INSTRUMENTATION
instrument abstracts
Cary Applied Physics
Corporation/Pasadena/California
Cary Vibrating Reed Electrometer simplifies C 1 4 , H 3 and S 3 5 determinations
DETECTS AS LITTLE AS 1 0 1 2 CURIES-The
high sensitivity and high precision of the Cary Model 31 Electrometer p e r m i t m i n i m u m a m o u n t s of costly "tagged" materials to be used in radio active isotope studies, saving enough to pay for the instrument in a short time .and materially reducing the hazard to living experimental subjects. This greater sensitivity, plus the de velopment of simplified experimental procedures, make the Cary Model 31 particularly valuable in determination of C 1 4 and H 3 in biological and chemi cal s a m p l e s . W i t h t h e s e n e w t e c h niques, t h e smaller samples may be used and the use of a precipitate with its inaccuracies and time-consuming preparation is eliminated. Instead, sam ples are directly converted into a gas which can be measured with an ioniza tion chamber and a Cary Model 3 1 . The ionization chamber and vibrating reed electrometer offer the only conve nient accurate method of measuring radioactivity of CC*2-air mixtures in flowing systems, such as are encoun tered in in-vivo studies. One research group led by Dr. Bert M. Tolbert has had considerable suc cess in applying these procedures to a wide variety of samples and research problems, including studies of animals. NEW REVIEW PAPER
Dr. Tolbert, now at the University of Col orado, has authored a 46-page paper cover ing detailed proce d u r e s f o r C1* a n d Tritium assays, ionι chamber theory, ._.] samples a n d sample preparations, combustion of organic comoounds to CO2, design and con-
struction of ion chambers and meas urement of ion chamber currents and approximate calibration data. Copies of the paper are available from Technical Reports Section, Department of Com merce, Office of Technical Services Washington 25, D.C., for $1.25 each. When requesting a copy, please ask for Bulletin UCRL-3499. OTHER USEFUL A P P L I C A T I O N S
Measurement of radioactivity is only one of many applications w h e r e t h e Model 31 can be used advantageously. For example, amplification and meas urement of ion currents in mass spec trometry, p H determinations, precise measurements of small charges, cur rents, or voltages from a high imped ance source can all be made faster, simpler, less expensively and far more accurately using the Model 3 1 . BRIEF SPECIFICATIONS O F THE M O D E L 3 1 Accuracy —Measurements reproducible to within 1 % . Accuracy limited only by. the accuracy of the recorder, potentiometer, or meter used. Reliability —No grid current, greater freedom from zero drift. Much more rugged than other types of electrometers. Stability —Open circuit input; less than 6 χ 1 0 " coulombs rms short period noise; less than 5 χ 1 0 - " amperes steady drift. Short circuit in put; less than 0.02 mv rms short period noise; less than 0.2 mv per day steady drift. 10 standard r a n g e s - R a n g e s provided on the Model 31 are 1, 3, 10, 30, 100, 300, 1,000 mv, and 3, 10, 30 volts. The output of the Model 31 will operate a 1 ma recording milliammeter or a standard recording potentiometer. Accessories—Ionization chambers, recorders and various special modifications and accessories are available for all types of electrometer uses.
A new catalog on the Cary Model 31 is available. Write for your copy today to Applied Physics Corporation, 362 West Colorado St., Pasadena 1, California. Ask for Data File A9-68.
For further information, circle number 6G A on Readers' Service Card, page 89 A
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ANALYTICAL CHEMISTRY
sitive. The sample is dissolved in the scintillating liquid or gel. A system of this sort will detect as little as 25 μμο. of tritium. (It will be recognized that this claim amounts to approximately 0.1 c.p.m., which would require the best suppression of random or back ground count.) There is now a large background of experience in liquid scin tillators. The five components of a good scintillation solution are (1) an aromatic solvent, (2) a fluorescent dye, (3) a wave length shifter, (4) a diluent in which the sample can be dissolved, and (5) naphthalene as a light restorer. Toluene, xylene, triethylbenzene, and ethylhexene are the usual solvents. Terphenyl and diphenyloxazole (PPO) are the most useful dyes. The object of the wave length shifter is to re-emit the absorbed light at a wave length closer to the optimum of the photomultiplier tube. The favorite for this purpose is phenyl-oxyzol-phenyl-oxyzol-phenyl (POPOP). Whenever a dil uent or solvent necessary to dissolve the sample is added, some light may be absorbed and the addition of naphtha lene restores some of the light. The use of a two-channel pulse ana lyzer permits the simultaneous count ing of tritium and C 14 and thus one can count both hydrogen- and carbonlabeled atoms. Gas counting techniques depend upon the conversion of the tritium-labeled compound into a suitable gas, and these methods have been developed to a high degree. This excellent revie\v discusses appli cations of tritium labeling to problems in biology and drugs and petroleum technology. The radioautographic uses are also described. Forty refer ences to the subject provide a good contemporary view of the field. Recording Differential Thermobalances
Although scientists can now purchase elegant recording balances, new devel opments are constantly appearing. One of the most interesting and stimu lating papers which it has been our privilege to read in many years is by P. L. Waters of the Coal Research Sec tion, Commonwealth Scientific and In dustrial Research Organization, North Pyde, N.S.W., Australia. In describing new types of recording differential ther mobalances, he not only gives practical and useful designs for such instruments, but a wealth of stimulating suggestions [J. Sci. Instr. 35, 41 (1958)]. Silver-Coulometer Type. One in genious sj'stem is a silver-coulometer type differential thermobalance. Mo tion of the balance pointer is detected photoelcctrically. The photocurrent is
