Background radiation equivalent time (BRET) or background equivalent radiation time (BERT) is a
unit of measurement
A unit of measurement is a definite magnitude (mathematics), magnitude of a quantity, defined and adopted by convention or by law, that is used as a standard for measurement of the same kind of quantity. Any other quantity of that kind can ...
of
ionizing radiation
Ionizing radiation (or ionising radiation), including nuclear radiation, consists of subatomic particles or electromagnetic waves that have sufficient energy to ionize atoms or molecules by detaching electrons from them. Some particles can travel ...
dosage amounting to one day worth of average human exposure to
background radiation
Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources.
Background radiation originates from a variety of sources ...
.
BRET units are used as a measure of low level radiation exposure. The health hazards of low doses of ionizing radiation are unknown and controversial, because the effects, mainly
cancer
Cancer is a group of diseases involving abnormal cell growth with the potential to invade or spread to other parts of the body. These contrast with benign tumors, which do not spread. Possible signs and symptoms include a lump, abnormal b ...
and
genetic damage
In biology, a mutation is an alteration in the nucleic acid sequence of the genome of an organism, virus, or extrachromosomal DNA. Viral genomes contain either DNA or RNA. Mutations result from errors during DNA or viral replication, mitos ...
, take many years to appear, and the incidence due to radiation exposure can't be statistically separated from the many other causes of these diseases. The purpose of the BRET measure is to allow a low level dose to be easily compared with a universal yardstick: the average dose of
background radiation
Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources.
Background radiation originates from a variety of sources ...
, mostly from natural sources, that every human unavoidably receives during daily life. Background radiation level is widely used in radiological health fields as a standard for setting exposure limits. Presumably, a dose of radiation which is equivalent to what a person would receive in a few days of ordinary life will not increase his rate of disease measurably.
Definition
The BRET is the creation of Professor J R Cameron. The BRET value corresponding to a dose of radiation is the number of days of average natural background dose it is equivalent to. It is calculated from the
equivalent dose
Equivalent dose is a dose quantity '' H '' representing the stochastic health effects of low levels of ionizing radiation on the human body which represents the probability of radiation-induced cancer and genetic damage. It is derived from the ...
in
sievert
The sievert (symbol: SvNot be confused with the sverdrup or the svedberg, two non-SI units that sometimes use the same symbol.) is a unit in the International System of Units (SI) intended to represent the stochastic health risk of ionizing radi ...
s by dividing by the average annual
background radiation
Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources.
Background radiation originates from a variety of sources ...
dose in Sv, and multiplying by 365:
:
The definition of the BRET unit is apparently unstandardized, and depends on what value is used for the average annual
background radiation
Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources.
Background radiation originates from a variety of sources ...
dose, which varies greatly across time and location. The 2000
UNSCEAR
The United Nations Scientific Committee on the Effects of Atomic Radiation (UNSCEAR) was set up by resolution of the United Nations General Assembly in 1955. 21 states are designated to provide scientists to serve as members of the committee which ...
estimate for worldwide average natural background radiation dose is 2.4 mSv (240 mrem), with a range from 1 to 13 mSv. A small area in India as high as 30 mSv (3 rem).
"Monazite sand does not cause excess cancer incidence"
''The Hindu'' (WayBack archive) Using the 2.4 mSv value each BRET unit equals 6.6 μSv.
BRET values for diagnostic radiography procedures range from 2 BRET for a dental x-ray
An X-ray, or, much less commonly, X-radiation, is a penetrating form of high-energy electromagnetic radiation. Most X-rays have a wavelength ranging from 10 picometers to 10 nanometers, corresponding to frequencies in the range 30&nb ...
to around 400 for a barium enema
A lower gastrointestinal series is a medical procedure used to examine and diagnose problems with the human colon of the large intestine. Radiographs (X-ray pictures) are taken while barium sulfate, a radiocontrast agent, fills the colon via an ...
study.
See also
* Background radiation
Background radiation is a measure of the level of ionizing radiation present in the environment at a particular location which is not due to deliberate introduction of radiation sources.
Background radiation originates from a variety of sources ...
* Banana equivalent dose
Banana equivalent dose (BED) is an informal unit of measurement of ionizing radiation exposure, intended as a general educational example to compare a dose of radioactivity to the dose one is exposed to by eating one average-sized banana. Bananas ...
* Flight-time equivalent dose
* Radiology
Radiology ( ) is the medical discipline that uses medical imaging to diagnose diseases and guide their treatment, within the bodies of humans and other animals. It began with radiography (which is why its name has a root referring to radiat ...
References
{{reflist
* https://web.archive.org/web/20060105033541/http://www.radiationcontrol.utah.gov/XRAY/BRET.HTM
Radioactivity
Background radiation
Equivalent units