Developments in the U.S.A. dominated in the period from 1930-1950, as turmoil in Europe diverted scientific work on the Continent, and was the time when many of the leading scientists fled the continent. Research in Bohr’s Copenhagen laboratory was a major exception continuing up to 1943. After the war, nuclear science and research recommenced and accelerated in many countries.

The invention of the cyclotron by Ernest Lawrence in Berkeley, California in 1929/30 was THE single event that stimulated the rapid development of biochemical, physiological and and basic biological knowledge based on the use of radioactive tracers, resulting ultimately the field of nuclear medicine. The availability of new radioactive tracers made it possible to  test new ideas on site at Berkeley and later with collaborators at places without their own accelerators/reactors.

The cyclotron accelerated charged particles in a circular path to a velocity and energy that transformed stable elements hit by targets in the beam inducing them to radioactive isotopes of the same or closely related elements. Lawrence developed a series

of increasingly powerful cyclotrons, and cartoons illustrate how the cyclotron was variously perceived. The Berkeley 4” magnet (1930), was followed in 1932 by an 11” magnet that accelerated protons to energies above 1 Mev. A 27″ cyclotron was running in the Berkeley “Rad Lab” by September 1932 where it accelerated protons to 3.6 million electron volts, shortly followed by a 37″ cyclotron that accelerated deuterons to 8 MeV and alpha particles to 16 MeV. This was the beam that produced the first artificial element, technetium which became the most widely used radioisotope in clinical medicine the discovery of which is attributed to Emilio Segre. The story of Technetium is divided into 3 parts. Part 1 is Segre’s discovery,  discussed below. Part 2, involves the production of the generator at Brookhaven National Lab and Paul Harper at the Univ of Chicago. It and  Part 3 of the story follow in the 1960s when clinical applications were developed and widely disseminated.

Part 1. The discovery of element 43  in December 1936  occurred at the University of Palermo, Sicily  by Carlo Perrier and Emilio Segrè. This followed Segrè’s  visits to Columbia University in New York and then to the  Berkeley Laboratory. At Berkeley, he persuaded cyclotron inventor Ernest Lawrence to let him take back some discarded cyclotron parts that had become radioactive. Lawrence mailed  him a molybdenum foil that had been part of the deflector used in the cyclotron.

Segrè enlisted his colleague Perrier to attempt to prove, through comparative chemistry, and confirm that the molybdenum activity was indeed from an element with Z = 43. They succeeded in isolating the isotopes technetium-95m and technetium-97. University of Palermo officials wanted them to name their discovery “panormium”, after the Latin name for Palermo, Panormus. However, in 1947 element 43 was named after the Greek word τεχνητÏŒς, meaning “artificial”, since it was the first element to be artificially produced. Segrè returned to Berkeley and met Glenn T. Seaborg. They isolated the metastable isotope technetium-99m, which is  used in  more than ten million medical diagnostic procedures annually.

A detailed review of the history of Tc and Iodine is given in an Italian article “The Discovery of technetium-99 and iodine-131” (translated by Google) by Modoni and colleagues. For more on the I-131 story click here). The Use of Radioactive Iodine in the Diagnosis and Treatment of Thyroid Diseases  by J. Howard Means, the founder of the MGH Thyroid clinic provides a scholarly history of iodine and the thyroid. The Saul Hertz family web site posts some original written documents and video histories.

In 1935, Ernest Lawrence added physicians to the Rad Lab’s roster starting with his brother, John Lawrence, an Internist recruited from Yale. He was shortly joined by physicians Joseph Hamilton, and Paul Aebersold, with physician collaborators from the UC San Francisco (UCSF) faculty. The addition of physicians and biologists to the Rad Lab’s staff required the construction of a new building adjacent to the Rad Lab. It was named the Crocker Radiation Laboratory after the UC Regent (William Crocker).  Crocker had donated money to construct the facility to house the large 60″ cyclotron (accelerating chamber diameter measured in inches) with a magnet that weighed 220 tons. While the UC cyclotrons were gaining importance for nuclear physics and biomedical applications, Bohr in Copenhagen, Dubridge in Rochester, and Physicists at Michigan, Harvard, Tokyo, and MIT were actively developing their own facilities.

The 60-inch Crocker lab cyclotron began operations in 1939, the year Lawrence won the Nobel Prize in Physics for the invention of the cyclotron. The end of the decade saw the siting of the 184″ machine that more than doubled the size of the 60-inch cyclotron. This required more space for the Rad Lab than the campus could provide, and the new facility was located in the hills above the campus. The mountainous Berkeley topography was well-suited for circular cyclotrons, but not for the next generation of long, high energy linear accelerators that required large flat land sitings. These new National Lab accelerator labs were located elsewhere, i.e. the Stanford Linear Accelerator (SLAC) at Palo Alto, CA; Fermi National Accelerator Lab (FNAL) at Batavia IL; and the largest and most powerful CERN, located in Geneva Switzerland.

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