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By G. B. Kasik, George Sachs, George Espey

IT has been reported frequently that the hardness and strength vary over the cross section of cold-worked, particularly cold-drawn, material. Brass rod and wire usually has been found to possess a maximum strength and hardness near the surface.1,2 According to Sachs,1 the center fiber has about the same strength as a wire stretched by the same amount in a tensile-test machine, the strength increasing toward the surface (Fig. I). These differences are particularly large for wire given a small reduction on drawing through a die with a wide opening. However, with increasing reduction and hardness, a tendency to form a thin soft surface skin becomes apparent. On the contrary, copper wire has usually been found to possess a soft surface skin" and it has been reported by Harris3 that during the cold-drawing of hot-rolled wire the surface layer becomes increasingly softer than the core, while the layer of maximum strength moves toward the core, it being found near the surface at first. The increase of strength and hardness from the core to the skin is readily explained by the observation that, in addition to the stretching, the layers of a rod or wire are sheared more the closer they are to the surface.1,6-8 However, the presence of a soft surface layer can be attributed only to an annealing effect. The source of such a softening might be the extremely high temperature that originates from the friction between [ ]

Jan 1, 1941

By R. W. Raymond

(Chattanooga Meeting, October, 1908.) THE immense commercial value of the Gayley dry-blast process has been established beyond controversy. The testimony of practical blast-furnace managers, on both sides of the Atlantic, agrees that it reduces the cost of pig-iron about $1 per ton; but from the same testimony it appears that this direct economy does not by any means cover its commercial advantages-in fact, that under conditions frequently encountered in practice, it presents other benefits of even greater immediate financial importance. To this point I shall recur in a later part of the present paper. The history of the reception given to this invention, especially on the other side of the Atlantic, has repeated an experience familiar to American engineers. First, the reports of our practice were rejected as theoretically impossible, according to generally accepted notions and formulas; then the figures were reluctantly accepted ; and finally the attempt has been made to explain how they could have been obtained. As to the Gayley dry blast, we Americans have been for several years in the last stage of the discussion, and the rest of the professional world is rapidly coming to it. Meanwhile, the remark has been repeatedly made that, whatever Mr. Gayley's process may turn out to be worth, it was not an invention on his part, but simply the energetic and persevering execution of a procedure already proposed by others. This question I wish to discuss first in the present paper. I. WHAT DID MR. GAYLEY INVENT Realizing that this is not the place for detailed argument on an issue of patent law, I shall not undertake to quote and criticise the publications prior to Mr. Gayley's first patents. It may be admitted, without such critical analysis, that the possi-

Jan 1, 1909

By Cyril Stanley Smith, Earl W. Palmer

STRIP of any of the metals used for deep drawing operations occasionally yields cups that are defective because of a rim that varies in height around the cup in a wave-like manner. Some such defects are traceable to tools or other press factors, but when the protuberances formed (usually four in number on brass and other copper alloys) are symmetrically disposed with respect to the rolling direction of the strip, they are invariably attributable to the metal. The effect is known as "earing" and the protuberances are called "ears." Other terms frequently heard are "tips," "scallops," and "corners." It is recognized that the effect is most commonly a result of a directional crystal structure produced by rolling and annealing operations in the manufacture of the metal strip. 'Numerous papers dealing with various aspects of the earing effect have appeared in the literature, those listed in the references1 being especially interesting and valuable. An investigation of the factors influencing earing of brass cups has been in progress in the laboratories of the American Brass Co. for several years, and it was thought desirable to make some of the results generally available in summarized form. The present paper discusses many factors that do and do not contribute to ear formation. In addition, a section is devoted to methods of minimizing the earing tendency of brass sheet by proper selection of the cold-rolling and annealing schedule by which it is produced. In the space available, it is impossible to quote detailed experimental procedures and numerical results. However, the authors make no statement that they do not believe to be properly substantiated, either by experimental evidence obtained under laboratory conditions or by experience in the actual production of deep-drawing brass in the brass mill. MECHANISM OF EAR FORMATION It must be clearly understood that the formation on cups of symmetrical ears, four or more in number, is attributable solely to the strip metal, and results from the strip having different deformation characteristics in different directions. The tools used in the drawing process, or the type and completeness of lubrication of the strip, have nothing to do with the problem of ears, although they do, of course, greatly affect the "drawing quality" of the strip and the general appearance of the cup. A single tip may be drawn up on the rim of a cup because of misalignment of the tools, or because the gauge of metal varies from side to side of the strip. The two-ear form that sometimes appears is also traceable to gauge variations. However, the four-ear and six-ear symmetrical forms that we are concerned with here are caused by factors inherent in the structure of the metal itself.

Jan 1, 1942

By T. L. Joseph, G. Bitsianes

The gaseous reduction of dense iron ore is a topochemical process in which reduction takes place at distinct interfaces between solid phases or layers. Under normal conditions, these interfaces remain parallel to the exterior surface of the ore body as they move inward. Certain conditions, such as cracking, high porosity, impurities, entrapped residual oxides, may cause departures from normal topochemical behavior. THE gaseous reduction of dense iron ore proceeds at interfaces between several solid phases or layers.',' Under normal conditions, these interfaces progress inward and remain parallel to the exterior surface of the ore body. This topochemical behavior is clearly illustrated in Fig. 1 which shows partially reduced specimens of natural and synthetic hematite. Using a coordinated sequence of macro, micro, and X-ray examinations, the authors1-'2 found that the number of interfaces and participating phases was in agreement with the Fe-0 system. Above 570°C, reduction of the ore involved a maximum of three common boundaries between four solid phases: iron, wiistite (Fe,O), magnetite (Fe,O,), and hematite (Fe,O,). Below 570°C, reduction proceeded through two interfaces between three phases: iron, magnetite (Fe,O,), and hematite (Fe,O,). The decrease in the number of phases below 570°C was due to the instability of wiistite below this temperature. The sequence of phases was also consistent with the equilibrium requirements. For example, the layers of iron oxides that were formed in topochemical fashion were always orientated in the order of increasing oxygen content. Thus, in Fig. 1 an outer layer of metallic iron is followed in turn by a thick intermediate band of black wiistite, by a thin layer of light magnetite, and finally by a relatively large core of hematite. This arrangement of the oxide layers was due to restrictions in reducing conditions which were imposed by the physical structure of the solid. The highly reducing gas on the outside of the particle gradually lost its reducing power as it penetrated into the specimen. On a macro scale, the layers of the various oxides appeared to be sharply defined and uniform in composition. Microexamination of the sections, however, revealed that the interfaces did possess measurable widths which varied with the porosity and chemical activity of the oxide phase undergoing reduction. For example, Fig. 2 shows three interfaces in a dense hematitic ore which was partially reduced at 850°C. At the iron-wiistite interface where the greatest porosity developed, the reaction proceeded over a zone 25 to 30 microns in width. Toward the interior, the interfaces became progressively narrower until at the magnetite-hematite boundary the reaction zone was about 1 micron wide. In this region the structure was exceedingly dense; the hematite possessing a porosity on the order of 3 pct. A careful micro study across polished layers of the various oxides revealed generally homogenous and single-phase structures. As reported in a previous paper,' the wiistite layer was characterized by an increase in oxygen content with depth of penetration. The topochemical behavior of reduction was studied in six types of ore of different origin, composition, and physical structure. In most cases, reduction proceeded at the boundaries of well defined layers or phases, and this behavior may be regarded as normal for most dense fine grained ores. Deviations from Ideal Topochemical Behavior A number of deviations from the normal topochemical behavior were noted. In these cases, the continuity of the reduction interfaces was disrupted in one of four ways: 1—Cracking of the specimen interrupted the geometric configuration, and the interfacial advance was no longer parallel to the exterior surface. 2—As a result of high porosity, the interfaces were spread over an appreciable distance and all but obliterated. 3—Impurities in the ore promoted a variety of deviations, including cracking. 4—A residual oxide phase was entrapped in the reaction product and left behind the advancing macro interface. Results from Cracking: A crack leading into the interior of an ore specimen presents a path of least resistance for the counter-flow of reducing gases and gaseous reduction products. Higher reducing conditions can be maintained along such cracks and reduction accordingly will propagate well ahead of the normally advancing reduction interfaces. Cracking was caused by a number of factors, one of which was the thermal spalling of impurities in the massive form. A more general type of cracking was due to reduction and was found in all dense varieties of natural and synthetic hematite, particularly in the temperature range of 500" to 700°C. The effect is shown clearly in Fig. 3. In this case, a dense sphere of pure hematite was partially reduced at 650°C for 100 min. The macrosection shows that one large reduction crack had penetrated the specimen and disrupted the normal topochemical advance of the interfaces. The outer layer of iron was only slightly affected but the thin dark layer of wiistite, adjacent to the ferrite, had widened perceptibly as it progressed along the crack. Farther inward, the magnetite layer was greatly disrupted and had penetrated irregularly to form islands of unaltered white hematite. A great deal of internal cracking is evident in the magnetite phase. From a practical point of view, the cracking of dense ores in the blast furnace could lead to desirable as well as undesirable effects. The general result

Jan 1, 1956

By N. B. Pilling

THE development of a proper treatment for shells in connection with war contracts has brought to our attention the fact that the temperature of the liquid bath in which steel is quenched has a decided influence on the speed of cooling in the case of some liquids and very little in the case of others. Widely different physical results have been obtained by the use of water spray, water immersion, and oil immersion and further experiment has shown that the quenching effect of water used as a spray or an immersion varies greatly with the temperature of the water. The present experiments were undertaken with the idea of obtaining information of a quantitative nature regarding the quenching properties of a number of liquids used commercially in hardening steel. The general features of such cooling media are common knowledge and in the literature may be found records of numerous attempts to evaluate the cooling power of a liquid when used as a quenching bath. Much, if not most, of the data given on this subject is in the form of a simple statement of the time required for a certain heated mass to cool between two arbitrary temperatures when immersed in the liquid, quite regardless of the path of the temperature change. Our own purpose has been somewhat different. We have attempted to isolate that property of these. liquids having to do with their ability to absorb heat rapidly, as distinct from the behavior of a considerable mass when exposed to different thermal environments. More specifically, from the data obtained through autographically recorded cooling curves of a small standard mass quenched under various conditions, we have tried to analyze the mechanism of heat absorption by the several liquids, measure the changes in its rate as a function of the temperature of the surface of transference, and ascertain the influence of the temperature of -the liquid itself upon both.

Jan 9, 1919

By A. B. Stickney

UPWARDS of 200,000 engineers in this country are sufficiently interested in engineering as a profession to have joined a society, but not over 10% of them belong to any one society. There is a widely-felt need of an over-all organization of all the societies to act as spokesman for all engineers on matters of common concern. On a local basis, over 100,000 engineers in 35 metropolitan areas have organized themselves into local councils, and are doing an effective job of intersocietal co-operation within their sphere of activity. In the last few years much has been said and written about a similar organization on a national scale. Everybody wants iteverybody is talking about it-it's in the air-it's coming-it's inevitable. Although it is no longer necessary to talk about why or whether there should be such an organization, there is no such unanimity about what it should be like. This paper outlines a proposed organization by answering four questions-who, how, what, and who will pay for it.

Jan 1, 1946

By Hans Lundberg

IN ORDER to comprehend the help and information that may be expected from electrical prospecting, it is necessary to have at least a general knowledge of the methods and principles involved in preparing and interpreting results obtained in the field. Electrical prospecting is rather complicated, both in theory and practice, and in order to make a brief description clear to the practical mining man it has been necessary to idealize and generalize the problems, at the risk of having such simplification criticized by the theoretical man. This simplification must not be misinterpreted as showing a lack of theoretical knowledge. FIG. 1.-FLOW OF CURRENT IN AND AROUND A CONDUCTING BODY. For its operation, electrical prospecting mainly depends on the fact that most metallic ores conduct an electric current much more readily than barren rocks. If an electric current flows through a block of ground within which a body of chalcopyrite is enclosed in country rock of schist, the current will find less resistance to its passage through the chalcopyrite than through the schist, even though the passage through the latter be much shorter. This is because the longer path through the chalcopyrite offers less resistance, owing to the superior electrical conductivity of the chalcopyrite (Fig. 1).

Jan 1, 1928

By R. E. Allen

ONE of the most unusual oil field engineering accomplishments of the past two years is the development and rapid advance in the directed drilling of wells. Directed drilling as referred to herein is the controlled steering of the drill stem in the required direction to a given location in the oil sand. The deliberate drifting of holes is an act so far removed from what has been considered good drilling practice that all of the old questions of correlation, drillability and production difficulties are revived. Only a few years ago, during the boom days of Seminole and Santa Fe Springs, the crooked-hole problem, as it was then called, occupied a primary position among the topics of the day in the fields of California and the Mid-Continent. The net result of all the discussion and study at that time was the conclusion that oil wells should be drilled with as little deviation from

Jan 1, 1933

By Charles M. Cooley

With explosives representing over 10 pct of the cost of operating the entire company, the Maumee Collieries Co., Terre Haute, Ind., inaugurated a program to develop a low-cost blasting agent. Results of more than two years' work were announced on May 1 by Hugh B. Lee, president of the company. Utilizing a mixture of commercial-grade ammonium nitrate and carbon black packed in polyethylene bags, Maumee has been able to reduce blasting costs by 50 pct. The lower costs are brought about principally by elimination of high transportation charges on fixed explosives and use of low-cost material (commercial NH,NO, and carbon black). The Akremite blasting method incorporates a 20-lb cap-sensitive primer to detonate the stable explosive. Maumee now uses Akremite exclusively in its stripping operations producing more than 2 million tons of coal per year. The explosive is employed to break about 25 million cu yd of overburden that covers the coal

Jan 5, 1955

By J. McD. Porter

In many of the old placer-mining districts are still to be found large tracts of gold-bearing gravel not suitable to be worked with a dredge, because the bed is too shallow or the gulch too narrow. Frequently there is not enough grade to handle the gravel successfully by ground-sluicing or a bedrock flume, or it contains too many boulders to be worked succeeefully with the ordinary hydraulic pipe or tube elevator. In southwestern Oregon, two practical placer-miners named Ruble, after working for years trying to make money out of placer-ground coutaining many large boulders, invented and patented a hydraulic elevator of an entirely new type, and one that has been found to work very successfully in flat ground and in gravel containing many large boulders. It is a very simple contrivance. A few years ago I acquired the property near Pierce City, Idaho, known as the American placer-mine. Various attempts had been made to work this ground. A bed-rock flume had been installed by one company, an Evans elevator by another, and still other methods were tried on a smaller scale. All were

Jan 1, 1910

By Milton Williams

A comparison is made between the amount of interstitial water found by analysis in cores and that estimated from the resistivity curve of the electric log for the corresponding strata of producing reservoirs. It is shown that while the determined and the estimated water saturations are in good agreement in some cases, this agreement may be due to a fortuitous compensation of errors. Estimates of water saturations made from the electric 1og by use of existing relations should, therefore, be employed with caution. Also presented are data on the variation of salinity of interstitial waters in reservoir sands, and on the effect of variation of salinity and porosity on the validity of estimates of water content made from the electric log. INTRODUCTION Throughout the history of electric logging there have been recurrent cycles of optimism and pessimism as to the value of the electric log in the quantitative estimation of reservoir fluid content. The very early days of electric logging were an optimistic period, in which there was widespread faith in the ability of the resistivity curve to reflect fluid content, and in the ability of the potential curve to indicate textural characteristics. In time the accumulation of exceptions to this idealistic behavior brought about a general disillusionment, and caused the more pessimistic of those dealing with electric logs to believe that the sole importance of the log lay in stratigraphic correlation. Within the last several years optimism as to the quantitative use of the electric log has been revived, primarily as the result of the stimulating work of C. E. Archie' on the estimation of interstitial water in sands from resistivity data. Even though the general trend of thought on the quantitative value of the electric log reflects optimism, it is inevitable that there are some widely divergent opinions of the validity of quantitative estimates based on the electric log. A valid method of estimation of fluid content by means of the electric log and a general knowledge of the textural character of the reservoir rock would be of signal importance, not only in that it would save time and money in securing information on reservoirs now being drilled, but also because it would permit the evaluation of reserves in many fields drilled without adequate core data subsequent to the advent of electric logging. Because of this importance, Humble's Production Research Division, in cooperation with various other company divisions, initiated several years ago series of tests designed to evaluate the reliability of estimates of fluid content made from the electric log. The investigation was limited at the outset to sand reservoirs, since it was felt that the inclusion of limestone reservoirs would entail needless complications. In devising these tests it was immediately apparent that the chief difficulty in evaluating the worth of any method of estimation lay in establishing the true value of fluid content. The results of direct analyses of cores cut with ordinary mud were not sufficient, because of the probability of contamination of the fluids by filtrate from the drilling mud; the results of restored state tests on cores were deemed unsuitable because these results can hardly be said to furnish a primary standard. The method adopted was the direct analysis of cores cut with an oil-base drilling fluid. Such cores, when properly handled, are believed to afford the most precise determination of water content available at the present, and, in addition, lend themselves readily to the determination of various other properties which are pertinent to the estimation of fluid content from the electric log. Since it was desired to compare the fluid contents estimated from the electric log run in ordinary mud with cores cut in the same hole, the use of oil-base fluid necessitated the changing over, after all cores were cut, to a conventional mud. This procedure presented several advantages, one of which was that the use of oil-base fluid permitted

Jan 1, 1950

By R. J. Sweigard, R. V. Ramani

Demands on available lands will continue to increase due to the projected population increase and industrial expansion. Though there is an upper limit on available lands, the multi-use nature of the lands will make it possible to meet these demands. However, this will not happen without adequate planning. Land uses can be broadly categorized as nonrenewable and renewable. Lands with minable resources can be dedicated at some Point to the extraction of resources. Such a dedication, however longterm, is only temporary because of the nonrenewable nature of the minable resources. The land will be available before and after mining for other uses. Planning for such lands must have the objective that, as far as practicable, no nonrenewable uses are preempted and no renewable uses are permanently destroyed. This paper addresses primary aspects of this planning process. These aspects include a discussion of planning responsibility, data needs and availability, the integration of mine planning and post-mining land use planning, and a long-term plan for resource conservation and utilization. Minerals, with agriculture and forest products, are the primary sources of wealth. Therefore, to amid land development that may preempt future mineral resource utilization, local planning groups must be aware of the mineralization and mining potential. Much work needs to be done to identify and characterize the mineral resources. Even more land use planning is needed for lands with mineral deposits.

Jan 1, 1985

By James Norman

SPODUMENE is a lithium-bearing pyroxene, and is an important source of lithium compounds. Because of its high alumina and lithia content, it might be a desirable constituent of glass batches. The use of spodu-mene in ceramics will undoubtedly increase, as it has been shown that a mixture of the proper proportions of this mineral with soda feldspar and potash feldspar has a much lower maturing temperature upon firing than has any one of the three components.1 The mineral spodumene seldom occurs as pure mineral, but ordinarily with feldspars, mica and quartz. All spodumene-bearing rocks tested contained these minerals as gangue. Small amounts of iron and manga-nese oxides also were present, usually as stains on the silicate grains. Mica associated with the spodumene carried a considerable amount of lithia. This was discovered in flotation tailings, which, although virtually free of spodumene grains when examined microscopically, showed 0.4 to 0.5 per cent Li2O on chemical analysis. The lithia content of micas picked from the North Carolina spodumene rock was variable. Some samples contained little lithia, others more than 3 per cent. In 1938, under the supervision of Oliver C. Ralston, ? the Bureau of Mines, in cooperation with the Tennessee Mineral Products Corporation, undertook to study the beneficiation of North Carolina spodumene by froth flotation. The Bureau had previously published investigations on the beneficiation of spodumene.2,3 The methods described in the second publication' did not give good results with badly weathered spodumene rock, so that more thorough investigation of the subject was warranted.

Jan 1, 1940

By Dell H. Adams

COAL EXPLORATION Coal exploration may be defined as the acquisition of data necessary to define and acquire a block of coal which can be mined at a profit. Unlike ore minerals, coal resources are widespread and relatively abundant with supply exceeding demand in almost every case. Thus simple discovery of coal is generally not enough. The chemical and physical variability of individual coal seams, the capital intensive nature of coal mine development, and the changing patterns of utilization require that a multiphase, three-dimensional evaluation be made of each potential reserve. Factors which must be investigated include not only the quantity and quality of the coal but also the geologic, hydrologic, and engineering characteristics of the seam and its surrounding strata. Acquisition of property to provide a secure base for exploration and mine development is equal in importance to the geologic and engineering programs. The successful development of a coal reserve requires that control of coal and, in the case of a strip mine, the surface be in the form of contiguous blocks of sufficient size to support mining. PHASES OF EXPLORATION The high capital risks of coal exploration and land acquisition dictate that a multiphase program be utilized to minimize initial risk. In such a program, phased development of the data insures that each increase in capital expenditures will be justified by a corresponding increase in the level of confidence in the ultimate success of the project. Each phase is designed to provide sufficient data and property control to facilitate the decision whether to proceed to the next phase of development or to discontinue the program (Table 1). The first phase of a typical exploration program consists of a pre-

Jan 1, 1981

By William Sellers

tested without knowing anything of their chemical composition. I had these pieces separately placed upon 10-inch bearings under a 7-gross ton lianlrner, a piece of 2½-inch round iron laid upon them as a fuller, and the hammer allotved to fall from 20 inches above the fuller, which, according to Haswell, gave a ldow of 67.75 gross tons. The pieces were then turned orcr, the fuller placed upon the convex surface, and the harnnler allowed to fall from 13 inches above the fuller, giving a blow of 58.46 gross tons. You will see that the rails do aot show ally bigrls of ruptnre, and their color at the points of torture prove them to have been absolutely cold when the test was made. I thirk these rails ought to be reasonably safe in the track. As you see by this piece of the head of one of these rails, I had it plarred, and then some teeth cut in it by a cold clrisel, and one-half of them pounded down with a hammer. The teeth of my rack did not break off. The analyses of these rails substquently made are: I. 11. Carbon,... 0.110 0.880 Silicon,..0.050 0.058 Phosphorus ,..0.086 0.082 Manganese,.. 0.042 0 840 In conclusion, I will say that Dr. Dudley's paper as a contribu tion to our knowledge of steel rails is valuable and interesting, but I protest against his conclusions king reoeived as manufacturing or comtnercial axioms. From its being presented in the form-of a report to the leading railroad of the country from one of its trusted officers, as well as from the tone of the concluding deductions, it is liable to be so received by railroad men. If any railroad com pany desires rails made under either of Dr. Dudley's formulas, and are willing to pay a price large enough to cover the loss in making them, dl and good; but so long as the rail makers are compelled to gwrrantee the wear of their rails for a given number of years, justice reqnires that. the composition of the steel from which these rails are made should be left to them. WILLIAM SELLERS, PHILADELPHIA: The very interesting paper upon the wear of steel rails that has just been read preseak the record of a series of investigations that are extreniely valuable, and the deduction that bas been drawn from the results noted seems to be unavoidable; the tests, however, to which it is proposed steel rails shall be subjected hereafter, with a view to determine their quality, sllould

Jan 1, 1881

Jan 1, 1915

In the last decade the railroads have been making tremendous strides in the development of services for the handling of bulk materials, the equipment for handling them, and the efficiency of handling, which resulted in lower costs to shippers. Pressure differential cars, giant tank cars and covered hopper cars, high capacity transloaders, and unit trains have led to substantial advances in expeditious, efficient, and economic handling of bulk materials.

Jan 1, 1973

By John T., Ryan

THE subject assigned me, "Safety in Mining," is a very broad one and only the high spots can be covered in this short paper. As this is a meeting of the Coal Division, these remarks will be directed largely to coal mine safety, although the principles of safety and effective accident prevention methods are relatively the same in every branch of mining or industrial work. The coal mining industry should take pride in the part it has played in the development of the accident prevention movement, and there is ample proof for the statement that the first real organized accident prevention, work, both abroad and in this country, was con- ducted in the coal mining industry.

Jan 1, 1930

By R. P. Dolan, W. M. Shedd, B. L. Buchanan

Analytical expressions are derived from empirical data relating the basic physical device parameters to the radiation dose. To put in perspective and justify the approach taken, the overall problem and methods of attempted solution of radiation damage to transistors in a missile or satellite environment is briefly examined. The main emphasis is on a new criteria for neutron radiation hardness and the device design implications resulting from using this criteria. Contrary to other derived criteria, the derived bipolar hardness relation depends mainly on the initial lifetime rather than the base transit time. It is shown, that contrary to previously accepted beliefs, the inherent attainable radiation tolerance of JFET's is at least a factor of ten greater than the radiation tolerance ofbipolars. Experimental results on JFET's designed for maximum neutron radiation tolerance are presented. The accuracy, utility, and range of possible validity of various published lifetime and carrier removal damage constants are discussed. It is well known that transistors are subject to damage due to radiation at much lower radiation levels than those which would cause structural damage to a missile or satellite. The three principal categories of radiation damage to transistors are displacement, ionization, and thermomechanical. The main cause of displacement damage is fast neutrons, and the main effects which permanently degrade transistor operation are minority carrier lifetime reduction and carrier removal. A second-order effect is mobility reduction. The main cause of ionization damage is gamma radiation which results in permanent effects due to charge build-up in the oxide and transient effects due to photo-current generation. The transient effects are usually handled by using circumvention techniques in the electronics system. The extent of the transistor degradation due to displacement and ionization damage depends strongly on the transistor type, whereas the extent of thermomechanical damage does not depend on the transistor type, but depends mainly on packaging and metallization which are common to all transistor types. The standard transistor types are categorized in Fig. 1 and typical cross-sections are shown in Fig. 2. The original reason for the designation of the two classes of transistors was that the unipolar operation depends on only one carrier (majority) and the bipolar operation depends on both minority and majority car- riers. The bipolar is then seriously degraded by minority carrier lifetime reduction, whereas the unipolar or field effect transistor is not. One of the two principle classes of field effect transistors, the junction field effect transistor (JFET), depends strongly on carrier removal. However, the insulated gate (MIS) is little affected by either carrier removal or lifetime changes, but is virtually eliminated as a radiation resistant device because of permanent charge build-up in the insulator caused by ionizing radiation. The bipolar and JFET suffer only minor effects due to charge build-up in the oxide passivation when compared1 to the MOS. This is because the active region of the MOS is adjacent to or part of the oxide layer. It is then the bipolar and JFET which are potentially resistant to permanent radiation damage. DERIVATION OF RADIATION TOLERANCE RELATIONS Criteria. The bipolar is by far the most widely used transistor type. The usual criteria for hardening bipo-

Jan 1, 1970

The regular activities of the Institute are financed mainly by income derived from members' dues, from advertising in MINING AND METALLURGY, and from the sale of publications to the public In addition, collateral activities and special projects are financed each year by means of income from endowed funds controlled and administered by the Institute In the aggregate, the amount of these endowments totals more than $830,000 An active effort is being made to increase the endowment funds of the Institute through a standing committee, of which Harvey S Mudd is Chairman, and

Jan 1, 1952