Isotopic analysis of uranium and plutonium mixtures by resonance ionization mass spectrometry

Abstract

The technlque of resonance lonlzatlon mass spectrometry (RIMS) has been applled to the measurement of U and Pu Isotope ratlos. The RIMS technique offers the advantage of high elemental selectlvlty compared to conventlonal thermal lonlzatlon mass spectrometry. Measurements of selectlvlty ratlos for U vs. Pu are presented at two different wavelengths of laser excltatlon. The preclslon obtalned for repllcate analyses of NBS standard reference materlals Is equal to that obtalned by single-fllament thermal lonlzatlon methods. Sample slzes of 10 ng for each element were adequate for measurement of the 240Pu/23gPu, z41Pu/230Pu, and 235U/238U Isotope ratlos. Sensitivity was enhanced by using a pulsed thermal atomization technique which resulted In a 10-fold Improvement In sample usage compared to continuous atomlzatlon. The RIMS technique Is, therefore, potentially useful In safeguards and nuclear materials accountancy, where preclse and accurate Isotope ratio measurements are Important.One of the problems in isotopic analysis of P u and U is isobaric interferences a t masses 238 and 241. Both elements have isotopes at mass 238; it is a particular problem in P u analysis because that isotope is usually a major component of U and a minor one of Pu. For the specific case of spent reactor fuels, the U/Pu ratio is usually about 100, and complete chemical separation of the two elemenk is difficult and time-consuming. The resin bead method of sample preparation (1-3) has eliminated most of the chemistry required, but, for full exploitation of the technique, the elements are run sequentially from the same filament loading, making correction a t mass 238 essential.At the mass 241 position, buildup of %lAm from the decay of 241Pu (half-life 14.3 years) becomes significant after only a few weeks. It is not always possible to analyze samples quickly enough for 241Am to be of no consequence, and it is impossible to correct for its contribution to the P u signal because no Am isotope is available to monitor for this purpose.Because of its importance to safeguards, it is important to obtain as accurate an assay of the 241Pu as possible.The recently developed technique of resonance ionization mass spectrometry (RIMS) offers the ability to perform the required isotopic analyses with little or no isobaric interference. RIMS has been described, and its use in eliminating isobaric interference in mass spectrometric analysis of Nd and Sm has been demonstrated (4). The technique can be applied to samples loaded onto typical thermal ionization filaments. For RIMS detection, neutral atoms evaporated from the filament are photoionized by a several-photon process operating via allowed transitions through intermediate resonant levels (4). In a previous report, a number of possible two-photon RIMS-active wavelengths were presented by which P u can be ionized by photons in the wavelength range of 431 to 451 nm (5). Uranium is expected to have a large number of lines in this region, so many that selectivity could be compromised. In this paper we des...

Isotope ratio analysis of actinides, fission products, and geolocators by high-efficiency multi-collector thermal ionization mass spectrometry

“…Thermal ionization mass spectrometry (TIMS) [72,[108][109][110][111][112], inductively coupled plasma mass spectrometry [113][114][115][116][117][118][119][120], secondary ion mass spectrometry (predominately for particle or surface analysis) [71,54], accelerator mass spectrometry (predominately for high abundance sensitivity analysis) [10,[121][122][123][124], and resonance ionization mass spectrometry (high elemental selectivity) [19,[125][126][127][128] are frequently utilized for analysis of actinides and other radionuclides. Glow discharge mass spectrometry has been used for isotope ratio analysis of actinides, such as uranium [129][130][131], as well as fission-track TIMS for particles [132].…”

Quantifying Uranium Isotope Ratios Using Resonance Ionization Mass Spectrometry: The Influence of Laser Parameters on Relative Ionization Probability

“…RIMS has been shown to be a potential tool for quantifying uranium isotope ratios [28,29,30,31,32]. Early approaches used a single pulsed broadband dye laser (0.063 -0.1 nm bandwidth) tuned to a one-color (591 nm), three-photon ionization scheme.…”

Low-Level Detection of Actinides by Laser Resonance Photoionization

“…In recent years laser resonance ionization mass spectrometry has gained much interest [2][3][4][5]. The detection of plutonium by resonance ionization was first reported by DONOHUE et al [6,7] and KRÖNERT et al [8]. In these experiments excitation and ionization was achieved with a single wavelength either from a cw-laser or from a pulsed laser with a repetition rate of 1 to 30 Hz.…”

“…In these experiments excitation and ionization was achieved with a single wavelength either from a cw-laser or from a pulsed laser with a repetition rate of 1 to 30 Hz. Mass analysis was performed with a magnetic spectrometer [6,7] or by a time-of-flight technique [8]. We have set up a facility for three step photoionization using pulsed lasers with a high repetition rate followed by time-of-flight mass spectrometry [9].…”