1. GENERAL REVIEW

On March 3, 1961, the National Bureau of Standards completed 60 years of service to science, industry, and commerce. Throughout this period it has been concerned with precision physical measurement, with the promotion of reliable and uniform measurement in the United States, and with a wide variety of research activities.

For measurements to have general meaning and validity, they must be based on common units and standards that are precisely and reliably known. Only then can there be effective interchange of information among scientists, realistic utilization of scientific data by engineers and technologists, orderly exchange of goods in commerce, and realization of the concept of interchangeable parts throughout industry. It is the Bureau's responsibility to develop and maintain the national standards upon which all measurements in this country are based, and to see that these standards are made available to science and industry through suitable calibration services.

A second important responsibility of the Bureau is to provide reliable and precise data on the basic properties of matter and materials that are of importance to science and industry. As such data are obtained by precise measurement, the performance of this function both draws upon and at the same time increases the Bureau's background of knowledge and competence in the field of measurement.

Through a broad program of research in the physical sciences, the Bureau continually strives to keep abreast of the measurement requirements of American science and technology. To insure that measurement inadequacies do not retard progress, it must anticipate tomorrow's measurement problems and lead in their solution, developing new standards and measurement techniques as new fields open up or become more active.

Such a research program provides a broad basis for service to the Government and the Nation in a variety of other ways. These include the development of test methods for materials, cooperation in the establishment of codes and specifications, and advisory services to other Government agencies on technical problems.

A third major NBS responsibility is the operation of central research and technical service programs for the Federal Government. Included in this category are the Central Radio Propagation Laboratory, the Data Processing Systems Laboratory, the Building Research Division, the National Hydraulics Laboratory and the Cryogenic Engineering Laboratory.

This report attempts to present the highlights of the Bureau's program for the fiscal year 1961. In section 2, the body of the report, representative studies and achievements from the various fields in which the Bureau is active

have been selected for brief presentation. However, the breadth of the program and the diversity of projects may make it difficult for the reader to obtain a coherent picture of the year's activity. The remainder of section 1 is therefore devoted to a brief summary of the more important accomplishments and activities of the year.

Progress in Measurement Standards

To provide a basis for accurate electrical measurements, the Bureau maintains very precise standards of electrical resistance and voltage from which all other electrical and electronic standards are derived. The values assigned to these two basic electrical standards are calculated from extremely precise measurements made in terms of the basic units of length, mass, and time. Such measurements, which must be periodically repeated, serve to fix the relation between the electrical and mechanical units so that they may be used together with consistent results.

During the year, the NBS unit of resistance was redetermined by a new, more accurate method. The determination made use of a capacitor whose value can be calculated to a high degree of accuracy from its dimensions. The NBS unit of resistance was then evaluated by comparison with this capacitor. The value obtained was self-consistent to better than a part in a million and was within approximately two parts per million of the value of the ohm as maintained by NBS on the basis of earlier measurement techniques. A basic problem in electrical standardizing laboratories has been to translate direct-current measurements, which are closely related to the fundamental standards, into alternating-current measurements at the frequencies used in electrical power generation and in radio and electronics work. A recent contribution to the solution of this problem was the development of a "differential thermocouple voltmeter" which indicates directly the percentage difference between an unknown alternating voltage and a previously standardized voltage.

The Bureau's atomic standard of frequency, which is now maintained by means of a natural frequency of the cesium atom, was operated on a regular basis throughout the year and was used to monitor the NBS standard frequency broadcasts. International comparisons showed continued agreement between this standard and the atomic frequency standards of Switzerland and the United Kingdom to 1 or 2 parts in 10 billion. The high stability of atomic frequency standards led to active consideration, on the international level, of specific plans for a redefinition of the second in terms of an atomic frequency.

To disseminate the frequency standard more effectively, the Bureau is working toward the construction of a standard frequency broadcast station to be located near Fort Collins, Colo. The new station will transmit frequencies of 20 and 60 kilocycles. Because these lower frequencies are transmitted directly along the surface of the earth rather than by reflection from the ionosphere, the received signals are much more stable. This permits

their transmission over great distances with greater accuracy than the shortwave broadcasts of NBS stations WWV and WWVH. The new station will have a much higher radiated power than the Bureau's existing low-frequency stations near Boulder, Colo.

Intensive research programs were continued to develop standards and measurement techniques for very high temperatures and pressures. Reliable temperature measurements were made by spectroscopic techniques in the vicinity of 16,000 °C, and extremely compact equipment recently developed for generating pressures in excess of 1 million pounds per square inch was further refined. Pressures reached in an experiment with this equipment can now be predicted within a few percent, as compared with 20 percent a year ago.

In recent years there has been great scientific interest in research at extremely low temperatures, within a few degrees or less of absolute zero. In this temperature region the molecules of which matter is composed become less active in their constant motion, so that much can be learned about the ultimate nature of matter.

As the success of physical research at the low temperatures depends to a great extent upon the accuracy with which temperatures can be measured in this region, the Bureau has been conducting an active program to provide a temperature scale and thermometer calibration service in the range from 1.5 to 20 °K (-457 to −423 °F). In 1961 an acoustical interferometer was constructed and used successfully to measure very low absolute temperatures in the liquid helium range. Further development of this instrument, which makes use of the change in the velocity of sound in helium gas with temperature, is continuing. Favorable results were also obtained in investigations of carbon and germanium resistors for use as precision secondary thermometers in the liquid helium temperature region.

Reliable precision measurement techniques and standards for neutrons. are urgently needed both in the power reactor field and in various areas of basic and applied research, such as the study of radiation effects and the development of health physics instrumentation. Although the Bureau has developed a low-intensity neutron standard, it has lacked facilities for measur ing the high-intensity fluxes that occur in a nuclear reactor. At the close of the year design work was nearly complete for a high-flux research reactor to be constructed at the Bureau's new site at Gaithersburg, Md. The reactor, to be known as the NBSR, will enable the Bureau to fill its growing responsibilities in the many rapidly expanding fields of atomic energy. The reactor will advance the measurement and understanding of the effects of radiation on substances of all kinds, and will provide a powerful tool for analysis of atomic and molecular structure. Of particular importance among the basic processes to be studied is that of fission. Inadequate understanding of this process still limits the design of fissile material breeding plants.

The value of a uranium reactor fuel depends on the abundance of the uranium-235 isotope and accurate standards of composition are required to make precise mass spectrometric determinations of this abundance. During