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Taking Measure

Just a Standard Blog

Defining Ourselves Through Science

Chemist Savelas Rabb is bent over slightly, using a tool to check on the settings inside of a large instrument known as a mass spectrometer.

Checking "under the hood" of our lab’s mass spectrometer.

Credit: J. Stoughton/NIST

A few months ago, in November 2018, I experienced one of the most significant moments in my scientific career—the international ceremony ratifying the redefinition of the kilogram, mole and two other base units of the Système International d'Unités, or SI, in Versailles, France. My colleague Bob Vocke and I had contributed to the work on the redefinition of the kilogram and the mole, resulting from advances in the precise measurement of the molar mass of an unusual form of silicon in a kilogram of isotopically enriched silicon-28. Or, to put it another way, to put accurate and highly precise numbers on the two constants defining the kilogram and the mole: the Planck constant (h≡6.626 070 15 x 10-34kg·m2/s) and the Avogadro constant (NA ≡6.022 140 76 x 1023mol-1).

The feeling of accomplishment at the ceremony was very palpable, especially when all the participating members of the General Conference on Weights and Measures (CGPM) voted unanimously to adopt the new definitions of the kilogram, mole, ampere and kelvin and remove the link to any physical artifacts forever. It is amazing that the contributions from so many scientists across the globe could agree to make the redefinition ceremony possible.

Recently, we received NIST’s Samuel Wesley Stratton Award for this work. As a young kid growing up in South Carolina, I would not have imagined accomplishing such a feat. First, who knew that this could be done, and, second, that it was needed by the scientific community? By the time I finished my undergraduate education at Duke University, I knew I wanted my work to affect the community in a positive way that was tangible. After a summer internship at Colgate-Palmolive, I felt the area of consumer products was where I wanted to be.

During my graduate studies at Ohio State University, I became familiar with NIST and their innovative research. My research adviser John Olesik proposed that I contribute/continue the high-performance measurement work at NIST developed by Marc Salit and Greg Turk in the certification of reference materials. This research was the bridge to my later employment at the National Institute of Standards and Technology (NIST). As a chemist in the Inorganic Measurement Science Group in the Material Measurement Laboratory at NIST, I am tasked with the certification of standard reference materials, planning of standard programs and participation in collaborative studies with other national metrology institutes for the advancement of measurement science in standards research and development. Although I do not work with consumer products in the traditional sense, as I had hoped my work still affects change that can be appreciated by the global community.

To me, Black History Month is a way to pay homage to our ancestors for everything that they did, both big and small. It is important to know the achievements, but also remember the struggles many had to endure. We are often reminded during times of unrest or war that freedom is not free. No one should understand that statement more than African Americans. It is important that we fully understand our past and our worth; otherwise, we are destined to repeat the unsavory portions of it.

To the black youth interested in NIST or a scientific career, I say go for it! Ask your teachers and school administrators if there are any after-school science or technical enrichment programs that you are eligible to participate in. Visit the NIST website to learn more about our programs for high school students or undergraduates. Look for scientific mentors in your local community. Just do something! The opportunity will not likely fall in your lap without any action from you. My grandmother always told me that I would have to work hard for anything worth having. Her words continue to ring true today.

About the author

Savelas Rabb

Savelas Rabb is a research chemist in the NIST Inorganic Measurement Science group. He works to certify values of chemical constituents in a variety of reference materials using inductively coupled plasma optical emission spectrometry (ICP-OES) and mass spectrometry (ICP-MS). Currently, his spare time is spent entertaining his young son with the most popular nursery rhymes. Before his son came along, he enjoyed volunteering at science fairs and various food pantries. He has also participated in student enrichment activities sponsored by the Duke Alumni Association, as well as the Smithsonian.


Kudos to You !! I cannot imagine what a thrill it must have been for you - you embody #BlackExcellence ! Again, Congratulations :-)

Thanks for sharing this inspiring story!

You presented Avogadro and Planck constants as numbers, but they are not numbers! The numeric values of the constants depend on the units of measurement. You did not intentionally indicate units to hide errors in their definitions?

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