Beam Symmetry Research Articles

Picoampere Charged Particle Beam Monitor

A transmission ion chamber for charged particles was designed to give a continuous indication of beam symmetry and magnitude. Consisting of four separate ion chambers, the signals from opposing chambers were compared to determine beam symmetry and summed to obtain a beam intensity signal. The system is quite simple and offers good linearity at low cost for proton beam currents in the range of 1–100 pA.

Electron Beam Instability and Isodose Asymmetry Associated with a 35 MeV Medical Betatron

Initial dosimetry measurements on a Brown-Boveri 35 MeV betatron indicated poor reproducibility of electron beam isodose curves. An investigation showed that the beam position and shape depended strongly upon a given combination of electron energy and extraction voltage. Small changes in extraction voltages or small drifts in energy produced large asymmetries in the radiation field. Under normal operating conditions the asymmetries were large enough to present serious clinical problems. A special device subsequently developed by the manufacturers has eliminated these difficulties.To monitor beam symmetry, two cylindrical ionization chambers were mounted in the fringe of the radiation field. The output of these chambers is fed subtractively to a voltmeter located on the control console, symmetry being indicated by a voltage null. An auxillary extraction-voltage control has been incorporated in the system and symmetry is maintained by a manual adjustment of this control.

A survey of dental x-ray units in use in the United States Navy

A survey was made of all 485 dental x-ray units in use throughout the United States Navy to check the total filtration (inherent and added), symmetry and diameter of the useful x-ray beam, and the leakage from the portal end of the tube head. It was found that all but 39 units were operated at below 70 kvp. Filtration readings ranged from 0.6 mm of Al to 3 plus. Beam-diameter readings ranged from 1.2 to 7.5 in. The criteria used to determine an x-ray unit's need for corrective procedures were based on filtration with 2 mm Al up to 70 kvp and 2.5 mm above 70 kvp, and maximum beam diameter of 3.0 in. 277 units met the criteria established for filtration and 325 had a beam of 3.0 in. or less. A comparison was made between these units and 9950 units surveyed by the State Services Branch, Division of Radiological Health, United States Public Health Service. The use of high-speed film, electronic timers, and protective screens and lead-impregnated plastic and rubber aprons was recommended.

Dimensional tolerances in cathode-ray-tube guns. Effects of misalignment and electrode deformation on performance

Some problems of electron gun design are briefly discussed. The gun is analysed into two separate parts, the triode generator and the final lens, which are considered separately. Preliminary experiments show that cathode tilt in the triode has negligible effect on beam centrality and symmetry. Effects of lateral displacement and tilt of the first anode for various anode/grid spacings are experimentally determined for several types of triode geometry. The effects of displacement, tilt and deformation of the final lens are investigated. Two Appendices are given, the first discussing the experimental technique and the second applying the work to a form of ion-trap electron gun which has found wide use and which has advantages over all other forms of trap.

Circular Beams Loaded Normal to the Plane of Curvature—2

Abstract Expressions are presented in this paper for the deflection, angle of slope, and angle of twist of the free end of a circular cantilever beam with a bending moment applied at the free end. Like expressions are also given for the same beam with a twisting moment acting at the free end. The values of the reaction and the angles of slope and twist at the simple support are given for a circular beam built in at one end, simply supported at the other, and loaded as in each of the foregoing cases. Also, equations are included for the three internal reactions, i.e., bending moment, twisting moment, and shear existing at the plane of symmetry of a cantilever arc beam, built in at both ends, with an arbitrarily placed concentrated load acting perpendicular to the plane of the beam, and at its center line. Corresponding expressions for the same element with a uniformly distributed load covering the half of the beam to one side of the axis of symmetry, and an expression for the bending moment at the plane of symmetry of the same beam when its entire length is uniformly loaded, are also stated.