John W. Coltman

The Specification of Imaging Properties by Response to a Sine Wave Input

The imaging properties of an optical system can be in many cases completely specified by a function of a single variable. A convenient function is the response to a sine wave test pattern as a function of “frequency,” i.e., lines/mm. The difficulty of experimentally providing such a test pattern can be avoided by measuring the response to a square wave (bar pattern) and calculating by a simple formula the corresponding sine wave response factor. The convenience of the sine wave response factor in calculating system performance is illustrated by application to a fluoroscopic imaging system.

The Photo‐Multiplier Radiation Detector

The photo‐multiplier radiation detector consists of a commercial multiplier photo‐tube arranged to register the scintillations produced in a fluorescent screen by radiation quanta. The signal pulses thus obtained are large for alpha‐particles and other high velocity ions, much weaker for x‐rays, gamma‐rays, and high velocity electrons. The method is limited by the presence of noise pulses caused by electrons thermally emitted at the photo‐cathode; signal pulses can be discriminated from noise pulses only to the extent that their amplitudes are greater. Satisfactory detection of the weaker signal pulses has been accomplished by careful attention to (1) selection of photo‐tubes, (2) choice of fluorescent screen, (3) efficient collection of light, and (4) proper circuit design.The new detector is especially suited to narrow‐beam measurements where high counting rates are desired. However, it compares favorably with conventional detectors even when low counting rates and weak signal pulses are involved. The d...

Scintillation Limitations to Resolving Power in Imaging Devices

The theoretical performance limit of an imaging device may in many cases depend upon the quantum fluctuation noise of the signal itself. Experiments on the ability of the eye to recognize a regular pattern delineated by randomly fluctuating scintillations are described, and the data are used to calculate the resolving power of an ideal image intensifier used with an x-ray fluoroscope. It is shown that the ultimate resolving power in such a system may ideally exceed even that of ordinary screen-film radiography.

The Photomultiplier X‐Ray Detector

Our studies of the photomultiplier x‐ray detector reveal that it is not only simple, rugged, and adaptable but that its high speed of response and high sensitivity recommend its use as a primary research tool. It can follow x‐ray events as short as 10−5 second. Under optimum condition its sensitivity is limited only by the statistical noise of the incident x‐ray quanta. Its chief defect is fatigue, the mechanism of which has been studied. This paper includes a general discussion of the use of this detector and of its characteristics.

The Westinghouse Atom Smasher???An IEEE Historical Milestone

A history of the early Van de Graaff generator built by the Westinghouse Electric Corporation in 1937 is given, together with an outline of the succeeding events which led to that corporations major role in nuclear energy. The paper is based on a talk given on the occasion of the dedication of this machine as an IEEE Historical Milestone in May of 1985.