Marie Curie is perhaps the most famous woman of 20th-century science. Major motion pictures and best-selling biographies have chronicled her discovery of the radioactive elements polonium and radium, for which she shared the Nobel Prize in physics in 1903 and then received a second Nobel Prize, this time in chemistry, in 1911. Very little note, however, has been made of her leadership role in the development of radioactivity standards.
None of NIST’s recorded histories mentions Marie Curie, which I find a strange oversight. I came to NIST in 1972 and worked for 15 years in the Radioactivity Group, which maintains the national standards for radioactivity, including the standard for radium in solutions. In 1988, I took over the Dosimetry Group, which maintains national standards for radiation doses from sources including radium. Searching through my new laboratories, I found a framed 1921 photograph of Marie Curie from The Pittsburgh Sun on top of an old file cabinet and started to wonder: What was her connection to NIST, and why did my predecessors save this photograph?
In 1910, she was asked by her peers to prepare the world’s first radium standard: a glass ampoule containing 21.99 milligrams of radium chloride, whose mass and radioactivity had been carefully measured. She agreed, on the advice of Nobel laureate Ernest Rutherford, that this international standard would not be kept in her Paris laboratory, but would instead be stored at the International Bureau of Weights and Measures in Sèvres in the Paris suburbs. Scientists urgently needed such standards to support their studies of radioactivity, so the Czech/Austrian chemist Otto Hönigschmid was asked to prepare a set of seven secondary standards. Marie Curie calibrated these secondary standards against her primary standard. In December 1913, Secondary Standard No. 6, containing 20.28 milligrams of radium chloride, was delivered to the National Bureau of Standards, now known as the National Institute of Standards and Technology (NIST).
In 2015, NIST made a decision to dispose of these three standards as hazardous radioactive waste. Nearly 30 years later, I finally have some idea of how Marie Curie worked with our scientists as part of her leadership role in international radiation measurements and standards. And not a moment too soon! Essentially all of the radioactivity standards that she calibrated, including that first international (Paris) standard, have been disposed of as radioactive waste. However, Secondary Standard No. 6, which was made for the United States, is safely stored in a lead enclosure on our Gaithersburg, Maryland, campus along with two other international radium standards that we received in 1937. The certificates for these later sources were signed by Curie’s daughter, Irène Joliot-Curie, who took her mother’s place on the International Radium Standards Commission.
As I reflect on the situation, a few questions still linger in my mind. First, what importance did Marie Curie place on this one standard in the United States? Would she be amused or dismayed that this was the last Curie standard in existence? Also, what value do the three "Curie standards" in NIST's possession have that would preclude their destruction?
Marie Curie first visited the U.S. in May of 1921 on a mission to collect a gram of radium that had been donated to her by the women of the United States. She and her two daughters made a whirlwind tour of cities on the East Coast as she collected honorary degrees from several universities. During her visit to Washington, D.C., she met with President Warren Harding at the White House and received a certificate for the gram of radium and a ceremonial box for the radium. But the radium itself was contained in ten 100-milligram ampoules that had been prepared in Pittsburgh by the Standard Chemical Company and were, at the time of her visit, at NIST being calibrated by comparison with Secondary Standard No. 6.
As to the fate of these last “Curie standards,” my NIST colleague Ronald Collé and I published an article in the Bulletin of the International Radiation Physics Society (PDF) this past autumn in which we asked the international scientific community to offer reasons why these sources should not be destroyed. If these artifacts were normal objects, like the platinum-iridium kilograms from a century ago, it would be no problem to display them. But their hazardous nature dictates that they be handled with great care and stored in lead enclosures, making casual viewing significantly more complicated.
The organizing committee for her visit to Washington included Professor Samuel Wesley Stratton, our first director. On at least one morning during her days in Washington, Stratton hosted her at our original campus on Connecticut Avenue, where she examined the radium ampoules and discussed NIST’s gold-leaf electroscope measurement of the radium to assure herself that she was getting a full gram of the precious element. Her meetings with Stratton, and the follow-on visit she had with the chemists who separated the radium in Pittsburgh, were certainly the technical highlights of her visit to the U.S.
Frankly, I don’t know the answer. These standards are certainly important to the history of science, and I would like to see them preserved for posterity. We are looking forward to getting ideas from our colleagues on how we might save the last of the Curie standards from being swept into the dustbin of history.