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An Improved Medical Spectrometer

Oak Ridge National Laboratory, Oak Ridge, Tennessee

Correspondence: For reprints contact: D. A. Ross, Medical Nuclear Instrumentation Group, Oak Ridge National Laboratory, P.O. Box Y, Oak Ridge, Tenn. 37830.

ABSTRACT

A flexible, modularly-designed pulse-height spectrometer has been developed and is now under field test. Although planned primarily for the field of nuclear medicine, this unit may be used in other scintillation spectrometry applications. Designed for use with a sodium iodide detector, the instrument covers an energy range from a few keV to several MeV. The linear amplifier, with continuously variable gain from 30 to above 3,000, is linear to an output voltage of 10 volts, and may be operated in either single- or double-differentiating modes. The base line is stable at high counting rates, and pole zero compensation provides good overload performance. The pulse-height discriminator uses a zero crossover design with a window opening of up to 30% of the base level. A scaler-timer section provides preset time intervals from 0.1 to 200 min in convenient steps; it also provides preset counts ranging from 500 to 40,000 with the elapsed time displayed in steps of 0.01 min. A solid-state, series regulated supply provides high voltage for the photomultiplier tube, maintained to within 0.002% throughout a line-voltage range of 90 to 140 volts. The long-time drift is less than 0.025%/hr.

FOOTNOTES

^* Present address: Oak Ridge Technical Enterprises Corp., 100 Midland Rd., Oak Ridge, Tenn. 37830.