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UBC Theses and Dissertations

A survey of low-noise nucleonic amplifiers Heywood, Donald Robert


In nucleonic energy determinations, pulses from capacitive sources must be amplified with the addition of a minimum amount of noise. The problems encountered in this were considered both theoretically and experimentally. The "classical" theory of Gillespie for systems using ion chambers and tube amplifiers is generalized to include systems using the modern solid-state detectors and amplifiers. Expressions are found relating the "equivalent input noise charge" to the characteristics of the detector, the preamplifier, and the pulse-shaping network. A relationship is derived between the equiv-noise charge and the conventional noise figure of an amplifier. It shows that amplifiers suitable for nucleonic work have noise figures much lower than 1 db. The theoretical study shows that conventional vacuum tubes, Nuvistors, and field effect transistors are the best active devices for this application. Junction transistors, tunnel diodes, para-metric amplifiers and Masers are shown to be unsuitable. Experimental measurements made on preamplifiers built with tubes, Nuvistors, and field effect transistors confirm the theoretical predictions with good accuracy. When the detector capacitance is 20pf, the preamplifiers exhibited noise charges of 310, 360 and 670 electronic charges respectively. The E810F tube is superior to other tubes currently used, while the field effect transistor is, at present, the best solid-state device.

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