some new aspects of nuclear instrumentation in industrial electronics

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  • 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 toDuring the past ten years, the investment in process- the industrial measurement and control problems that can

    control 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

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