A CBNM isotopic reference material set for testing linearity of isotope mass spectrometers (CBNM IRM 072/1-15)

Certification of uranium hexafluoride reference materials for isotopic composition

“…The IRMM-074 series of gravimetric mixtures is characterized by major isotope ratios n( 235 U)/n( 238 U) of about 1.00026 with relative expanded uncertainties of 0.015 % (k = 2) and isotope ratios n( 233 U)/n( 235 U) ranging between 10 -6 and 1, with relative expanded uncertainties of 0.025 % (k = 2) [8]. In addition, it was shown in [8], that the major isotope ratios n( 235 U)/n( 238 U) in IRMM-074 were confirmed by TIMS measurements using the major amount ratios of the predecessor series IRMM-072 (similar isotope amount ratios [9,10], prepared about 10 years earlier) as calibrant. Using IRMM-072, also the isotopic composition of two further gravimetric mixtures, the IRMM-199 ( 233 U/ 235 U/ 238 U = 1/1/1) and the NBL (New Brunswick Laboratory) CRM U500 ( 235 U/ 238 U = 1/1), was confirmed at the same time [8].…”

Precise determination of femtogram quantities of radium by thermal ionization mass spectrometry

“…An Ortec preamplifier was coupled to a Stanford Research Systems SR400 gated photon counter. This system has an overall efficiency of >90% and is linear at count rates up to 3 X 106 counts s'1 (cps), demonstrated using the set of Central Bureau for Nuclear Measurement (CBNM) EEC uranium standards (see ref 9 and Cohen et al, in preparation). Because useful count rates for Ra+ in TIMS may be very low (<10 cps), a low-background ioncounting system is essential.…”

Transferring accuracy to the trace level and then to the field

“…An example of such a set is given in table 1. Its preparation is described elsewhere [1]. The built-in ratio 23 5 U/ 2 .. Uz 1 (certified to 0.02%) can be used to determine any systematic errors in the "excitation" or "ion" source and correct the observed 233u/235U or 233 U/ 23 'U ratios.…”