M. F. Vineyard

The CLAS drift chamber system

Abstract Experimental Hall B at Jefferson Laboratory houses the CEBAF Large Acceptance Spectrometer, the magnetic field of which is produced by a superconducting toroid. The six coils of this toroid divide the detector azimuthally into six sectors, each of which contains three large multi-layer drift chambers for tracking charged particles produced from a fixed target on the toroidal axis. Within the 18 drift chambers are a total of 35,148 individually instrumented hexagonal drift cells. The novel geometry of these chambers provides for good tracking resolution and efficiency, along with large acceptance. The design and construction challenges posed by these large-scale detectors are described, and detailed results are presented from in-beam measurements.

Fusion evaporation-residue cross sections for sup 28 Si+ sup 40 Ca at E ( sup 28 Si)=309, 397, and 452 MeV

Velocity distributions of mass-identified evaporation residues produced in the {sup 28}Si+{sup 40}Ca reaction have been measured at bombarding energies of 309, 397, and 452 MeV using time-of-flight techniques. These distributions were used to identify evaporation residues and to separate the complete-fusion and incomplete-fusion components. Angular distributions and upper limits for the total evaporation-residue and complete-fusion evaporation-residue cross sections were extracted at all three bombarding energies. The complete-fusion evaporation-residue cross sections and the deduced critical angular momenta are compared with earlier measurements and the predictions of existing models. The ratios of the complete-fusion evaporation-residue cross section to the total evaporation-residue cross section, along with those measured for the {sup 28}Si+{sup 12}C and {sup 28}Si+{sup 28}Si systems at the same energies, support the entrance-channel mass-asymmetry dependence of the incomplete-fusion evaporation-residue process reported earlier.

Construction of a scattering chamber for ion-beam analysis of environmental materials in undergraduate physics research

We have developed a new scattering chamber for ion-beam analysis of environmental materials with the 1.1-MV Pelletron accelerator at the Union College Ion-Beam Analysis Laboratory. The chamber was constructed from a ten-inch, Conflat, multi-port cross and includes a three-axis target manipulator and target ladder assembly, an eight-inch turbo pump, an Amptek X-ray detector, and multiple charged particle detectors. Recent projects performed by our undergraduate research team include proton induced X-ray emission (PIXE) and Rutherford backscattering (RBS) analyses of atmospheric aerosols collected with a nine-stage cascade impactor in Upstate New York. We will describe the construction of the chamber and discuss the results of some commissioning experiments.

Using PIXE To Teach Materials Analysis At Union College

Particle Induced X‐ray Emission (PIXE) spectroscopy, an ion‐beam analysis technique, is a powerful tool for studying the environment. The Union College Ion‐Beam Analysis Laboratory (UC–IBAL) provides a small group of students opportunities to explore experimental physics and complement their classroom training, by studying atmospheric aerosols and liquid precipitation from upstate New York using a tandem electrostatic particle accelerator. The students learn how to operate the accelerator and gain valuable laboratory skills in sample collection and preparation procedures and data acquisition and analysis techniques, as well as presentation skills.

PIXE Analysis of Synthetic Turf

We performed a proton-induced X-ray emission (PIXE) analysis of synthetic turf blade and crumb rubber infill samples to search for heavy metals and other possibly toxic substances. Samples were collected from eight FieldTurf athletic fields installed in the Capital District of New York between 2009 and 2016. The samples were bombarded with proton beams from the 1.1-MV tandem Pelletron accelerator in the Union College Ion-Beam Analysis Laboratory and the emitted X-rays were measured using a silicon drift detector with an energy resolution of about 130 eV. All of the infill samples contained Zn at levels above soil standards. Approximately 17% of the infill samples contained measurable concentrations of Pb and one had a level (110 ± 10 ppm) exceeding soil standards. Bromine was detected in approximately 42% of the infill samples with a maximum concentration of 1500 ± 200 ppm and may be due to the presence of brominated flame retardants. The distributions and relative concentrations of elements measured in synthetic turf blade samples of different colors are indicative of the metal-oxide pigments used to color the blades. For example, V and Bi observed in yellow blade samples are from the environmentally friendly, yellow pigment bismuth vanadate.