1958 Anton and Youdin: New Aspects of Nuclear Instrumentation 51

increasingly important rule in this march towards theCONCLUSION automatic plant. There is no foreseeable technical limit to

During the past ten years, the investment in process- the industrial measurement and control problems that cancontrol instruments in the chemical industry has risen be solved with the combination of electronics and otherfrom less than 2 per cent to 7 to 10 per cent of total plant techniques of applied physics. The primary factor regulat-investment. This trend will continue as long as plant ing the growth of electronics in industry is reliability. Withinvestment and operating costs can be reduced by using the advent of transistors, greatly improved reliabilitysmaller process equipment operating at higher speeds appears possible in the immediate future. The opportunitiesthat are in turn made possible by faster and more accurate and rewards to the electronic engineer in development,control. Electronic instruments, through their speed of design, and application within the chemical industry areresponse and almost unlimited sensitivity, are playing an surprisingly large and will grow at an accelerated rate.

Some New Aspects of Nuclear Instrumentationin Industrial Electronics*

N. ANTONt AND M. YOUDINt

T is often said that there is nothing new under the cost savings from radioisotopes now lie betweensun and, in a way, we are inclined to agree. However, $295,000,000 and $485,000,000 per year. Dr. Willard F.we must at the same time bear in mind that what is Libby, a member of the Atomic Energy Commission,

new to one person may be somewhat "old hat" to someone predicts that within a few years industrial savings fromelse. The term "new" applies equally to something that the use of radioisotopes will rise to $1,000,000,000 annually.has never been known until recently or to that which The application of isotopes to industrial use has alwaysonly recently has been made or manufactured. The been overshadowed by the explosive atom or the politicalengineer who has spent a few years of his life trying to dispute over how best to harness atomic power. By thebring to completion a prototype equipment whose principle end of last year, some 3663 organizations in this countrywas conceived in the laboratory some forgotten number had been licensed by the Government to possess and useof years back is perfectly aware of the several connotations radioisotopes. Of these, 1493 were industrial organizations.which are associated with the term "new." The petroleum industry to date has been the biggestWe deliberately have chosen to introduce this paper industrial benefactor of the radioisotope with savings

with these remarks because we are going to try to concern ranging from $140,000,000 to $215,000,000 annually.ourselves with nuclear instrumentation techniques in When one stops to think about it, it is very easy andindustry, which are new in the sense that they have stimulating to speculate about the applications of nuclearbecome feasible and possible as a result of recent circuit instrumentation to industrial electronics, because most ofor component development. They are not new from a these applications can be formulated in terms of threeconcept point of view. Everything which has the label elementary "black boxes." The first "black box" consists"nuclear" has received such a spectacular treatment of a radioactive source, which emits some form of wavefrom the press that it would be difficult indeed to find an or corpuscular radiation; the second "black box" is aapplication which some physicist has not already envi- detector for these radiations; and the third "black box"sioned and described in a speculative manner. * is a computer, which will resolve the data coming fromThe Atomic Energy Commission recently made a spot the detector. Using the three black boxes it is not difficult

check of the cost saving resulting from the use of radio- to illustrate how radioactive isotopes can be applied toisotopes in industry. This check indicated that industrial almost every phase of our daily existence.

The contributions which nuclear science will bring to* Presented at the Annual Conference on Electronics in Industry, industrial electronics wvill augment the prior art, rather

Chicago, Ill., April 9-10, 1957. than revolutionize it as in the field of power. The questiont President and Vice-President, respectively, Anton Electric

Labs., Inc., a subsidiary of United States Hoffman Machinery now very often asked by many electronics people is:Corp., Brooklyn, N.Y.. "Do we all have to become physicists?" The answer is,

52 IRE TRANSACTIONS ON INDUSTRIAL ELECTRONICS April

"No." The industrial applications engineer can learn all Neutrons, therefore, are very useful for gauging plasticthat he has to know to apply this new tool in the same laminates containing reinforcing glass fibres, because oflength of time that he requires to study the details of any the selective absorption characteristics of the boronservosystem or complex electronic control. Remember glasses. Neutrons are utilized also in the detection andthat the third black box; i.e., the computer, is not a new analysis of hydrogeneous materials.device. It usually consists of either a pulse counter or a The most common type of neutron source is the Ra-a-Below-current integrator, together with the necessary source. This type of source can be produced by slurryingamplifiers, power supplies, and controls which are utilized finely ground berylium powder in an aqueous solution ofin conventional monitoring and control equipment. Let radium bromide, evaporating to dryness, and compressingus now examine the first two of these black boxes in the residue into a pellet. The pellet is then sealed in agreater detail and stress those points which are of special gas-tight container to confine the radon decay products.importance to the industrial electronics engineer. Before a radioactive source can be chosen for a given

application, it is necessary to give consideration to theTHE FIRST BLACK BOX following basic parameters. The order in which they are

The first black box will usually consist of a radioactive presented here is not necessarily the order in which they aresource which will be capable of emitting alpha, beta, and best considered for any given application, because of theirgamma radiation either singly or in combination. For mutual interdependence.some gauging applications, which will be discussed laterin this paper, a neutron-emitting radioactive source may Strengthbe necessary. The nature of each of these radiations can The optimum strength of source which should be usedbe described briefly as follows. for any given installation depends primarily on the requiredAlpha particles, which are positively charged helium accuracy of the result, the half-life of the source, the

nuclei, have ranges up to several centimeters in air. A energy of the radiation source, the geometry of the setup,common pure alpha emitter is polonium (also called the efficiency of the detector, and the type of instrumenta-radium F). Alpha particles are heavy and, when shot at tion which will be utilized.solid matter, have practically no penetrating ability. Each nuclear disintegration of the source is a completelyThey are used chiefly where surface phenomena, such as random and independent process. Such a random processstatic electricity, are involved. will obey the laws of statistics (in this case the Poisson

Beta particles, which are electrons, may travel through distribution), which predict that even though there is aseveral meters of air. Common beta emitters are carbon 14, definite average rate of disintegration the number actuallystrontium 90, radium D + E, and technetium 99. These counted in a given time will show deviations from thisare all pure beta emitters which have appreciable half- average. As a result of this randomness alone, the mostlives. Beta particles can pass through as much as 4 inch probable error in any given reading will be equal toof plastic, 6 inch of aluminum, or 3 inch of steel and 0.67 X the square root of the total number of particlestherefore are useful for gauging operations of light ma- counted. Of course, to this must be added the effects ofterials. dead time in the case of counter tube, the resolving timeGamma rays (and X rays) are electromagnetic in nature of the computer, and the effect of the decay in activity of

and are energetic enough to pass through many inches of the source itself, which is discussed later.steel-hence their usefulness for gauging heavy materials The energy of the radiation source determines ultimatelyor thick sections of light ones. Some of the gamma emitters the ability of the particles or waves to penetrate matter.which are most commonly used for industrial applications Unfortunately, most sources are not "monochromatic."are radium, cobalt 60, and cesium 134. When gamma rays For example, beta particles given off from radioactivepass through matter, a portion of the rays are scattered nuclei show a continuous energy distribution from sub-backward, making possible a thickness gauge which stantially zero to a very definite maximum. Thus, only aneeds access to only one side of the material to be gauged, specific fraction of the available beta particles are of useas compared with a standard absorption type of thickness to us in any given application. The geometry of thegauge, which requires the source to be on one side and system (often given as a percentage) is the fraction of thethe detector to be on the opposite side of the material total solid angle about the source which is subtended byto be gauged. the sensitive volume or window of the detector. TheThe neutron is an elementary uncharged particle only efficiency of the detector itself, which is also stated in a

slightly heavier than the proton. Its lack of charge gives it percentage, is the ratio of the number of rays or particlesa very small interaction with electrons. It differs in this detected to the number incident.way from charged particles and from gamma photons.Interaction with nuclei is the only important flux-reducing Constancymechanism for neutrons passing through matter. Except If the application requires a quantitative result, thewhere the neutron-nuclear interaction is particularly source should, in general, havre as long a half-life as possible.great, matter is relatively transparent to neutrons. Half-life (sometimes called the period) of a source is the

195-8 Anton and Youdin: New Aspects of Nuclear Instrumentation 53

length of time in which one-half of the atoms in the source economic solution of the given problem. For example,will disintegrate. Of the common gamma sources, radium in the case of a liquid-level indicator or an oil-flow monitor,has the longest half-life ... 1620 years. Cobalt 60 has a the detector need only indicate the presence of radiation.half-life of only 5.3 years but is considerably less expensive In a thickness gauge, however, the presence of radiationthan radium. However, the initial cost of the source is not enough, since the quantity of radiation is a measureshould not be the only determining factor in making a of the parameter which is being monitored; namely,choice. The longer lasting radium may often obviate the thickness.need for providing an external calibration system and Detectors may take the form of a Geiger counter tube,will certainly eliminate the continuous need to compute an ionization chamber, a scintillation crystal-photomulti-the remaining radioactive output. The expense of replacing plier combination-and others too numerous to mention.cobalt 60 after it has decayed below the useful level must Great advances have been made of late in the developmentalso be considered. and production of rugged, dependable, and reproducibleCost detectors. Counter tubes for alpha, beta, and gamma

radiations which can operate at temperatures up toThis item has already been considered under "Con- 1750C and which can withstand the most severe environ-

stancy." The important point to be emphasized is that the mental conditions and mechanical abuse now are readilytotal cost of the source "black box" should take into available. These tubes are electrically stable, have longaccount not only the initial cost of the radioactive source, shelf and active life, and are as interchangeable electricallybut also the additional costs which will be incurred in the as any good receiving and power tubes. Since the counterproduction and maintenance of the equipment as a result tube produces a number of pulses which is proportionalof the choice of a given radioactive source material. to the number of events which are impinging on it, it is

Health Hazard generally utilized with some form of ratemeter or pulsecounter. The scintillator also yields a pulse-type output

Certain sources are more hazardous to have around and is utilized instead of a counter tube because of itsthan others from a contamination point of view. For greater efficiency for gamma radiation.example, plated polonium sources for alpha radiation have It is very dangerous to treat each class of detector byalways been a source of concern because of the tendency generalization, as is often done. The applications engineerfor the plating to peel off. Radium sources which have is cautioned not to succomb to such categorical ratingbeen sealed without proper drying have been known to but to investigate the merit of each detector in terms ofexplode and spew out their contents. Cobalt corrodes the application. A typical example is in order. A con-unless it is plated and thus may flake. This is especially ventional Geiger counter tube is approximately onetrue for large slugs of cobalt which are loaded under water. per cent efficient for gamma radiation. By suitable process-New methods of producing radioactive sources have ing of the cathode, this efficiency can be increased by a

resulted in the development of foils which consist of a factor of two. A crystal photomultiplier combination,sandwich of gold sheet on each side of a radioactive source with proper choice of crystal, can yield a gamma detectionmatrix. This technique lends itself equally to radium, efficiency of approximately 40-50 per cent. Yet, becausestrontium, etc., and is useful for alpha, beta, and gamma of their relatively small size, ruggedness, ability to operatesources. The leakage which results when this foil is cut is at high temperature, and the simplicity of the associatednegligible and can be sealed-off easily if necessary. electronics, Geiger counters are nevertheless utilized in

It should be borne in mind that the source "black box" bundles of several hundred per probe for certain deep oilmay often be required to withstand more severe environ- well logging operations instead of the photomultiplier,mental requirements than are demanded of the detector which is larger in diameter, considerably more fragile,and equipment. For example, there is a thickness gauge requires complicated electronics, and is extremely tem-available for application in chemical milling operations. perature dependent. Thus, efficiency per se is not neces-Here the source is affixed to the back side of the metallic sarily the sole criterion governing the choice of detectors.piece which is being etched by the chemical solution. In the example just cited, mechanical ruggedness, tem-Since this source is actually immersed with the work, it perature independence, and the simplicity of the associatedmust be packaged to withstand both the effects of the electronics were the determining factors. However, in aetching solution and the elevated temperature of the bath. similar application, where it was necessary to ascertain

the approximate energy of the unknown radiations, onlyTHESECONDBLACK Box ~the scintillator could be utilized, and equipment cooling

The second black box contains the detector for the became mzandatory.radiations which are being emitted by the radioactive In comparison with the Geiger counter, the ionizationsource. Depending on the application, the detector will be chamber yields an average current which is proportionalrequired to yield either a qualitative indication or a to the number of events which impinge on it. Whereasquantitative indication. The need for each is usually the counter tube produces rather husky output pulses ofseparate and distinct and has a direct bearing on the the order of volts, the scintillator produces millivolt

54 IRE TRANSACTIONS ON INDUSTRIAL ELECTRONICS April

pulses, and the ionization chamber yields only micro- undesirable. This last statement is not intended to bemicroampere currents. The associated electronics for the facetious. There is a tendency on the part of many of uslatter two require somewhat different and more elaborate to keep up to date by utilizing only the latest availabletechniques. techniques often without realizing that these newer

In the laboratory, where actual operating conditions techniques, though more glamorous or sophisticated,do not exist, one is prone to underestimate the effect of many times are not really the most efficient, direct,environmental conditions on detectors and on the resulting or economical.errors which will be introduced into their outputs as aresult of the effect of temperature, humidity, shock, and GAUGING APPLICATIONSvibration. For example, an ionization chamber which is Many references already have been made in this paperto be utilized for gauging paper thickness should be to gauging by means of radioisotope gauges. The trans-hermetically sealed, so as to avoid the errors introduced parency of matter to nuclear radiation makes possibleby the extreme variations of humidity such as one en- noncontact and nondestructive testing of many materials.counters in a paper mill. A counter tube utilized in any Thus, without touching it or changing its nature, weoutdoor installation must not be photosensitive, and its actually can see through and test material which isoutput must not vary with changes in the ambient opaque to our normal vision. The material whose thicknesstemperature. The dynode structure and cathode of a is to be measured is caused to pass between the sourcephotomultiplier which is to be used for gauging the and the detector, and the output meter can be readthickness of tin plate must be able to withstand the shock directly, either in thickness or weight of material perand vibration which it will encounter in a mill. unit area. A transmission-type gauge will detect thicknessAnother point to bear in mind is that the detector changes of as little as one-half per cent. It is especially

should always be installed so that it is readily accessible for useful for continuous production processes, particularlycleaning and maintenance. A coating of oil or dust on the of very thin materials, such as paper, plastic, rubber, andwindow or sensitive face of the detector can seriously thin metal, and it eliminates stopping or cutting the rollingaffect the accuracy of a thickness gauge. A photomultiplier sheet. Such a gauge is, of course, immediately adaptableshould be installed so that it can be replaced easily and to automatic control of roller settings.realigned with respect to the crystal scintillator. Another very useful type of thickness gauge utilizesThe applications engineer should seek the advice of the rays scattered back by the material being measured.

the detector manufacturer as to the relative merit of each This is based on the principle that the amount of backtype of detector for a given application. Information, such scattering increases with the atomic number and theas efficiency, output current or pulse amplitude, maximum thickness of the material being measured. It is being usedcounting rates, energy dependence, etc., is usually avail- with considerable success in the measurement of theable from the manufacturer's catalog sheets. internal corrosion of steel pipes without taking them out

of service. This type of gauge is also particularly usefulTHE THIRD BLACK Box for measuring the thickness of a material deposited on a

The contents of the third black box are not new to the base material. Thus it can be utilized to measure theindustrial electronics engineer. We will not discuss its thickness of protective coatings on metals and othercontents in any more detail than to say that it may materlals.containt depending on the detehtor and applitations A beta gauge has been developed to provide a simpler,contain, dependng on th detecto and appications

faster and more accurate means of making rapid quanti-such items as simple, pulse-amplitude discriminators,more complicated discriminator which re d oy t tative analyses of the hydrogen content and hydrogen-to-

pules whosmpliatudeicriinators whicrtainpint sclingo carbon ratio of a liquid hydrocarbon. The principle ofciruis,s gsteramplitdrsiver cir containg-rvat scaircui operation is based on the fact that the degree of absorptioncintgraiti crcuistes, puser apifcuies, eontc eci. c

c fil of beta rays is directly related to the electron density ofintegrating circuits, puls amp , e, w h fnally the absorber. Since hydrogen has a greater number ofterminate in conventional monitoring and control equip- ement. electrons per gram of the element than any other elemet,

the instrument can tell immediately the ratio of hydrogento other elements present. The hydrogen content of a

TO INDUSTRIAL ELECTRONICS liquid hydrocarbon can be determined from two measure-ments-one of beta-ray absorption and the other of

Hlaving completed our consideration of the three basic specific gravity taken under the same conditions.black boxes, nowwe turn to their application. The applica- Radioisotopes have been employed successfully totions chosen for consideration are representative, though measure the moisture content and density of soils forof necessity they can only be treated briefly. We would engineering purposes. Accuracies obtainable with theespecially like to discuss here only those applications nuclear method are comparable to those associated withwherein the atomic approach is really advantageous, conventional, direct-sampling techniques. MeasurementsWe would like to point out that this approach often has employing the nuclear method have the advantages thatsevere limitations and disadvantages which make it they are generally independent of soil type and are made

1958 Anton and Youdin: New Aspects of Nuclear Instrumentation 55

without disturbing the natural environment of the soil. This same principle can be utilized to measure a rapidThe measurement of soil moisture is based on the physical sequence of positions. In one application a small dab oflaws governing the scattering and moderation of neutrons. radioactive material is placed at a spot on the rim of aWhen a radioactive source of fast or high-energy neutrons rotating wheel. At another point opposite the wheel, ais placed in soil, the neutrons collide with the niuclei of the detector is positioned. As the wheel rotates, the detectoratoms comprising the soil mass. As a result of these receives a rapid sequence of on-off signals; the rate ofcollisions, the neutrons are scattered randomly in all signaling being proportional to the rotation rate of thedirections and lose a portion of their kinetic energy. This wheel. The speed of rotation, therefore, can be measuredprocess of scattering and energy reduction (moderation) accurately without any physical contact with the wheelcontinues until the neutrons are thermalized. With the or loading of its shaft.neutron source surrounded by soil, the number of slowneutrons found near the source is then a function of the GAS IONIZATION APPLICATIONSrelative number of atoms of low atomic weight present inthe soil. Since hydrogen is the only element of low atomic As a charged particle or photon traverses a givenweight found in ordinary soils in other than trace amounts m

t electrical potential be maintained across a gas-filled space,mheasumereoft wconcentraons oftydperoeniatoms in t ions and electrons will drift apart with speeds dependentmeasoil Howeve the hydcentrogeon is cyronine lar in the on the field gradient and the gas pressure. The net effectmoileculesveoffrewatrger,nd thus conthinedslowneurnc t is to produce a small flow of charge for a short period ofmolecules of free water, and thus the slow neutron count tm.Pemk iedtcosadvcu agshvbecomes a measure of the moisture content of the soil. time. Presmoke fire detectors and vacuum gauges have

Th soi dest deemnto is maewt. am been built using this principle as a basic part of theirsource adisdensimia inetecinatiq to a gammat operation. This field has hardly been touched and thesource and is similarintechniquetoagammathickne outlook for more unusual applications is most promising.gauge. In this application, however, the distance between The fire detector depends on the fact that combustionthe radiation source and the detector is one of the design .. ..

paraetes.Sncethe umbr ofeletron prsentpergas ions have a lower mobility than air ions. The moleculesparameters. Sil is approxm elycproprtiont te are ionized by alpha particles from a small amount ofunit volume of soil is posibleeto corte ath tie radium. When air ions enter the detector's collectiondensity of the soil, it iS possible to correlate the relative cabrte rdc pcfccret u evnumber of gamma rays scattered back to the detector withthe density of the soil. combustion particles move slower and are almost all

Problems concerned with the health and safety aspects neutralized before reaching the electrodes. This meansr I * * ~~~~~~~~~~thatcurrent drops sharply if a fire starts. A secondof radioactive thickness gauges for the most part have been that curen er shrly if af rts.rA seo

resolved. The source of radiation should be shielded on all ioniato chamertinacessides except the direction in which the radiation beam is Tandacure soure.

required In adiin th.ntsol b qipdwt The vacuum gauge uses a sealed radium pellet as asource of alpha particles to ionize gas molecules that

a movable shield, which can be used to close the beam c oopeinwenth uitisnotinopraio. hegagecollect on a plate to produce a pressure-measuring current.opening when the unit iS not in operation. The gauge

should also be checked carefully for the intensity f A gauge of this type can measure pressures from 1000 toradiation passing through and.beyondthematerial 0.0001 mm of mercury. One important advantage of thisradiation passing through and beyond the material to

be measured and the intensity of radiation reflected from gauge is that a vacuum failure cannot destroy or impairthe material, the detecting element.

POSITION INDICATION APPLICATIONS STATIC ELIMINATORS

While the radioactive gauge depends on the reduced A problem in many industrial processes is that of staticintensity of a transmitted or reflected radioactive beam, charge formation on rapidly moving insulating materials.the position indicator utilizes the principle of completely This build-up of static can cause severe difficulties in thecutting off the beam to the detector. Into this class of processing and handling of the product. For example, indevices fall all of the liquid-level and height indicators. the printing industry rapidly moving papers build upWhen the liquid, the height of which is being measured, static charges. Sometimes the papers repel each other,comes between the source and the detector, there is a and sometimes particles of opposite charge accumulate onsharp decrease in the detected radiation. In some appli- the sheets, resulting in attraction rather than repulsion.cations the encapsulated source actually floats on the This makes it difficult for the presses and binding machinessurface of the liquid and an entire series of detectors is to pile and handle the sheets of paper.arrayed vertically along one side of the tank, thus, To eliminate static build-up, one uses a radioactiveautomatically registering the positions of the liquid level, source which ionizes the surrounding air and allows theThe principal advantage of a gauge of this type is that static charge to be bled off. Static eliminators are com-the detector is usually located outside the liquid container mercially available using radium and polonium alpha-and therefore is not affected by corrosion and high tem- particle emitters, as well as strontium 90, which is aperature. beta emitter.

56 IRE TRANSACTIONS ON INDUSTRIAL ELECTRONICS April

Markets for static eliminators are found in the printing, excited by the neutron bombardment. The neutron curvetextile, plastic, rubber, and many other industries. might well be referred to as a fluid-content or hydrogen

curve, since hydrogen is the controlling factor on theRADIOACTIVITY WELL LOGGING action behavior of the curve in well logging. Where

For the past several years, radioactivity well logs have hydrogen is present in the strata, the curve is characterizedbecome increasingly popular as a technique for scientific by a low response; where there is no hydrogen, or very littlestudy of oil wells. Primarily designed for surveying old hydrogen present, the response is quite high in value. Itwells through the steel casing, for possible cased-off pro- matters not in what form the hydrogen occurs-whetherduction, the radioactivity log has found many varied in oil, water, or shales-the curve is characterized by auses in oil fields all over the world in both old and new low reading. For this reason a neutron curve used entirelywells. alone cannot be interpreted further than to point out the

Extensive investigations have shown that all terrestrial presence or absence of hydrogen.substances contain some radioactive material. In geology, The radioactivity log is at once the most recent develop-this radioactive material originally occurred in the primary ment in oil well logging and the most flexible. If a methodor igneous rocks. During the processes of erosion and can be developed which will identify the fluid content, theredistribution, this radioactivity was unequally distributed radioactivity log will have achieved perfection.through the sedimentary beds. In conclusion, we hope that we have been able to show

It has been proved further by both laboratory analyses that nuclear instrumentation can be handled by theand radioactivity logs that, as a general rule, limestones, industrial electronics engineer in much the same manner assandstones, and dolomites are very low in radioactivity that in which he has successfully handled many other morecontent. Black shales and marine shales have the highest conventional radiations, such as visible, infrared, orvalue of radioactivity encountered during most well ultraviolet light and all of the frequencies associated withsurveys. radio, television, and radar. We especially hope that weGamma rays are detected in well surveys by a sub- have been able to inform you with regard to the applica-

surface instrument which contains many individual counter tions of nuclear instrumentation and have indicatedtubes clustered for increased sensitivity. Passing this how to approach a problem in which isotope techniquesdetector through the various strata results in a graphic are feasible and economically attractive. A large numberpicture of relative radioactive values plotted vs depth of clever and sophisticated applications have alreadywhich can be interpreted to determine the accurate thick- been developed, but the great potentialities of thisnesses of the geological formations existing in the well. field have barely begun to be exploited. The number ofNeutron well logging is the process of bombarding the new applications are unlimited, and their successful

strata with a strong source of fact-moving neutrons and accomplishment is dependent only on the ingenuity of therecording the secondary gamma rays which have been industrial electronics engineer.

Process Monitoring by Dielectric Constant*WILFRED H. HOWEt

INTRODUCTION its dielectric to the capacitance of the same capacitor

IELECTRIC constant is a fundamental property vwhen the substance between the plates has been replacedofELateria. .cnstanttia f daefnta prety by vacuum."' In practice, air with a dielectric constantV)of materials. Technically it iS definedl as "thatproperty which determines the.electrostatic of 1.000536 is usually used as the reference rather thanproperty winch dmetermines tne electrosta,ll

enegytoed er ni voum fo uni poeta gain."', vacuum. While dielectric constant is a property of materials.. . ~~~~~in general, its practical application is limited to insulatingIt~~~~~~~~~~ma.entdta hsdfnto sbsdo neeg materials. As insulation resistance decreases (conductivitycocpt rahe tha th mor usa cocp of "terai ncreases), the energy dissipated per unit volume for unitOf the capacitance Of a capacitor having the substance aspoetagrdntbcmslgeoprdtohenry

* Presented at the Annual Conference on Electronics in Industry stored. In other words, the resistive energy dissipatedChicago, Ill., April 9-10, 1957.

t Chief Engineer, The Foxboro Co., Foxborough, MIass.1 "American Standard Definitions of Electrical Terms," AIEE, 20. W. Eshbach, "Handbook of Engineering Fundamentals,"

New York, N. Y., definition 05.30.050, p. 50; 1941. John Wtiley and Sons, Inc., New York, N. Y., 2nd ed., pp. 9-44; 1952 .