Quadrupole, measurement system

Most isotope ratio measurements have been performed using sector mass spectrometers. Some work has been reported, notably by Heumann [35], in which a quadrupole-based system was used. Instruments used for measurement of isotope ratios are most often dedicated to that purpose. In most instances only a relatively small mass range needs to be monitored, just enough to encompass the isotopes of the analyte element. Without the ability to scan the entire elemental mass range [usually from mlz = 6 (Li) through mfc = 238 (U) for elemental analysis], mass spectrometers designed to measure isotope ratios cannot readily be adapted for other purposes. See Chapter 2 for a discussion of instrumentation required for elemental analysis of solid materials and Chapter 3 for a treatment of the in-strumenation needed for elemental analysis of solutions. 

Py-GC/MS measuring system using a microfurnace pyrolyzer, GC equipped with a capillary separation column, and a quadrupole mass spectrometer, from Ref. 15. 

FIGURE 2.9 Separation on Sm and Nd in irradiated mixed oxide sample after injection of 1 mL containing 20 pg fuel mL- measured with the HPLC-Quadrupole ICPMS system. (From Gunther-Leopold, I. et al.. Characterization of spent nuclear fuel by an online combination of chromatographic and mass spectrometric techniques, in Proceedings of the Seventh International Conference on Nuclear Criticality Safety, ICNC, Tokai, Japan, October 2003, JAERI-Conf 2003-019, 2003. With permission.)... 

Preliminary measurements were made with a quadrupole-based system and reported (Gunther-Leopold et al. 2003), but after a multicollector ICPMS was installed in the hot laboratory, more precise isotope ratio measurements were made. The results were adjusted by use of internal correction (known isotope ratio of the same element) or by a bracketing procedure with certified reference materials (external correction). Additional measurements were made with a specially designed laser-ablation system that was coupled to the ICPMS instrument. The nuclear fuel burn-up assessment was based on measurement of the ratio between Nd isotope and the four main fissionable nuclides ( U, Pu, and " Pu) for UOj or MOX fuel. " Nd is formed... 

The term Q/TOF is used to describe a type of hybrid mass spectrometer system in which a quadrupole analyzer (Q) is used in conjunction with a time-of-flight analyzer (TOP). The use of two analyzers together (hybridized) provides distinct advantages that cannot be achieved by either analyzer individually. In the Q/TOF, the quadrupole is used in one of two modes to select the ions to be examined, and the TOF analyzer measures the actual mass spectrum. Hexapole assemblies are also used to help collimate the ion beams. The hybrid orthogonal Q/TOF instrument is illustrated in Figure 23.1. 

The central transport chamber is an 80-cm-diameter stainless steel vessel, and is pumped by a 1000-1/s turbomolecular pump, which is backed by a small (501/s) turbomolecular pump to increase the compression ratio for hydrogen, and by a 16-m /h rotating-vane pump. UHV is obtained after a bake-out at temperatures above 100°C (measured with thermocouples at the outside surface) of the whole system for about a week. A pressure in the low 10 " -mbar range is then obtained. With a residual gas analyzer (quadrupole mass spectrometer, QMS) the partial pressures of various gases can be measured. During use of the system, the pressure in the central chamber is in the low 10 -mbar range due to loading of samples. Water vapor then is the most abundant species in the chamber. 

The partial pressures of the stable neutral molecules in the discharge (silane, hydrogen, disilane, trisilane) can be measured by a quadrupole mass spectrometer (QMS). The QMS usually is mounted in a differentially pumped chamber, which is connected to the reactor via a small extraction port [286]. In the ASTER system a QMS is mounted on the reactor that is used for intrinsic material deposition. The QMS background pressure (after proper bake-out) is between 10 and 10 mbar. The controllable diameter in the extraction port is adjusted so that during discharge operation the background pressure never exceeds 10"" mbar. 

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