Radiation basics

chinacdc.cn | Updated: 2022-03-01
What is radiation?
Radiation is energy or particles from a source that travel through space or othermedia. Light, heat, and the microwaves and radio waves used for wireless communications are all forms of radiation.
Radiation is often categorized as either ionizing or non-ionizing depending on the energy of the radiated particles.
Ionizing radiation is electromagnetic waves with a short wave length and high energy (photon energy > 12.4 eV or wavelength < 100 nm, such as X-ray and Gamma ray) or a subatomic particle beam (such as α Ray, β rays, neutrons), the energy of which is sufficient to remove electrons in atoms or molecules (atomic clusters) from their orbits upon collision with them.
Types and sources of radiation
α ray, helium nucleus: common nuclides include radium-226, polonium-210 and uranium-235.
β ray, electron beam: common nuclides include carbon-14, phosphorus-32 and fluorine-18.
γ ray, photon: common nuclides include cobalt-60 and iridium-192.
X-ray (roentgen ray), photon: electromagnetic radiation generated by high-speed electron beams hitting metal targets in vacuum glass tubes.
Neutron, californium-252, etc.
Sources of ionizing radiation
Decay of radionuclides: The radionuclides exist until they decay. The half-life spans 55 orders of magnitude, ranging from a few minutes to more than a billion years.
Artificial sources: such as cobalt-60 and cesium-137 for food irradiation processing, fluorine-18 for PET examination in nuclear medicine, iodine-131 and for the treatment of hyperthyroidism and thyroid cancer.
Natural sources: such as uranium-235 used in nuclear power plants, and kalium-40, radium-226 and radium-228 widely existing in food.
Radiation-producing devices: such as X-ray machines, CT machines, accelerators, etc., which can release X-rays and electromagnetic radiation. But the radiation disappears after the power of the devices is cut out. 
Measuring radiation: Common doses and units
Activity:  Measures the quantity and strength of radioactive sources and substances. 
The unit is Becquerel (Bq), in memory of French physicist Becquerel or Curie (Ci, in memory of French scientist Pierre Curie and his wife Marie Curie). 1 Bq = the average nuclear decay of a radionuclide in 1 second. 1 Ci= 3.7 × 1010 Bq.
Absorbed dose: Measures the transfer and deposition of energy in matter. 
The unit is Gy (commemorating British radiobiology Gray), 1 Gy = 1 J / kg.
Equivalent dose: Equivalent dose (HT)  represents 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 calculated by multiplying the absorbed dose to the organ or tissue (DT) with the radiation weighting factor, wR. This factor is dependent on the type and energy of the incident radiation. The value of wR is 1 for x-rays, gamma rays and beta particles, but higher for protons (wR = 5), neutrons (wR is between 5 and 20 depending on energy), alpha particles and heavy fragments (wR = 20) etc.
Effective dose: Measures the risk of radiation carcinogenesis.
Different human organs have different probabilities of developing cancer and react differently to radiation exposure. Organs with rapid renewal, such as red bone marrow and thyroid, are more sensitive. The effective dose is calculated by multiplying the equivalent dose (HT) by a tissue weighting factor (WT). The unit is Sv (in memory of Swedish Radiation protection expert Sivert). 
These mentioned units are very large, commonly used are: milli- (m, 10-3) , micro- (μ, 10-6) ,nano-(n, 10-9).
Radiation exposure and cancer
Radiation carcinogenesis has a certain incubation period. The incubation period of leukemia is 2-5 years, and the incubation period of other cancers is more than 10 years, with lifelong manifestations.
Radiation exposure, especially to X-rays and γrays, can cause various kinds of cancer, such as leukemia, breast cancer and so on. It is generally believed that chronic lymphocytic leukemia may not be related to ionizing radiation. Radiation-induced cancer also has no special tissue type.
Exposure to ionizing radiation increases the risk of cancer. The risk of cancer for children and adolescents who are exposed to ionizing radiation is much higher than that of adults.