Inductive coupled plasma mass spectrometry with an enlarged sampling orifice and offset ion lens. I. Ion trajectories and detector performance

AbstractA new inductively coupled plasma mass spectrometer (ICP-MS) with four stages of differential pumping is described. The relatively large sampling orifice (1.31-mm dia.) improves signals for metal ions and resists plugging from deposited solids. A new ion lens is described that deflects ion off center and then back on center into the differential pumping orifice; there is no photon stop in the center of the beam. Calculations of ion trajectories using SIMION show that only those ions that leave the skimmer on center are transmitted, whereas most other lenses used in ICP-MS transmit only ions that leave the skimmer off axis. The performance of a Channeltron electron multiplier is compared to that of Daly detector. Both detectors yield similar sensitivities of ∼ 106 counts s−1 per ppm and detection limits of ∼ 1 pptr. The background with a Channeltron electron multiplier is only 0.4 counts s−1 and is only slightly higher than the dark current count rate. Presumably the offset ion lens used in the present work efficiently screens the detector from photons emitted by the plasma. The background with the Daly detector is 4 counts s−1, which represents a substantial improvement over the background obtained in previous use of the Daly detector with ICP-MS

Materials Reliability Program Resistance to Primary Water Stress Corrosion Cracking of Alloys 690, 52, and 152 in Pressurized Water Reactors (MRP-111)

Over the last thirty years, stress corrosion cracking in PWR primary water (PWSCC) has been observed in numerous Alloy 600 component items and associated welds, sometimes after relatively long incubation times. Repairs and replacements have generally utilized wrought Alloy 690 material and its compatible weld metals (Alloy 152 and Alloy 52), which have been shown to be very highly resistant to PWSCC in laboratory experiments and have been free from cracking in operating reactors over periods already up to nearly 15 years. It is nevertheless prudent for the PWR industry to attempt to quantify the longevity of these materials with respect to aging degradation by corrosion in order to provide a sound technical basis for the development of future inspection requirements for repaired or replaced component items. This document first reviews numerous laboratory tests, conducted over the last two decades, that were performed with wrought Alloy 690 and Alloy 52 or Alloy 152 weld materials under various test conditions pertinent to corrosion resistance in PWR environments. The main focus of the present review is on PWSCC, but secondary-side conditions are also briefly considered

Interspecific Reassortment of Genomic Segments in the Evolution of Cucumoviruses

AbstractSegmented genomes of RNA viruses are thought to evolve and be maintained in analogy to sexual recombination and reassortment in eukaryotic systems. If reassortment among genomes is an important event in cucumoviral evolution, then such events should be detectable among extant viruses. In this study, phylogenetic analyses of cucumoviruses were performed using aligned amino acid sequences. The results reveal different relationships among species when the three genomic segments are compared, suggesting that reassortment events have given rise to extant forms. In addition, we describe a cucumovirus isolate that is composed of genomic segments from two distinct viral species. These results indicate that reassortment events may provide a mechanism for speciation in cucumoviruses