Extended range geiger counting apparatus and method utilizing a single geiger-mueller tube

A method of effectively extending the dynamic count range of radiation measurement apparatus utilizing a single Geiger-Mueller tube (GMT) to enable the GMT to detect radiation count rates in excess of count rates limited by a recovery time of said GMT, said recovery time comprising the time it takes a charged particle to clear said GMT once said charged particle has been detected, said method comprising the steps of:

• (a) incrementing a first counter upon the detection of a charged particle by said GMT;
• (b) waiting a first prescribed period of time subsequent to the detection of a charged particle in step (a), said first prescribed period of time being greater than said recovery time;
• (c) incrementing a second counter at each conclusion of a second prescribed period of time within a sequence of the second prescribed periods of time, said sequence commencing at each conclusion of said first prescribed period of time and concluding at the detection of a subsequent charged particle by said GMT;
• and
• (d) statistically determining the radiation count, wherein said radiation count is R.sub.g, to which said GMT has been exposed as a function of the count held in said first counter, N.sub.P, and the count held in said second counter, N.sub.T, comprising computing R.sub.g from the relationship:
• R.sub.g =f.sub.osc.ln[N.sub.T /(N.sub.T -N.sub.P)]/S
• where S is the sensitivity of said GMT, and wherein f.sub.osc is equal to 1/T.sub.W, wherein T.sub.W is a fixed period equal to the second prescribed period of time;
• wherein the steps of incrementing said first and second counters include not incrementing said first and second counters during said first prescribed period of time.

A method of operating radiation measurement apparatus having a single Geiger-Mueller tube (GMT) comprising:

• (a) establishing specified initial conditions of said GMT, whereby said GMT is enabled to detect a charged particle, including establishing a first prescribed anode voltage for said GMT, said first prescribed anode voltage being less than an operating voltage of said GMT, and establishing a second prescribed anode voltage after a dwell time period subsequent to detecting a charged particle by said GMT, said second anode voltage being at least equal to said operating voltage;
• (b) generating detection and elapsed time data indicative of the detection of a charged particle by said GMT and the time interval between enabling said GMT and the detection of the charged particle by said GMT, comprising:
• detecting the charged particle entering said GMT,
• triggering the beginning of said dwell time period upon the detection of the charged particle by said GMT, and
• generating a prescribed clock signal having a period;
• (c) discarding a first portion of the detection and elapsed time data, said first portion of data including at least that portion of the data during which the initial conditions associated with said GMT are uncertain, including
• not counting the number of periods of the prescribed clock signal during said dwell time period, and
• not counting the number of periods of the prescribed clock signal until a prescribed number of the clock periods have elapsed after the termination of said dwell period;
• and
• (d) processing a second portion of said detection and elapsed time data to determine the radiation dosage rate to which said GMT has been exposed, said second portion of data not including said first portion of data;
• and
• (e) repeating steps (a) through (d) for each charged particle detected by said GMT.

A method of measuring radiation to which a single Geiger-Mueller tube (GMT) is exposed over a wide range of radiation dosage rates, from low radiation dosage rates where a small number of charged radiation particles are present per unit of time, to high radiation dosage rates where a large number of charged radiation particles are present per unit of time, said GMT producing an electrical pulse upon the detection of each charged radiation particle, said GMT exhibiting a recovery time, said recovery time comprising the time it takes a charged radiation particle to clear said GMT once said charged particle has been detected, said radiation measuring method comprising:

• applying an anode voltage of a first prescribed value to said GMT, the anode voltage of said first prescribed value enabling said GMT to detect a charged radiation particle and produce said electrical pulse;
• generating a clock signal having a fixed clock period, said fixed clock period repeating in a recurring cycle;
• incrementing a first counter when enabled in response to an electrical pulse produced by said GMT, whereby a count value is maintained in said first counter corresponding to the number of electrical pulses produced by said GMT during the time that said first counter is enabled;
• triggering a prescribed dwell period in response to an electrical pulse produced by said GMT;
• lowering the anode voltage below said first prescribed value in response to an electrical pulse produced by said GMT;
• raising the anode voltage to said first prescribed value in response to the elapse of a first number of said fixed clock periods subsequent to the conclusion of said prescribed dwell period, whereby said GMT is enabled to detect a charged radiation particle at the conclusion of a first time period comprising said dwell period plus said first number of fixed clock periods;
• disabling said first counter and a second counter during a second time period comprising said dwell period plus a second number of said fixed clock periods;
• incrementing said second counter when enabled at the conclusion of each of said recurring clock periods, whereby a count value is maintained in said second counter corresponding to the number of said fixed clock periods that elapse during the time that said second counter is enabled;
• and
• computing the radiation dosage rate to which said GMT has been exposed as a function of the count values maintained in said first and second counters.

Radiation measurement apparatus comprising:

• a single Geiger-Mueller tube (GMT);
• initial condition means for establishing specified initial conditions of said GMT, whereby said GMT is enabled to detect a charged particle, comprising:
• anode voltage switching means for switchably altering an anode voltage applied to said GMT between two values, including trigger means responsive to the detection of a charged particle by said GMT that automatically lowers the anode voltage to said second value, and time means for maintaining said anode voltage at said second value for a prescribed dwell time period,
• a first anode voltage value having a magnitude that enables said GMT to detect a charged particle, and
• a second anode voltage value having a magnitude that disables said GMT from detecting a charged particle;
• measurement means for measuring detection and elapsed time data indicative of the number of charged particles detected by said GMT and the time interval between enabling said GMT and the detection of a given charged particle by said GMT, including:
• first counting means responsive to said trigger means for counting the number of charged particles detected by said GMT,
• clock generating means for generating a clock signal having a fixed period, and
• second counting means coupled to said clock generating means for counting the number of said fixed periods of said clock signal that elapse while said second counting means is enabled;
• discarding means for discarding a first portion of the detection and elapsed time data, said first portion of data including at least that portion of the data during which the initial conditions associated with said GMT are uncertain, including
• time sequencer means for disabling said first and second counting means during said prescribed dwell time period, and for disabling said first and second counting means during a first prescribed wait period;
• the detection and elapsed time data occurring during said first prescribed wait period corresponding to said first portion of data;
• and
• processing means for processing a second portion of said detection and elapsed time data to determine the radiation dosage rate to which said GMT has been exposed, said second portion of data comprising the detection and elapsed time data occurring when said first and second counting means are enabled.

Radiation measurement apparatus comprising:

• a single Geiger-Mueller tube (GMT), said GMT producing an electrical pulse upon the detection of a charged radiation particle, said GMT exhibiting a recovery time, said recovery time comprising the time it takes a charged radiation particle to clear said GMT once said charged particle has been detected;
• voltage control means for applying a voltage of a first prescribed value to said GMT in response to a first timing signal, and for applying a voltage of a value less than said first prescribed value to said GMT in response to a second timing signal, a voltage of said first prescribed value enabling said GMT to detect a charged radiation particle and produce said electrical pulse, and a voltage of a value less than said first prescribed value disabling said GMT;
• oscillator means for generating a clock signal having a fixed clock period, said fixed clock period repeating in a recurring cycle;
• first counter means coupled to said GMT for maintaining a count of the number of electrical pulses produced by said GMT when enabled by a first enabling signal;
• second counter means coupled to said GMT for maintaining a count of the number of specified clock transitions that occur within said clock signal when enabled by a second enabling signal;
• dwell means coupled to said GMT for generating said second timing signal and for triggering a prescribed dwell period in response to an electrical pulse produced by said GMT;
• time sequencer means responsive to said dwell period and said clock signal for generating said first timing signal and said first and second enabling signals, said time sequencer means being disabled during said dwell period, said first timing signal being generated a prescribed number of specified clock transitions subsequent to said dwell period, and said first and second enabling signals being generated an assigned number of specified clock transitions subsequent to said dwell period;
• and
• processing means coupled to said first and second counter means for computing the radiation dosage rate to which said GMT has been exposed as a function of the respective counts maintained within said first and second counters.

A method for controlling the operation of a Geiger-Mueller tube (GMT), said GMT being characterized by generating a GMT-pulse in response to the detection of a charged particle, and by having a prescribed high anode voltage that must be applied to the GMT prior to being able to detect a charged particle, and a recovery period that must elapse after detecting a charged particle before a subsequent charged particle can be detected, said method comprising the steps of:

• (a) applying a first anode voltage to said GMT, said first anode voltage having a magnitude that disables said GMT from detecting a charged particle;
• (b) waiting a first period of time subsequent to the application of the first anode voltage in step (a), said first period of time being greater than said recovery time;
• (c) applying a second anode voltage to said GMT at the conclusion of said first period of time, said second anode voltage having a magnitude at least equal to said prescribed high anode voltage;
• (d) waiting a second period of time subsequent to the application of the second anode voltage in step (c), said second period of time being sufficiently long to establish specified initial conditions on said GMT so as to ensure that the GMT is enabled to detect a charged particle;
• (e) incrementing a first counter after the conclusion of said second period of time for each basic time interval that elapses prior to the detection of a charged particle by said GMT, said first counter thereby having a count, N.sub.T, maintained therein;
• (f) incrementing a second counter after the conclusion of said second period of time for each charged particle detecting by said GMT, said second counter thereby having a count, N.sub.P, maintained therein;
• (g) repeating steps (a) through (f) for each charged particle detected by said GMT, thereby controlling when said GMT is allowed to detect charged particles;
• and
• (h) statistically determining the radiation count, R.sub.g, to which said GMT has been exposed as a function of the count held in said first counter, N.sub.T, and the count held in said second counter, N.sub.P, after a sufficient number of counts have accumulated in both counters.