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 4παß 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.

HOW OLD IS IT? - 241PU/241AM NUCLEAR FORENSIC CHRONOLOGY REFERENCE MATERIALS.

One material attribute for nuclear forensics is material age. 241Pu is almost always present in uranium- and plutonium-based nuclear weapons, which pose the greatest threat to our security. The in-growth of 241Am due to the decay of 241Pu provides an excellent chronometer of the material. A well-characterized 241Pu/241Am standard is needed to validate measurement capability, as a basis for between-laboratory comparability, and as material for verifying laboratory performance. This effort verifies the certification of a 38 year old 241Pu Standard Reference Material (SRM4340) through alpha-gamma anticoincidence counting, and also establishes the separation date to two weeks of the documented date.

International workshop on emergency radiobioassay: considerations, gaps and recommendations.

An international workshop on emergency radiobioassay was held in Ottawa, Canada, 1-3 September 2010. Sixty-five scientists and public health officials from five countries attended the workshop and gave 36 presentations. During the workshop, many considerations were raised, gaps identified, and recommendations given for emergency radiobioassay for both preparedness and response in case of a radiological or nuclear incident. In short, some bioassay methods and protocols need to be developed, validated, and exercised; national and international radiobioassay laboratory networks should be established; and communications and collaborations among public health officials, monitoring experts, and medical staff are encouraged. All these activities are required to make us better prepared for an RN emergency.

Emergency radiobioassay preparedness exercises through the NIST radiochemistry intercomparison program.

The present challenge for the international emergency radiobioassay community is to analyze contaminated samples rapidly while maintaining high quality results. The National Institute of Standards and Technology (NIST) runs a radiobioassay measurement traceability testing program to evaluate the radioanalytical capabilities of participating laboratories. The NIST Radiochemistry Intercomparison Program (NRIP) started more than 10 years ago, and emergency performance testing was added to the program seven years ago. Radiobioassay turnaround times under the NRIP program for routine production and under emergency response scenarios are 60 d and 8 h, respectively. Because measurement accuracy and sample turnaround time are very critical in a radiological emergency, response laboratories' analytical systems are best evaluated and improved through traceable Performance Testing (PT) programs. The NRIP provides participant laboratories with metrology tools to evaluate their performance and to improve it. The program motivates the laboratories to optimize their methodologies and minimize the turnaround time of their results. Likewise, NIST has to make adjustments and periodical changes in the bioassay test samples in order to challenge the participating laboratories continually. With practice, radioanalytical measurements turnaround time can be reduced to 3-4 h.

Ultra-low level plutonium isotopes in the NIST SRM 4355A (Peruvian Soil-1).

For more than 20 years, countries and their agencies which monitor radionuclide discharge sites and storage facilities have relied on the National Institute of Standards and Technology (NIST) Standard Reference Material (SRM) 4355 Peruvian Soil. Its low fallout contamination makes it an ideal soil blank for measurements associated with terrestrial-pathway-to-man studies. Presently, SRM 4355 is out of stock, and a new batch of the Peruvian soil is currently under development as future NIST SRM 4355A. Both environmental radioanalytical laboratories and mass spectrometry communities will benefit from the use of this SRM. The former must assess their laboratory procedural contamination and measurement detection limits by measurement of blank sample material. The Peruvian Soil is so low in anthropogenic radionuclide content that it is a suitable virtual blank. On the other hand, mass spectrometric laboratories have high sensitivity instruments that are capable of quantitative isotopic measurements at low plutonium levels in the SRM 4355 (first Peruvian Soil SRM) that provided the mass spectrometric community with the calibration, quality control, and testing material needed for methods development and legal defensibility. The quantification of the ultra-low plutonium content in the SRM 4355A was a considerable challenge for the mass spectrometric laboratories. Careful blank control and correction, isobaric interferences, instrument stability, peak assessment, and detection assessment were necessary. Furthermore, a systematic statistical evaluation of the measurement results and considerable discussions with the mass spectroscopy metrologists were needed to derive the certified values and uncertainties. The one sided upper limit of the 95% tolerance with 95% confidence for the massic (239)Pu content in SRM 4355A is estimated to be 54,000 atoms/g.

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.

The use of autoradiography for investigating the distribution of radioactivity in lung counter calibration sources.

This paper shows that autoradiography is a useful technique for investigating radioactivity distributions in lung phantoms and planar sources. It was applied to a sliced lung phantom that had activity homogeneously distributed throughout the tissue substitute material and to laminated planar sources in an attempt to answer three questions: 1) Was the activity distribution the same in each slice of the sliced homogeneous lung set? 2) Was the activity distribution the same for each of the laminated planar sources? and 3) Were the activity distributions the same between slices and planar sources? The activity distribution, including identification of some locations of elevated activity in the sliced homogeneous lungs, was easily obtained using autoradiography. This study demonstrates that neither the sliced homogeneous lung sets nor the laminated planar sources had a homogeneous distribution of radioactivity, as had been previously thought.

NIST radiochemistry intercomparison program: a summary of four-year performance evaluation study. National Institute of Standards and Technology.

This paper summarizes the methods currently applied by the National Institute of Standards and Technology (NIST) for the preparation and verification of environmental and radiobioaasay performance evaluation materials for the traceability testing of low-level radioactivity measurements. The evaluation of measurement quality of the all participants indicated that over 90% of the intercomparison results complied with ANSI N42.22 and/or HPS N13.30 standards. Overall, the differences from the NIST values observed for all test nuclides and matrices are less than -7%, with a typical measurement precision better than 10% (1 s). The dependency of measurement quality on the test radionuclides, sample matrices, and radiochemical methods is identified by statistical analyses.