Instrumentation teaching equipment. Part one: Optical devices

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Topics in..

. Chemical Instrumentation

Edited by S. Z. LEWIN, N e w York Universily, N e w York 3, N . Y.

1hese articles, most of which are lo be crml&Aed by guesl autbrs, are intended to serue the readers of this JOURNAL bv d i n o altenlia to new &elopments i n the theory, design, & availabi1ity of chnnicd-laborabny instrumenlalion, oi. by presenting useful insi>hfs and explanations of topics UuU are of practical importance to those who use, m leach the use of, modern instrumentation and instrumental techniques.

XVI. lnstrumentation Teaching Equipment. Part h e : Optical Devices

(Continued)

Leonard Eisner, Bornes Engineering Company, Stamford, Connecticut Lasers

tions by making use of the gas laser as a lieht source. The intensitv of the laser's cl:tYr;rvticdimitPd beam ia rewr.l o r d m uf rnny~hwlrl~iv,ltert h a n t h t of v t m v e v ~ timnl .imwes, rind r n w y h lighr ir avsilnl,lr so that interference patterns can be viewed conveniently in projection. Dutton and his colleagues a t the Institute of Optics, University of Rochester, have described' several experiments dealing with: lens aberrations; interference and diffraction phenomena; and the Abbe theory of the microscope; and some practical optical systems far performing them with a h e r . . 4 reprint of this article has been published by Spectra-Physics, Inc., i n their "Laser Technical Bulletin No. 3." ~

Applications of the laser are increasing almost daily, and the well-informed chemist or chemistry teacher must have some familiarity with this interesting device. To begin with, some elementary experiments in optics, usually limited t o individual observations in the laboratory, can be adapted for presentation to larger groups ha lecture or classroom demonstr* . .... ., ,, ,..:., ... .

Figure 11.

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traversahls take place in the standard 4 ml cell. Excitation energy is further conserved by coating the cell windows with multi-layer dielectric, reflective films, tuned to l.he laser output a t 6328 A. Emi~sionspectroscopy has also benefited from laser technology. The Jsrrell.4sh Laser Microprobe focusses a microscopic image of the intense output of s. pulsed ruby laser onto a pre-selerted site: The material thus vaporized is electrically excited by two small electrodes positioned just above the sample, and on the axis of a n associated emission spectrngraph. A wide variety of samples may be studied, ranging from metallic inclusions in an ore body, t o trace elements in microtomed brain tissue. In contrast t o some other techniques, the sample need not be made electrically conductive, and because only about 10-'gis vaporized, the sample may he retained for other types of investigation. Light elements such as beryllium and boron may be as readily analyzed as heavier metals. Spectra-Physics, Perkin-Elmer, and other companies make CW Lasers that can be used for instruc.tiana1 as well as research purposes. Most of these cost several thousand dollars. A lower-cost instrument ($750) is the Bendix TL-1 instructionel gas laser (Fig. l l ) , which was especially designed for demonstrating and teaehing the basic propertien of lasera. Such features as manochromatil:ity, coherence, cavity problems, and lasing thresholds m e easily demonstrated with this unit. Atomic Laboratories alao sells a rontinuous gas laser designed specifically for classroom and laboratory demonstrations in optien (No. 87290-3, $850), as well

BendixTL-1, Instructional He-Ne-Gar Laser. A rugged, compact, low-cost unit, mountable Laser tube is visible throqh an amber plastic cover.

on toble top, optical bench or tripod.

Figure 10. Sample ore. of Perkin-Elmer's Romon Spectrometer. Helium-neon iorer beam is multiply reflected within the rompie cell below it. The rconered radiation ir dirpemed into a Roman spectrum, b y a specially derigmd double-pars grating monachromotor.

Besides its use as s n interesting teaching aid, the laser is being used as a component of chemical instruments, e.g., the PerkinElmer laser-excited Raman spectrometer (Fig. 10). The laser's high energy density together with its extreme monoehromaticity, make it a n ideal source for exciting Raman spectra. The laser is mounted vertically and its beam falls on the sample cell, which is slightly wedged in order to produce multiple travemalls and thus insure maximum excitation. Approximztelg 150

as a 400-joule-input pulsed ruby laser, (No. 87290-1, $1795). The latter provides a 500 microsecond, 1 kw output pulse with x nominal beam divergence of 1.5 min a t threshold. Dyna Lite, Inc., Hartford, Conn., ~ o l l s a "Laser-Maser Kit" $9.95, for use as a teaching device in connection with their ot,her visual display equipment ("Viewing Ilevice" $80). E. Luescher st the Uni(Conlinz,ed on page A552)

Vol. 47, No. 8, August 7964 / A551

versity of Illinois has built an analog device to demonstrate optical pumping, using water to symbolize the degree of

occupation of the ground and excited states.

Part Two: Electronics and Nucleonics Electronics

In any list of instruments used by chemists, from Alpha-ray spectrometer to X Y recorder (or even Zeta-potentiometer), the majority will be found to use electronic comoonents and circuits. The neaobvte . c.r h l d i n ~young wirntirt ~ : r tw~q u i r e a wwkm): kr.trwlcJ~euf n t lcmt t1w rlemcntv uf clwtnm~vswith the aid uf ktrd rlmt are available from many companies. As an example, American Basic Science Club, Inc., Siln Antonio, Terns, sells a set of four kits for $17.80. The first deals with ac and do circuits, transformers, electrochemistry, and so on, up to the fourth kit which dedls with audio-amplifiers, tuned circuits, regeneration, and signal tracing. Ealing supplies three "Minilabs" for training in experimental eleotronics (Nu. 32-501, $12; No. 32-502, $39.50; No. 32-503, $69.50). With the first, the student can build a 3-~tsgetransistor amplifier, multivihrator circuits, complementary symmetry amplifier, Class B amplifier, a negative resistance oscillator, etc. The second builds most of the oircuits encountered in college electronics courses, including regulated power supplies, diode logic circuits, transistor power amplifiers, rectifier and filter circuits, 4transistor amplifier, 3-stage vacuum tuhe amplifier, and a. vacuum tube voltmeter circuit, for example. The third is recommended fur use by advanced students, for demonstration purposes in the laboratory, and for industrial breadboarding. The Minilabs use s. Miniplug hoard whose rigidly mounted, hollow metal pins accommodate many as fifty or more component-as seven terminating in a single pin (see Fig. 12). Typical contact resistances of these solderlese connectors (formed hv insertine t o o l h p i ~ kinlo ~ lllc hlllam !,inn! inre i l l tine 1 10 I l l ntllliohm rmgc S ~ i > C l h t~t c n t u , ~ ~ t u thr dcpipn uf pin ~ p a c ~ nr,l>nlumcs g tlw need to re-bend leads, so component loss through lead breakage is negligible. Solderless breadboarding is also a fe3i

.

Figure 12. A regdoted power supply assembled with Minilab 32-503. Note use of toothpick connectors; Minicord circuit diagram slips beneath Miniplvg card; both slip free of the charsir if required.

A552 / Chemical Education

ture of the "Erec-Tronic System" offered by Science Electronics, Inc., Cambridge, Massachusetts (Fig. 13). This is mare flexible and requires considerably less time than that required if conventional soldering practices were used. Phcsphor-bronze clipon connectors are used, reputed to have a maximum contact resistance of 0.005 ohms and to he good for at least 7000 connections. There is a wide variety of hlank bases which can be adapted to particular needs. The terminal pasts can handle multiple connectors, any of which can he easily removed for circuit testing.

Figure 13. Breadboard of o transistor gote circuit b e e ichernoticl, conrtrvcted with parts of Science Electronicr' "Erectronic" System BE-8.

A "Basic Electronics" parkage (BE5, $225) can be used as an introduction. For those who acquired their electronic knowledge in the "horse-and-buggy" pretransistor era, Science Electronics offers its "Comprehensive Transistor Set" (BE8, $175). Tbis set includes 23 transistors from five different mmufxturerr, to familiarize the student with various types of transistors. By following the text "Transistors" by Kiver and the associated "Traneistor Lzboratory Manual" by Kiver and Emden 1MrUraw-Hill Book Co.).., tbe vwlent is wpycwl t ( f ~ ~ m t the er Imiv ~n.incilrll.dof 1r:~nsirIurrand crf wrnmmly used transistor circuits. A comprehensive "Industrial Electronics Set" (BE-7, $750, Fig. 14) features experiments on gaseous rectifiers, thyratrons and thyratron control, time constants, vacuum tuhe and transistor time-delay relays, photo-electric control, phototransistor relays, saturable reactor, peaking transformer, motor control, regulated power supplies, radio and tone control systems, synchros and servomechanisms, as well as the elements of (Continued on page ,4554)

assembled) which, when connected to the terminals of any meter, VOM or VTVM, duplicates its readings on a roll-up 3 X 4 f t wall scale. Heath also offers a. basic electricity kit (EK-1, 519.95) and others dealing with vacuum-tube voltmet,en, oscilloscopes, and signal generators. One of their most popular items is the EU-100A Instrumentation Laboratory Station ($1100!. This was originally developed by Prof. H. V. Malmstadt, University of Illinois, and Prof. C. G . Enke, Princeton IJnivenity, to provide professional scientistsns well as students with afirmworkinr knowledge of circuits and modern instrumentatiun. I n its teaching application, the equipment is used to perform the experiments described in the text, "Elertronirs for Scientists" by Malmstadt and Enke. I t includes meters, signal sources, and a n oseilloecooe:, meeisl chassis modules and electronic parts for rapid circuit construction; tools; connecting leads; pon,er sources; and a servo recorder and control amplifier unit. The instruments used in the EU-100A may also be purchased individually. They are of research quality, which facilitates the transition from understanding to application. Nearly all the laboratory supply houses offer numerous electronirs teaching aids, such as: demonstration multimeters (Welch, No. 3065,887.50); student patentiometers (Welch, No. 2817, $64.75, or L & N, $190); thennocouple kit (Edmund Scientific, No. 70417, $6.50); photoelectric cell demonstration kit (Cenca, No. 809Ofi, $45); dissectible transformers (Leybolrl, IT.S. distributor LaPine Scientific Co.)

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All controls and a small monitor scope n w located on the rear panel for convenient, operation by the inst,ructor. (Welch, NI,. 2140A, $390). Welch s l m has a series of circuits, such as sawtooth sweep generator (No. 2139K, 555) and vertical deflection amplifier (No. 21395, $67.50) laid out on schematic psnel board for use with a cilth2139, 8159.50). ode ray oscilloscope (KO. and intended to familiarize the student with theanatomy of nn oscilloscope. Vickers Ine. makes an Educational Magnetic Amplifier (Welch No. 2642, $99.50) to acquaint students with the properties of t,his papular control device. Other simple teaching aids in this field are: a kit to demonstrate hysteresis on an oscilloscope, available for 3;30 from Magn e t i c ~ ,Inc., E a t Northport, New York; and a kit to demonstrate magnetic domains, available for $25 from Churchill Ca., Inc., Science Department, 4G8 Broadway, New York 12, N. Y.

Physical Electronics Whereas most of the devices mentioned so far have dealt with electronic componenta and circuits, another aspect of elertmnics, known as physical ekdmnirs, deals with such things as thermionic emission and electron-optics (the trajectories of electrons and ions in electric and magnetic fields, such as in cyclotrons, mass spectographs, electron microscopes, phatamultipliers, etc.). To acquaint the student. with electron trajectories and such can(Continued on page A560)

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cepts as equi-potentials and ourrent flow lines, that occur in electron-optics, various analogs have been used, including steel halls rolled along stretched membranes, and electrolytic tanks. A more convenient veraion of the latter is offered by Harwil Company, Santa Monica, California, in the form of their "Electro-Plot" (S-200, $29, and 1-201, $49) (SeeFig. 15), and by Welch (Electric Field Mapping Set, No. 1960, $19.50). Metsl electrodes are placed in a desired configuration upon a sheet of conducting paper. The student connects 31 battery to theae electrodes, adjusts the volt,sge, and plots directly a series of equipotential lines. Repetition of this process producee a family of equi-potentials. The 1-201 is a larger version of the $200, intended for use before larger group^. Since the mathematical description of current flow in 2 dimensions, namely Laplace's equation, is the same as that for beat flow, fluid flow, and many other phenomena, the latter may dso be investigated with devices of this sort.

Figure 15. Electro-Plot 5-200. for observing flow liner and equipotentiolsin the vicinity of electrodes momted in any desired configuretionon a dry, conducting-paper bore.

Nucleonics Nueleonirs is the science of nuclear phenomena. The instruments used in nucleonics and nuclear rhernistry draw heavily a n electronics. Previous articles in this series, discussed detectors for nuclear r a d i a t i ~ n , ~ a nelectronicgear d used innuclear stuclim.' We *hall now describe some equipment used for teaching some of the fundamental principles and applieations of nuclear physics and chemistry. An inexpensive cloud chamber, (such as Macalaster Corporation's No. 17100, $3, or Welch's No. 2158B, $18.25, and No. 2158, $49.50), permits direct observztion and study of tracks left by charged particles emitted in radioactive decay. Students can make range measurementson the tracks and estimate the penetrating power of direrent particles. Nuclear Chicago's "Cloudmaster" is a continuouely sensitive cloud chamher which provides a speetacular display of tracks caused by alpha, heta, gamma, and meson radiation. (Continued on page A562)

Another instructive way for acquainting students with some of the properties of nuclear particles (especially some of the less familiar ones) is the nuclear track plate. Supply houses such as Cenco sell microscope slides that have been coated with special emulsions and exposed to highaltit,ude cosmic radiation ($34.20), and a manual and syllabus for instructim in nuclear emulsion research. Cenco makes a. radioactivity demonstrator (KO.71201, 5179.50), plus GM Tube (Nu. 71227, 514.50) for classnmn use. A transistorized scaler is also available (No. 71208, $205). Atomic Laboratories, Ine. makes s. Nuclear Training System (Series 11, No. 71293, 5695, and Series 111, No. 71205, $79.5). The latter includes a coupon book for 13 different radioisotopes, which the purchaser can use as he sees fit. The activity of these sources (all in solution) ranges from 1 to 50 microeurierr. Both training systems use the six-decade NTSI1 Scaler (No. 712941, $495). Use of transistors and printed circuit boards has repuked in substantial size and weight reductions compared to vacuum-tube sealers, together with a maximum counting rate of 200,000 per sec. There are a t least three reasons why such a high counting rate is desirable, namely: 1) statistical accuracy incresses with the square root of the total count; 2 ) the background count and its fluctuations become less important; 3) the capabilities of fast counters can be exploited. GM counters will saturate a t count rates greater than about 20,000 per see, whereas scintillation counters can count millions per second. The N T S I I Scaler outnut is disolaved , in laree. - , briehtlv L. " illuminated numerals-s, desirable feature for lecture demonstrations. Atomic Accessories, Inc. makes a. series of rugged, luw-cost systems, designed especially for teaching nuclear science on all academic levels. Among these are: "Sralette" Low-Cost Srder and GM Counting System, SC-355C, 8353; Ksdiaassay Electroscope Kit, RE-1050K, %125; "Minilab" Miniaturized Nuelem Lahorxtory, ML-295B, 5194; Autoradiogranhv Kit. AR-356. $37.50: Radioehmma-

.

Nuclear-Chicago makes a full line of rugged, completely transistorized, teaching equipment, including Model 6263, Classmaster I1 System (5104.50) and Model 4001, Nuclear Teaching System, (8705). The latter is a complete portable classroom laboratory including scaler; timer, Gdgertube, sources, sample preparation apparatus, and manuals for instructor and students. A gas-flaw counting system, including a carbon-14 beta, source (Model 402, $200) and a. scintillation counting system (Model 405. 9500) are also available. Figure 16 shows Atomic Laboratories' new Portable Modular Radiation Lahoratory (No. 71200, approximately $2800 with the components shown in the figure). Modules can he connected and lurked together bath mechanically and elwtricnlly. Important design features are loa(Continued on page A564)

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current, ultra-fast latch-type ring circuitry, and a power supply stable to better than 0.1%. In portable operation, the power module uses three common 6 v lantern batteries. The Victoreen Instrument Co. makes basir, intermediate, and advanced educational, nuclear counting kits at prices ranging from $765 to $4,180.25. The

Basic Educator Kit, used for radioisotope counting, includes accessories such as standard sources, absorbers, and a healthphysics slide rule. The advanced kit is suitable for quantitative measurements of the activity of samples of natural and artificial nuclides. A fairly sophisticated nuclear pulseheight analyzer, known as the Gamma-

scope, ir made by Technical Measurement Corp., North Haven, Connecticut, for $5990. This instrument stores pulses, according to height, in one of 100 memory clrameh. The build-up of the energy spectrum can be observed on a cathode ray tube, and the counts in each ohannel of the complete spectrum can be printed out an paper tape in digits1 form. A n average analvsis takes onlv a few minutes. I n a manual accompanying thie instrument, there is s. description of 10 experiments that can he done with it, such as 7-ray spectroscopy, neutron activation, and Compton scattering. Picker X-ray Corporation offers a. lie of compact nuclear instruments for training in isotope techniques. They are also capable of use with such advanced techniques as pulse-height analysis, and rate function studies. Picker's Nuclear Division has also prepared an extensive Radioisotope Training Manual, including 60 nares of radioisoto~e ex~erimentsoriei~~

are groups of experiments on qualits&ivtive analysis, quantitative analysis, organic chemistry, and physical chemistry. The Picker Nuclear Division offers to help interested institutions in drawing up training programs in the use of nuclear techniques in chemistry and other fields. Helpful information on the development of course materials and special training aids may be obtained from Dr. Ruseell S. Poor, Direotor, Division of Nuclear Education and Figure 16. Portable Modulor Radiation Laboratory. Front and rear views of four interconnected modulea Recorder; 7-decodt:Scaler; Ratemeter; Power module and tunnel diode level detector.

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(Continued on page A566)

Training, U. S. Atomic Energy Commission, Washington25, D. C. Most of the companies making nuclear instruments also sell some radioactive sources. To help foster the use of radioisotopes for instrurtianal purposes, the Atomic Energy Commission has allowed certain quantities of such isotopes to be used under a "general license.'' The term "license-free" in sometimes used to designate surh quantities. Uranium and thorium salts often sufiire for demonstration purposes. These have very long halflives. In more advanced work, such as studies of eherniesl reaction mtea, and diffusirm in liquid media, it is essential to use isotopes whose lives are measured in minutes ur hours. The use of such isotnpes was difficultor impractical in schools because the radioactivity would decay to an ineignifirant level before or during delivery. Rerently, however, as a result of an inexpensive ion-exchange process, developed by Rrookhaven Sational Laboratttorv, short-half-life radioisatopes can be produced by students or research groups in their own laboratory. An isotope such as Ba-137 (half-life 2.6 min) is separated chemicdy from its parent Cs-137 (half life 30 years) by a reagent. Tho Ba137 is washed off the ion-exchange column, collected in a flask, and is available for immediate use. Atomic Laboratories sells several surh "Radioisotope Milkers" for $40 each. However, inasmuch as the 10 microcuries activity of the parent isotope exceeds that permitted under a general license, purchasers must have an AEC or State License. There is a gmwing trend towards the use of solid state radiation detectors (4). Atomic Laboratories' Xenar Instrument (KO.i123G,$450) permits interchangeable use of two separate detectors: 1 ) a silicon p-n junction diode for ar counting; 2 ) a lithium-drift p-n detector for 0, 7 , and nentmn counting. Personal radiation monitors are common in a radiochemistry laboratory. For student training purposes, Bendix offers the Model 863YS Direct Reading Dosimeter, rrmsisting of a quartz fiber electrometer and ion chamber. The regular unit price of $27 is discounted by 50y0 to qualified edm!stir,nal institutions. (This special price is only ahout one-third of the cost of most regular 200 mr dosimeters.) A separate, transistorized charger (Model 006), for zeroing the dosimeter, costs $20 (rompared to 313.5 for the charger-reader required for indirerbresding dosimeters). Except for small direrences in percentage accuracy and in electrical leakage, whir:h are not critical for teaching applicatk,ns, these dmimeters meet the same speeificatinns as the regular Rendir dosimeter^. Irrndi~tionof materials by y rays, Xmys, neutrons, m d charged particles, is heing used for many purposes, such as sterilization and polymerization. I t is also being used to study the degradation of mnterinls in n space environment. Feut r m generators and miniature electrical particle accelerators are lowered into oilwell shafts to analyze the eurmunding rock formations. Companies like Iiarnan Nuclear, and the General Atomic Division of General Ifynamics, make neutron genera-

(Continued on page A568)

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turs for activation analysis. High Voltage Engineering Corporation makes a 400 kv Van de Graaff Accelerator for teaching and research. I t can be used to accelerate positive ions or electrons. As 8, positive ion accelerator, it e m produce three different react,iom yielding neutrons of 0.3,2, and 14 Mev respectively. With rs gold or tungsten target in place of the electron window, the instrument becomes a source of X-rays. Atomic Lahuratories sells a low-oost, electrostatic generator and particle acrelerator (Rayotran, 8295). This e m deliver 20 micmarnperes a t a potential of 500 kv. With an inexpensive miniature high voltage generator, the Atomotron (No. 71846 for $19.95), a number of high voltage phenomena can he demonstrated. For the detailed study of neutron radiation and its effects in the classroom or laboratory, Atomic Accessories, Inc. offers a "Neutron Howitzer" (ND-327, $1375, and a smaller version ND-342, $675). These devices permit a. wide range of experiments on the properties of neutnms and their interadion with matter. A sealed Pu-Be neutron source is surrounded by water in a transparent Plexiglsss container. The water acts as a moderator and shield. Materids can he exposed a t any point within the moderator itself. Two horizontal expasure ports make it possible to obtain fast neutrons. A eet of foils is supplied for neutron activation experiments. For training in nuclear reactors, Atomic Laboratories offers the Ray-Actor for 6345.

Figure 17. Model Nucleor Reactor (Roy-Actor). Exploinr d l important arpectr of reoctor operotion, fmm start-up to criti