US3902092A

US3902092A - Vibration resistant geiger-mueller tube

Info

Publication number: US3902092A
Application number: US460229A
Authority: US
Inventors: James Clark
Original assignee: US Air Force
Current assignee: US Air Force
Priority date: 1974-04-11
Filing date: 1974-04-11
Publication date: 1975-08-26
Anticipated expiration: 1992-08-26

Abstract

A halogen quenched, Geiger-Mueller tube having a stannic oxide coated tubular glass anode supported in delineated clearance-fit supports, with dynamic vibration absorbers, provides a multiplesupported, substantially resonate free, anode structure and an improved Geiger-Mueller tube that withstands extreme vibratory components.

Description

United States Patent Clark Aug. 26, 1975 VIBRATION RESISTANT 2,683,234 7/1954 Lynch 4. 313/93 GEIGER MUELLER TUBE 3.030539 4/l962 Dilanni H 313/93 3,048,730 8/[962 Chubb or 3l3/93 Inventor: James Clark. n g. 3.784.860 1 1974 Cocks et 21!, 313/93 Netherlands [73] A gi Th U it d St t of A i as Primary Iimrninen-Saxfield Chatmon, Jr.

represented by he Secrmary f the Attorney. Agent, or Firm-Joseph E. Rusz; Robert K Air Force, Washington. D/(, Duncan [22] Filed: Apr. 11. I974 [57] ABSTRACT [2!] App]. No: 460,229

A halogen quenched. Geiger-Mueller tube having 11 q J stunnic oxide coated tubular glass anode supported in {5;} 313/262; 313/93? 5 2 delineated clearance-fit supports, with dynamic vibra- [51] '3 H011 1H8; HOIJ lf/lz lion absorbers, provides a multiple-supported, sub [58] Fmld of Search 313/931 269; 250/374 stzmtiully resonate free anode structure and an improved Geiger-MueHer tube that withstands extreme (56] References L'ted vibratory components.

UNITED STATES PATENTS 1474.85l 7/1949 Licbsen 313/93 25 D'awmg F'gures PATENTED M1826 [9T5 SEEK l D? 9 N NN W rm

PATENTED M182 6 I975 SiIET 2 UP 9 PATENTEUAUBZB I975;

All u {IF 9 w 0 6 a P re an O o m DI PS 5 m s a m L P IVQTI B IIIIIBV 3 n z n h x. k 8 0 r 1. M 0 0 y mfi d 1 M rd a a a T z n z b IIL PATENTEDAUBZBQYS saw 7 BF 9 Fig-EU VIBRATION RESISTANT GEIGER-MUELLER TUBE RIGHTS OF THE GOVERNMENT The invention described herein may be manufactured and used by or for the Government of the United States for all governmental purposes without the payment of any royalty.

BACKGROUND OF THE INVENTION The field of the invention is in the Geiger-Mueller tube art. The prior art metal anode Geiger-Mueller tubes, when subjected to vibration, have been quite susceptable to failure from fatiguing of the metal anodes. In addition, when halogen quenching gas is used in the tubes the metal anodes are attacked and deteriorated by the halogen gas, particularly when the tubes are placed in high temperature environments.

An improvement over the metal anode tubes is obtained by using a stannic oxide coated tubular glass anode structure as disclosed by Lawrence P. Tessler in patent application Ser. No. 423,858. Typical examples of prior art radiation detector tubes, (Geiger-Mueller tubes), are demonstrated by the following U.S. Pat. Nos. and patentees: 2,48l,506, Gamertsfelder; 2,962,6l5, Anton; 2,974,247, Anton; 3,297,896, Anton; and 3,346,754, Natanagara et al.

SUMMARY OF THE INVENTION A nonresonant Geiger-Mueller tube structure is provided that will withstand and operate satisfactorily in over 20.0 g vibration environments.

BRIEF DESCRIPTION OF THE DRAWING FIG. I is a pictorial cross-section view of a typical prior art GeigenMueller tube;

FIG. 2 is a representative pictorial view of a typical prior art liquid level measuring system using a Geiger- Mueller tube detector;

FIG. 3 is a schematic cross-section view of a metal shell coated glass anode, embodiment of the invention with melt-back glass dynamic vibration absorbers;

FIG. 4 is a schematic cross-section view of a glass enclosed, coated glass anode, embodiment of the invention with tubular glass sleeve dynamic vibration absorbers;

FIG. 5 is a full section schematic view through the center of the tube represented in FIG. 4.

FIG. 6 is a schematic cross-section view of an embodiment of the invention without dynamic vibration absorbers;

FIG. 7 is a schematic view of a means of making an electrical contact with the coated tubular glass anode;

FIG. 8 is a view of a typical glass end-seal and anode support member;

FIG. 9 is a schematic view of another means for making electrical contact with a coated glass anode;

FIG. 10 is a typical vibration spectrum at a typical Geiger-Mueller tube mounting location;

FIG. lIa is a pictorial view representing schematically in cross-section, an end support of a multisupported anode;

FIG. 11b shows schematically the equivalent spring support representation of the end support shown in FIG. 11a,-

FIG. 116 is a representative force-displacement diagram of the end support shown in FIG. 11a;

FIG. 12 is a representative plot showing the points of modal pattern formations during a single vibration excitation cycle with respect to the amplitude of the excitation over the vibratory period in connection with the following four figures;

FIG. 13 is a schematic view of a representative rod member supported at the ends by a support as shown in FIG. 11a;

FIG. 14 is a representative plot showing the vibratory characteristics of the rod member of FIG. 13 when vibrating as a free-free beam during the times of the excitation vibratory cycle indicated in FIG. 12;

FIG. 15 is a representative plot showing the vibratory characteristics of the rod member of FIG. 13 when vibrating as a simply-supported beam during the times of the excitation vibratory cycle indicated in FIG. 12;

FIG. 16 is a representative plot showing the vibratory characteristics of the rod member of FIG. 13 when vibrating as a multiple-supported beam during the times of the excitation vibratory cycle indicated in FIG. 12;

FIG. 17 is a plot of the variation of the amplitude of vibration of a typical rod member of FIG. 13 plotted against the ratio of depth of end of the rod in the support over the outside diameter of the rod;

FIG. 18 is a schematic representation of a multiplesupported rod structure as shown in FIG. 13 with dynamic vibration absorbers added;

FIG. 19 is a plot of the transmissibility of forces across typical supporting structures of the prior art and structures of this invention, versus frequency at the individual maximum transmissibility frequencies of each structure;

FIG. 20 is a plot of representative transmissibility function characteristics for various degrees of damping showing the comparison of linearly supported members with members supported as disclosed herein;

FIG. 21 is a plot showing the relationships of the phase angle between force and displacement as a function of frequency for various values of damping;

FIG. 22 is a plot showing typical static deflections of an anode electrode; and

FIG. 23 is a showing of the relationships of the clearance around the anode, the supporting structure constants and the resonant frequency.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Typical current state of the art Geiger-Mueller tube construction is shown in FIG. I. A typical conventional usage of both prior art Geiger-Mueller tubes, and those of this invention, for measuring the fluid level in a container is shown in the system represented in block form FIG. 2. In many instances the container is an aircraft fuel tank. A Geiger-Mueller tube 21 is positioned and supported at the top of the tank by clamps or

brackets

22 and 23. In metal shell tubes these clamps commonly provide the electrical ground connection to the tube. In tubes having a separate ground lead, the ground lead may be connected to the tank or brought out separately, along with the anode lead, to the conventional electrical voltage source and amplifier 24. An indicator 25 is calibrated to indicate the quantity of liquid in the tank. A radioactive source 26 such as Krypton is placed at the bottom of the tank. (The radioactive source may also cover a portion of both the bottom and side walls of the container.) As is well known in the art, systems of this type will accurately give an indication of the amount of fuel in the tank substantially independent of the attitude of the plane. The conventional electronic circuits correlate the amount of radiation impinging on the Geiger-Mueller tube with the amount of fluid in the container and display the equivalent quantity of fluid on the indicator 25.

The conventional Geiger-Mueller tube construction as shown in FIG. 1 has a solid wire anode l I suspended under tension by ceramic insulators l2 and 13. The anode wire extends through the insulators and connects with the metal terminals 14, and IS. The insulators are fused or otherwise conventionally sealed to the cathode shell 16 and to the

terminals

14 and 15. The anode wire is also connected with the terminals to provide a gas tight seal. The tube is partially evacuated and contains a quenching gas as is well known in the art. Electrical contact is made to the metal shell 16 (cathode) and to the anode wire 11 at either one (or both)

terminals

14 and 15. Radiation enters the tube through the cathode shell. When the tube is positioned in a vibrating environment the anode wire 11 is very prone to fatiguing at

points

17 and 18. The relatively short life of the tube is also accelerated by the reaction of the quenching gas on the wire anode. Halogen type quenching gases are generally preferred even though they are quite destructive to the wire anode. particularly if the tube is positioned in an environment having an elevated temperature.

The preferred embodiments of this invention as shown in FIGS. 3, 4, 5, and 6 are constructed with tin oxide (SnO coated tubular glass anodes. The coating of the tin oxide on the surface of the glass tube can be done by any of the well known conventional means. One such suitable means is to heat the tube to approximately 500C and to pass SIIOCIg gas over the hot glass tube. US. Pat. Nos. 3,647,531 and 3,705,054 both to patentees Matswshita et al. disclose suitable coating methods. The SnO, coated tubular glass anodes are preferred for this invention because they are impervious to attack by the halogen quenching gas and glass being amorphous is not subject to fatigue. Pyrex (burosilicate) glass such as Corning Glass number 7740 is an example of suitable glass from which to construct the anode. One alternative, but generally not as desirable an anode, may be constructed from a capillary tube fabricated (without any coating) from glass which has a high bulk conductivity. Also anodes may be constructed by sputtering a coating of 85 percent Pt-IS percent Ir on a glass tube, however the tin oxide coating is generally preferred.

FIG. 7 shows the generally preferred way to make electrical contact to the tin oxide coated anode 71 by winding a few turns of 85 percent Pt, 15 percent Ir wire 72 around the tube and tightly twisting the one end back around the lead wire. An alternative, but more complicated way is shown in FIG. 9. In this way of making connection the tin oxide coated tube 91 has a few turns of 85 percent Pt, 15 percent Ir wire 92 wound tightly over the tin oxide and a sufficient current is passed through the turns of wire, under tension, to fuse the turns together and on cooling the wire shrinks into firm contact with the tin oxide coating and the tube. A conductive lead wire 93 also of 85 percent Pt, l percent Ir is then spot welded to the fused turns.

In the embodiments of a Geiger-Mueller tube shown in FIGS. 3, 4, 5, and 6 the

cathodes

31, 41, and 61 are relatively thin 85 percent Pt, percent Ir cylinders. In

the embodiments as represented by FIG. 3 the metal cathode forms the outside shell of the device and electrical connection is made through the supporting clamps as in the prior art devices as shown in FIG. 1. In the embodiments represented in FIGS. 4, 5, and 6 the cathode is internal the glass (preferably pyrex) envelope and an electrical wire conductor from the cathode is brought through a glass seal in the envelope.

In the embodiments of the invention represented in FIG. 3 the

glass end pieces

32 and 33 are shown in FIG. 8 as they typically appear before sealing. These end pieces are inserted in the previously described Pt-lr tube 3] and conventionally hermetically sealed thereto. The tin oxide coated tubular glass anode 34, in FIG. 3, as shown in detail in FIG. 7 (or 9) is inserted through the two end pieces as shown in detail in FIG. 8. (One piece only is shown.) The ends of the anode are melted back (as will be described in detail later) forming

masses

35 and 36. The conductor 37 is brought out through the end piece 33 as the end piece is pinched off and sealed to the conductor so as to properly position the anode in the bore 38 of the end piece. The conductor positions the anode longitudinally in the tube while permitting free movement, radially, of the anode in the bore of the end piece. The right end piece 32, before sealing, is connected to a conventional vacuum and fill system, and the tube is filled in the conventional manner with a mixture of a conventional inert gas and a halogen quenching gas. Typical conventional gas mixtures are Neon, Argon, and either bromine or chlorine. Bromine has been found to be generally preferred to chlorine. After conventionally filling the tube with the gas the right end piece 32 is pinched off in the conventional manner to provide a gas tight seal. Conventional Soda Glass (such as Kimble type R-6) is suitable material from which to fabricate the

end pieces

32 and 33 of FIG. 3 and the

anode supporting members

42, 43, and 62, 63 of the glass envelope embodiments shown in FIGS. 4, 5, and 6.

In typical embodiments of the devices described the tin coated tubular glass anodes have lengths of approximately four and a half to 6 inches, outside diameters of approximately 0.032 inch and tube wall thicknesses of approximately 0.005 inch, specific details will be supplied later. The cathodes and all conductor wires are composed of approximately percent Pt, 15 percent Ir material. A suitable wire diameter for all electrical leads and the contacting wire to the anodes is 0.005 inch wire. Typical diameters of the tubular cathodes are approximately one-fourth inch. The wall thickness of the tubular cathodes in glass envelope embodiments is typically 0.005 inch. The wall thickness in the metal shell, external cathode embodiments as shown in FIG. 3 may be made slightly thicker for mechanical strength in handling. However, since the radiation reaching the inside of the tube must penetrate the shell and the sensitivity of the tube is inversely related to the cathode wall thickness, it is desirable that the wall thickness be the minimum to provide the necessary physical strength required. For most applications 0.005 inch is suitable. Typical active cathode lengths are approximately 4 inches.

One of the primary elements of this invention is the novel suspension of a rod member for use in a vibratile environment. The incorporation of this novel suspension in a Geiger-Mueller tube is an example of a spe cific embodiment of the invention cooperating in combination with other elements, some old and well known, to provide an improved vibration resistant Geiger-Mueller tube.

FIG. is a plot of a specific, typical, measured, vibration spectrum at the bracket supporting a Geiger- Mueller tube in an air-craft fuel tank. While this plot is typical of the maximum orders of vibratory forces generally encountered it is to be understood that these orders are not constant in either amplitude or frequency but change with the types of engines, engine speed, the percent of rated thrust developed, the location of the fuel tank, and the structure of the fuel tank. From this data it is apparent that to position the first mode resonant frequency of the anodes of conventional tube structures either above or below the frequencies of engine excitation orders would be exceedingly difficult. The resonant frequency of the anode in the conventional tube may generally be expressed by:

f= 20.2 V ElT/pL where:

f= resonant frequency E Modulus of Elasticity of the anode l Moment of inertia of the anode T Tension in the anode p Density of the anode L Unsupported length of the anode It has been discovered that by using a tubular glass tube electrode (anode) having linear mass and stiffness distribution which is loosely supported at the ends in a cavity, as shown in FIG. 11a, in which the inside diameter of the cavity d is greater than the outside diameter d of the glass tube a greatly improved structure is obtained. The dimension, a, as shown in FIG. 11a is the radial clearance between the outside of the glass tube electrode and the inside of the support structure. This support may be represented schematically as shown in FIG. 11b, with the equivalent force displacement diagram as shown in FIG. 110. An examination of these diagrams indicates that there is no restraint to the electrodes vibratory motion while it moves through the distance, a. In FIG. 110 it is seen the center electrode is loosely supported in the end insulator with a clearance a, between the outside diameter of the glass tube and the inside diameter of the center hole in the insulator. The equivalent spring support of the center electrode is shown in FIG. 11b in which the relationship of the electrode clearance, a, and the deflection, X of the insulator and its support are shown. The characteristics of the resultant force displacement diagram are shown in FIG. 11c. An examination of this diagram indicates there is no restraint to the electrodes vibratory motion while it moves through the distance, 0. (During this part of the vibratory cycle, the electrode tends to vibrate as a freefree beam without any support.) As soon as the outer surface of the electrode touches the inside surface of the insulator, it is subjected to a very high support stiffness with a consequently very small displacement, X This gives a very high nonlinearity to the electrode vibratory system. The resonant frequency of first mode bending of the electrode is given by the following equation:

where:

(0,, Frequency of non-linear system rad/sec.

k Spring rate of insulator and outer shell lbs/in.

m Mass of electrode lbs/g a Clearance between electrode and support in.

X Total displacement of end of electrode in.

X,, Displacement of end of electrode due to stiffness of insulator and outer shell in. The foregoing equations may be used to plot the curve shown in FIG. 23. In FIG. 23 is is seen the greatest reduction in resonant fequency occurs when the clearance, a, shown in FIG. 11a, approaches the total vibratory amplitude, X of the end of the center electrode. By using the following equation the vibratory amplitude, X of the Geiger-Mueller tube anode may be obtained for various frequencies and acceleration levels:

where:

X,- Vibratory amplitude of Geiger-Mueller tube anode in.

g Acceleration level gs f Frequency of vibration Hz If the clearance, a, shown in FIG. 11a is made equal to X /2 at the lowest excitation frequency, the center electrode will essentially remain stationary in space, with very low vibratory stresses, while the envelope of the tube vibrates about it. Or looking at the anode from the tube envelopes viewpoint the anode bounces" in the mounting holes of the supports. It has been found that in some instances in order to decrease the stress in the electrical conductor lead connecting with the anode, while the anode is bouncing in its support, the clearance, a, may be made slightly smaller than X /2 without increasing a serious amount the vibratory stresses that occur in the anode under the worst vibratory conditions. Considering typical vibratory environments, a rough approximation of the radial clearance around the anode in the bore of the support has been found to be approximately 3 percent of the outside diameter of the anode, e.g., a 0.033 outside diameter anode in a 0.035 bore hole.

Considering a complete vibratory cycle as shown in FIG. 12 acting on the beam 131, (such as a glass tube anode of a Geiger-Mueller tube), loosely supported by supporting

members

132 and 133 as shown in FIG. 13, the glass tube 131 tends to rattle during part of the vibration cycle. During that portion of the vibration cycle when the glass tube does not touch the inside surface of the end supports, the glass tube vibrates as a freefree beam as shown schematically in FIG. 14. Once the glass tube touches the inside of the support structures, it vibrates as a simply supported beam as shown schematically in FIG. 15. When the beam vibrates as a simply supported beam it is supported by reactions R as shown in FIGS. 13 and 15. When the beam further deflects during its vibration cycle, the end of the beam touches the inside of the support structure and reactions R come into action as shown in FIGS. 13 and 16. When this occurs reactions R and R generate a couple in the end of the beam which tend to reduce the bending moment in the beam at R due to its unsupported length between the supports points. This small couple generated by R and R tends to cancel out some of the bending moments transmitted from the insupported beam to these supports, thereby changing the shape of the resultant modal vibration pattern of the beam as shown in FIG. 16. The frequency equations for the first mode bending of each one of these modal patterns is shown in FIGS. 14, 15, and 16. In each of these equations it is seen there is an appreciable change in the resonant frequency of the beam depending on the way in which it is supported. The value a, in these equations is the mass per unit length of the beam. The important point to note here is that during each vibration cycle to which the glass tube electrode and its supports are subjected, they rapidly change from one vibration pattern to another in such a manner that it is impossible for the glass tube electrode to develop any consistent vibration pattern and, therefore, any resonant frequency. The sequence of these modal pattern formations during a single vibration excitation cycle is shown in FIG. 12. In this figure it is seen that during a single excitation cycle the modal pattern of the glass tube electrode changes nine times. As each one of these patterns change the electrode tends to start to vibrate at a different resonant frequency as shown by the frequency equations discussed above. Therefore, it is impossible for the glass tube electrode to develop a consistent resonant vibration condition. The variable end restraints of the electrode during a vibration cycle may be considered to have nonlinear support reactions since it is constantly changing throughout the excitation cycle. The changing end restraint of the glass tube electrode from FIGS. 15 to 16 was demonstrated in the laboratory by mounting a typical anode electrode and its support structure in a vibration jig and loading the center of the beam with small weights and observing the deflection of the electrode with the microscope and calibrated eyepiece. This particular electrode and support had the following parameters:

Outside diameter of electrode d 0.032 inch Inside diameter of electrode d 0.0l55 inch Diameter of electrode mounting hole d, 0.033 inch Depth of electrode in mounting hole I 0.128 inch Free length of electrode =1 4.00 inches The resultant load-deflection curve for such a beam is shown in FIG. 22. This curve indicates that the loaddeflection curve for the beam on simple supports has a slope which is entirely different from that of the beam when the outer ends of the electrode contact the inside of the support bringing reactions R into play. From these static tests it is evident the end supports and resultant modal pattern change each time the center of the electrode has an amplitude of 0.008 inch. The point at which this support transition occurs from a simplysupported beam to a multiple-supported beam is controlled by the clearance, a, between the outside diameter of the electrode and the inside diameter of the support hole as shown in FIG. 13. The time or vibration phase angle between the simply supported beam and the multiple-supported beam is shown in FIGS. and 16. This may be controlled by varying the length of the end of the beam in the support as shown in FIG. 13. Thus, by varying the ratio of l,/d,,, the vibration amplitude of the electrode may be controlled over a certain range as shown in FIG. 17. In this figure it is seen that for the previously enumerated electrode having an outside diameter of0.032 inch and a ratio of depth of electrode mounting hole to the outside diameter of 4.0 gave a minimum vibration amplitude of 0.030 inch at 5 gs acceleration. A completed embodiment of the invention in a Geiger-Mueller tube having loosefit anode supports is shown in FIG. 6.

As a further explanation of the action of this nonlinear electrode supports reference is made to FIG. 21. This well known plot of the phase angle, d), the angle between the vibratory excitation force and the vibratory displacement for various values of damping plotted against the forced vibration frequency to over the undamped natural frequency w shows that the vibratory excitation force and the electrode vibration displacement must be if resonance is to occur, that is, when the forced vibration frequency and the natural frequency are the same. If there is a slight variation in this phase angle, above or below 90, there is a large change in vibration amplitude, especially for the low damping in the electrode structure as taught herein. The effect of slight variations in the phase angle, (1), is also indicated indirectly as a large reduction in the transmissibility of the system as shown when FIG. 20 is viewed along with FIG. 21. (Transmissibility (transmitted force/impressed force). By the electrode being forced to try to vibrate at different frequencies during separate parts of the excitation cycle as shown in FIG. 12, the resulting phase angle changes provide large reductions in the systems transmissibility. Since a multisupported beam (the anode electrode) cannot make a complete vibration cycle at any one of the different resonant frequencies, its resultant amplitude of motion when excited by the complete vibratory spectrum (FIG. 10) is very low (as represented by bar graph 191 in FIG. 19).

In addition to varying the modal shape or vibration patterns of the glass electrodes for different types of end support conditions as shown in FIG. 13, it was also found the vibration response of this glass tube electrode assembly could be further reduced by employing the principles of dynamic vibration absorbers, or the employment of secondary vibrating masses so connected to the vibrating body that these secondary vibrating masses would feed a moment back into the ends of the glass tube electrode in such a manner as to reduce the vibration emplitude of the electrode. The use of these dynamic absorbers is shown schematically in FIG. 18 in which

small weights

181 and 182 are attached to the end of the glass tube electrode projecting through the mounting reaction points R, and R The location and magnitude of these weights on each end of the glass tube electrode can be varied in such a manner that they practically cancel out vibration response of the glass tube electrode. When conducting vibration tests with the structure as shown schematically in FIG. 18 is was found that the tube support at each end of the electrode could be moved slightly so that the reflected moment from the weight and overhanging end of the glass tube electrode would exactly cancel the moment generated by the unsupported length of the electrode. Thus, it was found that by combining these various techniques described above a structure could be fabricatcd to eliminate any vibration resonant conditions in a glass tube electrode in a Geiger-Mueller tube when it was subjected to the engine forcing function shown in FIG. I0. Examples of Geiger-Mueller tubes having embodiments of the invention including dynamic vibration absorbers fabricated in the anode structures are shown in FIGS. 3 and 4.

The techniques of undamped dynamic vibration absorbers, particularly in simple systems, in which the natural frequency V k/m (the square root of the stiffness of attachment over the mass) of the attached absorber is chosen to be equal to the fequency w of the disturbing force such that the main mass to which the absorber is attached does not vibrate at all, are not new. (See text Mechanical Vibrations, by J. P. Den Hartog, fourth edition, published by McGraw-Hill Book Co., pages 87 through 93.) FIG. 18 shows schematically the combining of dynamic

vibration absorber masses

181 and 182 with the previously described nonlinear electrode supports. In embodiments of Geiger- Mueller tubes these weights (masses) may be formed at the ends of the anode electrode by melting back the ends of the glass electrode as shown 35 and 36, in FIG. 3, or the weights may be short sections of glass tubing fused to the ends of the electrode as shown, 44 and 45 in FIG. 4. In vibratory environments, such as shown in FIG. 10, embodiments constructed as represented by FIGS. 3 and 4 exhibit a pseudo-resonant frequency shown as a peak 201 in the dotted line of FIG. 20. It is to be noted that even at this pseudoresonant peak that the transmissibility to the electrode is less than L0. This illustrates the effectiveness of combining the nonlinear characteristics of the disclosed electrode supports with the characteristics of dynamic vibration absorbers. When the disclosed devices are operating above the pseudo-resonant frequency shown as the peak 201 in FIG. 20, the electrode is completely free of its supports from a vibration viewpoint, and essentially floats free in space without any sinusoidal vibratory forces being imparted to it. This is never true of conventionally supported electrodes, which possess *spring" characteristics in their support suspensions, irrespective of how well damped the systems are, as shown by the solid curves of FIG. 20.

The peak transmissibility 201 of FIG. occurs when the amplitude of the vibration excitation is substantially exactly the same as twice the clearance, a, (FIG. 18) between the outer diameter of the electrode and the diameter of its mounting hole. At this particular frequency and amplitude, the electrode bounces" in its mounting hole. At frequencies above this point as shown by the dotted line 202 of FIG. 20 the amplitude of vibration is less than this clearance, a, which results in the electrode floating in its mounting with substantially zero transmissibility. At this pseudo-resonant point, with the proper length, l between the support points, R,, (FIG. 18) a vibration node occurs, at these points, between the dynamic vibration absorbers and the mass and effective stiffness of the electrode support. This effectively removes that portion of the electrode between supports, R,, from this coupled vibratory system and results in aa transmissibility of less than l.0 of this pseudo-resonant point.

At these modal points located at, R as described above, there is a balance of vibratory energy, in both amplitude and phase, between the parts of this coupled vibratory system. The weights of the masses of the dynamic vibration absorbers may be calculated using the conventional Holzers method for flexural critical speeds as described in the foregoing referenced text, Mechanical Vibrations" by Den Hartog, on pages 229 through 23l. The mathematics may be difficult, thus a generally sufficiently close (but not technically correct) approximation may be arrived at by assuming the bending moments about R to be zero. The primary reason that this is not technically correct is due to the fact that the weights of the dynamic vibration absorbers and the portions of the electrode supporting them both have distributed mass and stiffness. In practice it may be easier to arrive at the approximately correct value as indicated and then slightly adjust the distant, 1 between the supports R until a minimum value of transmissibility is reached. On an individual basis for a first piece of a particular design this may be determined by moving one, or both, of the

end support members

32 and 33 of FIG. 3 or the

supports members

42 and 43 of FIG. 4 slightly in the cathode 31 of FIG. 3 while observing its vibratory characteristics with the unit on a vibration table before sealing the end pieces to the cathode. In a similar manner the

supports

42 and 43 of the embodiments as represented by FIG. 4 may be adjusted before sealing the ends of the glass envelope 46. In these embodiments (FIG. 4) generally the supports are a relatively tight fit in the glass envelope and when the ends are sealed the envelope is drawn down so as to position the supports firmly in place.

It is preferred to construct the devices as taught herein such that the pseudo-resonant frequency point as illustrated at 201 in FIG. 20 occurs at a lower frequency than that of the first major low frequency excitation frequency of the environment, such as the frequency of peak 101 of FIG. 10.

As a typical example, an operating embodiment of the invention, having anode structures as shown schematically in FIG. 18, had the following parameters in addition to those previously indicated:

Weight (mass) of coated tubular glass rod Using the approximate method of determining the weight of the dynamic vibration absorbers, as previously outlined it is to be noted, in considering the moments about point R at either end of the structure, that the effective arm" length of the unsupported center portion of the anode 183 is approximately l0. 16/2) X 1/2) 2.5 cm, providing a couple about R of approximately 0. l2 gr-cm, and that the couple of the dynamic vibration absorber mass about its effective arm length is approximately 0.08 X O.l55 O.l2 gr-cm.

A comparison of the effectiveness of the structures as taught herein with those of the prior art under sinusoidal vibratory excitation is shown in FIG. 19. The data was taken from embodiments of the invention having the previously stated parameters of tubular glass anodes of approximately 0.032 inch outside diameters and unsupported lengths of approximately 4.0 inches. The figure is a plot of the transmissibility versus the resonant frequency of the anode electrodes of devices of this invention and those of the prior art. There are two curves 192 and 193 encompassing two sets of data in this figure. The first set of data, curve 192 shown in the upper right-hand portion of the figure represents the vibration characteristics of prior art devices having linear beams on linear supports. The upper point 194 of curve 192 represents the transmissibility of a conventional type H2 Geiger-Mueller tube. It is seen that it had a transmissibility of 4,600 at an electrode resonant frequency of 825 Hz. The remaining test points shown on these two curves were obtained with a glass electrode having an outside diameter of 0.032 inch with various types of end supports. The data represented by graph 195 is from a glass electrode beam fixed at both ends. It is seen that this configuration gave a transmissibility of 490 at a resonant frequency of 610 Hz. The data represented by graph 196 consisted of mounting the glass tube electrode assembly as a beam with pin joint ends. This electrode support arrangement gave a transmissibility of 66 at a resonant frequency of l90I-Iz. It is interesting to note that for linear beams on linear supports both the transmissibility and resonant frequency increased as the fixation of the end of the beam increased, i,e., as the end of the beam is made more rigid whereby it can transmit a bending moment to its end supports.

A series of linear beams on nonlinear supports, operating under identical conditions, except the glass tube electrodes were supported in types of end mounts as taught herein are shown by bar graphs I91, 197, and 198 and represented by curve 193. Bar graph 191 is data taken from an embodiment represented schematically in FIG. 13 and in a complete Geiger-Mueller tube in FIG. 6. It had a transmissibility of 15.6 and a resonant frequency of 353 Hz. Embodiments having dynamic vibration absorbers, as shown schematically in FIG. 18 and pictorially in FIGS. 3 and 4, produced the results shown by bar graph 197. The magnitude of the weights were the approximate calculated values. This device had a transmissibility of 1.56 at a resonant frequency of 170 Hz. The length 1,, (FIG. 18) was then adjusted by slightly shifting one of the anode electrode supports in small increments until the minimum transmissibility of 0.96 at a frequency (pseudo-resonance) of 130 Hz was obtained as shown by bar graph 198. For tubes constructed using these particular materials, having these particular constants, this determined the optimum anode length, 1,, between supports. (It is to be noted that this is below all the major excitation frequencies shown in FIG. 10, the environment for which this particular embodiment of the invention was constructed.) All of the vibration characteristics shown in FIG. 19 were run at an acceleration level of 5.0 gs except for that of the conventional type I-I-2 Geiger- Mueller tube as shown in FIG. 1 whose vibrating anode electrode started touching of the sides of the insulating sleeves at

points

17 and 18 with imminent impending failure at an acceleration level of 0.2 g.

Embodiments of this invention having dynamic vibration absorbers on hollow glass tube anodes of 0.033 inches outside diameter, 0.0l inches inside diameter, an unsupported length of approximately 4 inches, and a 0.001 inch clearance between the outside diameter of the anode and the supporting members, have been constructed that have had a transmissibility as low as 0.79 which is much less than the minimum of 1.28 obtainable with prior systems using linear supports and having critical damping. Fatigue tests were conducted on this electrode assembly as represented by FIG. 18 by exciting it with an acceleration level of 5.0 g's at this resonant condition. This electrode assembly was subjected to this sinusoidal excitation for a period of L0 X cycles. During this fatigue test, a tin oxide coated anode electrode was used and connected in a bridge circuit. Platinum-lrridium leads were manually twisted around this electrode, while viewed under a microscope, until the various turns of the wire were tightly bound against the tin oxide coating on the tube as shown in FIG. 7. This electric connection proved adequate throughout the long series of fatigue tests in that there was no unbalance detected in the electric bridge circuit during these tests. As a final fatigue test, the electrode assembly was subjected to an acceleration level of 20 gs at its resonant frequency for 1.0 X 10 cycles. Only during the last portion of this 20 g level test was there any evidence of a slight open curcuit in the bridge test circuit. At this elevated 3 level the glass tube still did not fail or was there any detectable deterioration of the tube, its coating, or its mounts.

After the sinusoidal fatigue tests at an elevated acceleration level of 20 gs, the electrode assembly was subjected to a series of random vibration tests. An examination of FIG. 10 indicates the maximum random vibration level is approximately 0.100 g /Hz. A power spectral density test spectrum was set up from data ob tained from the random vibration data in FIG. 10. The electrode assembly shown schematically in FIG. 18 was tested at power spectral density levels of 0.025, 0.050, 0.075, 0.100, 0.300 and 0.500, although a random vibration test at a power spectral density of 0.500 glI-Iz is a very severe test, there was no indication of any failure or deterioration of the electrode assembly and its mounts, or of its electrical transmission characteristics in the bridge circuit.

I claim:

1. The improvement in a Geiger-Mueller tube having an electrically conductive tubular glass anode of determined length and outside diameter, an electrically conductive, radiation permeable thin cylindrical shell cathode, a gaseous mixture including a halogen gas contained between the said anode and cathode, and means for making electrical connections to the said anode and to the said cathode, the said improvement comprising:

a. a first and a second anode support member each having a bore of determined diameter larger than the said outside diameter of the said anode and each having a determined length of bore greater than the said outside diameter of the said anode; and

b. means cooperating with the said support members for loosely positioning the said anode in the said first and second support members providing axial confinement of the said anode in the said support members with substantially free radial movement of the said anode throughout the length of the said support members.

2. The improvement as claimed in claim 1 wherein the said bore has a radius approximately 3 percent greater than the said outside diameter of the tubular anode and the said length of the bore is approximately 4 times the said outside diameter of the said anode.

3. The improvement in a Geiger-Mueller tube having a tubular tin oxide coated glass anode of determined length and outside diameter, concentrically located in an electrically conductive, radiation permeable, thin cylindrical shell cathode, a gaseous mixture including a halogen gas contained between the said anode and cathode, and means for making electrical connections to the said anode and to the said cathode, the said improvement comprising:

a. a first and a second anode support member each having a bore of determined diameter larger than the said outside diameter of the said anode and each having a determined length of bore greater than the said outside diameter of the said anode;

b. a dynamic vibration absorber weight positioned at each end of the said anode; and

c. means cooperating with the said support members for loosely positioning the said anode in the bores of the said support members providing axial positioning of the said anode in the said support members and providing substantially free radial movement of the said anode throughout the length of the said support members.

4. The improvement as claimed in claim 3 wherein the said bore diameter is approximately 6 percent greater than the said outside diameter of the said anode, and the length of the said bore is approximately four times the said outside diameter of the said anode.

5. The improvement in a radiation detector Geiger- Mueller tube having a tubular, conductively coated, glass anode of determined length and outside diameter; an electrically conductive, radiation permeable thin cylindrical shell cathode; a gaseous mixture, including a halogen gas, contained between the said anode and cathode; and means for making electrical connections to the said anode and cathode; the said improvement providing a vibration resistant Geiger-Mueller tube for operation in a vibration environment having a known acceleration 3 force on the anode at a known anode resonant frequency, f, the said improvement comprismg:

a. a first and a second anode support member each having a bore diameter that is larger than the said outside diameter of the said anode by an amount approximately equal to the amount expressed by dividing the said g force by the product of 0.05! l times the square of said frequency f, and a magnitude of bore length of approximately 4 times the magnitude of the said outside diameter of the said anode;

b. means for positioning the bores of the said support members around the said tubular anode providing an inner edge of the bore of the said first support member, an inner edge of the bore of the said second support member and an unsupported length of the said anode between the said inner edges;

c. a dynamic vibration absorber weight positioned by each end of the said tubular anode; and

means for positioning the said tubular anode in the said bores of the said support members making the bending moments of the said dynamic vibration absorber weights about the said inner edges of the bores of the said support members approximately equal to the bending moments of the unsupported length of the said anode about the said inner edges of the bores of the said support members.

Claims

1. The improvement in a Geiger-Mueller tube having an electrically conductive tubular glass anode of determined length and outside diameter, an electrically conductive, radiation permeable thin cylindrical shell cathode, a gaseous mixture including a halogen gas contained between the said anode and cathode, and means for making electrical connections to the said anode and to the said cathode, the said improvement comprising: a. a first and a second anode support member each having a bore of determined diameter larger than the said outside diameter of the said anode and each having a determined length of bore greater than the said outside diameter of the said anode; and b. means cooperating with the said support members for loosely positioning the said anode in the said first and second support members providing axial confinement of the said anode in the said support members with substantially free radial movement of the said anode throughout the length of the said support members.

3. The improvement in a Geiger-Mueller tube having a tubular tin oxide coated glass anode of determined length and outside diameter, concentrically located in an electrically conductive, radiation permeable, thin cylindrical shell cathode, a gaseous mixture including a halogen gas contained between the said anode and cathode, and means for making electrical connections to the said anode and to the said cathode, the said improvement comprising: a. a first and a second anode support member each having a bore of determined diameter larger than the said outside diameter of the said anode and each having a determined length of bore greater than the said outside diameter of the said anode; b. a dynamic vibration absorber weight positioned at each end of the said anode; and c. means cooperatinG with the said support members for loosely positioning the said anode in the bores of the said support members providing axial positioning of the said anode in the said support members and providing substantially free radial movement of the said anode throughout the length of the said support members.

5. The improvement in a radiation detector Geiger-Mueller tube having a tubular, conductively coated, glass anode of determined length and outside diameter; an electrically conductive, radiation permeable thin cylindrical shell cathode; a gaseous mixture, including a halogen gas, contained between the said anode and cathode; and means for making electrical connections to the said anode and cathode; the said improvement providing a vibration resistant Geiger-Mueller tube for operation in a vibration environment having a known acceleration g force on the anode at a known anode resonant frequency, f, the said improvement comprising: a. a first and a second anode support member each having a bore diameter that is larger than the said outside diameter of the said anode by an amount approximately equal to the amount expressed by dividing the said g force by the product of 0.0511 times the square of said frequency f, and a magnitude of bore length of approximately 4 times the magnitude of the said outside diameter of the said anode; b. means for positioning the bores of the said support members around the said tubular anode providing an inner edge of the bore of the said first support member, an inner edge of the bore of the said second support member and an unsupported length of the said anode between the said inner edges; c. a dynamic vibration absorber weight positioned by each end of the said tubular anode; and d. means for positioning the said tubular anode in the said bores of the said support members making the bending moments of the said dynamic vibration absorber weights about the said inner edges of the bores of the said support members approximately equal to the bending moments of the unsupported length of the said anode about the said inner edges of the bores of the said support members.