Rolf Sievert, the man and the unit
The Department of Medical Radiation Physics was founded in 1938 and has so far had three professors:
- Rolf Sievert 1941-1965
- Rune Walstam 1966-1988
- Anders Brahme 1988-
Before 1938 the department was called The Physics Laboratory of Radiumhemmet.
Since 1995 the department of Medical Radiation Physics and four other departments were merged into the new Department of Oncology-Pathology.
Professor Rolf Sievert, 1896-1966.
One of the main initiators of both ICRP and ICRU, 1929.
Chairman of ICRP 1956 - 1962.
Chairman of UNSCEAR 1958 - 1960.
Professor at the Department of Medical Radiation Physics in Stockholm 1941 - 1965.
Rolf Maximilian Sievert was born in Stockholm on May 6, 1896. He was the son of the entrepreneur Max Sievert. After his matriculation in Stockholm 1914 he continued his studies at the Karolinska Institutet and at the Royal Institute of Technology in Stockholm, and obtained a Master of Science degree at Uppsala University in 1919. His PhD degree was obtained in 1932 with the thesis titled "Eine Metode zur Messung von Röntgen-, Radium- und Ultrastrahlung nebst einiger Untersuchungen über die Anwendbarkeit derselben in der Physik und der Medizin. Mit einem Anhang enthaltend einige Formeln und Tabellen für die Berechnung der Intensitätsverteilung bei Gamma-Strahlungsquellen". The same year he became associate professor in medical physics at Stockholm University.
The Sievert integral for calculation of air kerma rate to a point
From 1924 to 1937 Rolf Sievert was head of the Physics Laboratory at Radiumhemmet. In 1937 he was appointed head of the department of radiation physics at Karolinska Institutet and in 1941 professor in radiation physics at Karolinska Institutet.
After his retirement in 1965 until his death on October 3, 1966 he continued to take a very active part in the national and international co-operation in his particular field of interest, radiation dose measurement and radiation protection, were he had played a pioneering role.
Already in 1919 Rolf Sievert took contact with radiologists and offered them his co-operation in the attempt to solve the physical problems linked with the usage of radiation for diagnosis and therapy. His unremunerated co-operation continued until 1924, when the Cancer Society in Sweden decided to remunerate Sievert as head of the physics laboratory of Radiumhemmet, which he had organized and financed on his own. Under the leadership of Sievert the laboratory was developed into a world-wide known centre for radiation physics. In 1938 the laboratory moved to the Karolinska Hospital and was named Department of Radiation Physics.
In the early part of the 1920s, no standardization of patient doses for different hospitals was performed. For that reason, Sievert started an organization in 1925 which was made responsible for the continuous control of dosage levels at all clinics in the country performing radiation treatment. The control programme was extended as time went by, and eventually included control of all work with radiation, medical as well as industrial. On the initiative of Rolf Sievert, the government passed Sweden's first radiation protection law in 1941. The law gave the Department of Radiation Physics the task to supervise all such activities.
Rolf Sievert in his laboratory 1929
In the years 1920-40 Rolf Sievert gave his most important contributions to the field of clinical physics. He developed the basics on how to calculate the absorbed dose to tumours from intracavitary and interstitial sources, he developed new devices for patient irradiation and pointed out the importance of the contribution of secondary radiation. Furthermore, he invented a number of ingenious instruments for dose measurements, among other the world-wide known Sievert chamber.
In its original form, the Sievert chamber is a sphere or cylinder of a magnesium alloy placed in the centre of a hollow sphere of the same material. The inner electrode is fixed in its position by amber isolators. Through an opening in the outer sphere they could be charged to a well-known potential. The opening is the closed with a lid equipped with a rod acting as a holder of the chamber. If the chamber is exposed to ionizing radiation, the air in the cavity between the inner and the outer sphere becomes conducting through the ion pairs formed, and the charge of the chamber is reduced by the current formed. The charged reduction can then easily be measured on a separate instrument at some other location. The reduction of the charge is a measure of the radiation dose received by the chamber. Such a chamber can be transported long distances without affecting the readout. The diameter of the chamber can be as small as a few millimetres.
The Sievert chamber
In the 1930s Sievert worked primarily with the biological effects of ionizing radiation, and particularly the effects of the low doses received by radiologists in their daily work, and for comparison, the effects caused by unavoidable natural radiation background that we all are exposed to. Several years before the question of radioactive fallout was raised Sievert studied the matter by gathering available data on the spreading of ashes in the atmosphere after volcano eruptions.
During the last 20 year of his life, Sievert spent most of his time working with radiation protection issues, and made the plans for what was to become the Swedish Radiation Protection Institute, SSI.
The Unit Sievert
To honour Rolf Sievert, the CGPM-conference of 1979 accepted the Sievert, Sv, as the unit for equivalent dose and efficient dose.
1 Sv = 1 J/kg
The unit for equivalent dose and efficient dose, the Sievert.