Intercomparison of the Radio-Chronometric Ages of Plutonium-Certified Reference Materials with Distinct Isotopic Compositions

Abstract

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 234 U/ 238 Pu, 235 U/ 239 Pu, 236 U/ 240 Pu, and 241 Am/ 241 Pu 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 234 U/ 238 Pu, 235 U/ 239 Pu, 236 U/ 240 Pu, and 241 Am/ 241 Pu model purification ages as well as other multigenerational radio-chronometers such as 237 Np/ 241 Pu. 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.

New Experimentally Observable Gamma-ray Emissions from 241Am Nuclear Decay

“…Uncertainties in parentheses represent 67% confidence intervals. * The 241 Am/ 241 Pu comes from [12] and has separation date of 28-4-2016, different from the certificate value for the Pu isotopics.…”

“…Each of these determinations and their combined value with uncertainty is given in Figure 3. The 241 Am content for the two CRM samples is taken from a recent intercomparison exercise analysis of certified reference materials [12], whereas other values come from the certificate values (given in Table II). Uncertainties (67% confidence intervals) taken into account include declared 241 Pu and 241 Am mass fractions for Pu items, 241 Pu and 241 Am branching fractions at 208.0 keV, half-lives, and net peak area least-squares fit uncertainties.…”

Atomic spectrometry update: review of advances in the analysis of metals, chemicals and materials

“…In another study by Mathew et al, four different plutonium CRMs were used to compare radio-chronometric ages. 215 An intercomparison exercise assessed different facilities, mass spectrometric capabilities and chronometers ( 234 U/ 238 Pu, 235 U/ 239 Pu, 236 U/ 240 Pu), with lower uncertainties in model ages achieved for laboratories set up for trace level analysis.…”

Improved Plutonium and Americium Photon Branching Ratios from Microcalorimeter Gamma Spectroscopy

“…Activity ratios, α is , with respect to 239 Pu for each isotope i for each spectrum s, are determined by decay-correcting the mass fractions from Table 2 to the spectrum measurement dates. For CRMs 136-138, the amount of 241 Am was taken from the recently published forensics intercomparison exercise analysis of certified reference materials [27]. Decay-corrected activity ratio uncertainties include half-life, mass fraction, and molar mass uncertainties from Table 4.…”