Automatically adjustable radioactive radiation detector circuit

Claim 2

A detector circuit for sensing sudden variations from the ambient input level of a source subject to gradual variations in its ambient input level to indicate the magnitude of said sudden variations as a proportion of the previous ambient level comprising: input means responsive to the instantaneous input level from the source for generating a First signal directly proportional to the instantaneous input level from the source; a time averaging circuit having a relatively short time constant for developing an output signal level directly proportional to the present average energy level of said first signal; feedback circuit means responsive to said output signal for developing a feedback signal, said feedback circuit means comprising a memory circuit with a relatively long time constant for delaying changes in said feedback signal for an extended time interval much greater than the time required for said sudden variations in the input level from said source and; controllable impedance means responsive to changes in said feedback signal and coupled to said input means for controlling the average energy level of said first signal to maintain the output signal developed by said time averaging circuit at a substantially constant level during gradual variations in the ambient input level of the source.

Claim 3

A detector circuit for sensing sudden variations from the ambient input level of a source subject to gradual variations in its ambient input level to indicate the magnitude of said sudden variations as a proportion of the previous ambient level comprising: input means responsive to the instantaneous input level from the source for generating a First signal directly proportional to the instantaneous input level from the source; a time averaging circuit having a relatively short time constant for developing an output signal level directly proportional to the present average energy level of said first signal; feedback circuit means responsive to said output signal for developing a feedback signal, said feedback circuit means comprising a memory circuit with a relatively long time constant for delaying changes in said feedback signal for an extended time interval much greater than the time required for said sudden variations in the input level from said source and; controllable impedance means responsive to changes in said feedback signal and coupled to said input means for controlling the average energy level of said first signal to maintain the output signal developed by said time averaging circuit at a substantially constant level during gradual variations in the ambient input level of the source.

Claim 4

A detector circuit for sensing sudden variations from the ambient input level of a source subject to gradual variations in its ambient input level to indicate the magnitude of said sudden variations as a proportion of the previous ambient level comprising: input means responsive to the instantaneous input level from the source for generating a First signal directly proportional to the instantaneous input level from the source; a time averaging circuit having a relatively short time constant for developing an output signal level directly proportional to the present average energy level of said first signal; feedback circuit means responsive to said output signal for developing a feedback signal, said feedback circuit means comprising a memory circuit with a relatively long time constant for delaying changes in said feedback signal for an extended time interval much greater than the time required for said sudden variations in the input level from said source and; controllable impedance means responsive to changes in said feedback signal and coupled to said input means for controlling the average energy level of said first signal to maintain the output signal developed by said time averaging circuit at a substantially constant level during gradual variations in the ambient input level of the source.

Claim 5

A detector circuit for sensing a sudden variation from an ambient input level of a source subject to gradual variations in its ambient level to indicate the magnitude of said sudden variation as a proportion of the pre-existing ambient level comprising: input means responsive to the input from the source for generating a first signal level directly proportional to the instantaneous input level; circuit means responsive to the first signal level from said input means for developing an output signal level directly proportional to the existing average level of said first signal; feedback means coupled to receive said output signal level for developing a feedback signal, said feedback means having a memory circuit with a relatively long time constant to delay selected changes in said feedback signal for an extended time interval greater than the interval required for said sudden variations in the input level; and signal variable impedance means responsive to changes in said feedback signal and coupled to said input means for controlling the average of said first signal level to maintain the output signal level developed by said time averaging circuit at a substantially constant level during gradual variations in the ambient input level of the source.

Claim 6

A detector circuit for sensing a sudden variation from an ambient input level of a source subject to gradual variations in its ambient level to indicate the magnitude of said sudden variation as a proportion of the pre-existing ambient level comprising: input means responsive to the input from the source for generating a first signal level directly proportional to the instantaneous input level; circuit means responsive to the first signal level from said input means for developing an output signal level directly proportional to the existing average level of said first signal; feedback means coupled to receive said output signal level for developing a feedback signal, said feedback means having a memory circuit with a relatively long time constant to delay selected changes in said feedback signal for an extended time interval greater than the interval required for said sudden variations in the input level; and signal variable impedance means responsive to changes in said feedback signal and coupled to said input means for controlling the average of said first signal level to maintain the output signal level developed by said time averaging circuit at a substantially constant level during gradual variations in the ambient input level of the source.

Claim 7

The detector circuit of claim 2 further comprising: an output circuit including voltage limiting means coupled to receive said output signal level for preventing said output signal level from exceeding a predetermined full scale level; and wherein said feedback means and said signal variable impedance means comprise a high gain feedback path for controlling the average amplitude of said first signal.

Claim 8

The detector circuit of claim 2 wherein: the input from said source constitutes random input triggering pulses generated at an average frequency indicative of said input level and , said input means comprises a one-shot multi-vibrator circuit having a variable timing circuit including said signal variable impedance means for generating pulses of fixed amplitude and variable duration in response to each of said triggering pulses; and, the duration of said pulses is varied by changing the impedance of said signal variable impedance means in response to said feedback signal to tend to increase the duration of said pulses in response to gradual decreases in said output signal level.

Claim 9

The detector circuit of claim 4 wherein: said memory circuit comprises a storage capacitor with a high capacitance value and a network connected in series for applying said output signal level to storage capacitor, said network having a discharging resistor means having a very high resistance value and a unidirectional current flow element, coupled in parallel said capacitor being quickly charged by said output signal level through said unidirectional element to provide feedback signal and being capable of being discharged only through said resistor means with said relatively long time constant, whereby only decreases in Said feedback signal are delayed for said extended time interval.

Claim 10

A radiation detection circuit for measuring a sudden variation in the radiation level of a radioactive source to indicate the proportional variation from a pre-existing ambient radiation level comprising: a sensor means adjacent said source for sensing the existing radiation level to generate random triggering pulses at a rate proportional to the instantaneous radiation level; variable multivibrator means responsive to said triggering pulses for generating a repetitive pulse signal with each pulse being generated in response to one of said triggering pulses and having a selectively variable duration and amplitude characteristic; a time averaging circuit with a relatively short time constant substantially less than the duration of said sudden variation for developing an output signal voltage directly proportional to the average amplitude of said pulse signal over at least several pulse intervals feedback means for receiving said output signal to develop a feedback signal having a relatively long time delay substantially greater than the duration of said sudden variation in radiation level; and, signal variable impedance means coupled to receive said feedback signal for selectively controlling said multi-vibrator means to vary the duration and amplitude characteristics of said pulses to maintain said output signal level at a substantially constant predetermined level to compensate for the radioactive decay of said source.

Claim 11

A radiation detection circuit for measuring a sudden variation in the radiation level of a radioactive source to indicate the proportional variation from a pre-existing ambient radiation level comprising: a sensor means adjacent said source for sensing the existing radiation level to generate random triggering pulses at a rate proportional to the instantaneous radiation level; variable multivibrator means responsive to said triggering pulses for generating a repetitive pulse signal with each pulse being generated in response to one of said triggering pulses and having a selectively variable duration and amplitude characteristic; a time averaging circuit with a relatively short time constant substantially less than the duration of said sudden variation for developing an output signal voltage directly proportional to the average amplitude of said pulse signal over at least several pulse intervals feedback means for receiving said output signal to develop a feedback signal having a relatively long time delay substantially greater than the duration of said sudden variation in radiation level; and, signal variable impedance means coupled to receive said feedback signal for selectively controlling said multi-vibrator means to vary the duration and amplitude characteristics of said pulses to maintain said output signal level at a substantially constant predetermined level to compensate for the radioactive decay of said source.

Claim 12

The radiation detection circuit of claim 6 further comprising: output circuit means for limiting said output signal voltage to a predetermined full scale level.

Claim 13

The radiation detection circuit of claim 7 wherein: said feedback means comprises a storage capacitor coupled to be charged by said output signal and discharging resistor means having a very high resistance value to permit only very slow discharge of said storage capacitor to provide said relatively long time delay.

Claim 14

The radiation detection circuit of claim 8 wherein: said variable multivibrator means includes a timing circuit coupled between its input and output that determines the duration of each pulse in said pulse signal; and, said signal variable impedance means includes a field effect transistor having its drain and source terminals coupled to form a variable resistance path from the output of said multivibrator means and having its gate terminal coupled to receive said feedback signal for selectively controlling the amplitude and duration characteristics of said pulse signal.