Патент USA US2405572код для вставки
Aug. 13, 1946. H. FRIEDMAN 2,405,572 RADIOGRAPHIC EXPOSURE METER Filed Aug. s, 1945 732 Elma/Mm HERBERT FRIEDMAN MW P'aiented Aug. 13, 1946 2,405,572 UNITED STATE S PATENT OFFICE 2,405,572 RADIOGRAPHIC EIQOSURE METER Herbert Friedman, Arlington, Va. Application August 3, 1943, Serial No. 497,271 4 Claims. (Cl. 250-835) (Granted under the act of March 3, 1883, as amended April 30, 1928; 370 0. G. 757) 1 2 This invention relates to an exposure meter for the determination of photographic exposures to penetrating radiations and particularly to a form of Geiger-Mueller tube for inclusion in a meas uring circuit to make a radiographic exposure meter. It is an object of the invention to provide a comprising capillary tubes 22 and 23 and spring member 24, respectively. Electrical connection is made to the tube by way of the hole in end cap 12 which is aligned with anode cap 25 on the tube. use‘ In general, in constructing the tube it is desirable to make it of material highly permeable to Geiger-Mueller tube for use in an exposure me the radiation which is to be measured. Inasmuch ter sensitive to all penetrating radiations harder as it is contemplated that the speci?c tube will than about 100 kilovolt X-rays. 10 ?nd its greatest application in radiography of Another object includes the provision of a metals and like materials to determine exposure form of sensitive element having a built-in times, the parts should be of material permeable to X-rays of all degrees 05 hardness commonly standard of calibration to check circuit adjust ments quickly and to eliminate the need for used in such practices, gamma rays, and alpha highly stabilized circuits. 15 particles. Since these radiations are all inher Other objects and advantages will be apparent ently very penetrating, such common materials The invention, accordingly, comprises a radia as glass or quartz for end caps I‘! and IB, alumi num, beryllium, copper, brass, or bronze for the tion intensity measuring and comparing appa tube body it, and Bakelite, or laminated cloth from the following description. 4 ratus embodying in a Geiger-Mueller tube the 20 and Bakelite, for the outer casing, ll, I2, I3, are eminently suitable. Within the tube, the anode features of construction, combination of ele 2| is preferably of a high grade wire such as ments, and arrangement of parts, which will be exempli?ed in the construction hereinafter set steel piano wire and the spacers I9 and 20 are preferably of mica. forth and the scope oi the invention will be in The gas ?lling of the tube may be any of the dicated in the claims. 25 gases ordinarily used in Geiger-Mueller tubes, In order that the invention may be fully un i. e., the inert gases, hydrogen, argon, neon, derstood, it is described in detail with reference krypton. I have found that argon in the tube at to the accompanying drawing in which, a pressure of about four centimeters of mercury Figure 1 is a sectional view of a Geiger-Mueller counter tube for use in the type of measurement 30 serves well. A mixture of argon and ethyl alco hol vapor, the partial pressure of the argon being to be made; four centimeters and that of the alcohol about Figure 2 is a diagram of a frequency measuring four millimeters of mercury, functions well as circuit which can be employed with the Geiger gas ?lling for a fast counter. Mueller tube to form an exposure meter. The construction of the tube is preferably such Referring to Figure 1, It! represents a. Geiger 13 MI that a known “active" or “counting‘ volume is Mueller tube enclosed in an insulating casing de?ned by the body I6 and spacers l9 and 20. which comprises a plurality of sections, ll, l2 This volume is preferably predetermined so that and I3, the first being a body section and the its projected area, namely, that identified as the other two end pieces. Body section II is a sub stantially cylindrical member open at one end 10 rectangle developed by taking a section through the body and the spacers and indicated by the and having an axial hole 14 in the other end. letters a, b, c, d, in Figure 1 is relatively small The open end of section II is closable by a cap and known. If the body of the tube l0 be cylin i2 having a hole therein to provide for electrical drical and the tube oriented with its longitudinal connection to parts within the case. The closed axis parallel to a given plane, e. g., the plane of end of section Ii is made engageable with an in a photographic ?lm, the area abcd remains ternally recessed cap 13, the recess l5 in cap l3 constant for all positions of rotation of the tube being made to match the hole M in the end of section II in order to permit the insertion of about its axis, or movements in the Plane of its a standard radiation source into said recess. axis. This has the distinct advantage of caus~ The Geiger-Mueller tube proper comprises a ing the active volume of the tube to intercept radiation over a constant irradiated area and radiation permeable body I6, which serves as a cathode ?tting snugly in section II, radiation makes relatively simple the scanning of a very permeable end caps I1 and I8 sealed to body It, much larger area. Other geometrical con?gura internal insulating supports l9 and 20, anode 2i, tions of the tube body can be used, but they have and anode guide and tension sustaining means the disadvantage that rotation about the longi 2,405,572 , 3 tudinal or anodic axis of the tube varies the area used to intercept radiation. In the internal recess l5 within cap l3 there current pulses through the counter tube l0 con trol the magnitude of the current ?owing in the tube 21 which is indicated by the meter 32. The is placed a radiation source in the form of a indication of the meter thus becomes a measure radioactive button enclosed in container 23. The button is made of known size and material of the intensity of the radiation to which the tube It is exposed. A variety of sensitivity ranges for the meter and acts as a constant known source of radia tion. By ‘making its container 26 of lead, provid can be obtained by providing a selection of grid resistors as shown in Figure 2. When the grid container in place in the recess to align it co 10 resistance is less than one hundred megohms the axially with the tube, the emanations from the current flow through the tube In is not appre button can be collimated and directed through ciably aifected by the external resistance and the the end of the tube proper into its active volume potential developed at the grid 28 is therefore to initiate discharges therein. In this manner, a nearly proportional to the magnitude of the ex direct comparison of the unknown radiation in 15 ternal resistance. By varying the grid resistors tercepted by the active volume of the tube (or in the range from one megohm to one hundred the area indicated by abcd in Fig. 1) with the megohms a series of sensitivity ranges can be standard source can be achieved. Knowledge of established to permit determination in a few the exposure time required to photograph prop minutes of exposure times from a few minutes to erly the emanations from the button gives a di 20 several hundred hours, the ranges commonly en rect measure of the exposure time needed to pho countered in gamma ray and X-ray radiography, tograph any portion of the area scanned. If the different resistances for the several sen The manner of using the tube in an exposure sitivity ranges merely served to alter the scale of meter can be readily understood by reference to the ampli?er circuit, it would be simpler to pro Figure 2 which is a circuit diagram of a simple 25 vide corersponding shunts for meter 29. The exposure meter employing a Geiger-Mueller tube grid resistance, however, does more than merely as a detector in, cooperation with a measuring determine the current gain of the ampli?er. A circuit. In the diagram, It! represents diagram high grid resistance gives a high sensitivity but matically a Geiger-Mueller tube corresponding to the response saturates quickly with increasing in that shown in Figure 1 which has a cathode l6 30 tensity. The lowering of the grid resistance de and an anode 2|. The Geiger-Mueller tube is creases the ampli?cation but brings about a lin ing it with a small hole 26a, and fastening the connected to an electronic amplifying circuit which includes tube 21, having a grid 28, plate 29 ear response at high intensities. When using the device as an exposure meter, and cathode 30, The tube 21 is shown as a tri the specimen which is to be photographed is in ode for the sake of simplicity but actually can be 35 terposed between a radiation source such as radi a tetrode or pentode or, like multi-grid tube um or an X-ray source and the detector tube held The cathode i5 of the Geiger-Mueller tube I0 is in the position which would be occupied by the photographic ?lm. The entire area correspond ing to the area of the ?lm can easily be scanned held at a high positive d1rect potential by con 40 in a few minutes for the sensitivity of the de nection to a potentiometer 3i which voltage tector is such that a. reading which will indicate should be from about 600-1200 volts and should an exposure time of 100 hours can be made in a be regulated well enough to keep the tube in its few minutes. range of constant operating or counting char Since certain changes may be made in the acteristics. The regulation can be readily ac above construction and different embodiments complished by means of a series of gas regulator of the invention could be made without depart tubes connected across the high voltage source in ing from the scope thereof, it is intended that all connected to the grid of the amplifying tube The anode ‘M of the Geiger-Mueller tube is conventional manner. matter contained in the above description or In the amplifying and measuring circuit com shown in the accompanying drawing shall be in prising tube 21 and meter 32, cathode 30 of the 50 terpreted as illustrative and not in a limiting tube is grounded and a positive potential is ap sense. plied to plate 29 through the meter 32. The The invention described herein may be manu ground return of the grid 28 includes any one of factured and used by or for the Government of several resistance-capacitance circuits 33, 34, 35, the United states of America for governmental 36, or 31, the particular one desired being selected 55 purposes without the payment of any royalties by means of switch 38. In order to maintain the thereon or therefor. current in tube 2'! at a minimum, or zero, when I claim: the tube in is not being activated by received 1. A Geiger-Mueller tube for comparing hard penetrating radiation, a suitable negative bias is radiation of unknown intensity with hard radia applied to the grid 28 by means of potentiometer 60 tion of a known intensity comprising, a radia 39, the positive end of which is at ground poten tion-permeable tubular member forming a cath tial. ode, an anode extending axially therethrough, In operation, when hard radiation impinges insulating disks closing the ends of said cathode on tube to and penetrates the active volume, a thereby de?ning an active tube volume, a radia pulsating current is initiated and flows in the cir 65 tion permeable envelope for said anode, cathode, cuit comprising tube ill, the high potential source and disks, and means for exposing the active and one of the resistance capacitance circuits. volume de?ned by the cathode of said tube to The capacitance in the circuit serves to average a source of constant radiation impinging on said out the irregularities in the current flow so that tube from a direction substantially coaxial with a substantially constant potential will be applied 70 the tube axis. to the grid 28 of tube 27, which potential will in 2. A Geiger-Mueller tube for measuring the turn depend upon the ?xed bias applied to the intensity of hard radiation comprising, a radia grid and the potential drop across the resistance tion-permeable tubular member forming a cath of the said resistance-capacitance circuit. In ode, said cathode having its ends closed by in this manner the frequency and intensity of the 75 sulating disks thereby de?ning a ?xed active vol 2,405,:72 ume, an anode extending axially therethrough and means for exposing said tube to a source of constant radiation impinging on said tube from a direction substantially coaxial with the tube. 3. A Geiger-Mueller tube for measuring the 5 intensity of penetrating radiation comprising, a . radiation-permeable tubular member forming a cathode, mica disks closing the ends of said cathode thereby de?ning a ?xed active counting volume, an anode wire extending axially there' through, and means comprising a recessed con tainer associated with said tube having a known quantity of radioactive material therein and a radiation-collimating aperture for directing radi ation into the tube for exposing said active vol ume to a collimated constant known source of” radiation impinging’ on said tube from a_ direc tion substantially parallel to the axis of said tube. 4. A Geiger-Mueller tube for comparing the intensity of-penetrating radiation of unknown intensity with penetrating radiation of known in tensity comprising, a radiation-permeable me tallic tubular member forming a cathode, said cathode being closed at its ends by mica disks to de?ne a ?xed active volume having a constant projected area in a plane parallel to its longi tudinal axis, an anode extending axially there-h through and means comprising radioactive ma terial in a recessed container associated with said tube for exposing said active volume to radiation collimated by the exit from said container in a direction substantially parallel to the longitudi nal axis of the tube.