P.F. Hinrichsen

Heavy-ion energy resolution of SSB detectors

Abstract The energy resolution of the silicon surface barrier detectors currently used for ERD (elastic recoil detection) and HIRBS (heavy-ion Rutherford backscattering spectroscopy) limits both the mass and depth resolution achieveable. Although the timing properties and pulse height defect of SSBDs have been well documented, only limited studies of their heavy-ion energy resolution in the energy range 5–20 MeV were available. Data on the energy resolution and line shape of two Ortec BA-017-100-100 detectors are presented and compared with a survey of SSB detector resolution data available in the literature.

An ERD/RBS/PIXE apparatus for surface analysis and channeling

Abstract A system for surface analysis, lattice localisation of impurities, defect studies in crystalline solids and routine ERD (elastic recoil detection) is described. The apparatus features a high vacuum chamber, a computer controlled precision goniometer and an energy plus time-of-flight mass discrimination system. First results of channeling/ERD experiments using 15–30 MeV 35Cl beams on silicon crystals implanted with B+ and BF2+ are presented, as well as data on the effect of beam induced damage on the boron distribution.

The detection of heavy ions with PIN diodes

Abstract The pulse height defect (PHD) and the resolution (ΔE) of a low-cost PIN photodiode (Hamamatsu Model S 1223-01) have been studied for 11B (0.2–16.2 MeV), 35Cl (1.0–8.2 MeV) and 81Br (0.5–8.0 MeV) ions, and found comparable to those of ORTEC silicon surface barrier detectors. The major contribution to the difference in performance of the PIN diode may come from the surface dead-layer which was measured to be 90 ± 11 nm. The dependence of diode properties on the bias voltage shows that even at 0 V the relative pulse height is ≥95% of the value of saturation which is attained within 5 V. The relative resolution (ΔE/E) is nearly constant for all bias values up to 30 V (maximum reverse bias). Some preliminary results on the effect of radiation dose on the leakage current are also presented. These results demonstrate that the low-cost PIN diode can be successfully used as a charged-particle detector in applications such as ion beam analysis (RBS, HIRBS, ERD) and space technology.

The microbeam facility at the University of Montreal

Abstract The 4.5 MV Dynamitron injector for our 6 MV Tandem is now used to provide a proton beam for a dedicated FIXE, RBS, PIGE microbeam facility. An electrostatic quadrupole triplet lens produces a beam spot of 20 μm diameter. The target chamber, which is a modified 4 in. Dependex cross, houses an electron flood gun, and SB detectors. The targets are mounted on a stepper motor controlled HPT 040 micromanipulator. A 30 mm2 Si(Li) detector (FWHM = 154 eV at 5.9 keV) is used for PIXE measurements. Data on the impurities found in “water trees”, which are associated with breakdown in electrical cables, will be presented.

Trace element and surface analysis at the University of Montreal

The Tandem at the Laboratoire de Physique Nucleaire is now used for: Rutherford backscattering spectroscopy (RBS) and elastic recoil detection (ERD) with time of flight (TOF), channeling-ERD/RBS/PIXE, high energy implantation, and PIXE (proton induced X-ray emission) trace element analysis. A PIXE/RBS microbeam on the 4.5 MV Dynamitron will also be described.

Micro-PIXE analysis of impurity distributions in “trees” grown in high-voltage cables

Abstract Water treeing and electrical treeing are degradation processes occurring in the polyethylene insulation of underground high-voltage cables that can lead to premature breakdown. In order to determine the nature and content of impurities present in the trees, which typically have dimensions of 50–200 μm, a PIXE (proton-induced X-ray emission) microbeam system with a beam-spot diameter of less than 20 μm has been installed on a 4.5 MV Dynamitron accelerator. The capabilities of this system are illustrated by multi-element radial scans that show the presence of a wide variety of contaminants in the trees.

Migration of impurities from cable shields and tree initiation in XLPE

The authors present laboratory results obtained with plaques of cable-grade XLPE (cross-linked polyethylene) pressed on plaques made of commercial shield compound. The samples were kept at various temperatures in air and in water for several weeks. The local impurity contents were measured at various distances from the shield-insulation interface by micro-PIXE (proton induced X-ray emission). The correlation between the impurity kinetics thus measured and impurities detected in water trees grown in XLPE cables is discussed. In addition to the elemental analysis, ionic content measurements were also performed on resins, and the ions detected correspond to the major elemental contaminants. Although it is not yet clear whether impurities affect tree growth, the fact that water and electrical trees are heavily contaminated suggests the possible influence of contamination. The nature of the most mobile impurities is also the same as those of the major contaminants in trees. The inorganic ions also correspond to these elements, which adds further evidence for their possibly detrimental role in XLPE cable aging.<<ETX>>

Quantitative PIXE analysis of impurities and their influence on the electrical properties of metal-free phthalocyanine

The impurity content of commercial metal-free phthalocyanine (H2Pc) powder has been determined by proton-induced X-ray emission (PIXE), and high concentrations of some elements, including highly conducting iodine, were found. The effects on the impurity concentrations of heating the H2Pc to 400° C for 1, 2, 3 and 4 h were investigated. This purification procedure leads to smaller although not negligible impurity content. Some electrical properties of H2Pc were also measured as a function of purification time and it is shown that they are, as expected, greatly dependent on the impurity content.

Two-dimensional Microbeam-pixe Elemental Scanning Of Water Trees In Field Aged Hv Cables

Two-dimensional microbeam-PIXE scans of a water tree (2 mm x 1 mm) in a 25 kV XLPE underground cable taken from service after 18 years have been made with 50 micron spacing at a bombarding energy of 1.0 and 2.5 MeV. The spatial distributions of Mg, Si, S, Cl, K, Ca and Pe were measured. While Si and S show only small variations, except for the change at the semicon-XLPE interface, the distributions of Mg, Cl and Ca show tree-like structures. The large concentrations of Mg, Cl and Ca in the tree region suggests the diffusion of these impurities via the outer semiconductor. A high spatial correlation between K and Cl was observed.

Two-dimensional impurity distributions in “water trees” occurring in field aged HV cables

Abstract Two-dimensional mu-PIXE scans of sections through large (1 to 2 mm) vented “water trees”, found at the inner semicon-XLPE (cross-linked polyethylene) interface in underground HV cables, were made at 50 μm spacing with a proton energy of 1.0 MeV. The visual appearance of one tree is reproduced by the spatial distributions of the elements Na, Cl, K and Ca, while Si and S show only minor variation except for the change at the semicon-XLPE interface. A second sample with three adjacent trees shows little or no correlation between the visual trees and the impurity distributions, although a high spatial correlation between Na and Cl suggests the presence of NaCl in one of these three trees.