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Home , Photomultiplier tube, Triode

April 29, 1952 L. F. WOUTERs 2,594,703 CIRCUIT Filed March 7, 195l.

62

222 34

A2

SQUARE WAVE VOLTAGE GENERATOR

INVENTOR, LOUIS F WOUTERS BY 424-21%-4---- ATTORNEY. Patented Apr. 29, 1952 2,594,703

UNITED STATES PATENT OFFICE 2,594,703 PHOTOMULTIPLERTUBE CIRCUIT Louis F. Wouters, Oakland, Calif., assignor to the United States of America as represented by the United States Atomic Energy Commission Application April 17, 1951, serial No. 221,396 4 Claims. (CL 250-207) 2 This invention relates to a photomultiplier prising a plurality of similar and tube circuit and more particularly to a method similar 8, is connected between the and apparatus for increasing the output of a and penultimate with intermedi photomultiplier tube. ate connections thereof connected to the first In many circuits utilizing photomultiplier tubes s seven , so that a and a it is necessary to amplify the output of such are parallel-connected between each of such elec tubes so that they may be applied to auxiliary trodes. In the present embodiment of the inven circuits. Thus, if the source of is faint, tion the penultimate dynode is connected directly the multiplication of the photomulti to ground by a lead 2 while the cathode is con plier tube may be insufficient to raise the output () nected to one side of a storage capacitor 22 by to a readily useful level requiring expensive, as a lead 23. The other side of the capacitor 22 is well as, extensive circuits. In some connected to the of a type tube 26, instances the desire to maintain the pulse shape the Cathode of which is grounded. and resolution time of the output requires addi As a means for supplying unidirectional tionally complex pulse forming and shaping am 5 age to the photomultiplier tube 3 there is pro plifiers. . . vided a conventional power supply 3. having. a The present invention provides a photomulti plurality of output voltages. For purposes of plier tube circuit which overcomes the above illustration the values of such output voltages outlined difficulties by operating the photomulti will hereinafter be numerically identified by the plier tube at voltages many times the normal op 20 voltage existing with respect to a grounded ter erating voltages for such tube. The foregoing minal 32, but should not be understood as limit is made practical by pulsed operation which pre ing the circuit to the exact voltages set forth. vents deleterious overloading of the photomulti A negative terminal 33 having a value of -100 plier tube. - is connected to the of the tube It is therefore an object of the present inven 25 26 through a resistor 36. A positive 'ter tion to provide a new and improved photomulti minal 35 having a value of -2000 voltS. is con plier tube circuit. nected through a dropping resistor 36 to the Another object of the invention is to provide anode of the tube 26 to supply operating voltage a photomultiplier tube circuit which may di thereto and also a charging voltage to the rectly drive an auxiliary circuit. 30 capacitor 22. A second positive terminal 37 Still another object of the invention is to having a value of -250 volts is connected to provide a photomultiplier tube circuit having a the final dynode of the tube 3 to Supply a Suit pulsed power supply therefor to provide greater able operating potential thereto through a drop amplification through such tube...... ping resistor 38. A third positive terminal 39 A further object of the invention is to provide 35 having a value of --500 volts is connected to a photomultiplier tube circuit which is simple in the anode of the tube 13 through a dropping construction and which eliminates the necessity resistor 40 to supply a suitable operating poten of in the output circuit. - tial thereto...... Still further objects and advantages of the It will be seen that with the power supply 3 invention will be apparent from the following 40 suitably energized that the capacitor 22 will be description and claims considered together with come charged to the value of the power Supply the accompanying drawing which is a schematic terminal 35, that is --2000 volts, but that the side wiring diagram. - of the capacitor connected to the cathode of the Referring to the drawing in detail there is tube 3 is at ground potential. Now, if the posi provided a source of light, Such as a Scintilla 45 tively charged side of the capacitor 22 is Sud tion crystal f, placed in the path of a beam of denly connected to ground, the voltage of the charged particles 2. Disposed adjacent the cathode of the tube 3 will be effectively lowered crystal it is a photomultiplier tube f3 in Such to a value of -2000 volts which will be evenly position that light from the crystal falls upon distributed across the resistors f to ground, the light-sensitive cathode of the tube. The 50 Thus the photomultiplier tube 3 will be opera photomultiplier tube 3, as illustrated in the tive to pass between the cathode and drawing, has nine dynodes disposed between the. anode by way of the dynodes upon activation of cathode and anode and it will be readily ap the cathode by light striking thereon. To ac parent that other types of photomultiplier tubes complish Such mode of operation a Square Wave may be substituted. A 6, com 55 voltage generator 46 of conventional design and 2,594,708 3 4 having an output sufficient to overcome the the other side of the resistor 52 by the capacitor negative grid bias of the tube 26 is connected 57 the unidirectional voltages at such between the control grid and cathode thereof. are blocked and only the varying voltage caused The duration of the square wave output of the by the electron flow is passed. Such varying generator 46 should be short as compared to the voltage establishes a push-pull voltage across the time constant of the capacitor 22 and the re resistor 52 and thereby causes deflection of the sistance of the resistors so that the high Volt electron beam of the oscilloscope 59. Thus a age across the elements of the photomultiplier pattern of the magnitude and duration of the tube will not be damaged by prolonged over light scintillation at the crystal is formed on voltage. The repetition rate of the generator 46 O the Screen of the Oscilloscope 59. is not critical, but should be sufficiently rapid to From the foregoing it will be readily apparent energize the circuit for each Scintillation of the that any desired light source may be utilized in crystal in the present embodiment of the in the position of the crystal . It will also be vention and still have an average value which readily understood that numerous types of loads is not in excess of the voltage rating of the may be connected to the output of the photo tube f3. multiplier tube to be driven thereby, in the place The output of the photomultiplier tube 3 may of the OScilloscope 59. be taken from between the final dynode and While the salient features of this invention anode thereof and will be of sufficient magnitude have been described in detail with respect to one to directly drive an auxiliary circuit. As illus 20 embodiment it will, of course, be understood that trated in the drawing a lead 5 is connected to numerous modifications may be made within the the final dynode of the tube 3 and coupled to Spirit and Scope of the invention and it is there one end of a center-grounded resistor 52 by a ca fore not desired to limit the invention to the exact pacitor 53. A lead 56 is similarly connected to details shown except insofar as they may be de the anode of the tube 3 and coupled to the other ; fined in the following claims. end of the resistor 52 by a capacitor 57. Thus a What is claimed is: push-pull voltage is developed across the re 1. In a photomultiplier tube circuit, the comi sistor 52 which may then be impressed between bination comprising a source of light, a photo the vertical deflecting plates of an oscilloscope multiplier tube having an anode, a plurality of 59. The oscilloscope 59 is equipped with a power dynodes, and a cathode with substantially low Supply 6 to energize the electron gun and to values of operating voltages, said tube being dis energize the Sweep generator 62 which is in turn posed adjacent Said source to receive light there connected to the horizontal deflecting plates. from, a voltage divider having a plurality of Now consider the operation of the present in equally Spaced taps connected between the penul wention, as described above, with the power Sup timate dynode and said cathode with the taps plies 3 and 6 and the square wave generator respectively connected to the dynodes, said penul 46 suitably energized. Under such condition a timate dynode being connected to ground, said Square Wave of voltage at the output of the gen cathode being connected to a storage capacitor, erator 46 renders the triode tube 26 conductive power supply means having a grounded terminal, to ground the positively charged side of the a positive terminal connected to said capacitor capacitor 22. Thus the cathode of the photo for charging the capacitor to a high value of multiplier tube f3 is biased to -2000 volts. Such Voltage, and terminals connected to said anode voltage difference with respect to ground is and penultimate for impressing suitable evenly divided across the voltage divider 6 so biasing voltages, and means connected to the that each successive electrode of the tube 3 is power Supply side of Said capacitor for intermit substantially 250 volts more positive than the tently grounding said capacitor to apply high preceding electrode. The particular type of potentials to Said dynodes with respect to said photomutliplier tube 3 selected for purposes of Substantially low values of operating voltages. the description has a maximum rated Voltage dif 2. In a photomultiplier tube circuit, the com ference between successive electrodes of approxi bination comprising a source of light, a photo mately 150 volts. It is thus seen that the voltage multiplier tube having an anode, a plurality of of the electrodes of the tube 3 is in excess of the dynodes, and a cathode with substantially low rated value So it is necessary to maintain a repe Values of Operating voltages, said tube being dis (tition rate of the generator 46 at such a value posed adjacent Said source to receive light there that the average Voltage of the electrodes does from, a voltage divider having a plurality of not exceed the maximum rated voltage. equally Spaced taps connected between the penul While the voltages of the electrodes of the tube timate dynode and Said cathode with the taps 3 render the tube operative a charged particle respectively connected to the dynodes, said penul striking the crystal results in light reaching the timate dynode being connected to ground, said cathode of the tube. Such light at the cathode 60 Cathode being connected to a storage capacitor, frees electrons which are accelerated at greater power Supply means connected to said capacitor than the normal rate to the first dynode because and to said anode and penultimate electrode, a -of the higher Voltage. Since triode tube having an anode, control grid, and is directly proportional to the acceleration of the cathode With the anode thereof connected be-, electron striking, it will be seen that a greater 65 tween said capacitor and power supply and the than normal number of secondary electrons will cathode thereof connected to ground, means for result at the first dynode and be attracted to applying a negative voltage to the control grid of the second dynode. Each of the successive Said triode tube, and a square wave generator dynodes and the anode are similarly biased so connected to the control grid of said triode tube that the electron flow between the final dynode 70 for intermittently rendering, said triode tube con and the angde is much larger than would exist ductive. under the condition of rated voltages applied to 3. In a photomultiplier tube circuit, the com the tube 3. By coupling the final dynode of the bination comprising a source of light, a photo. tube 3 to one side of the center-grounded re multiplier tube having an anode, a plurality of sistor 52 by the capacitor 53 and the anode to 75 dynodes, and a cathode with substantially low 2,594,703 6 values of operating voltages, said tube being dis values of resistance therebetween with Such taps posed adjacent said source to receive light there Sequentially connected to said dynodes, a power from, a voltage divider having a plurality of Supply having a terminal connected to ground equally spaced taps connected between the penul and positive terminals connected to said anode timate dynode and said cathode With the taps and final dynode to furnish operating Voltages respectively connected to the dynodes, said penul thereto, energy storage means connected between timate dynode being connected to ground, said Said Cathode and a positive terminal of said power cathode being connected to one side of a storage Supply, electronic switching means connected to capacitor, power supply means connected to the the junction between said energy storage means other side of said capacitor, to said anode, and to O and said power supply for the recurrent ground said penultimate electrode, and electronic ing thereof, and means coupled to said anode and ing means connected to the junction between Said final dynode for developing an output voltage to capacitor and said power supply for recurrently directly drive an auxiliary circuit. grounding said capacitor. LOUIS F, WOUTERS. 4. In a photomultiplier tube circuit, the com s bination comprising a source of light, a photo multiplier tube having an anode, a plurality of iREFERENCES CITED dynodes, and a cathode, Said tube having Sub he following references are of record in the stantially low values of Operating Woltages and file of this patent: being disposed adjacent said Source to receive 20 UNITED STATES PATENTS light therefrom, a voltage divider connected at Number Name Date one end to ground and to the penultimate dynode 2,430,265 Weisglass ------Nov. 4, 1947 and at the other end to said cathode, said voltage 2,576,661 Wouters ------Nov. 27, 1951 divider having a plurality of taps with equal