A measurement, accurate to 3 ppm, is reported of the 2 3 Pi-2 3 P 2 fine structure in He 4 . An atomic-beam optical-microwave resonance technique was used. Two sets of measurements were made on the transition 2 3 P 1 (mj=0)<->2 3 P 2 (mj = 0). The first set was in a magnetic field of about 100 G ("low" field), where the uncertainties arose from field-dependent asymmetries in the line shape. The second set of measurements was in a field of about 500 G ("high" field), and here the main uncertainties were in the field measurements and the calculation of g factors. The results of the two sets were in good agreement: low field: £(2 3 Pi)-E(2 3 P 2 ) = 2291.188±0.015 MHz; high field: £(2 3 P 1 )-E(2 3 P 2 ) = 2291.197±0.008 MHz; weighted mean: E{2*Pi)-E{2 Z P 2 ) = 2291.195±0.007 MHz. The advantages of the atomic-beam technique and the possible importance of this fine-structure measurement are discussed. measurement of hydrogen hyperfine structure); S. D. Drell and J. D. Sullivan, Phys. Rev. 154, 1477 (1967) (most recent discussion of the theoretical hyperfine structure).
We have measured the energy dependence of the 4610-and 4765-A lines of Ar + excited in low-energy He + + Ar collisions from threshold to 700 eV He + energy. The 4610-A line rises sharply with energy to a peak near threshold, while the rise of the 4765-A line is more gradual than previously reported and than most other lines excited in this process. The 4765-A line still shows, however, a much lower energy peak than predicted by the adiabatic hypothesis. The threshold behavior of the 4610-and 4765-A lines appears to be typical of lines emitted from levels with X D and 3 P parent terms, respectively.
A new, large-scale, vy low dose cabinet X.ray system has been installed at the newly-completed commercial bor& aossing facility located at Otay Mesa, California, a few miles south of San Diego. The system has two separate 450 kV flying-spot X-ray sources, each with its own sets oftransmission and backscatter detectors. The sources are located below grade, and are arranged to illuminate the undercarriage and the sides ofthe truck symmetrically from below. This geometry allows close proximity ofthe sources to the truck, resulting in improved imaging performance. The point-bypoint mapping sequence ofa flying-spot scan enables both transmission and backscatter images to be obtained simultaneously. The system is intended primarily for the inspection ofempty trucks, but it can also be used to inspect loaded vehicles up to 80,000 pounds gross weight and 65' long. It will be operated by U.S. Customs Service personnel.The system and its planned operations are described. Key issues involve vehicle and driver logistics, vehicle handling within the X-ray facility, throughput, ease of use, and radiation safety. The results of radiation survey measurements and Initial test images will be presented.
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