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Isotope dilution mass spectrometry using traceable standards as spikes coupled with isotope ratio measurements by thermal ionization or inductively coupled plasma mass spectrometer instruments is the preferred methodology for element content determinations and isotopic composition measurements in a variety of applications, especially those involving highly radioactive isotopes like the actinide elements. This assay measurement technique takes advantage of the sensitivity of modern mass spectrometry instrumentation to minimize the amount of material utilized for the measurement and enables the measurement sequence to be automated, with minimal intervention from analyst during the measurement process. LA-UR-20-28878.

Plutonium certified reference materials (CRMs) 136, 137, and 138 were produced, characterized, and certified in the period 1966 through 1971 by the National Bureau of Standards. The thermal ionization mass spectrometry (TIMS) instruments and the analytical methodologies evolved significantly since the characterization of these Pu isotopic standards. Given the excellent precision of modern TIMS and inductively coupled plasma instruments, systematic biases at the major and minor isotope ratios of these plutonium (Pu) isotopic standards (compared to the certified values) are to be expected. Studies on the major and minor isotope ratios of uranium (U) CRMs indicated systematic bias in the certified ratios of several of these standards. We present a systematic investigation of the 240Pu/239Pu major isotope ratio of Pu isotopic CRM138. The 240Pu/239Pu isotope ratio is shown to be biased by ~ 0.07–0.08%, larger than the bias seen in the major isotope ratio of any of the U CRM from New Brunswick Laboratory (NBL).

An intercomparison of the radio-chronometric ages of four distinct plutonium-certified reference materials varying in chemical form, isotopic composition, and period of production are presented. The cross-comparison of the different 234U/238Pu, 235U/239Pu, 236U/240Pu, and 241Am/241Pu model purification ages obtained at four independent analytical facilities covering a range of laboratory environments from bulk sample processing to clean facilities dedicated to nuclear forensic investigation of environmental samples enables a true assessment of the state-of-practice in "age dating capabilities" for nuclear materials. The analytical techniques evaluated used modern mass spectrometer instrumentation including thermal ionization mass spectrometers and inductively coupled plasma mass spectrometers for isotopic abundance measurements. Both multicollector and single collector instruments were utilized to generate the data presented here. Consensus values established in this study make it possible to use these isotopic standards as quality control standards for radio-chronometry applications. Results highlight the need for plutonium isotopic standards that are certified for 234U/238Pu, 235U/239Pu, 236U/240Pu, and 241Am/241Pu model purification ages as well as other multigenerational radio-chronometers such as 237Np/241Pu. Due to the capabilities of modern analytical instrumentation, analytical laboratories that focus on trace level analyses can obtain model ages with marginally larger uncertainties than laboratories that handle bulk samples. When isotope ratio measurement techniques like thermal ionization mass spectrometry and inductively coupled plasma mass spectrometry with comparable precision are utilized, model purification ages with similar uncertainties are obtained.

Thorough physical and chemical characterization of plutonium–beryllium (PuBe) neutron sources is an important capability with applications ranging from material accountancy to nuclear forensics. Characterization of PuBe sources is not trivial owing to range of existing source designs and the need for adequate infrastructure to deal with radiation and protect the analyst. This study demonstrates a method for characterization of three PuBe sources that includes physical inspection and imaging followed by controlled disassembly and destructive analysis.

Large, fluorescently stained restriction fragments of lambda phage DNA are sized by passing individual fragments through a focused continuous wave laser beam in an ultrasensitive flow cytometer at a rate of 60 fragments per second. The size of the fluorescence burst emitted by each stained DNA fragment, as it passes through the laser beam, is measured in one millisecond. One hundred sixty four seconds of fluorescence burst data allow linear sizing of DNA with an accuracy of better than two percent over a range of 10 to 50 kbp. This corresponds to analyzing less than 1 pg of DNA. Sizing of DNA fragments by this approach is much faster, requires much less DNA, and can potentially analyze large fragments with better resolution and accuracy than with gel-based electrophoresis.