CA1262192A - Radiation detection module - Google Patents
Radiation detection moduleInfo
- Publication number
- CA1262192A CA1262192A CA000499679A CA499679A CA1262192A CA 1262192 A CA1262192 A CA 1262192A CA 000499679 A CA000499679 A CA 000499679A CA 499679 A CA499679 A CA 499679A CA 1262192 A CA1262192 A CA 1262192A
- Authority
- CA
- Canada
- Prior art keywords
- output
- pulse
- radiation detector
- radiation
- set forth
- Prior art date
- Legal status (The legal status is an assumption and is not a legal conclusion. Google has not performed a legal analysis and makes no representation as to the accuracy of the status listed.)
- Expired
Links
Classifications
-
- G—PHYSICS
- G01—MEASURING; TESTING
- G01T—MEASUREMENT OF NUCLEAR OR X-RADIATION
- G01T1/00—Measuring X-radiation, gamma radiation, corpuscular radiation, or cosmic radiation
- G01T1/16—Measuring radiation intensity
- G01T1/20—Measuring radiation intensity with scintillation detectors
- G01T1/208—Circuits specially adapted for scintillation detectors, e.g. for the photo-multiplier section
Landscapes
- Physics & Mathematics (AREA)
- Health & Medical Sciences (AREA)
- Life Sciences & Earth Sciences (AREA)
- General Physics & Mathematics (AREA)
- High Energy & Nuclear Physics (AREA)
- Molecular Biology (AREA)
- Spectroscopy & Molecular Physics (AREA)
- Measurement Of Radiation (AREA)
Abstract
ABSTRACT
A radiation detector module characterized by the integration in a compact package of a scintillator probe and supporting electronics having provision for high and low level discrimination. The radiation detector module may be set to provide digital pulse count signals in response to detected scintillations produced by only that radiation falling within an energy window i.e., between upper and lower radiation energy limits, for selective radiation detection. The detector is further characterized by an integrated high voltage power supply for n photomultiplier tube and pro-vision is made for mechanically decoupling the photomultiplier tube for vibration and shock resistance.
A radiation detector module characterized by the integration in a compact package of a scintillator probe and supporting electronics having provision for high and low level discrimination. The radiation detector module may be set to provide digital pulse count signals in response to detected scintillations produced by only that radiation falling within an energy window i.e., between upper and lower radiation energy limits, for selective radiation detection. The detector is further characterized by an integrated high voltage power supply for n photomultiplier tube and pro-vision is made for mechanically decoupling the photomultiplier tube for vibration and shock resistance.
Description
Titles "R~diation Detector Module"
DISCLOSURE
The invention herein disclosed relates generally to radihtion detection ~nd flcguisition systems having wide applications including, inter alia, parts presence dctermination, process control, thickness ~uging, moisture content analysis and radiation level detection such as in the vicinity of nuclear reactor chambers. More particularly, the invention relates to R radiation detector module for use in such systems.
BACKGROUND
Radiation detection and acquisition systems have had many applications. Many such systems are characterized by a radiation detector probe employed at ~ radifltion detection site and electrically coupled to a probe output si~nal processing unit commonly referred to as a nuclear instrumentation module. One common type of detector probe is based on a scintillator crystal combined with a photomultiplier tube. The scintillator crystal converts impinging invisible rædiation to bursts of visible light which are converted by the photomultipLier tube to electrical analog signQls. The radiation involved may be gamma rays, X-rays, high energy or thermal neutrons, etc.
DISCLOSURE
The invention herein disclosed relates generally to radihtion detection ~nd flcguisition systems having wide applications including, inter alia, parts presence dctermination, process control, thickness ~uging, moisture content analysis and radiation level detection such as in the vicinity of nuclear reactor chambers. More particularly, the invention relates to R radiation detector module for use in such systems.
BACKGROUND
Radiation detection and acquisition systems have had many applications. Many such systems are characterized by a radiation detector probe employed at ~ radifltion detection site and electrically coupled to a probe output si~nal processing unit commonly referred to as a nuclear instrumentation module. One common type of detector probe is based on a scintillator crystal combined with a photomultiplier tube. The scintillator crystal converts impinging invisible rædiation to bursts of visible light which are converted by the photomultipLier tube to electrical analog signQls. The radiation involved may be gamma rays, X-rays, high energy or thermal neutrons, etc.
2 ~ Heretofore, the scintillator crystal and photomultipli~r tube were packaged in ll common housing for positioning and mounting at the detection site. The analog output of the photomultiplier tube would be line coupled to the usually remotely located nuclear instrumentation module which processed the analog output of the photomultiplier tube so as to provide, for example, pulse count data to an associated display or system controller.
One problem with this prior system was that the nuclear instrumentation module had to be located relatively close to ttle detector probe to avoid loss of signal integrity resulting from induced line noise, line losses, etc. Also, the nuclear instrumentation modules could not be used uni~rersally with different detector probes operative to sense respective types of rediation. Instead, a specific instrumentation module had to be used for each radiation type detector probe. Moreover, the output of such system was not as reproduceable or repeatable as might be desired in some ~pplications le~ding to larger margins of error or reduced reliability.
Still another problem was the variance in outputs from detector probe to detector probe. This necessitated tedious and time consuming calibration of the nuclear instrumentation modùles to gain matching data output under identical radiation conditions. Many times d good match could not be obtained because of substantial variance in the detector probes and calibration limitations of the nuclear instrumentation modules.
Such systems also required a separate nuclear instrumentation module for each detector probe in multiple channel systems. In flddition to being costly, large control panels were required to house the nuclear instrumentation modules and associated equipment such as pulse count rate displaysO
RELATED APPLICATION
~ co~ending U.S, Patent Application Serial No. 637,434J filed August 3, 1984 ~nd entitled "Radistion Detection and Acquisition System", there is disclosed ~ r~diation detector probe or module and associated acquisition system which eliminates or minimizes the afores~id and other 2 problems, and whiah has a wide range of applications. The radiation detector module is characterized by the integration in a compact package of scintillator probe and ~upporting electronics which provide digital pul~e count signals in response to detected seintillations that may be transmitted by a differential line driver on twisted shielded wire pairs over great distances, as on the order of several thousand feet, to a count signal processing unit while maintaining signal integrity. The digital pulse count output is independent of the type of radiation detected, i.e., gamma raysl X-rays, thermal neutrons, etc., whereby the same count signal processing unit mfly be employed w;th different detectors for respective different radi-
One problem with this prior system was that the nuclear instrumentation module had to be located relatively close to ttle detector probe to avoid loss of signal integrity resulting from induced line noise, line losses, etc. Also, the nuclear instrumentation modules could not be used uni~rersally with different detector probes operative to sense respective types of rediation. Instead, a specific instrumentation module had to be used for each radiation type detector probe. Moreover, the output of such system was not as reproduceable or repeatable as might be desired in some ~pplications le~ding to larger margins of error or reduced reliability.
Still another problem was the variance in outputs from detector probe to detector probe. This necessitated tedious and time consuming calibration of the nuclear instrumentation modùles to gain matching data output under identical radiation conditions. Many times d good match could not be obtained because of substantial variance in the detector probes and calibration limitations of the nuclear instrumentation modules.
Such systems also required a separate nuclear instrumentation module for each detector probe in multiple channel systems. In flddition to being costly, large control panels were required to house the nuclear instrumentation modules and associated equipment such as pulse count rate displaysO
RELATED APPLICATION
~ co~ending U.S, Patent Application Serial No. 637,434J filed August 3, 1984 ~nd entitled "Radistion Detection and Acquisition System", there is disclosed ~ r~diation detector probe or module and associated acquisition system which eliminates or minimizes the afores~id and other 2 problems, and whiah has a wide range of applications. The radiation detector module is characterized by the integration in a compact package of scintillator probe and ~upporting electronics which provide digital pul~e count signals in response to detected seintillations that may be transmitted by a differential line driver on twisted shielded wire pairs over great distances, as on the order of several thousand feet, to a count signal processing unit while maintaining signal integrity. The digital pulse count output is independent of the type of radiation detected, i.e., gamma raysl X-rays, thermal neutrons, etc., whereby the same count signal processing unit mfly be employed w;th different detectors for respective different radi-
3 0 ations. The same electronics are employed in the detector probe for different radiations and radiation energies through analog gain adjustment of the scintillator probe output. The detector module may also have an ~nalog signal OUtpllt so that it may be interfaced to an anfllog signal analyzer such as a conventional nuclear instrumentation module. A third output of the detector module provides a digital output signal that reflects saturation of the electronics due to a high rate o detected scintillation events (pulse pile-up). The persistence of this pulse pile-up signal for periods greater than a preselected time period such as one millisecond may be related to the occurrence of a criticality condition.
A single, remotely located, rnicroprocessor~ased si~nnl pro-cessing unit also is provided to acquire count signals receSved on multiple channels from respective detector probes, to display such dat~ and to transmit such data to ~ controller or monitor for process control and/or monitoring. Acquisition is effected Yia at least one detector/processor interface tnodule having plural tr~nsmission line inputs for connection to respective detection modules and a common transmission line output for connection of said inputs to the signal processing unit.
More particularly, the radiation detector module includes a scintillator for receiving radiation to be detected and for emitting scintilla-tion light in response to received radiation, a photoelectric transducer optically coupled to the scintillator for generating electrical analog output sign~ls in response to detected scintillations, n low level discriminator foP
2Q genersting pulse count signals in response to analog output signals exceeding a threshold level, and a differential line driver for digitally transrnitting ~he pulse output signals to a remotely located differential line receiver ~g m~y be associate.d with a slgnal processing unit. The low level discrimin~tor may be set to prevent a pulse count signal from being generated at the output of the detector in response to detected scintillations caused by incident radifltion having an energy level below a specified value or lower limit.
Acoordingly~ scintillations produced by low energy background radiation or low energy radi~tion caused by secondary reaotions in the scintillator msy be excluded from the count.
l[n some applications, it also would be desirable to exclude from the pulse count output of a detector those scintillations produced by incident radiation having an energy level above a specified upper limit ~s well as those scintillations produced by incident radiat;on below a specified 19~
lower limit. That is, only those scintillations caused by incident radi~tion having an energy level f~lling between the upper and lower limits would result in a pulse count signal being generated at the output of the detector~
E}y way o~ example, a r~diation detector may be used for ~uging of sheet metal. The sheet metal to be gauged is passed or placed between a source of radiation and the radistion detector such that the detector will be located in the shadow of the sheet met~l. The radiation emitted by the source thereof will theP~ have to pass through the sheet metal in order to produce a scintillation at the front end of the detector. lf the radiati >n is of a type that will be attenuated as a function of sheet metal thickness, the rate ~t which scintillations are produced in the detector by such radiation will ~lso be a function of sheet metal thickness. If only the sc;ntillation~
c~used by the attenuated radi~tion result in pulse count signals at the output of the detector, the r~te of such pulse count output signals likewise would be H function of metal thickness - the hi~her the rnte, the thinner the material.
The radiation source, however, may c~use plural radiation in-duced pealcs in the scintillator which correspond to different energy leveJs of incident radiation. The low energy radiation may be attenuated by the sheet metsl as discussed sbove but the high energy radiation might pass essentially freely through the sheet metal and not be attenuated. Accord-ingly, the high energy r&diation which is nvt sttenuated will produce s~intillations in the detector at a rate independent of the thickness of the sheet metal. It would be desirable th~t the scintillations produceà by the high energy r~diation not result in pulse count signals at the output o~ the detector while the scintillations produced by the low ener~y (attenuated) rsdi~ion result in pulse count output signsls at a r~te proportionally related to the thickness of the sheet metal.
Of course there may be other applications wherein radiatîon events associated with high energy radiation desirably are not to be included in the pulse count output o~ Q detector. ~loreover, it would be highly desirable to provide for high level ~s well ~s low level discriminfltion in comp~ct detector module ~e.pable of transmitting its pulse count output digitally over relatively long dlstances. Further, it would be desirable to elimin~te the need for a high voltage supply line leading to a detector utili~ing a photomultiplier tube ss its photo-electric $rans;3ucer.
SUMMARY OF THE INVENTION
The present invention provides a novel radiation detector probe or module characterized by the integration in a compact package o~ a scinti~lator probe and suppor$ing electronics hav;ng provision for high and low level discrimination. The radiation detector module may be set to provide digital pulse count signals in response to detected scintillations produced by only that radiation falling within an energy window, i.eO, between upper and lower radiation energy limits, for selective radiation detection.
More particularly, the radiation detector module includes a scintil~ator for receivinK radiation to be detected ~nd for emitting scintilla-tion light in response to received radiation, a photo-electric transducer optically coupled to the scintillator for generating electrical analog output signals in response to detected scintillations, a discriminator for generating pulse count signals in response to analog output signals falling between lower and upper threshoid levels, and a differential line driver for digitally tr~nsmitting the pulse output si~nals to a remotely located differenti~l line receiver. Provision is made for base line adjustment of the analog output of the transducer and the discriminator includes high speed lower ~nd upper comparators and associsted logic circuitry for generating ~ pulse count signal in response to a pulse produced by the lower limi~ comparator only when no corresponding pulse is produced by the upper limit comparator.
Further in accordance with the invention, the photo-electric trensducer may include a photomultiplier tube powered by a high voltage power supply integrally included in the radiation detector module. Provision also is made for mechnnically decoupling the photomultiplier tube ~or 3 o vibration ~nd shock resistance.
To the accomplishment of the forego;ng and related ends, the invention, then) comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the allnexed drawings s~tting forth in detail a certnin illustrative embodi~nent of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed.
BRIEF DESCRIPTION OF THE DRAWINGS
In the annexed drawings:
Fig. 1 is a perspective view, partly broken away, of a radiation detection rnodule according to the invention;
Fig. 2 is a diagrammatic illustration of the radiation detection module;
Figs. 3 and 4 are circuit schernatics of the electronics illustrated in Fig. 2; and Fig. 5 is a fragmentary cross-section taken substantially along the line 5-5 of Fig. 1.
DETAILED DE~SCRIPTION
Referring now in detail to the drawings and initially to Fig. 1, a radiation detector module according to the invention is designated generally ~y. reference numeral 10. The radiation detection module 10 generally comprises a scintillator probe or detector front end 11 integrated with supporting electronics 12 in a single housing 13. The housing 13, a~ will be 2 0 appreciated, may be quite compact.
As is depicted in Fig. ~, the scintillator probe 11 includes a scintiLlation element 16 optically coupled to a photo-electric transducer 17.
The scintillation element may be A scintillation crystal such as one sold under the trademarlc POLYSCIN by the Harshaw/Filtrol Partnership o Cleveland, Ohso, and the transducer may be a photomultiplier tube of suitable type. By w~y of example~ the crystal may be a 1.0 inch diameter, 1/4 inch thick disc optically coupled to the face of a 1.0 inch diameter photomultiplier tube. There may also be provided e, collima~or 18 flnd as best seen in Fig. 1, the crystal, photomultiplier tube and collimator 3 o preferably are hermetically sealed in an aluminum cylinder 18 which provides the necessary electrostatic shielding. As discussed in greater detail below, the scintillator probe is mounted in the housing 13 but mechanically decoupled at both ends for vibration resistance. There may also be mounted in the housing a high voltage power supply 19 for powering the photomultiplier tube. The power supply preferably is a miniature DC-DC converter which is adjustable to deliver between 500-1000 volts to the high voltage terminals of the photomultiplier tube from a 15 volt battery. Such a power supply i5 available from Bertan. The provision of an internal high voltage power supply eliminates the need for ~n external high voltage power supply line and connection which may create a potential hazard in explosive detector environments.
In Fig. 29 the electronics or electronic circuitry 12 is also dia-grammatically illustrated. The circuitry 12 generally cornpr;ses a low noise charge sensitive pre-amplifier 24~ a differentiator 25 with ~ pole/zero adjust, a pulse shaper amplifier 26, a base line restore 27, fl lower limit and window discriminator 28, and a differential line driver 29 for transmitting digital pulse count data. Low voltage electric power may be provided from a conventional power supply, as to convention~l filtered input regulators 30-32 (if necess~ry or desired) as seen in Fig. 3.
Referring now to the circuit sehematic seen in Figs. 3 and 4, the output of the photomultiplier tube 17 applied to input terminal 33 is AC
coupled by input capacitor 34 to the input of the low noise charge sensitive pre-amp` 24. Also provided is a diode clipping c;rcuit 35 which protects the input circuitry illustr~ted from excessively large signals coming from the photomultiplier tube. If desired, a test input tlerminal 36 m~y be provided ~nd connected by an RC circuit 37 to the inverting input 38 of the pre-amp 24.
As light is produced in the scintillation crystal 16, such light impinges on the photomultiplier tube 17 causing the same to output a charge pulse via terminal 33 and capacitor 34 to the charge sensitive operational amplifier 40 of the pre-amp ~4 to produce on line 41 an amplified pulse proportionately representative of the intensity of light impinging on the photomultiplier tube. The response time of the pre-amp a4 may be less than one microsecond, with a decay time ¢onstant of lS microseconds; these values, of course, are exemplary only and others could be employed by altering the various components used in the circuitry.
~t~ 3~
The output of the pre-amp 24 on line 41 is delivered by the differentiator 25 to the pulse shaper amplifier or integrator 26. The differentiator 25 is an RC differentiation circuit and the decay time o~ such circuit is set by capacitor 44 and the resistance vnlue of an adjusting potentiometer ~5 which is adjustable for pole/zero compensation.
The pulse shaper amplifier 26 may include one or more conven-tional low pass filter stages although only one is shown. The parsllel connected, feed~ack capacitor 46 and resistors 47 and 48 across the operational amplifier 49 determine the cut~ff frequency of the pulse shaper amplifier 26, and the capacitor 50 is provided for damping. The capacitor 50 decreases the rise time of the pulse signal and produces a more symmetrical wave shape. The output of the pulse shaper amplifier 26 will be a subst~qntially symmetric~1 wave shs~pe with an amplitude of say 5 volts for the incident radiation peak energy adjusted by controlling the value o the operAting high voltage supplied to the photomultiplier tube by the intern~l high voltage power supply 19. This gain adjust permits the scilltill~tion probe 11 to be matched to a specific radiation source, i.e., to fix ~t a specified amplitude, say 5 volts, the analog signal peak height corresponding to the incident rsdiation pealc energy. The rise ~nd f~ll of the pulse signsl output of the pulse shaper ~mpliIier 26 should be complete within 5 microseconds.
As is seen in Fig. 4, the output of the pulse shaper ~mplifier 26 on line 54 is buffered by an amplifier circuit 55 and the buffered output on line 56 is AC coupled via capacitor 57 to the junction 58 of the base line restore circuit 27 and the discriminator as. The buffered output on line 56 is also delivered via an RC circuit and impedance matching ampUfier circuit 59 to an analog output S9a to which say a 50 ohm coaxial cable m~ be connected.
The base line restore circuit 27 includes an operAtional ~mplifier 60 having its negative or inverting input connected to the output of the shaper amp 26 and to a -12 voltL~ge level via resistor 61. The positive or non-inverting input of the operational amplifier 60 is connected to d base line adjusting potentiometer 62 which may be adjusted to vary the DC volt~ge added to the analog output of the shaper amplifier 26 for adjusting the base line of such analog output at the junction 58, which also is the input to the discriminator 28.
The discriminator 28 includes a high speed lower limit com-parator 66 having its inverting input connected to the junction 58 which receives the base line adjusted output of the shaper amp 26. The non-inverting input of the comparator ~6 is connected to ground to provide a reference voltage level to which the base line adjusted analog output of the shaper amp is compared. Only when the base line adjusted shaper amp output exceeds the reference voltage level upon the occurrence of a scintillation of sufficient energy detected by the photomultiplier tube will a pulse output be passed by amplifier 69 in the lower limit comparator S6 to line 70. That is, a squared pulse output is obtained on line 70 when the input si~nal to the comparator 66 is greater than the reference voltage whereby pulses generated by low level energy scintillations may be effectively excluded, i.e., not result in a pulse output on line 70. A feedback resistor 71 is incll~ded to induce hysteresis into the circuit to avoid isolations when the input signal level passes through the threshold region. A resistor 72 tied to the +5 volt source is included as shown on the output of the comparator to 2 0 produce a squared pulse output signal of desired amplitude on line 70.
By adjusting the base line ~djusting potentiometer 62, the base line of the shaper amp 26 analog output at junction 58 m~ be ~djusted relative to the fixed reference voltage at the positive input of the lower limit comparator 6B. ln this manner, a low threshold level or lower limit may be determined. By lowering the bsse line, a higher amplitude pulse at the negative input ~f the lower limit comparator would be needed to cause a pulse output on line 70. Conversely, the base line may be raised so that lower amplitude pulses will result in corresponding pulses on line 70. The basc lins adjusting potentiometer 62 preferably is adjustable to provide for low level discrimination from 10 KeV to 100 KeV for Am-241, it again being noted that the shaper amp 26 analog output is proportionately related to the intensity of ~ scintillation produced in the scintillation crystal 16 wh~ch in turn i8 proportlonately r~lated to the energy o~ the radiation callsing the 3~
scintillation. It also is noted that the time duration of a squared wave pulse on line 70 will be dependent on the amount of time that the amplitude of the base line adjusted output of the shaper amp 26 exceeds the reterence voltsge.
The discriminator 28 also includes a high speed upper limit comparator 80 having its inverting input 81 connected to receive the base line adjusted analog output of the shaper amp 26 tat junction 58) and its non-invèrting input connected to an upper threshold adjusting potentiometer 83.
Only when the base line adjusted shaper amp output exceeds the upper threshold level determined by the zener diode reference voltage generating circuit 84 according to the adjustment of the potentiometer 83, upon the occurrence of e scintillation of sufficient energy detected by the photo-multiplier tube 17, will a pulse output be passed by operational amplifier 85 to line 86. That is, a squ~red pulse output is obtained on line 36 when the input signal to the comparator 80 is greater than the upper threshold voltage determined by fhe circuitry coupled with respect to the potentiometer 83.
A feed-back resistor S7 is included to induce hysteresis into the circuit to ~void isolations when the input signal level passes through the threshold region. A resistor 88 tied to the +5 volt source is included as shown on the output of the comparator 80 to produce a sguare wave pulse of desired voltage on line 86 whenever the input si~nal to the upper limit compar~tor i9 greater than the upper threshold voltage. The time durAtion of the square wave pulse on line 86 will be dependent on the amount of time thst the ~mplitude o~ the base line adjusted input signsl to the upper l;mit com-parator 80 exceed~ the upper threshold voltage.
As will be seen, a square wave pulse on Iine 70 will only result in a TTL compatible pulse output signal on line 90 when no corresponding square wave pulse is produced on line 86. Accordingly, only those pulses at the output of the shaper amp 26 having an amplitude greater than the low threshold level determ;ned by base line adjustment but less than the upper threshold limit determined by adjustment of the potentiometer 83 will result in an output si~nal on line 90 connected to the output of the discriminator 28. Since an adjustment of the base line ~djusting potentiometer 62 will 3~
result in a change in the minimum amplitude of A sh~per arnp pulse required to produce a pulse on lin~ 86, the upper limit comparator actually defines a range of amplitudes above the low level threshold that will result in a pulse sign~l on line 86 but no pulse count signal on line 90. If the amplitude of the shaper amp output falls outside this amplitude r~nge or window, either no pulses ~ill appear on lines 70 and 86 or a pulse will appear on both lines 70 and 86. These pulses on lines 70 and 86 serve as logic input signals to a logic circuit 93 which determines whether or not a pulse count signal is to be produced at the output of the differentiator. The upper threshold Rdjusting potentiometer 83 preferably is adjustable to provide for upper level dis-crimination from 10 KeV to 100 KeV.
The logjc circuit 93 includes a one-shot multivibr~tor 94 h~vlng an AND logic gate 95 at its input. The AND gate 95 has two inputs, one input connected to the output of the lower limit comparator 66 and an inverted input connected to ground. As long as the output of the lower limit comparator remains at logic one, ~s when the amplitude of the base line adjusted an~log output of the shaper amp 26 is below the reference voltage input to the lower limit comparator, the AND gate ~5 will maintain ~ logie one signal at the input of the one-shot multivibrator 94. However, upon detection of a scintillation exceeding the low threshold level, a logic zero square wave pu~se will be produced on line 70 and the AND g~te will produce a logic zero at the input o the one~hot multi~vibr~tor for the duration of such logic zero p~se. When a logic one signal again is produced an line 70 at the tr~iling end of the pulse produced ~t the output of the lower limit comparator, the AND gate will again produce a logic one sign~l and trigger the one-shot multivibrator 94 unless it has been turned off by connection of it~ inverted clear input to ground via line 96 and ~ flip-flop circuit 100.
When triggered, the one-shot multivibr~tor will produce a TTL compatible output signal on line 90 for a period determined by the resistor 97 and 3 0 capacitor 98, say 1 microsecond~
The line 96 is connected to the output of the flip-flop circuit 100.
Ench time the flip-flop circuit 100 is reset, R logic low voltage, such as O
volts, i~ produced on line 96 thereby turning on the one-shot multivibr~tor 9~ at its inverted clear input.
- - .
As shown9 the inverted CLK input of the flip-flop circuit 100 is connected to the output oI the upper limit comparator 80 by line ~6. As long as the output of the upper limit comparator remains at logic one, a~
when the Hmplitude of the base line adjusted Hnalog output of the sh~per amp 26 is below the reference voltage input to the upper limit compar~tor, the flip-flop will rem~in unchHnged and continue to apply a negative volta~e on line 96. However, upon detection of a scintillation exceeding the upper threshold level, a logic zero squ~re wave pulse will be produced on line 86 and the flip-flop will ch~nge its state ~nd connect the line 96 to ground.
10Accordingly, a scintillation exceeding the upper threshold level will turn off the one-shot multivibrator 94.
In the event of a scintillation exceeding the upper threshold level, both the lower limit and upper limit comparators 66 and 8û will produce a sgu~re wave pulse respectively on lines 70 and 86. Bec~use of the ~ener~lly symmetrical wave sh~pe of the shaper amp (26~ pulse output, the pulse produced by the upper limit comparator 30 will begin after and end sooner than the pulse produced by the low limit comparator 66. Accord-ingly, the flip-flop circuit mo will have been caused to change state before the one~hot multivibrator 94 can be triggered at the trailing end of the 20 pulse output signHl OI the low limit comparator 66. As a result of this~ the one~hot multivibrHtor 94 will not produce a pulse output signnl on line 90.
- If the scintillation exceeds only the lower threshold level, the lower limit compar~tor 66 will produce a pulse on line 70 but the upper limit compar~tor 80 will not produce a pulse on line 8B. Accordingly, the nip-nop circuit 100 will not be caused to change state and the one-shot multivibrator 94 will remain on to produc~ a pulse output signal on line 90. Qf course, no pulse output signal will be produced on line 90 if the scintillHtion is below the low ths eshold level.
As is further seen in Fig. ~, there is provided ~nother one-shot 30 multivibrator 104 having an AND logic gHte lOS at its illpUt. The AND gate lOS has two inputs, one input connected to the output of the lower limit comparator 66 and an inverted input oonnected to ground. As lon~ HS the output of the low~r limit comparator remains at logic one, the AND ~ate . ~_ , .
will maintain a logic one signal at the input of the one~hot multivibrator 104. However, upon detection of a scintillation exceeding the low threshold level, the logic zero square wave pulse produced on line 70 will cause the AND gate 105 to produce a log~c zero at the input of the one-shot multivibrator 104 for the duration of such logic zero pulse. When a logJic one signal again is produced on line 70 at the trailing end of the logic zero pulse produced at the output of the lower limit comparator 66, the AND gate 105 will again produce a logic one signal and trigger the one-shot multiYibrator 104. When triggered, the one~hot multivibrator 104 wi~l supply a negative going voltage pulse signal via an RC circuit 107 to the inverted clear input of the flip~flop circuit 100 to reset such flip-nop circu;t. The RC circuit 107 factors in a time delay of say 40 nanoseconds to prevent premature resetting of the flip-flop c;rcuit. Regardless of its prior stste, the flip-flopcircuit when reset will then eause a logic low voltage to be applied to the inverted clear input of the one-shot multivibrfltor 94.
The output of the differentiator 28 is inputted via line 90 to the difîerential line driver 29 which preferably is an RS~22 balanced differerl-tial line driver which digitally transmits the pulse count signals receiv~d from the discriminator. The differential line driver has two logic gates, one an AND gate 110, and one a NAND gate 111. The illustrated connections in Fig. 4 provide three OI the inputs to each of the gate~ with a +5 volta~e level signal and one input to each of those gates is connected to line 90 to receive the TTL compatible signal output from the discriminator. Accord-ingly, when there is a logic one signal on line 90, for example upon occurrence of a scintillation detected by the radiation detection module falling between the upper and lower threshold levels (within the energy window), the AND gate 110 will produce a logic one signal on its output line lla, and the NAND gate 111 will produce a logic ~ero signal on its output line 113. Similarly, when a zero signal is spplied on line 90, the AND gate produces a logic zero signal at its output and the NAND gate produces a logic one signal at its output.
Since the outputs oî lines 112 and 113 always are opposite each other, signal integrity with minimum loss is possible for transmission o~ler rclatiYely long distances of, for example, 3,000 feet. The udvantage to such lengthy transmission is the abi1ity to Iocate, for example, a single signal processing unit (including a receiver operated in b~l~nced configuration with the driver) at a remote location from the radiation detection module 10.
The signal processing unit may conveniently monitor many radiation detec-tion modules at respective remote locations~ For further details respecting a preferred signal processing un;t and assoc;ated components such as ~
detectorJprocessor interface module, reference m~ be had to Canadian Patent ~p~Iication Serial No. 482,733, filed May 29, 1985 and entitled "Radiation Detection and Accumulation System". The herein disclosed radiation detector module may be substituted for detector disclosed in such ~pplica-tion in the overall detect;on end accumulat;on system.
~ s will be appreciated, the scintillator probe 11 of the herein disclosed radiation detector module 10 may take other forms than the illus-trated probe utilizing ~ photomultiplier tube. For example, the scintillator probe may compr;se a scintillation crystel optically coupled to a photodiode as in the manner described in the above-referenced application wh;ch is hereby fully incorporated herein by reference.
Referring now $o Figs. 1 and 5, the housing 13 includes a frame consisting of four parallel rails 120 secured to 8 rectangular support block 121dt respecti~e corners of the lstter. The support block 121 is located intermediate the lengths of the rails which extend between opposite ends of the housing. A~ each end of the housing, a respective front and rear end plate 122, 123 is secured to the ends of the bars with a housing cover 124 trapped therebetween. The SLIpport block 121 ;s spaced from the front end plate 122 by a distance approximately equal the length of the scintillator probe 11.
As seen in Fi~. 5~ the front end plate 122 includes a bore 126 aligned with the front end of the scintillator probe 11. At the inner side o~
the front end platet there is provided a cylindrical counterbore 12~ sized to receive an O-r;ng 12~ closely circumscrib;ng the scintillator probe. The O-ring 128 is retained between an annular flange 129 on the scintillator probe caslng 18 and the bottom of the cylindrical counterbore 127. A similar but ,~
oppositely disposed arrangement is provided at the support block 121. That is, the support block has a circular bore through which the scintillator probe extends andt at its side facing the front end plate, a cylindrical counterbore for receiving an O-ring gasket retained between the bottom of the counter-bore and an annular flange on the scintillator probe casing. When the front end plate is secured to the ends of the rails by screws, the front end plate and support block will firmly yet resiliently hold therebetween the scin-tillator probe. With this arrangement, the scintillator probe is mechanically decoupled for vibration resistance by reason of the O-rings which resiliently hold the probe in the housing. As a result, the detector mRy withstand high g forces such as lU g's or even as high as 20 g's without damage to the scintillator probe.
Although the invention has been shown and described with respect to a preferred embodiment, it is obvious that equivalent alterations and modiications will occur to others skilled in the art upon the reading and understanding of the specification. The present invention includes all such ~quiv~lent alterations and modifications, and is Limited only by the scope of the following claims.
A single, remotely located, rnicroprocessor~ased si~nnl pro-cessing unit also is provided to acquire count signals receSved on multiple channels from respective detector probes, to display such dat~ and to transmit such data to ~ controller or monitor for process control and/or monitoring. Acquisition is effected Yia at least one detector/processor interface tnodule having plural tr~nsmission line inputs for connection to respective detection modules and a common transmission line output for connection of said inputs to the signal processing unit.
More particularly, the radiation detector module includes a scintillator for receiving radiation to be detected and for emitting scintilla-tion light in response to received radiation, a photoelectric transducer optically coupled to the scintillator for generating electrical analog output sign~ls in response to detected scintillations, n low level discriminator foP
2Q genersting pulse count signals in response to analog output signals exceeding a threshold level, and a differential line driver for digitally transrnitting ~he pulse output signals to a remotely located differential line receiver ~g m~y be associate.d with a slgnal processing unit. The low level discrimin~tor may be set to prevent a pulse count signal from being generated at the output of the detector in response to detected scintillations caused by incident radifltion having an energy level below a specified value or lower limit.
Acoordingly~ scintillations produced by low energy background radiation or low energy radi~tion caused by secondary reaotions in the scintillator msy be excluded from the count.
l[n some applications, it also would be desirable to exclude from the pulse count output of a detector those scintillations produced by incident radiation having an energy level above a specified upper limit ~s well as those scintillations produced by incident radiat;on below a specified 19~
lower limit. That is, only those scintillations caused by incident radi~tion having an energy level f~lling between the upper and lower limits would result in a pulse count signal being generated at the output of the detector~
E}y way o~ example, a r~diation detector may be used for ~uging of sheet metal. The sheet metal to be gauged is passed or placed between a source of radiation and the radistion detector such that the detector will be located in the shadow of the sheet met~l. The radiation emitted by the source thereof will theP~ have to pass through the sheet metal in order to produce a scintillation at the front end of the detector. lf the radiati >n is of a type that will be attenuated as a function of sheet metal thickness, the rate ~t which scintillations are produced in the detector by such radiation will ~lso be a function of sheet metal thickness. If only the sc;ntillation~
c~used by the attenuated radi~tion result in pulse count signals at the output of the detector, the r~te of such pulse count output signals likewise would be H function of metal thickness - the hi~her the rnte, the thinner the material.
The radiation source, however, may c~use plural radiation in-duced pealcs in the scintillator which correspond to different energy leveJs of incident radiation. The low energy radiation may be attenuated by the sheet metsl as discussed sbove but the high energy radiation might pass essentially freely through the sheet metal and not be attenuated. Accord-ingly, the high energy r&diation which is nvt sttenuated will produce s~intillations in the detector at a rate independent of the thickness of the sheet metal. It would be desirable th~t the scintillations produceà by the high energy r~diation not result in pulse count signals at the output o~ the detector while the scintillations produced by the low ener~y (attenuated) rsdi~ion result in pulse count output signsls at a r~te proportionally related to the thickness of the sheet metal.
Of course there may be other applications wherein radiatîon events associated with high energy radiation desirably are not to be included in the pulse count output o~ Q detector. ~loreover, it would be highly desirable to provide for high level ~s well ~s low level discriminfltion in comp~ct detector module ~e.pable of transmitting its pulse count output digitally over relatively long dlstances. Further, it would be desirable to elimin~te the need for a high voltage supply line leading to a detector utili~ing a photomultiplier tube ss its photo-electric $rans;3ucer.
SUMMARY OF THE INVENTION
The present invention provides a novel radiation detector probe or module characterized by the integration in a compact package o~ a scinti~lator probe and suppor$ing electronics hav;ng provision for high and low level discrimination. The radiation detector module may be set to provide digital pulse count signals in response to detected scintillations produced by only that radiation falling within an energy window, i.eO, between upper and lower radiation energy limits, for selective radiation detection.
More particularly, the radiation detector module includes a scintil~ator for receivinK radiation to be detected ~nd for emitting scintilla-tion light in response to received radiation, a photo-electric transducer optically coupled to the scintillator for generating electrical analog output signals in response to detected scintillations, a discriminator for generating pulse count signals in response to analog output signals falling between lower and upper threshoid levels, and a differential line driver for digitally tr~nsmitting the pulse output si~nals to a remotely located differenti~l line receiver. Provision is made for base line adjustment of the analog output of the transducer and the discriminator includes high speed lower ~nd upper comparators and associsted logic circuitry for generating ~ pulse count signal in response to a pulse produced by the lower limi~ comparator only when no corresponding pulse is produced by the upper limit comparator.
Further in accordance with the invention, the photo-electric trensducer may include a photomultiplier tube powered by a high voltage power supply integrally included in the radiation detector module. Provision also is made for mechnnically decoupling the photomultiplier tube ~or 3 o vibration ~nd shock resistance.
To the accomplishment of the forego;ng and related ends, the invention, then) comprises the features hereinafter fully described and particularly pointed out in the claims, the following description and the allnexed drawings s~tting forth in detail a certnin illustrative embodi~nent of the invention, this being indicative, however, of but one of the various ways in which the principles of the invention may be employed.
BRIEF DESCRIPTION OF THE DRAWINGS
In the annexed drawings:
Fig. 1 is a perspective view, partly broken away, of a radiation detection rnodule according to the invention;
Fig. 2 is a diagrammatic illustration of the radiation detection module;
Figs. 3 and 4 are circuit schernatics of the electronics illustrated in Fig. 2; and Fig. 5 is a fragmentary cross-section taken substantially along the line 5-5 of Fig. 1.
DETAILED DE~SCRIPTION
Referring now in detail to the drawings and initially to Fig. 1, a radiation detector module according to the invention is designated generally ~y. reference numeral 10. The radiation detection module 10 generally comprises a scintillator probe or detector front end 11 integrated with supporting electronics 12 in a single housing 13. The housing 13, a~ will be 2 0 appreciated, may be quite compact.
As is depicted in Fig. ~, the scintillator probe 11 includes a scintiLlation element 16 optically coupled to a photo-electric transducer 17.
The scintillation element may be A scintillation crystal such as one sold under the trademarlc POLYSCIN by the Harshaw/Filtrol Partnership o Cleveland, Ohso, and the transducer may be a photomultiplier tube of suitable type. By w~y of example~ the crystal may be a 1.0 inch diameter, 1/4 inch thick disc optically coupled to the face of a 1.0 inch diameter photomultiplier tube. There may also be provided e, collima~or 18 flnd as best seen in Fig. 1, the crystal, photomultiplier tube and collimator 3 o preferably are hermetically sealed in an aluminum cylinder 18 which provides the necessary electrostatic shielding. As discussed in greater detail below, the scintillator probe is mounted in the housing 13 but mechanically decoupled at both ends for vibration resistance. There may also be mounted in the housing a high voltage power supply 19 for powering the photomultiplier tube. The power supply preferably is a miniature DC-DC converter which is adjustable to deliver between 500-1000 volts to the high voltage terminals of the photomultiplier tube from a 15 volt battery. Such a power supply i5 available from Bertan. The provision of an internal high voltage power supply eliminates the need for ~n external high voltage power supply line and connection which may create a potential hazard in explosive detector environments.
In Fig. 29 the electronics or electronic circuitry 12 is also dia-grammatically illustrated. The circuitry 12 generally cornpr;ses a low noise charge sensitive pre-amplifier 24~ a differentiator 25 with ~ pole/zero adjust, a pulse shaper amplifier 26, a base line restore 27, fl lower limit and window discriminator 28, and a differential line driver 29 for transmitting digital pulse count data. Low voltage electric power may be provided from a conventional power supply, as to convention~l filtered input regulators 30-32 (if necess~ry or desired) as seen in Fig. 3.
Referring now to the circuit sehematic seen in Figs. 3 and 4, the output of the photomultiplier tube 17 applied to input terminal 33 is AC
coupled by input capacitor 34 to the input of the low noise charge sensitive pre-amp` 24. Also provided is a diode clipping c;rcuit 35 which protects the input circuitry illustr~ted from excessively large signals coming from the photomultiplier tube. If desired, a test input tlerminal 36 m~y be provided ~nd connected by an RC circuit 37 to the inverting input 38 of the pre-amp 24.
As light is produced in the scintillation crystal 16, such light impinges on the photomultiplier tube 17 causing the same to output a charge pulse via terminal 33 and capacitor 34 to the charge sensitive operational amplifier 40 of the pre-amp ~4 to produce on line 41 an amplified pulse proportionately representative of the intensity of light impinging on the photomultiplier tube. The response time of the pre-amp a4 may be less than one microsecond, with a decay time ¢onstant of lS microseconds; these values, of course, are exemplary only and others could be employed by altering the various components used in the circuitry.
~t~ 3~
The output of the pre-amp 24 on line 41 is delivered by the differentiator 25 to the pulse shaper amplifier or integrator 26. The differentiator 25 is an RC differentiation circuit and the decay time o~ such circuit is set by capacitor 44 and the resistance vnlue of an adjusting potentiometer ~5 which is adjustable for pole/zero compensation.
The pulse shaper amplifier 26 may include one or more conven-tional low pass filter stages although only one is shown. The parsllel connected, feed~ack capacitor 46 and resistors 47 and 48 across the operational amplifier 49 determine the cut~ff frequency of the pulse shaper amplifier 26, and the capacitor 50 is provided for damping. The capacitor 50 decreases the rise time of the pulse signal and produces a more symmetrical wave shape. The output of the pulse shaper amplifier 26 will be a subst~qntially symmetric~1 wave shs~pe with an amplitude of say 5 volts for the incident radiation peak energy adjusted by controlling the value o the operAting high voltage supplied to the photomultiplier tube by the intern~l high voltage power supply 19. This gain adjust permits the scilltill~tion probe 11 to be matched to a specific radiation source, i.e., to fix ~t a specified amplitude, say 5 volts, the analog signal peak height corresponding to the incident rsdiation pealc energy. The rise ~nd f~ll of the pulse signsl output of the pulse shaper ~mpliIier 26 should be complete within 5 microseconds.
As is seen in Fig. 4, the output of the pulse shaper ~mplifier 26 on line 54 is buffered by an amplifier circuit 55 and the buffered output on line 56 is AC coupled via capacitor 57 to the junction 58 of the base line restore circuit 27 and the discriminator as. The buffered output on line 56 is also delivered via an RC circuit and impedance matching ampUfier circuit 59 to an analog output S9a to which say a 50 ohm coaxial cable m~ be connected.
The base line restore circuit 27 includes an operAtional ~mplifier 60 having its negative or inverting input connected to the output of the shaper amp 26 and to a -12 voltL~ge level via resistor 61. The positive or non-inverting input of the operational amplifier 60 is connected to d base line adjusting potentiometer 62 which may be adjusted to vary the DC volt~ge added to the analog output of the shaper amplifier 26 for adjusting the base line of such analog output at the junction 58, which also is the input to the discriminator 28.
The discriminator 28 includes a high speed lower limit com-parator 66 having its inverting input connected to the junction 58 which receives the base line adjusted output of the shaper amp 26. The non-inverting input of the comparator ~6 is connected to ground to provide a reference voltage level to which the base line adjusted analog output of the shaper amp is compared. Only when the base line adjusted shaper amp output exceeds the reference voltage level upon the occurrence of a scintillation of sufficient energy detected by the photomultiplier tube will a pulse output be passed by amplifier 69 in the lower limit comparator S6 to line 70. That is, a squared pulse output is obtained on line 70 when the input si~nal to the comparator 66 is greater than the reference voltage whereby pulses generated by low level energy scintillations may be effectively excluded, i.e., not result in a pulse output on line 70. A feedback resistor 71 is incll~ded to induce hysteresis into the circuit to avoid isolations when the input signal level passes through the threshold region. A resistor 72 tied to the +5 volt source is included as shown on the output of the comparator to 2 0 produce a squared pulse output signal of desired amplitude on line 70.
By adjusting the base line ~djusting potentiometer 62, the base line of the shaper amp 26 analog output at junction 58 m~ be ~djusted relative to the fixed reference voltage at the positive input of the lower limit comparator 6B. ln this manner, a low threshold level or lower limit may be determined. By lowering the bsse line, a higher amplitude pulse at the negative input ~f the lower limit comparator would be needed to cause a pulse output on line 70. Conversely, the base line may be raised so that lower amplitude pulses will result in corresponding pulses on line 70. The basc lins adjusting potentiometer 62 preferably is adjustable to provide for low level discrimination from 10 KeV to 100 KeV for Am-241, it again being noted that the shaper amp 26 analog output is proportionately related to the intensity of ~ scintillation produced in the scintillation crystal 16 wh~ch in turn i8 proportlonately r~lated to the energy o~ the radiation callsing the 3~
scintillation. It also is noted that the time duration of a squared wave pulse on line 70 will be dependent on the amount of time that the amplitude of the base line adjusted output of the shaper amp 26 exceeds the reterence voltsge.
The discriminator 28 also includes a high speed upper limit comparator 80 having its inverting input 81 connected to receive the base line adjusted analog output of the shaper amp 26 tat junction 58) and its non-invèrting input connected to an upper threshold adjusting potentiometer 83.
Only when the base line adjusted shaper amp output exceeds the upper threshold level determined by the zener diode reference voltage generating circuit 84 according to the adjustment of the potentiometer 83, upon the occurrence of e scintillation of sufficient energy detected by the photo-multiplier tube 17, will a pulse output be passed by operational amplifier 85 to line 86. That is, a squ~red pulse output is obtained on line 36 when the input signal to the comparator 80 is greater than the upper threshold voltage determined by fhe circuitry coupled with respect to the potentiometer 83.
A feed-back resistor S7 is included to induce hysteresis into the circuit to ~void isolations when the input signal level passes through the threshold region. A resistor 88 tied to the +5 volt source is included as shown on the output of the comparator 80 to produce a sguare wave pulse of desired voltage on line 86 whenever the input si~nal to the upper limit compar~tor i9 greater than the upper threshold voltage. The time durAtion of the square wave pulse on line 86 will be dependent on the amount of time thst the ~mplitude o~ the base line adjusted input signsl to the upper l;mit com-parator 80 exceed~ the upper threshold voltage.
As will be seen, a square wave pulse on Iine 70 will only result in a TTL compatible pulse output signal on line 90 when no corresponding square wave pulse is produced on line 86. Accordingly, only those pulses at the output of the shaper amp 26 having an amplitude greater than the low threshold level determ;ned by base line adjustment but less than the upper threshold limit determined by adjustment of the potentiometer 83 will result in an output si~nal on line 90 connected to the output of the discriminator 28. Since an adjustment of the base line ~djusting potentiometer 62 will 3~
result in a change in the minimum amplitude of A sh~per arnp pulse required to produce a pulse on lin~ 86, the upper limit comparator actually defines a range of amplitudes above the low level threshold that will result in a pulse sign~l on line 86 but no pulse count signal on line 90. If the amplitude of the shaper amp output falls outside this amplitude r~nge or window, either no pulses ~ill appear on lines 70 and 86 or a pulse will appear on both lines 70 and 86. These pulses on lines 70 and 86 serve as logic input signals to a logic circuit 93 which determines whether or not a pulse count signal is to be produced at the output of the differentiator. The upper threshold Rdjusting potentiometer 83 preferably is adjustable to provide for upper level dis-crimination from 10 KeV to 100 KeV.
The logjc circuit 93 includes a one-shot multivibr~tor 94 h~vlng an AND logic gate 95 at its input. The AND gate 95 has two inputs, one input connected to the output of the lower limit comparator 66 and an inverted input connected to ground. As long as the output of the lower limit comparator remains at logic one, ~s when the amplitude of the base line adjusted an~log output of the shaper amp 26 is below the reference voltage input to the lower limit comparator, the AND gate ~5 will maintain ~ logie one signal at the input of the one-shot multivibrator 94. However, upon detection of a scintillation exceeding the low threshold level, a logic zero square wave pu~se will be produced on line 70 and the AND g~te will produce a logic zero at the input o the one~hot multi~vibr~tor for the duration of such logic zero p~se. When a logic one signal again is produced an line 70 at the tr~iling end of the pulse produced ~t the output of the lower limit comparator, the AND gate will again produce a logic one sign~l and trigger the one-shot multivibrator 94 unless it has been turned off by connection of it~ inverted clear input to ground via line 96 and ~ flip-flop circuit 100.
When triggered, the one-shot multivibr~tor will produce a TTL compatible output signal on line 90 for a period determined by the resistor 97 and 3 0 capacitor 98, say 1 microsecond~
The line 96 is connected to the output of the flip-flop circuit 100.
Ench time the flip-flop circuit 100 is reset, R logic low voltage, such as O
volts, i~ produced on line 96 thereby turning on the one-shot multivibr~tor 9~ at its inverted clear input.
- - .
As shown9 the inverted CLK input of the flip-flop circuit 100 is connected to the output oI the upper limit comparator 80 by line ~6. As long as the output of the upper limit comparator remains at logic one, a~
when the Hmplitude of the base line adjusted Hnalog output of the sh~per amp 26 is below the reference voltage input to the upper limit compar~tor, the flip-flop will rem~in unchHnged and continue to apply a negative volta~e on line 96. However, upon detection of a scintillation exceeding the upper threshold level, a logic zero squ~re wave pulse will be produced on line 86 and the flip-flop will ch~nge its state ~nd connect the line 96 to ground.
10Accordingly, a scintillation exceeding the upper threshold level will turn off the one-shot multivibrator 94.
In the event of a scintillation exceeding the upper threshold level, both the lower limit and upper limit comparators 66 and 8û will produce a sgu~re wave pulse respectively on lines 70 and 86. Bec~use of the ~ener~lly symmetrical wave sh~pe of the shaper amp (26~ pulse output, the pulse produced by the upper limit comparator 30 will begin after and end sooner than the pulse produced by the low limit comparator 66. Accord-ingly, the flip-flop circuit mo will have been caused to change state before the one~hot multivibrator 94 can be triggered at the trailing end of the 20 pulse output signHl OI the low limit comparator 66. As a result of this~ the one~hot multivibrHtor 94 will not produce a pulse output signnl on line 90.
- If the scintillation exceeds only the lower threshold level, the lower limit compar~tor 66 will produce a pulse on line 70 but the upper limit compar~tor 80 will not produce a pulse on line 8B. Accordingly, the nip-nop circuit 100 will not be caused to change state and the one-shot multivibrator 94 will remain on to produc~ a pulse output signal on line 90. Qf course, no pulse output signal will be produced on line 90 if the scintillHtion is below the low ths eshold level.
As is further seen in Fig. ~, there is provided ~nother one-shot 30 multivibrator 104 having an AND logic gHte lOS at its illpUt. The AND gate lOS has two inputs, one input connected to the output of the lower limit comparator 66 and an inverted input oonnected to ground. As lon~ HS the output of the low~r limit comparator remains at logic one, the AND ~ate . ~_ , .
will maintain a logic one signal at the input of the one~hot multivibrator 104. However, upon detection of a scintillation exceeding the low threshold level, the logic zero square wave pulse produced on line 70 will cause the AND gate 105 to produce a log~c zero at the input of the one-shot multivibrator 104 for the duration of such logic zero pulse. When a logJic one signal again is produced on line 70 at the trailing end of the logic zero pulse produced at the output of the lower limit comparator 66, the AND gate 105 will again produce a logic one signal and trigger the one-shot multiYibrator 104. When triggered, the one~hot multivibrator 104 wi~l supply a negative going voltage pulse signal via an RC circuit 107 to the inverted clear input of the flip~flop circuit 100 to reset such flip-nop circu;t. The RC circuit 107 factors in a time delay of say 40 nanoseconds to prevent premature resetting of the flip-flop c;rcuit. Regardless of its prior stste, the flip-flopcircuit when reset will then eause a logic low voltage to be applied to the inverted clear input of the one-shot multivibrfltor 94.
The output of the differentiator 28 is inputted via line 90 to the difîerential line driver 29 which preferably is an RS~22 balanced differerl-tial line driver which digitally transmits the pulse count signals receiv~d from the discriminator. The differential line driver has two logic gates, one an AND gate 110, and one a NAND gate 111. The illustrated connections in Fig. 4 provide three OI the inputs to each of the gate~ with a +5 volta~e level signal and one input to each of those gates is connected to line 90 to receive the TTL compatible signal output from the discriminator. Accord-ingly, when there is a logic one signal on line 90, for example upon occurrence of a scintillation detected by the radiation detection module falling between the upper and lower threshold levels (within the energy window), the AND gate 110 will produce a logic one signal on its output line lla, and the NAND gate 111 will produce a logic ~ero signal on its output line 113. Similarly, when a zero signal is spplied on line 90, the AND gate produces a logic zero signal at its output and the NAND gate produces a logic one signal at its output.
Since the outputs oî lines 112 and 113 always are opposite each other, signal integrity with minimum loss is possible for transmission o~ler rclatiYely long distances of, for example, 3,000 feet. The udvantage to such lengthy transmission is the abi1ity to Iocate, for example, a single signal processing unit (including a receiver operated in b~l~nced configuration with the driver) at a remote location from the radiation detection module 10.
The signal processing unit may conveniently monitor many radiation detec-tion modules at respective remote locations~ For further details respecting a preferred signal processing un;t and assoc;ated components such as ~
detectorJprocessor interface module, reference m~ be had to Canadian Patent ~p~Iication Serial No. 482,733, filed May 29, 1985 and entitled "Radiation Detection and Accumulation System". The herein disclosed radiation detector module may be substituted for detector disclosed in such ~pplica-tion in the overall detect;on end accumulat;on system.
~ s will be appreciated, the scintillator probe 11 of the herein disclosed radiation detector module 10 may take other forms than the illus-trated probe utilizing ~ photomultiplier tube. For example, the scintillator probe may compr;se a scintillation crystel optically coupled to a photodiode as in the manner described in the above-referenced application wh;ch is hereby fully incorporated herein by reference.
Referring now $o Figs. 1 and 5, the housing 13 includes a frame consisting of four parallel rails 120 secured to 8 rectangular support block 121dt respecti~e corners of the lstter. The support block 121 is located intermediate the lengths of the rails which extend between opposite ends of the housing. A~ each end of the housing, a respective front and rear end plate 122, 123 is secured to the ends of the bars with a housing cover 124 trapped therebetween. The SLIpport block 121 ;s spaced from the front end plate 122 by a distance approximately equal the length of the scintillator probe 11.
As seen in Fi~. 5~ the front end plate 122 includes a bore 126 aligned with the front end of the scintillator probe 11. At the inner side o~
the front end platet there is provided a cylindrical counterbore 12~ sized to receive an O-r;ng 12~ closely circumscrib;ng the scintillator probe. The O-ring 128 is retained between an annular flange 129 on the scintillator probe caslng 18 and the bottom of the cylindrical counterbore 127. A similar but ,~
oppositely disposed arrangement is provided at the support block 121. That is, the support block has a circular bore through which the scintillator probe extends andt at its side facing the front end plate, a cylindrical counterbore for receiving an O-ring gasket retained between the bottom of the counter-bore and an annular flange on the scintillator probe casing. When the front end plate is secured to the ends of the rails by screws, the front end plate and support block will firmly yet resiliently hold therebetween the scin-tillator probe. With this arrangement, the scintillator probe is mechanically decoupled for vibration resistance by reason of the O-rings which resiliently hold the probe in the housing. As a result, the detector mRy withstand high g forces such as lU g's or even as high as 20 g's without damage to the scintillator probe.
Although the invention has been shown and described with respect to a preferred embodiment, it is obvious that equivalent alterations and modiications will occur to others skilled in the art upon the reading and understanding of the specification. The present invention includes all such ~quiv~lent alterations and modifications, and is Limited only by the scope of the following claims.
Claims (15)
1. A radiation detector comprising:
scintillator means for receiving radiation to be detected and for emitting scintillation light in response to received radiation, photoelectric transducer means optically coupled to said scintillator means for generating electrical analog signals in response to detected scintillations, discriminator means for generating pulse count signals in response to analog signals falling between lower and upper threshold levels, and differential line driver means for digitally transmitting the pulse output signals to A remotely located differential line receiver.
scintillator means for receiving radiation to be detected and for emitting scintillation light in response to received radiation, photoelectric transducer means optically coupled to said scintillator means for generating electrical analog signals in response to detected scintillations, discriminator means for generating pulse count signals in response to analog signals falling between lower and upper threshold levels, and differential line driver means for digitally transmitting the pulse output signals to A remotely located differential line receiver.
2. A radiation detector as set forth in claim 1, wherein said scintillator means, transducer means, discriminator means and driver means are mounted in a common housing.
3. A radiation detector as set forth in claim 1, wherein said transducer means includes a photomultiplier tube and a charge sensitive amplifier electrically coupled to said photomultiplier tube.
4. A radiation detector as set forth in claim 3, further comprising a high voltage power supply for said photomultiplier tube having provision for adjusting the value of the operating high voltage of said tube to produce a desired voltage analog output signal for the incident radiation peak energy.
5. A radiation detector as set forth in claim 4, wherein said scintillator means, photomultiplier tube, discriminator means, driver means and high voltage power supply are mounted in a common housing, and said high voltage power supply includes a DC-DC converter.
6. A radiation detector as set forth in claim 1, further comprising resistance driver means for transmitting the analog output signal to a remotely located receiver therefor.
7. A radiation detector as set forth in claim 1, further comprising base line adjustment means for adjusting the base line of the analog output of said transducer means, and wherein said discriminator means includes a high speed lower limit comparator having one input connected to the base line adjusted output of said transducer means and its other input connected to reference value means, whereby the base line of the analog output may be adjusted relative to said reference value means to determine the lower threshold level.
8. A radiation detector as set forth in claim 7, wherein said discriminator means further includes a high speed upper limit comparator having one input connected to the base line adjusted output of said transducer means and its other input connected to upper threshold adjusting means, whereby the upper threshold adjusting means may be adjusted relative to the lower threshold level to determine the upper threshold level of a window.
9. A radiation detector as set forth in claim 8, wherein said lower limit comparator produces a pulse output only in response to the base line adjusted analog output exceeding the lower threshold level, said upper limit comparator produces a pulse output only in response to the base line adjusted analog output exceeding the upper threshold level, and said discriminator means further including logic circuit means for generating a pulse count signal in response to a pulse produced by said lower limit comparator only when no corresponding pulse is produced by said upper limit comparator.
10. A radiation detector as set forth in claim 9, wherein said logic circuit means includes one-shot multivibrator circuit means connected to the output of said lower limit comparator such that said one-shot multivibrator circuit means will normally be triggered to produce a pulse count signal by the trailing edge of a pulse produced by said lower limit comparator, and flip-flop circuit means connected to the output of said upper limit comparator for turning off said one-shot multivibrator circuit means when a pulse is produced by said upper limit comparator to prevent a pulse count signal from being generated by the trailing edge of a corres-ponding pulse produced by said lower limit comparator.
11. A radiation detector as set forth in claim 10, further comprising reset means connected to the output of said lower limit comparator for resetting said flip flop circuit means after each pulse produced by said lower limit comparator.
12. A radiation detector comprising:
scintillator means for receiving radiation to be detected and for emitting scintillation light in response to received radistion, photoelectric transducer means optically coupled to said scintillator means for generating analog electrical pulses in response to detected scintillations at an output thereof, and electronic circuit means electrically coupled to the output of said transducer means, said electronic circuit means including amplifier means for amplifying said analog electrical pulses, discriminator means for generating pulse count signals in response to the amplified analog electrical pulses exceeding a lower threshold level but not an upper threshold level, and balanced differential line driver means for digitally transmitting the pulse output signals to a remotely located differential line receiver.
scintillator means for receiving radiation to be detected and for emitting scintillation light in response to received radistion, photoelectric transducer means optically coupled to said scintillator means for generating analog electrical pulses in response to detected scintillations at an output thereof, and electronic circuit means electrically coupled to the output of said transducer means, said electronic circuit means including amplifier means for amplifying said analog electrical pulses, discriminator means for generating pulse count signals in response to the amplified analog electrical pulses exceeding a lower threshold level but not an upper threshold level, and balanced differential line driver means for digitally transmitting the pulse output signals to a remotely located differential line receiver.
13. A radiation detector as set forth in claim 12, wherein said scintillator means, transducer means and electronic circuit means are mounted in a common housing.
14. A radiation detector as set forth in claim 13, wherein said transducer means includes a photomultiplier tube, and further comprising mechanical decoupling means for resiliently supporting said photomultiplier tube in said housing.
15. A radiation detector as set forth in claim 14, wherein said mechanical decoupling means includes a pair of end supports for said photomultiplier tube and O-rings supporting said photomultiplier tube at respective ends in said end supports.
Priority Applications (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| CA000499679A CA1262192A (en) | 1985-04-11 | 1986-01-16 | Radiation detection module |
Applications Claiming Priority (3)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| US72210985A | 1985-04-11 | 1985-04-11 | |
| US722,109 | 1985-04-11 | ||
| CA000499679A CA1262192A (en) | 1985-04-11 | 1986-01-16 | Radiation detection module |
Publications (2)
| Publication Number | Publication Date |
|---|---|
| CA1262192C CA1262192C (en) | 1989-10-03 |
| CA1262192A true CA1262192A (en) | 1989-10-03 |
Family
ID=24900543
Family Applications (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| CA000499679A Expired CA1262192A (en) | 1985-04-11 | 1986-01-16 | Radiation detection module |
Country Status (2)
| Country | Link |
|---|---|
| CA (1) | CA1262192A (en) |
| DE (1) | DE3611685A1 (en) |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7612338B2 (en) | 2006-11-28 | 2009-11-03 | Veritainer Corporation | Real time system for monitoring containers from a quayside crane |
| US7661738B2 (en) | 2006-11-28 | 2010-02-16 | Veritainer Corporation | Radiation detection unit for mounting a radiation sensor to a container crane |
Families Citing this family (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| DE10112297B4 (en) * | 2001-03-08 | 2005-03-24 | Silicon Instruments Gmbh | Apparatus and method for determining the position of a positron emitter in a material |
| JP4891828B2 (en) * | 2007-04-04 | 2012-03-07 | 浜松ホトニクス株式会社 | Photomultiplier tube module |
-
1986
- 1986-01-16 CA CA000499679A patent/CA1262192A/en not_active Expired
- 1986-04-08 DE DE19863611685 patent/DE3611685A1/en not_active Withdrawn
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| US7612338B2 (en) | 2006-11-28 | 2009-11-03 | Veritainer Corporation | Real time system for monitoring containers from a quayside crane |
| US7661738B2 (en) | 2006-11-28 | 2010-02-16 | Veritainer Corporation | Radiation detection unit for mounting a radiation sensor to a container crane |
Also Published As
| Publication number | Publication date |
|---|---|
| DE3611685A1 (en) | 1986-10-16 |
| CA1262192C (en) | 1989-10-03 |
Similar Documents
| Publication | Publication Date | Title |
|---|---|---|
| US4482808A (en) | Apparatus for measuring neutrons and gamma rays | |
| US4598202A (en) | Nuclear and pressure sensitive line/perimeter detection system | |
| US9366768B2 (en) | Radiation detector system and method | |
| US4677300A (en) | Radiation detection and acquisition system | |
| EP3637147A1 (en) | Gain correction apparatus and method for scintillation detector | |
| CN111175804B (en) | Pulse radiation detection circuit and device | |
| US3105149A (en) | Geophysical propecting device for identifying radioactive elements | |
| US4092539A (en) | Radiation monitor | |
| CA1262192A (en) | Radiation detection module | |
| US5594250A (en) | Method for detecting water equivalent of snow using secondary cosmic gamma radiation | |
| JPH0274890A (en) | Coupling type scintillator | |
| US3800143A (en) | Agc for radiation counter | |
| US4381450A (en) | Pulsed radiation dosimetry apparatus | |
| US3842278A (en) | Liquid scintillation unit with low background noise | |
| US3914602A (en) | Plutonium monitor | |
| US4880981A (en) | Low level radiation measurement device | |
| US4400621A (en) | Detector device | |
| JPH0634763A (en) | Radioactive ray detector | |
| US4295045A (en) | Background compensation type plutonium air monitor | |
| US3296438A (en) | Nuclear particle detection system and calibration means therefor | |
| US4251744A (en) | Pulse conversion circuit | |
| US4638159A (en) | Graded shaped spatial resolution nuclear detectors | |
| JPH033198B2 (en) | ||
| US3797802A (en) | Radiation measuring system utilizing a charge sensitive amplifier | |
| Horn et al. | Suppression of background radiation in BGO and NaI detectors used in nuclear reaction analysis |
Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| MKLA | Lapsed | ||
| MKLA | Lapsed |
Effective date: 19930404 |