very small quantities of plutonium. The amount of plutonium in samples associated with nuclear safeguards and

A new highly enriched 233U reference material for improved simultaneous determination of uranium amount and isotope amount ratios in trace level samples

January 26, 2021
Author(s)
Richard Essex, Ross W. Williams, Kayron T. Rogers, Cole R. Hexel, Tashi Parsons-Davis, Kerri C. Treinen
A highly-enriched 233U reference material (>0.99987 n(233U)/n(U)) has been prepared and characterized for use as an isotope dilution mass spectrometry spike. An ion exchange separation was performed on 1 gram of high purity 233U to further reduce trace

Preparation and calibration of a Protactinium-231 reference material

August 22, 2019
Author(s)
Richard Essex, Ross W. Williams, Kerri C. Treinen, Ronald Colle, Ryan P. Fitzgerald, Raphael Galea, John Keightley, Jerome LaRosa, Lizbeth Laureano-Perez, Svetlana Nour, Leticia Pibida
A 231Pa reference material has been characterized for amount of Pa. This reference material is primarily intended for calibration of 233Pa tracers produced for 231Pa - 235U model age measurements associated with nuclear forensics and nuclear safeguards

A Reference Material for Evaluation of Cs-137 Radiochronometric Measurements

August 16, 2018
Author(s)
Kevin B. Lavelle, Richard Essex, Jeffrey T. Cessna, Kevin P. Carney, Cole R. Hexel
A new nuclear forensic reference material has been characterized as a standard for radiochronometric determination of the model purification date for 137Cs sources. The purification date of a radioactive source is a potentially diagnostic nuclear forensic

New determination of the 229Th half-life

July 23, 2018
Author(s)
Richard Essex, Jacqueline L. Mann, Ronald Colle, Lizbeth Laureano-Perez, Megan E. Bennett, Heather Dion, Ryan P. Fitzgerald, Amy M. Gaffney, Amelie Hubert, Robert E. Steiner, Ross W. Williams, Alkiviadis Gourgiotis, William S. Kinman
A new determination of the 229Th half-life was made based on measurements of the 229Th massic activity of a high-purity solution for which the 229Th molality had previously been measured. The 229Th massic activity was measured by direct comparison with SRM

New thorium-229 standard reference material

July 27, 2017
Author(s)
Richard Essex, Jacqueline L. Mann, Ross W. Williams, William S. Kinman, Amelie Hubert, Megan E. Bennett
A new reference material, preliminarily designated as SRM 3059, was characterized for 229Th molality (mol•g-1) and thorium isotope amount ratios. This SRM is intended for use in nuclear forensic analyses as an isotope dilution mass spectrometry spike. The