Activation Analysis More Sensitive Lithium-drifted detectors may have resolutions 10 times that of sodium iodide scintillators An increase in sensitivity can be ex pected in neutron activation analyses from the introduction of semiconduc tor detectors. Lithium-drifted ger manium detectors, for example, may have resolutions as much as 10 times better than the now widely used so dium iodide (tellurium-activated) scintillators. Ge(Li) detectors also offer other improvements in activation analysis, Dr. Stanley G. Prussin of Lawrence Radiation Laboratory (University of California, Berkeley) told the 1965 International Conference on Activa tion Analysis held at Texas A&M Uni versity. These include improvements such as reducing or possibly eliminat ing the need for chemical separations, possibly increasing the number of ele ments that can be determined, and ending tedious decomposition in anal ysis of complex photo peaks in the spectra. Activation analysis has been known since shortly after its discovery as a technique with high potential sensitiv ity for many elements; it can be used to determine elements only, not chem ical compounds, Dr. Prussin explains. The technique requires no reagent blank, a common requirement for other analytical techniques. It also involves little interference from neigh boring elements because decay prop erties of radioactive isotopes don't re late to their chemical properties. Limited Use. Even with these ad vantages, activation analysis has found limited use. In many practical sam ples, a number of readily activated elements yield complicated gammaray spectra because each of several radioisotopes produced may have a number of gamma rays in its charac teristic spectrum. Sodium iodide de tectors have relatively poor resolving power, and this results in an overlap of spectra. To sort out and identify the gamma-ray lines, elaborate and time-consuming chemical separations are often used. Another method of attack involves indirect methods such as synthetic analysis of the spectrum using complex computer programs. To demonstrate the value of Ge(Li) detectors, Dr. Prussin and co
workers J. A. Harris and Dr. J. M. Hollander analyzed aluminum samples ranging in purity up to 99.9999%. These samples, along with appropriate standards, were irradiated for periods of two to 90 hr. in the Livermore re actor. With short irradiation times of two hours, small concentrations of copper, manganese, gallium, and so dium were detected. Not all of these elements were determined for each aluminum sample, but for the 99.9999% material, copper concentra tion appeared below 0.3 to 0.4 p.p.m. and gallium below 0.14 p.p.m. By comparison, 99.99% aluminum sam ples contained 10 to 13 p.p.m. copper and 1.4 to 3.4 p.p.m. gallium. Long irradiation times of 90 hr. were used to determine iron, cobalt, chromium, hafnium, and scandium in aluminum. This longer time increases longer-lived activities induced in the aluminum. A 10-day period is used to allow practically all sodium-24, copper-64, and gallium-72 to decay to permit observation of gamma rays from the other elements of interest. Iron and cobalt were not found in the 99.9999% aluminum, although 5300 p.p.m. iron and 0.88 p.p.m. co balt were found in the aluminums of
lower purities. In 99.9999% alu minum, 0.17 p.p.m. scandium, 0.48 p.p.m. hafnium, and 0.47 p.p.m. chro mium were found. Comparison. The scientists made various comparison tests of Ge(Li) detectors and conventional sodium io dide detectors. Among these tests— the mercury-203 279-k.e.v. line, for example—the efficiency of a Ge(Li) detector with dimensions of 6 sq. cm. by 9 mm. is 1.3 Χ 1 0 2 relative to that of a detector with a 3-in.- by 3-in.-diameter sodium iodide crystal. This Ge(Li) detector shows a line width of about 4 k.e.v., Dr. Prussin says. A smaller detector, 2 sq. cm. by 7 mm., shows a line width of about 2 k.e.v. By comparison, typical so dium iodide detectors show a re sponse of about 20 k.e.v. at energies used in tests with the 122-k.e.v. gamma ray of cobalt-57, according to Dr. Prussin. The Lawrence Radiation Labora tory group operates their Ge(Li) de tectors in vacuum (about 2 χ 10 -5 microns) at approximately 77° K. These detectors are mounted on a copper plate which makes contact with a liquid-nitrogen reservoir cryo stat. The front window of the detector is aluminum, 0.020 in. thick. Electron ics include a low-noise, low-capacity preamplifier and biased amplifier sys tem built in the laboratory. Pulses from the amplifier system are routed to a 400-channel pulse-height ana lyzer for sorting.
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C&EN
57
New Data-Logging System Offered by GE New expandable systems for industrial process data handling have been in troduced by General Electric. The new systems, GE/PAC data loggers, are designed for use where plans may involve growing step-by-step into a full-scale computer control operation. GE points out that many processes not yet under computer control can be studied to get enough data for effec tive programing prior to automation. The GE/PAC data loggers can per form this function and can also pro vide an expandable base on which au tomation can proceed. Where the
plant or process is not suited to auto mation, the data logging system can be used to provide conventional proc ess control information. In the past, loggers have been in herently inflexible, according to GE. The GE/PAC data loggers can be adapted to a specific type of applica tion. Five levels of capability are available. Each level of logger is de signed to perform given functions. The lower levels are logic-data type and can be attached to a GE/PAC process computer. The upper levels have simple stored programs and can be expanded into a standard GE/PAC computer. The systems will scan up to 15
points per second and at higher rates and at higher accuracies than can be found in present systems, GE says. Construction of all loggers is modular. This makes it possible to add options to build the system to full capacity without penalizing the small user who does not need or want these options. The loggers can monitor all types of analog, digital, contact closure, and pulse inputs. Point identification can be numeric or alphanumeric charac ters. The systems are capable of op erating at 32° to 131° F. The new GE/PAC data logging line includes systems with prices rang ing from $20,000 to $150,000. Op tions available include alarm logging, pulse accumulation, off-set correction, and on-line limit change. The system can also include high-scan rate, digi tal-trend logging, analog-trend log ging, and sequence of events record Ε 30 ing.
BRIEFS A catalytic muffler for buses which burn diesel fuel has been demon strated in Washington, D.C., by W. R. Grace. The catalyst used in the muf fler is similar to that used in an ex haust control device certified for use on new automobiles by the California Motor Vehicle Pollution Control Board. The new muffler uses an 850cu.-ft. catalyst bed and will reduce carbon dioxide, carbon monoxide, and carbonyls by about 20 to 30%.
U.S. Steel Corp. has ordered seven General Electric steam generators for use in its new gas processing facilities at the Clairton Works near Pittsburgh, Pa. The steam generators will use ex haust heat from gas turbines to gener ate steam for a turbine helper drive. The seven steam generators each have a rated output of 63,000 lb. of steam per hour at 600 p.s.i.g. and 659° F.
Glass-Fiber Plastics Bid for Construction Role Laborers dump a buggy load of concrete over molded glass-fiber forming pans during construction of a 14-story office building in Queens, N.Y. The lightweight pans, made by Molded Fiber Glass Co., of Ashtabula, Ohio, by matched metal die molding, are unaffected by the weight of buggies and other equipment. A switch from structural-steel framing to poured concrete grid slabs and the use of molded glass-fiber concrete-forming pans is expected to pare about $100,000 from the cost of constructing the office building. Molded Fiber Glass has 78,000 concrete-forming pans available for lease, and expects to have between 125,000 and 150,000 pans available by the end of this year.
58
C&EN
MAY 3, 1965
A new reactor concept that may lead to lower fuel costs in generating atomic power has been described by Dr. Peter Fortescue of General Atomic Division of General Dynamics Corp. Dr. Fortescue told a meeting of the American Nuclear Society that the new breeder reactor uses a gas coolant as the transfer medium instead of a liquid-metal coolant such as so dium.
Eastman Briefs FOR MAY
Eastman Inhibitor DOBP O H
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Form pale yellow flakes UU-U6°C. Melting point Solubility non-polar and polar organic solvents A highly effective ultraviolet light inhibitor for both polyethylene and polypropylene. Also shows promise in polyvinyl chloride, polystyrene and polyesters. Protects surface coatings containing such film formers as cellulose acetate butyrate, cellulose nitrate and acrylic resins.
Form white crystalline solid Melting point 182-185°C. Solubility most polar organic solvents Don't let the ester link fool you. Under the influence of UV, this molecule often converts to a hydroxybenzophenone. Excellent for protecting cellulosics, PVC and certain polyesters from light. Transpar ency remains high. Bastman C h e m i c a l Products, I n c .
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One oi a série* briefim describing G3Ê9s research in depth
Our Stirling Engine: Just Add Heat. It's a thermal engine—a remarkably quiet device that can run even on heat from the sun. There are no explosions in the cylinders, just quiet expansion and contraction of the working fluid, pushing the pistons. The fluid—hydrogen or helium—is sealed in the engine. Heat to expand it can come from any outside source . . . burning fuel, a nuclear reactor, a heat storage system, as well as the sun. The Stirling cycle is reversible, too. Crank in mechanical power and the engine absorbs heat, becomes a refrigerator. Invented back in 1816, the Stirling Thermal Engine is now becoming practical for modern applications. Current improvements have grown out of a cooperative development program with N. V. Philips' Gloeilampenfabrieken, of the Netherlands. Performance of the latest models is encouraging (40% thermal efficiency, for instance, compared to about 28% for conventional spark·* ignition engines). An experimental three-kilowatt generator set is being tested for Army field use, where quiet is important. Inaudibility at 300 feet has already been attained. The Research Laboratories and other GM groups are also studying Stirling systems from five to five thousand horsepower, for applications ranging from under the sea to outer space. At GM Research, engineers study all kinds of engines. The research may be all-encompassing, from basic thermodynamics and engine cycle analyses to the design of prototype units. It helps us find a better way.
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hearth-types available for processing, materials testing, or research and de velopment requirements, according to the company. Ε 36 Dual-purpose, automatic aerosol pro duction unit is available from General Kinetics division of GK Industries, Inc., of Atlanta, Ga. Model GK-20SFA is capable of filling, purging, crimping, and charging units with fluorinated hydrocarbon-type propellant. In addition, it can also handle products which use soluble gases, such as carbon dioxide and nitrous oxide, as propellants, the company says. Ε 37
Line of positive temperature-coeffi cient thermistors is available from
General Electric Co., of Edmore, Mich. Designated PTC, the ther mistors ofiFer an 8-sec. response to temperature changes and are rated for operation at temperatures up to 150° C. The thermistors are de signed for temperature compensation, measurement, and control applica tions, GE says. Ε 38
Two new vacuum evaporators are be ing marketed by Consolidated Vacuum Corp., of Rochester, N.Y. Models CVE-18 and CVE-19 are designed for large-scale manufacturing facilities, university laboratories, and other ap plications where equipment cost is an important limiting factor. Ultimate vacuum of 3.3 X 10~7 torr and 4 X 10 -8 torr, respectively, can be ob tained, the company says. Ε 39
May 3, 1965
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Halogenated, unsaturated monomer with about 40% chlorine is offered in research quantities by Diamond Alkali Co., of Cleveland, Ohio. Tetrachlorom-xylene can be used as a reactive component of allyl, acrylic, polyester, and similar systems to impart fire retardance, Diamond says. Advantage can be taken of the double bonds in the chemical to build the molecule into the final polymer. C 60 Double salts of two halides and two cyanates are offered in research quan tities by City Chemical Corp., of New York, N.Y. The halides are bismuth sodium iodide and cesium rubidium chloride. The cyanates are cobalt ammonium thiocyanate and potas sium selenocyanate. C 61 Butyltin compounds are now available in commercial quantities from Carlisle Chemical Works, Inc., of Reading, Ohio. Tributyltin derivatives are biologically active and are used to control microorganisms. Dibutyltin compounds are used as catalysts in rigid urethane foam manufacture, as promoters in esterification reactions, and as curing agents for silicone resins. C62
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Thioglycolic acid, 80% solution, is now available from Evans Chemetics, Inc., of New York, N.Y. Standard concentration of this acid was 70%. For use as an intermediate, a 98 to 99% product is also available. The highconcentration material is practically anhydrous, Evans Chemetics says. C63 Manganese carbonyl is being offered in 10-gram development quantities by Pressure Chemical Co., of Pittsburgh, Pa. The material has ligand-forming potential with organic chemicals, the company says. It also has shown antiknock and combustion improving potential, Pressure Chemical adds. C 64
Further information on keyed Equipment and Chemical items is readily available . . . Use handy coupon on page 64
MAY
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