In radiation protection, the sievert is a derived unit of equivalent dose and effective dose. The sievert represents the equivalent biological effect of the deposit of a joule of gamma rays energy in a kilogram of human tissue. Unit of sievert is of importance in radiation protection and was named after the Swedish scientist Rolf Sievert, who did a lot of the early work on dosimetry in radiation therapy.
One sievert is a large amount of equivalent dose. A person who has absorbed a whole body dose of 1 Sv has absorbed one joule of energy in each kg of body tissue (in case of gamma rays).
Equivalent doses measured in industry and medicine often have usually lower doses than one sievert, and the following multiples are often used:
1 mSv (millisievert) = 1E-3 Sv
1 µSv (microsievert) = 1E-6 Sv
Conversions from the SI units to other units are as follows:
- 1 Sv = 100 rem
- 1 mSv = 100 mrem
Examples of Doses in Sieverts
We must note that radiation is all around us. In, around, and above the world we live in. It is a natural energy force that surrounds us. It is a part of our natural world that has been here since the birth of our planet. In the following points we try to express enormous ranges of radiation exposure, which can be obtained from various sources.
- 0.05 µSv – Sleeping next to someone
- 0.09 µSv – Living within 30 miles of a nuclear power plant for a year
- 0.1 µSv – Eating one banana
- 0.3 µSv – Living within 50 miles of a coal power plant for a year
- 10 µSv – Average daily dose received from natural background
- 20 µSv – Chest X-ray
- 40 µSv – A 5-hour airplane flight
- 600 µSv – mammogram
- 1 000 µSv – Dose limit for individual members of the public, total effective dose per annum
- 3 650 µSv – Average yearly dose received from natural background
- 5 800 µSv – Chest CT scan
- 10 000 µSv – Average yearly dose received from natural background in Ramsar, Iran
- 20 000 µSv – single full-body CT scan
- 175 000 µSv – Annual dose from natural radiation on a monazite beach near Guarapari, Brazil.
- 5 000 000 µSv – Dose that kills a human with a 50% risk within 30 days (LD50/30), if the dose is received over a very short duration.
As can be seen, low-level doses are common for everyday life. The previous examples can help illustrate relative magnitudes. From biological consequences point of view, it is very important to distinguish between doses received over short and extended periods. An “acute dose” is one that occurs over a short and finite period of time, while a “chronic dose” is a dose that continues for an extended period of time so that it is better described by a dose rate. High doses tend to kill cells, while low doses tend to damage or change them. Low doses spread out over long periods of time don’t cause an immediate problem to any body organ. The effects of low doses of radiation occur at the level of the cell, and the results may not be observed for many years.