| 摘要 |
A semiconductor diode scintillation detector probe, in conjunction with a base-line-stabilized, wide-bandwidth first amplifying circuit DC-coupled to a constrained-bandwidth second amplifying circuit DC-coupled, in turn, to a novel analog threshold discriminator circuit, suppresses base-line fluctuation and noise at low input count-rates, while providing a linear rate-meter response for time-random input pulse rates far in excess of what would otherwise—as in the prior art—be 100% saturation. |
| 主权项 |
1. An apparatus for extending a scintillation detector's dynamic range, said scintillation detector comprising a detector-transducer and associated preamplifier, in combination with the apparatus of the invention;
said apparatus comprising a two-section post-amplifier and a linear analog threshold discriminator circuit; said two-section post-amplifier comprising a high-gain, wide-bandwidth, first amplifying circuit DC-coupled to an input of a low-gain, constrained bandwidth, second amplifying circuit; the signal outputs of said first and second amplifying circuits having, respectively, a first baseline voltage and a second baseline voltage; said first amplifying circuit having a baseline sensor and feedback means to measure and to stabilize said first baseline voltage in the absence and in the presence of radiation-induced signal pulses over a wide range of pulse rates up to, and including, extreme signal pulse-rate overload; a pre-determined DC offset voltage being added to said first baseline voltage to establish a desired baseline common reference potential at the input to said second amplifying circuit; the amplified signal pulses at the input to said second amplifying circuit being unipolar with respect to said baseline common reference potential, said amplified signal pulses being superimposed upon unwanted, but concurrently-amplified, electronic noise, said signal pulses having a time-averaged mean voltage relative to said baseline common reference potential, said time averaged mean voltage being proportional to a dose-rate from radiation incident on said detector-transducer; the bandwidth of said second amplifying circuit being constrained so as to attenuate said unwanted electronic noise relative to said signal pulses; the output of said low-gain constrained-bandwidth second amplifying circuit being DC-coupled to an input of a linear analog threshold discriminator circuit; the input-output transfer characteristic of said linear analog threshold discriminator circuit being described by a plot-line on a graph, the abscissa and ordinate values on said graph representing, respectively, the voltage at the input of said analog threshold discriminator measured with respect to said baseline common reference potential, and the corresponding output current of said discriminator circuit; said ordinate value being equal to zero when the abscissa value is less than a pre-set threshold, said threshold setting being expressed with respect to said baseline common reference potential, said threshold being pre-set to a value greater than the peak amplitude of unwanted noise at the output of said second amplifying circuit; said ordinate value being equal to the product of the abscissa value multiplied by a pre-determined numerical constant when said abscissa value exceeds the pre-set threshold, said analog threshold discriminator circuit thereby blocking unwanted noise while transmitting wanted signal pulses, maintaining a linear dose-rate response when the signal pulse count rate is low; said low-gain, constrained bandwidth second amplifying circuit having a signal waveform at its input and at its output, said input signal waveform being unipolar relative to said baseline common reference potential, said output signal waveform being unipolar with respect to said second baseline;said second baseline voltage being equal to said baseline common reference potential when the signal pulse count-rate is low;
when said scintillation detector is exposed to increasing intensity of incident radiation, said input signal waveform and said output signal waveform displaying a progressively and correspondingly more dense superposition of time-random signal pulses; said DC coupling in combination with constrained bandwidth of said second amplifying circuit causing said output signal waveform to shrink toward its mean value, thereby causing said second baseline voltage to rise relative to said baseline common reference potential as the signal pulse count-rate is increased, until said second baseline exceeds said discriminator threshold setting, in consequence thereof said output signal waveform being transmitted directly through said linear threshold discriminator, thus yielding an output signal current from said linear threshold discriminator whose time-averaged mean value remains linearly proportional to dose-rate under conditions of extreme count-rate overload. |
