S. P. LaMont

Superconducting calorimetric alpha particle sensors for nuclear nonproliferation applications

Identification of trace nuclear materials is usually accomplished by alpha spectrometry. Current detectors cannot distinguish critical elements and isotopes. We have developed a detector called a microcalorimeter, which achieves a resolution of 1.06 keV for 5.3 MeV alphas, the highest resolving power of any energy dispersive measurement. With this exquisite resolution, we can unambiguously identify the P240u/P239u ratio in Pu, a critical measurement for ascertaining the intended use of nuclear material. Furthermore, we have made a direct measurement of the P209o ground state decay.

The urgent requirement for new radioanalytical certified reference materials for nuclear safeguards, forensics, and consequence management

A multi-agency workshop was held from 25 to 27 August 2009, at the National Institute of Standards and Technology (NIST), to identify and prioritize the development of radioanalytical Certified Reference Materials (CRMs, generally provided by National Metrology Institutes; Standard Reference Materials, a CRM issued by NIST) for field and laboratory nuclear measurement methods to be used to assess the consequences of a domestic or international nuclear event. Without these CRMs, policy makers concerned with detecting proliferation and trafficking of nuclear materials, attribution and retribution following a nuclear event, and public health consequences of a nuclear event would have difficulty making decisions based on analytical data that would stand up to scientific, public, and judicial scrutiny. The workshop concentrated on three areas: post-incident Improvised Nuclear Device (IND) nuclear forensics, safeguard materials characterization, and consequence management for an IND or a Radiological Dispersion Device detonation scenario. The workshop identified specific CRM requirements to fulfill the needs for these three measurement communities. Of highest priority are: (1) isotope dilution mass spectrometry standards, specifically 233U, 236gNp, 244Pu, and 243Am, used for quantitative analysis of the respective elements that are in critically short supply and in urgent need of replenishment and certification; (2) CRMs that are urgently needed for post-detonation debris analysis of actinides and fission fragments, and (3) CRMs used for destructive and nondestructive analyses for safeguards measurements, and radioisotopes of interest in environmental matrices.

A blueprint for radioanalytical metrology CRMs, intercomparisons, and PE

A workshop was held from 28 February to 2 March 2006 at the National Institute of Standards and Technology (NIST) to evaluate the needs for new directions for complex matrix reference materials certified for radionuclide content, interlaboratory comparisons and performance evaluation (PE) programs. The workshop identified new radioanalytical metrology thrust areas needed for environmental, radiobioassay, emergency consequence management, and nuclear forensics, attribution, nonproliferation, and safeguards.

Superconducting Transition-Edge Sensor Microcalorimeters for Ultra-High Resolution Alpha-Particle Spectrometry

Alpha-particle spectrometry is a powerful analytical tool for nuclear forensics and environmental monitoring. Superconducting transition-edge sensor microcalorimeters have been shown to yield unsurpassed energy resolution for alpha spectrometry. With nearly an order of magnitude better energy resolution (1.06 keV FWHM at 5.3 MeV) than the current state-of-the-art silicon detectors (8-10 keV at 5.3 MeV), it is possible to measure samples containing multiple radioisotopes that would require expensive and time-consuming radiochemical separation prior to measurement with a silicon detector. This paper presents recent results from the Los Alamos four-channel microcalorimeter alpha spectrometer. We have prepared a source from weapons-grade plutonium and demonstrated the ability of microcalorimeter alpha spectrometry to simultaneously resolve alpha energies from 239Pu, 240Pu, 238Pu, and 241Am. The low-energy performance of the spectrometer system has been improved to allow measurement of energies as low as 5 keV, which gives a dynamic range of 1000. We have demonstrated this capability by simultaneously measuring the alpha particles and low-energy x-rays and internal conversion electrons emitted by an electroplated 240Pu source.

Roadmap for radioanalytical reference and performance evaluation materials for current and emerging issues

Reference materials are fundamental tools for radiochemistry measurements laboratories to establish and evaluate analytical methods, test measurement capabilities, quantify radionuclides, compare analytical results, and establish legal confidence defensibility in measurement results. Over the past decades the focus of low-level environmental reference material producers have adapted to evolving national and international priorities and needs. This document provides a Roadmap of high priority current and future low-level radionuclide Certified Reference and Performance Evaluation Materials that subject-matter experts have identified at NIST and other public workshops (Blueprints) as crucial to metrologists and program directors to address national and international issues.

High Resolution Alpha Particle Spectroscopy with Cryogenic Microcalorimeters

We present measurements from a novel cryogenic microcalorimeter designed to detect alpha particles. We demonstrate a spectral resolution of 4.4 keV FWHM for 5.3 MeV alpha particles from a 210Po source. In addition, we present an alpha spectrum from a mixture of Pu isotopes demonstrating the feasibility of resolving the individual contributions of 239Pu and 240Pu. The unmatched resolution of microcalorimeter alpha detectors will provide new capabilities for actinide analysis. We discuss potential applications and also sensor design.

Alpha spectrometric characterization of process-related particle size distributions from active particle sampling at the Los Alamos National Laboratory uranium foundry

Uranium particles within the respirable size range pose a significant hazard to the health and safety of workers. Significant differences in the deposition and incorporation patterns of aerosols within the respirable range can be identified and integrated into sophisticated health physics models. Data characterizing the uranium particle size distribution resulting from specific foundry-related processes are needed. Using personal air sampling cascade impactors, particles collected from several foundry processes were sorted by activity median aerodynamic diameter onto various Marple substrates. After an initial gravimetric assessment of each impactor stage, the substrates were analyzed by alpha spectrometry to determine the uranium content of each stage. Alpha spectrometry provides rapid non-distructive isotopic data that can distinguish process uranium from natural sources and the degree of uranium contribution to the total accumulated particle load. In addition, the particle size bins utilized by the impactors provide adequate resolution to determine if a process particle size distribution is: lognormal, bimodal, or trimodal. Data on process uranium particle size values and distributions facilitate the development of more sophisticated and accurate models for internal dosimetry, resulting in an improved understanding of foundry worker health and safety.

Cryogenic Microcalorimeter System for Ultra‐High Resolution Alpha‐Particle Spectrometry

Microcalorimeters have been shown to yield unsurpassed energy resolution for alpha spectrometry, up to 1.06 keV FWHM at 5.3 MeV. These detectors use a superconducting transition‐edge sensor (TES) to measure the temperature change in an absorber from energy deposited by an interacting alpha particle. Our system has four independent detectors mounted inside a liquid nitrogen/liquid helium cryostat. An adiabatic demagnetization refrigerator (ADR) cools the detector stage to its operating temperature of 80 mK. Temperature regulation with ∼15‐μK peak‐to‐peak variation is achieved by PID control of the ADR. The detectors are voltage‐biased, and the current signal is amplified by a commercial SQUID readout system and digitized for further analysis. This paper will discuss design and operation of our microcalorimeter alpha‐particle spectrometer, and will show recent results.

MARC IX Introduction

The Ninth International Conference on Methods and Applications of Radioanalytical Chemistry (MARC IX) was held at the Sheraton Keauhou Bay Resort, Kona, Hawaii, March 25–30, 2012, and was attended by over 220 scientists and over 50 students representing 31 countries and two multinational organizations. A strong technical program, excellent venue, and numerous social events contributed to another successful MARC conference. Since MARC I in 1987, this series of conferences has become the major international forum for presenting advances in radioanalytical chemistry and its applications, despite the somewhat remote location for many participants. The keen foresight of the MARC founding organizers to create a topical meeting dedicated to all aspects of radioanalytical chemistry was highlighted in MARC IX with sessions covering a broad range of both long-standing and emerging technical areas. These outstanding sessions are made possible by the hard work and dedication of the many session organizers who stimulate contributions from academia, government, and industry. A wide variety of topics were covered in the scientific program of MARC IX including environmental radioactivity measurements, activation analysis, biology and medical applications, actinide analytical chemistry, radiation detectors and instrumentation, proliferation prevention and safeguards, treaty monitoring, nuclear forensics, and radionuclide measurements using mass spectrometry. A highlight of MARC IX was the awarding of the Hevesy Medal to Professor Dr. Boris F. MYASOEDOV of the Russian Academy of Sciences for his lifetime achievements in radiochemistry. Over 400 presentations were given in both oral and poster sessions at the conference with over 200 of these submitted as full papers for the proceedings. As for previous conferences, all papers were peer-reviewed by at least two reviewers, as is the policy of the Journal of Radioanalytical and Nuclear Chemistry. Although this was an arduous and time-consuming process, most of the papers were improved as a result of peer review. We cannot express enough appreciation to the many reviewers who helped in the editorial process. We are particularly grateful to those who willingly reviewed several papers and/or participated in pre-review of papers to provide grammatical assistance to non-native English speakers. The pre-review received good feedback from all the participants and reduced the burden during the review process. We want to express our sincere appreciation to the many people who helped organize MARC IX. Our Finance and Housing Chair, Jim TANNER skillfully executed his fiduciary responsibilities. Ned WOGMAN and Robert STEINER served expertly as Assistant Program Chairs. Publicity Chair Harry Miley, ably assisted by co-Publicity Chair Robert Runkle ensured MARC IX was well supported by a diverse group of sponsors. Annie KERSTING and Richard RAGAINI served as terrific liaisons between MARC IX and the Northern California Section of the American Nuclear Society. Conference Secretary Patti WILSON did an exceptional job with administrative activities including registration. Sherry GLOVER, Proceedings Chair, proficiently collected and organized papers submitted for publication. The MARC IX website was expertly designed and maintained by Daniel GLOVER, and Joe SULLIVAN provided expert IT support. Many members of the Technical Program Committee made special efforts to organize topical sessions and develop the excellent scientific program for the conference. S. P. LaMont (&) S. E. Glover Los Alamos National Laboratory, Los Alamos, NM, USA e-mail: lamont@lanl.gov

New determination of the 229Th half-life

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 4328C using 4παβ liquid scintillation counting, NaI counting, and standard addition liquid scintillation counting. The massic activity was confirmed by isotope dilution alpha spectrometry measurements. The calculated 229Th half-life is (7825 ± 87) years (k = 2), which is shorter than the three most recent half-life determinations but is consistent with these values within uncertainties.