Overview
Radiation often raises curiosity and concern due to its association with potential health risks. To fully understand the nature of radiation, it is necessary to understand the main units used to measure it. In this article, we will delve into the subject of radiation units, explore the different ways in which radiation is measured, and highlight their importance.
Radiation and its Types
Radiation: It is the transmission or emission of energy, whether it is waves or particles, and it comes from a source and is transmitted through some materials or through space. Radiation is produced by radioactive decay, nuclear fission, nuclear fusion, chemical reactions, and hot bodies.
Radiation is divided into ionizing and non-ionizing, and each can be explained as follows:
1- Ionizing radiation
They are radiations that excite and interact with atoms of ionizing matter, including particle radiation and electromagnetic radiation.
2- Non-ionizing radiation
Radiation that does not have enough energy to remove electrons from atoms and therefore cannot interact with or ionize materials.
Radiation Units
Since radiation is used in hospitals for various purposes such as diagnostic imaging and radiotherapy, there are different units used to measure radiation dose within the medical field, and these units are:
1- Radiation Absorbed Dose Units (D)
A) Radiation absorbed dose unit (rad):
It is an old unit used to measure the amount of energy absorbed by a substance from ionizing radiation.
In the International System of Units, 1 Gy is equivalent to the absorption of 1 joule of energy per kilogram of the absorbent.
1 rad = 0.01 Gy = 0.01 J/kg
Nowadays, the rad is not commonly used in modern scientific and medical literature because the International System of Units (SI) has replaced it with the unit of gray (Gy) as the standard unit of absorbed dose.
B) The radiation absorbed dose unit (Gray) or (Gy):
The absorbed dose is a basic unit used to determine the amount of energy deposited by radiation in a given substance, and it is measured in a unit called Gray (Gy) and named after the British physicist Louis Harold Gray.
One gray equals one joule of energy deposited per kilogram of matter.
1 Gy = 1 J/Kg = 100 Rad
The absorbed dose provides an indication of the amount of energy transferred to tissues and is essential for evaluating the effects of radiation on living organisms.
2- Equivalent Dose Units (H)
A) Roentgen Equivalent Man or (REM):
It is a unit used to measure the biological effects of ionizing radiation on the human body and takes into account both the absorbed dose of radiation and the biological activity of the type of radiation involved.
1 REM is equivalent to 0.01 sv (Sv), or 10 millisievert (mSv). The conversion factor between the two units is based on the RBE of 1 for x-rays or gamma rays.
The rem is now considered obsolete and has been replaced by the SI (Sv) or sievert, however, the rem is still sometimes used in certain contexts, particularly in the United States.
The REM unit identifies potential biological harm from radiation exposure and explains the different types of ionizing radiation and their varying levels of biological effect.
B) Sievert or (Sv), divided into:
- Equivalent dose unit:
While the absorbed dose measures the energy deposited in a substance, it does not take into account the changing biological effects of different types of radiation. To address this, the equivalent dose is used. The equivalent dose takes into account the biological effectiveness of radiation by applying a radiation weighting (WR) factor, which reflects biological damage. Relative is caused by different types of radiation.
The equivalent dose unit is the sievert (Sv), one sv equals one gray multiplied by the radiation weighting factor, e.g. one gray for x-ray radiation is equal to one sv, while one gray for alpha particle radiation is 20 sv.
- Effective dose unit:
Radiation exposure may affect different organs and tissues in the body to varying degrees. To assess the overall risk for an individual, the concept of effective dose is used. The effective dose includes both the equivalent dose and the tissue weight factor (WT), which represents the sensitivity of different organs or tissues to radiation. The effective dose unit is the sievert. (Sv).
1 Sv = 1 Gy = 100 rads = 100 rem = 1 J/kg
3- Radiation Exposure Units:
A) Curie or (Ci):
It is an outdated unit of radioactivity named after the famous physicist and chemist Marie Curie and is no longer widely used in the scientific literature as it was replaced by the SI unit of radioactivity becquerel (Bq).
Each curie is equal to 3.7 * 10^10 becquerel (Bq) in SI units and a becquerel represents one decay per second, so a curie is a relatively large unit compared to a becquerel and nowadays radioactivity measurements are generally expressed in becquerels or multiples of becquerels.
If you need to work with measurements of radioactivity it is recommended to use the SI units becquerel (Bq) as it is the internationally recognized standard.
B) Becquerel or (Bq):
It is the unit of radioactivity in the International System of Units (SI) and is named after the French physicist Henri Becquerel who discovered radioactivity in 1896. The becquerel is defined as the activity of a quantity of radioactive material in which one nucleus decays per second.
The becquerel unit measures the rate at which radioactive materials undergo radioactive decay (radioactive decay: is the process by which unstable atomic nuclei spontaneously transform into more stable forms, releasing radiation in the process), and the becquerel is a measure of the number of radioactive decays that occur in sample per unit time.
A sample with activity of 1 becquerel means that one atomic nucleus in that sample will decay every second, and becquerels are often used in scientific and medical contexts to measure and compare the radioactivity of various materials and sources.
4- Radiation Intensity Units
A) Exposure (coulombs per kilogram):
Exposure measures the amount of ionization produced in the air by x-rays and gamma rays and is measured in coulombs per kilogram (C/kg).
Exposure is useful in occupational radiation protection, especially in the context of radiation workers who are exposed to external sources of ionizing radiation.
B) Roentgen or (R):
It is a unit of measurement used to determine the dose of ionizing radiation in air resulting from X-rays or gamma rays and is named after the German physicist Wilhelm Conrad Röntgen, who discovered X-rays in 1895.
A Roentgen unit is defined as the amount of radiation produced by one electrostatic unit (either positive or negative) in one cubic centimeter of dry air at standard temperature and pressure (STP) conditions.
It is important to note that the Roentgen unit measures ionizing radiation in air and not the dose absorbed in human tissue.
Conversion From Old Units to New Units
The following table shows the conversion of values from the old units of radiation to the new units in force according to the International System of Units SI, and each unit is multiplied by a specific conversion factor as follows:
Conclusion
Understanding radiation units is essential to understand the potential risks associated with radiation exposure and to assess the required safety measures. Absorbed dose, equivalent dose, effective dose, activity, and exposure are critical units that help in assessing the impact of radiation on living organisms and the environment. By being aware of these units and their importance, people can make appropriate decisions about Radiation protection and participate in productive discussions on radiation-related topics.
#nuclear_medicine #radiation_units #old_units_radiation #new_units_radiation #radiation_types
