the EDITOR'S

column L.T. H a l l e t t , E d i t o r

Γ Γ Η Ε INTERNATIONAL COMMITTEE on Weights and Measures has

recommended general worldwide use of a Helium-3 temperature scale derived by Los Alamos Scientific Laboratory scientists. The new scale, "Helium-3 Vapor Pressure Scale of Temperatures," measures temperature in the realm of 0.25° to 3.32° above Absolute Zero Kelvin.

The recommendation was an­nounced by Dr. A. V. Astin, Di­rector of the U. S. Bureau of Stand­ards and a member of the Interna­tional Committee. Action was taken at an October meeting in Paris of the Advisory Committee on Thermometry, at which time Dr. Thomas R. Roberts, physicist in the Los Alamos Cryogenics Group, ex­plained the new scale.

For more than a decade there was international disagreement over scales set up using the isotope Helium-4. Finally, in 1958 agree­ment on a Helium-4 scale was reached. However, Helium-4 can­not be used for accurate measure­ments at temperatures below 2.2° K. without the use of very complicated apparatus and procedures. The va­por pressure becomes so small it is difficult to measure and the liquid becomes a "super-fluid." In this state the "liquid" will actually crawl uj) the walls of any container.

Helium-3 with a higher vapor pressure does not become super-fluid. At 3.32° K., the vapor pres­sure is 3,670,000 times greater than at 0.25° K., permitting very sensi­tive measurements in this range.

The new scale involves use of an intricate equation by which tem­peratures can be determined to a few ten-thousandths of a degree. Comparative measurements made with the Helium-4 scale show the new one to be several tenths of a

A Student Experiment for Measuring The Half Life of Thoron (Rn )

Welch EMANATION ELECTROSCOPE

Student plots radioactivity decay curve and computes half life to within two seconds

Adapted from an apparatus originally developed for use at Harvard University by Profes­sors K. T. Bainbridge, Gerold Hollon, and J. C. Street.

Radioactive source included

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Circle No. 144 on Readers' Service Card

VOL 34, NO. 13, DECEMBER 1962 · 7 9 A

and

Microscope

Ionization Chamber

Electrostatic Charger, Filter, Radioactive

Source, and Emanation Pump.

EDITOR'S COLUMN

per cent different at 1° K. from earlier Helium-3 scales.

Pr imary Standards L a b o r a t o r y

The N a v y Bureau of Ordnance has established a Western Pr imary Standards Laboratory at Pomona, Calif., which has one of the most complete facilities for instrument testing in the world. This labora­tory is operated by Convair D i ­vision of General Dynamics Cor­poration under a N a v y contract. The principal function of the labo­ra tory is to certify instruments t ha t are being used as local, or "second­a ry" s tandards by companies under contract to the Navy . Through in­ter-service agreements all Defense Depar tment installations may also use the laboratory. Certification is accomplished by comparing the per­formance of the instrument under test with a "pr imary s tandard" which is maintained and sent pe­riodically to Washington, D. C , for pr imary certification by the N a ­tional Bureau of Standards. The certification service of the Pomona Laboratory is free of charge. How­ever, the laboratory also adjusts and repairs instruments before certifica­tion if this is requested and charges for this service.

Before the establishment of this laboratory each contractor was checking his own carefully cali­brated s tandard instruments, but there was no assurance t ha t one company's s tandards equalled those of any other. The Nat ional Bureau of Standards in Washington had the facilities to make the necessary tests, but with a limited staff, it took months to return instruments sent in for test.

A survey revealed tha t 4 5 % of the instruments in use were off-s tandard ; thus it was decided to create the Standards Laboratory. Instruments are tested by the hun­dreds each month. These tests cover four basic areas: electrical, electronic, microwave, and electro­mechanical and include various a.c. and d.c. measurements, tempera­ture, pressure, acceleration, and mass measurements.

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V O L 34 , N O . 13, DECEMBER 1962 · 8 1 A

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