Needs for Radioactivity Standards and Measurements in Different Fields

This 1973 paper was written at a critical point in the development of applications of radioactivity and nuclear power, and it defined the needs of standards laboratories of the world for the remainder of the century. Although the paper [1] was co-authored by members of the Radioactivity Section, it was largely written by Wilfrid Mann and represents the fruition of his years of reflection on radionuclide metrology. Standards are needed for radioactive materials to permit their accurate measurement for purposes of health, worker protection, and public safety. The National Bureau of Standards developed a program for standards and calibrations of radium-226 (1600 year half life) in the early part of the century [2,3], but this program was limited mainly to naturally-occurring radionuclides in the uranium and thorium series until the late 1940s. Following World War II, man-made radionuclides from reactors, linear accelerators, and cyclotrons became available for more routine uses in medicine, agriculture, and industry. The Bureau then began development of primary standardization techniques that could be applied to classes of radionuclides, such as pure beta-particle emitters [4], gamma-ray emitters, and alpha-particle emitters. In 1951, Lauriston S. Taylor envisioned a world-leadership role for NBS in radionuclide metrology and recruited Wilfrid Mann from the Chalk River laboratories in Canada. Throughout the 1950s and 1960s Mann built and expanded the Bureau’s capabilities in radionuclide metrology [5], including techniques such as microcalorimetry, betagamma coincidence counting, gas counting, defined solid-angle alpha counting, and photon spectrometry. Metrology also required developing expertise in sample preparation, radiochemistry, isotope separation, sampling for environmental analyses, and measurement quality assurance. Thus, by the end of the 1960s NBS was ready to assume national leadership in measurements for radioactivity, and a timely report from the National Academy of Sciences [6] stressed the needs for radioactivity standards for public health, medicine, and nuclear science. Needs for Radioactivity Standards was written just as the applications of radiopharmaceuticals in nuclear medicine were beginning a very rapid expansion. During the same period, the U.S. nuclear industry (and the industrialized world) were very positive about the prospects for cheap, abundant “atomic energy,” and the utilities were building new nuclear power stations all over the country. Most of the 104 power reactors operating today were ordered during the 1970s. In each of the national standards laboratories, metrologists were considering how to meet the needs of these emerging technologies. This paper was the keynote presentation of the formative meeting of the International Committee for Radionuclide Metrology (ICRM). The paper both summarizes the status of radionuclide standards and explores the needs for standards, measurements, and traceability for the emerging fields of nuclear medicine and nuclear power. It provided a blueprint for national and international traceability. In the first nine pages Mann laid the foundation for radionuclide metrology by introducing the concepts, terminology and historical developments of measurement standards and radioactivity standards. This entertaining and informative introduction was absolutely necessary to his later development of the concept of traceability. He points out that “criterion” and “standard” are synonyms in the English language. Criterion comes from the Greek, while standard is derived from the old French “estandart.” It was a flag raised on a pole to indicate the rallying point of an army. Our battlefields of today have shifted from armed combat to economic warfare, and this sense of the word standard still resonates with U.S. industry. Derived standards of radioactivity differ from the base quantities of time, length, and mass in two important respects. First, radioactivity is an ephemeral quantity. The substance is decaying with some half life (a good example is the 6 hour half life Tc used in nuclear medicine) such that often the material no longer exists after the measurements are completed. In most cases, the standard must reside in a system (protocol, people, detector, and associated electronics) that can be used to measure a disintegration rate (activity) from first principles. Second, there are a few thousand radionuclides, and they are found in many matrices (gas, liquid, solid, soil, air filters), so that choices must be made on the select few nuclides and matrices for “national standards.” Needs for Radioactivity Standards addressed the basic issues of identifying emerging technologies, ordering priorities, developing measurement quality assurance programs, and establishing traceability for key measurements at the national and international levels. Following the historical background, Mann gave special emphasis to needs for radiopharmaceuticals and for monitoring radioactivity in the environment.