Rolf Sievert

It’s the birthday of Rolf Sievert, who was born in 1896 in Stockholm, Sweden. Sievert studied at Stockholm’s Karolinska Institute and at the city’s Royal Institute of Technology. In 1932 he earned a PhD at Uppsala University with a thesis on a new method for measuring radiation. Sievert applied his expertise to medical physics, where he focused on the diagnosis and treatment of cancer. Later he worked on the biological effects of repeated low doses of radiation. The SI unit of ionizing radiation dose, the sievert (Sv), is named in his honor. Like its close relative, the gray (Gy), the sievert quantifies the amount of ionizing energy deposited in units of joules per kilogram. Unlike the gray, the sievert accounts for the effectiveness of different types of radiation via a dimensionless quality factor. For example, the quality factor for x rays is 1; for alpha particles, it’s 20. In cancer therapy, x-ray diagnostics and radiation safety, doses are typically given in millisieverts. A dose of a few sieverts received over a short period will likely cause radiation sickness, cancer and even death.

Date in History: 6 May 1896