The production and certification of a plutonium equal-atom reference material: NBL CRM 128

Abstract

This reportwas preparedas an accountof work_-_nsorcdby an agcncyof the UnitedStates Government.Neither the United StatesGovernmentnorany agencythereof,norany of their employees, makesany warranty, expressor implied,or assumesany legal liabilityor responsibility for the accuracy,complctcness, or usefulnessof any information, apparatus, product, or processdisclosed,or representsthat its use wouldnot infringeprivatelyownedtights,Rcfcr-cnc¢hereinto any specificcommercial product, process,or serviceby tradename,trademark, manufacturer, or otherwisedoes not ne, c, essarilyconstituteor imply its endorsement, recommendation, or favoringby the UnitedStates Govcrnmcnt or any agencythcrco[ The vi¢.ws and opin!onsof authors expressedherein do not necessarilystate or reflectthose of the UnitedStates Government orany agencythcrcof. L, IST OF FIGURES F_gure No, Page I Mass Spectrometric _tomie Weight Method,.. 3 2 NBS-Design 3C)-cm Radius oi" Curvature, 90°Magneti,c Sector' Sol ld Sample Mass Speetr'ometer 9 AC, KNOWLEIX]I_NTS

Critical need for plutonium and uranium isotopic standards with lower uncertainties

“…Attempts were made to identify, eliminate, reduce, or control probable sources of systematic uncertainty attributable to instrumental factors. 1,2 Through systematic studies it was demonstrated that, for isotope ratio measurements by TIMS, even when uncertainty contributions from chemistry and instrumental factors were negligible, signicant biases were possible because of differences in the sample mounting or the pattern of lament heating. The NBS measurement approach was: evaluate the degree of constancy of the isotopic ratio bias under various operating conditions, the best set of conditions (in terms of smaller absolute magnitude of the bias and its variability) were adopted for analyses, the constancy of the bias was veried using standards of known isotopic composition, and the same bias correction was applied on the unknown samples.…”

“…SRM 996, plutonium-244 spike assay and isotopic standard, was characterized in 1981 and the equal-atom Pu CRM 128 was characterized by NBL in 1990. 2,22 Mass bias correction for SRM 996 was based on measurements of SRMs 947 and 948 analyzed concurrently with the characterization aliquots of SRM 996. For CRM 128, the correction for mass bias effects was based on gravimetric mixtures prepared using high-purity Pu isotopic end-members.…”

“…For CRM 128, the correction for mass bias effects was based on gravimetric mixtures prepared using high-purity Pu isotopic end-members. 2 CRM 122, the plutonium oxide -PuO 2 in powder form, was certied in 1985. 23 For an estimation of the mass bias correction in CRM 122, SRMs 946 and 948 were used.…”

“…Modern thermal ionization mass spectrometer (TIMS) instruments used for isotope ratio measurements are built on the foundations established during this early NBS work. 1,2 Mariam R. Thomas joined Los Alamos National Laboratory (LANL) as a mass spectrometrist in 2001. As a member of the Actinide Analytical Chemistry group at LANL, Mariam's major focus was on the Thermal Ionization and Gas Mass spectrometer instruments and became the Mass Spectrometry team leader in 2011.…”

High-Precision Measurement of the 238Pu/239Pu Isotope Ratio by TIMS

“…Instead, it was assumed that plutonium exhibits a mass bias comparable to uranium isotopes during the evaporation process in the thermal ion source. Thus, SRM 946–948 were certified employing the mass bias factor calculated using uranium isotopes. − The fractionation factor derived from the TIMS analysis of the aforementioned certified isotope ratios was subsequently employed for mass bias correction in the later prepared plutonium standards, specifically SRM 947 and 948 for SRM 996 and SRM 946 and SRM 948 for CRM 122. In contrast, mass bias estimation for plutonium isotope ratios in CRM 128 involves measuring gravimetric mixtures of highly enriched uranium isotopes alongside standard plutonium solutions. − In summary, the correction of mass bias for plutonium isotope ratios in the certification of isotopic standards depends upon assuming a parallel bias with uranium isotopes during the evaporation process in the thermal ion source.…”