When it passes through or collides with a substance, ionizing radiation—which is defined as radiation with enough energy to knock electrons out of atoms or molecules (groups of atoms)—occurs. The atom (or molecule) acquires a positive charge when one electron with its associated negative charge is lost. Ionization is the loss (or gain) of an electron, and an ion is a charged atom (or molecule). Note: Non-ionizing radiation includes, but is not limited to, microwave, infrared (IR), and ultraviolet (UV) radiation. The energy of non-ionizing radiation is insufficient to expel electrons.
What kinds of radiation are ionizing?
Ionizing radiation can come from both natural and man-made sources. X-ray machines, radioactive isotopes used in nuclear medicine, gamma cameras, nuclear gauges, and nuclear power plants are examples of artificial sources of radiation. An electromagnetic radiation known as an X-ray is produced when a powerful electron beam strikes metal inside a glass tube. This radiation has an extremely high frequency, ranging from 0.3 to 30 Ehz (exahertz or billion gigahertz). In contrast, FM radio stations use frequencies of about 100 MHz (megahertz) or 0.1 Ghz to deliver their signals (gigahertz). Background radiation from space, cosmic radiation from cosmic rays, terrestrial radiation from minerals in the earth's crust, inhaling radon gas, and drinking water that may contain radioactive potassium-40 are some examples of natural sources of radiation. When the nucleus breaks down or disintegrates, radioactive minerals like uranium and thorium emit radiation. Alpha, beta, and gamma rays are the three types of radiation produced by radioactive substances or sources.
When ionizing radiation is measured, what characteristics are taken into account?
The intensity or radioactivity of the radiation source, the energy of the radiation, the quantity of radiation in the environment, and the radiation dose—or the amount of radiation energy received by the human body—are all ways that ionizing radiation is quantified.
The radiation dose is the most significant factor when it comes to occupational exposure. The ACGIH TLVs and other occupational exposure limits are expressed in terms of the authorized maximum dose. The chance of contracting a radiation-related illness is influenced by the cumulative radiation dosage that individual receives over time.
What measurements of radiation are made in what units?
Units of becquerel are used to measure radioactivity or the strength of a radioactive source (Bq).
One incident of radioactive emission or disintegration per second is equal to one Bq.
Radioactivity in one becquerel is really minute. The Bq unit is frequently multiplied by kBq (kilobecquerel), MBq (megabecquerel), and GBq (gigabecquerel). 1 kBq is equal to 1000 Bq, 1 MB to 1000 kB, and 1 GB to 1000 MB. The curie is a traditional and still widely used unit of radioactivity measurement (Ci). 1 Ci equals 37 GBq, or 37000 MBq. There is a lot of radioactivity in one curie. mCi (millicurie), Ci (microcurie), nCi (nanocurie), and pCi are often used subunits (picocurie). 1 Ci = 1000 mCi, 1000 mCi = 1000 nCi, 1000 nCi = 1000 pCi, etc. 1 Bq = 27 pCi is another helpful conversion formula. A measurement of the rate—rather than the energy—of radiation emission from a source is the becquerel (Bq) or curie (Ci).
What does the term ""half-life"" mean when referring to radioactivity?
As more and more radioactive atoms (radionuclides) emit energy to become stable atoms, the radiation intensity from a radioactive source gradually decreases over time. The reduction in radiation intensity is known as radioactive decay. The half-life is the period of time after which a radiation dose is cut in half. This occurs because within one half-life time, half of the radioactive atoms will have decayed. For instance, after one half-life, a radioactive source with a mass of 50 Bq becomes a source with a mass of 25 Bq. Radioactive Decay Table 1 number of elapsed half-lives Radioactivity remaining as a percentage0100150225312.5546.2553.125 A fraction of a second to millions of years are the range of half-lives for various radioactive materials.
What measurements of radiation energy are made in what units?
Ionizing radiation's energy is expressed in electronvolts (eV). A single electronvolt is a minuscule quantity of power. Megaelectronvolt (meV) and kiloelectronvolt (keV) are two frequently used multiple units (MeV). 1 joule = 6,200 billion MeV joules per second equal one watt. 1000 eV = 1 keV, and 1000 keV = 1 MeV Watt is a unit of power that represents the amount of energy (or labor) in one unit of time (e.g., minute, hour).
What measurements of radiation exposure are made in what units?
Exposure to X-rays and gamma rays is frequently represented in units of roentgen ®. The roentgen ® unit refers to the amount of ionization present in the air. One roentgen of gamma- or x-ray exposure produces approximately 1 rad (0.01 gray) tissue dose (see next section for definitions of gray (Gy) and rad units of dose). Another unit of measuring gamma ray intensity in the air is """"air dose or absorbed dose rate in the air"""" in grays per hour (Gy/h) units. This unit is used to express gamma ray intensity in the air from radioactive materials in the earth and in the atmosphere.
What units are used for measuring radiation dose?
When ionizing radiation interacts with the human body, it gives its energy to the body tissues. The absorbed dose is the amount of energy absorbed per unit weight of the organ or tissue and is expressed in units of gray (Gy). One gray dose is equivalent to one joule radiation energy absorbed per kilogram of organ or tissue weight. Rad is the old and still used unit of absorbed dose. One gray is equivalent to 100 rads. 1 Gy = 100 rads Equal doses of all types of ionizing radiation are not equally harmful to human tissue. Alpha particles produce greater harm than do beta particles, gamma rays and X-rays for a given absorbed dose, so 1 Gy of alpha radiation is more harmful than 1 Gy of beta radiation. To account for the way in which different types of radiation cause harm in tissue or an organ, radiation dose is expressed as equivalent dose in units of sievert (Sv). The dose in Sv is equal to the total external and internal """"absorbed doses"""" multiplied by a """"radiation weighting factor"""" (WR - see Table 2 below) and is important when measuring occupational exposures. Before1990, this weighting factor was referred to as Quality Factor (QF). Table 2 Radiation Weighting Factors Column 1 Column 2 Item Type of Radiation and Energy Range Weighting Factor 1 Photons, all energies 1 2 Electrons and muons, all energies 1 1 3 Neutrons2 of energy < 10 keV 5 4 Neutrons2 of energy 10 keV to 100 keV 10 5 Neutrons2 of energy > 100 keV to 2 MeV 20 6 Neutrons2 of energy > 2 MeV to 20 MeV 10 7 Neutrons2 of energy > 20 MeV 5 8 Protons, other than recoil protons, of energy > 2 MeV 5 9 Alpha particles, fission fragments and heavy nuclei 20 1 Excluding Auger electrons emitted from nuclei bound to DNA. 2 Radiation weighting factors for these neutrons may also be obtained by referring to the continuous curve shown in Figure 1 on page 7 of the 1990 Recommendations of the International Commission on Radiological Protection, ICRP Publication 60, published in 1991. Source: The Canadian Radiation Protection Regulations, Schedule 2 (SOR/2000-203). Equivalent dose is often referred to simply as """"dose"""" in every day use of radiation terminology. The old unit of """"dose equivalent"""" or """"dose"""" was rem. Dose in Sv = Absorbed Dose in Gy x radiation weighting factor (WR) Dose in rem = Dose in rad x QF1 Sv = 100 rem 1 rem = 10 mSv (millisievert = one thousandth of a sievert) 1 Gy air dose equivalent to 0.7 Sv tissue dose (UNSEAR 1988 Report p.57) 1 R (roentgen) exposure is approximately equivalent to 10 mSv tissue dose
What is the relationship between SI units and non-SI units?
Table 3 shows SI units (International System of Units or Systéme Internationale d'unités), the corresponding non-SI units, their symbols, and the conversion factors. Table 3 Units of Radioactivity and Radiation Dose Quantity SI unit and symbol Non-SI unit Conversion factor Radioactivity becquerel, Bq curie, Ci 1 Ci = 3.7 x 1010 Bq = 37 Gigabecquerels (GBq) 1 Bq = 27 picocurie (pCi) Absorbed dose gray, Gy rad 1 rad = 0.01 Gy """"Dose"""" (Equivalent dose) sievert, Sv rem 1 rem = 0.01 Sv 1 rem = 10 mSv
What is a """"committed dose""""?
When a radioactive material gets in the body by inhalation or ingestion, the radiation dose constantly accumulates in an organ or a tissue. The total dose accumulated during the 50 years following the intake is called the committed dose. The quantity of committed dose depends on the amount of ingested radioactive material and the time it stays inside the body.
What is an """"effective dose""""?
The effective dose is the sum of weighted equivalent doses in all the organs and tissues of the body.
Effective dose = sum of [organ doses x tissue weighting factor]. Effective dose is measured in sieverts (Sv). Tissue weighting factors (Table 4) represent relative sensitivity of organs for developing cancer. Table 4 Organ Or Tissue Weighting Factors Column 1 Column 2 Item Organ or Tissue Weighting Factor 1 Gonads (testes or ovaries) 0.20 2 Red bone marrow 0.12 3 Colon 0.12 4 Lung 0.12 5 Stomach 0.12 6 Bladder 0.05 7 Breast 0.05 8 Liver 0.05 9 Oesophagus 0.05 10 Thyroid gland 0.05 11 Skin1 0.01 12 Bone surfaces 0.01 13 All organs and tissues not listed in items 1 to 12 (remainder organs and tissues) collectively, including the adrenal gland, brain, extra-thoracic airway, small intestine, kidney, muscles, pancreas, spleen, thymus and uterus 2,3 0.05 14 Whole body 1.0 1 The weighting factor for skin applies only when the skin of the whole body is exposed. 2 When the equivalent dose received by and committed to one of these remainder organs and tissues exceeds the equivalent dose received by and committed to any one of the organs and tissues listed in items 1 to 12, a weighting factor of 0.025 shall be applied to that remainder organ or tissue and a weighting factor of 0.025 shall be applied to the average equivalent dose received by and committed to the rest of the remainder organs and tissues. 3 Hands, feet and the lens of an eye have no weighting factor. Source: The Canadian Radiation Protection Regulations, Schedule 1 (SOR/2000-203).
What are the limits of exposure to radiation?
The Threshold Limit Values (TLVs) published by the ACGIH (American Conference of Governmental Industrial Hygienists) are occupational exposure limits adopted by many jurisdictions as guidelines or legal limits: 20 mSv - TLV for average annual effective dose for radiation workers, averaged over five years In Canada, the Radiation Protection Regulations set radiation exposure limits for the public and nuclear energy workers. The annual effective dose limit is 1mSv for the Canadian public. This dose limit aligns with the International Commission on Radiological Protection (ICRP) recommended annual dose limit of 1 mSv for the general public. Based on information from regular monitoring of the most exposed workers, such as a radiographer, shows that the average annual doses are 5 mSv per year.
What are the main ways to control radiation exposure?
The main ways to control radiation exposure include engineering controls, administrative controls and personal protective equipment. Examples of these controls include: Education and training Reducing exposure time Increasing the distance from the radiation source Using a physical barrier that modifies the pathway between worker and source of radiation e.g., concrete or lead Monitoring of exposures (individual and collective monitoring) Recording exposures Providing health surveillance Promoting a health and safety culture Complying with established radiation exposure (dose) limits Approximately forty-four (44) percent of monitored workers worldwide are exposed to artificial sources of radiation. Of those workers exposed to artificial sources, seventy-five percent work in the medical sector. Table 5 shows trends in global radiological exposure of workers since the 1970s. Table 5 Trends in Global Radiological Exposure of Workers (mSv)* Sources 1970s 1980s 1990s 2000s Natural Air crew - 3.0 3.0 3.0 Coal mining - 0.9 0.7 2.4 Other mining** - 1.0 2.7 3.0 Miscellaneous - 6.0 4.8 4.8 Total - 1.7 1.8 2.9 Artificial Medical uses 0.8 0.6 0.3 0.5 Nuclear industry 4.4 3.7 1.8 1.0 Other industries 1.6 1.4 0.5 0.3 Miscellaneous 1.1 0.6 0.2 0.1 Total 1.7 1.4 0.6 0.5 * Estimates of average effective dose per worker in a year.** Uranium mining is included in nuclear industry. Source: Radiation: Effects and Sources, United Nations Environmental Programme (UNEP), 2016
What effects do different doses of radiation have on people?
One sievert is a large dose. The recommended TLV is average annual dose of 0.05 Sv (50 mSv). The effects of being exposed to large doses of radiation at one time (acute exposure) vary with the dose. Here are some examples: 10 Sv - Risk of death within days or weeks 1 Sv - Risk of cancer later in life (5 in 100) 100 mSv - Risk of cancer later in life (5 in 1000) 50 mSv - TLV for annual dose for radiation workers in any one year 20 mSv - TLV for annual average dose, averaged over five years
What are """"working level"""" and """"working level month""""?
In underground uranium mines, as well in some other mines, radiation exposure occurs mainly due to airborne radon gas and its solid short-lived decay products, called radon daughters or radon progeny. Radon daughters enter the body with the inhaled air. The alpha particle dose to the lungs depends on the concentration of radon gas and radon daughters in the air. The concentration of radon gas is measured in units of picocuries per litre (pCi/L) or becquerels per cubic metre (Bq/m3) of ambient air. The concentration of radon daughters is measured in working level (WL) units this is a measure of the concentration of potential alpha particles per litre of air. The worker's exposure to radon daughters is expressed in units of Working Level Months (WLM). One WLM is equivalent to 1 WL exposure for 170 hours. 1 WL = 130,000 MeV alpha energy per litre air = 20.8 µJ (microjoules) alpha energy per cubic meter (m3) air WLM = Working Level Month = 1 WL exposure for 170 hours 1 WLM = 3.5 mJ-h/m3 Often people use the concentration of radon gas (pCi/L) in the air to estimate the WL level of radon daughters. Such estimates are subject to error because the ratio of radon to its decay products (radon daughters) is not constant. Equilibrium factor is the ratio of the activity of all the short-lived radon daughters to the activity of the parent radon gas. Equilibrium factor is 1 when both are equal. Radon daughter activities are usually less than the radon activity and hence the equilibrium factor is usually less than 1. mJ-h/m3 = millijoule hours/per cubic metre MBq-h/m3 = megabecquerel hours per cubic meter Joule is unit of energy 1 J = 1 Watt-second = Energy delivered in one second by a 1 Watt power source 1 calorie = 4.2 JMBq/m3 = megabecquerel per cubic metre WLM = Working Level Months"""