Abstract: A radiation detection system and method for scanning an object for ionizing radiation are generally characterized by at least one radiation detector which provides an output related to the level of ionizing radiation impinging thereon, a sensing device which evaluates and provides an output related to a shape characteristic of an object being scanned by the radiation detector, and a processor operatively connected to the radiation detector and sensing device for processing the outputs thereof. The output of the sensing device is used to compensate for variations in ambient background level arising from the sensed shape characteristic of the object. With such a system, the possibility of a geometry induced false alarm is minimized. In a preferred embodiment adapted for dynamic vehicle monitoring, the sensing device is a level detector operative to detect the level of the material in a truck or rail car passing by the radiation detector or detectors.

Abstract: An ion chamber type instrument for measuring radioactivity includes a high gain operational amplifier having a feedback network of range determining resistors connected between the amplifier output and input. Electronic switches in series with at least some of the range determining resistors function as range selector switches for the measuring instrument. Each switch includes two series-connected transistors and a third transistor, the interconnection point between the two series-connected transistors being connected to the electrical neutral point of a measuring circuit via the third transistor. Each switch, when in an "off" or non-conducting condition, provides a high effective resistance of, for example, 1.times.10.sup.15 ohms so as to minimize errors caused by leakage current fed back into the input of the high gain operational amplifier.

Abstract: A plastic scintillator element that is tissue equivalent is optically coupled to a photomultiplier tube that provides a pulse signal which contains information relating to radiation energy fluence, and having an undesirable "dark current" component. A direct current blocking element in the form of a capacitor isolates the input of an operational amplifier from the "dark current" component so that the output signal of the amplifier indicates the average current of the photomultiplier signal attributed only to detected, low level, environmental radiation in the range of 0-200 .mu.rem/h.

Abstract: A Geiger-Mueller tube-based radiation measurement device includes circuitry for the correction of the dead time losses associated with the Geiger-Mueller tube. As the event count rate rises, the transfer function (e.g., the closed loop voltage gain) of an operational amplifier responding to an event count rate signal is modified to compensate for dead time losses experienced at high count rates. Preferably, an analog switch controlled by the event count rate signal automatically sets the voltage gain of the operational amplifier at a level corresponding to the desired amount of dead time compensation required to provide an accurate measurement of actual events. The dead time correction circuitry disclosed herein finds practical application in the use of well-known analog rate meter circuits of the charge pump type.