WeUA EMANATION ELECTROSCOPE
the EDITOR'S column
A Student Experiment (or Measuring the Half Life of Thoron (Rn s s o ) Student plots radioactive decay curve and computes half life to within two seconds Electroscope and Measuring Microscope
L.T. H a l l e t t , E d i t o r
THE
NATIONAL R E F E R E N C E
GROUP
of standard cells maintained by the National Bureau of Standards was established to serve as the physical standard for the volt in the United States. The electromotive forces of cells within the group have varied by less than 7 parts per mil lion over a period of 50 years. These cells, which are of the cad mium sulfate type, provide the basis on which the Bureau determines the emfs of other cells to be used as standards. Saturated standard cells which have been compared with the cells in the National Reference Group are used as working standards within the Bureau. Furthermore, the Bureau provides calibration of unsaturated standard cells used in its own programs. Calibrations of saturated stand ard cells are performed for public utilities, universities, research insti tutions, other government agencies, and private industry. This service is achieved by means of working groups of saturated standard cells maintained at the Bureau's labora tories in Washington, D. C , and Boulder, Colo. The emfs of the cells in the working group at Washington are determined every four to six weeks by comparison with cells in the National Reference Group. The emfs of the cells in the working group at Boulder are determined using a transfer group of saturated standard cells, the mean emf of which is measured by comparison with cells in the National Reference Group at Washington, D. C. Saturated cells used as standards should be submitted to the Bureau for measurement every year for the first three years and every two to three years thereafter. Unsaturated cells should be calibrated using a group of saturated standard cells every year or at least every two
Adopted from an appara tus originally developed for use at Harvard Uni versity by Professor Κ. Τ, Bainbridae, Gerald H ton, and J . C. Street.
ionization Chamber
~]
Radioactive source included
Electrostatic Charger, Filter, Radioactive Source, and Emanation Pump.
No. 619
The Emanation Electroscope is intended for'use by students at the introductory level in phys ics or chemistry for measuring the half life of a radioactive material with complete safety and without requiring costly or complicated electronic equipment. The merit of this particular ap_ paratus is that it is so simple to understand, to operate, and to maintain. The radioactive material (thorium oxide) is included, one filling is adequate for years of use, and it never needs to be removed from the apparatus. R e c o m m e n d e d Accessories No 6 1 9 Each 464 75 STOP WATCH, 1/5 second. No. 823A. Each, $17.75 ' * ' ELECTRIC STOP CLOCK. No. 824L. E a c h , $39.50
T H E WELCH SCIENTIFIC COMPANY ESTABLISHED 1880 MAIN OFFICE: 1515 SEDGWICK STREET, DEPT. A-1, CHICAGO, ILLINOIS, U.S.A. 60610 NEW YORK OFFICE: 331 Ε. 38ΤΗ ST., NEW YORK, Ν. Υ. 10016
Now! New TUNGSTEN-RHENIUM Filaments!
GOW-MAC CHROMATOGRAPHY COMPONENTS A-GAS DENSITY DETECTORS for analysis without calibration. Β - T H E R M A L CONDUCTIVITY CELLS in stand ard designs. C - MICRO VOLUME T/C CELLS with thermistors internal vol. as low as 25 microliters. D — FILAMENTS to fit most commercial units. Corrosion problems? Try nickel! Ε —SPECIAL CELLS to your design with reliable filaments or thermistors. F - P O W E R SUPPLIES complete with bridge circuits. EXPERIMENTAL GAS CHROMATOGRAPHS in kit form.
SEE T H E M O N D I S Ρ L A Y - V I S I T
B O O T H F26 PITTSBURGH CONFERENCE O N APPLIED SPECTROSCOPY
G O W - M A C INSTRUMENT COMPANY 1 0 1 KINGS ROAD, M A D I S O N , N . J . 0 7 9 4 0 GAS
-
ANAirSIS
Telephone: 201-377-3450 INSTRUMENTS
SINCE
19 3 5
Circle No. 37 on Readers' Service Card VOL.
36, NO. 2, FEBRUARY 1964
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