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DOSES AND SOURCES OF RADIATION EXPOSURE

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1 DOSES AND SOURCES OF RADIATION EXPOSURE

2 DOSE CONCEPTS, QUANTITIES AND UNITS
Radiation is present throughout the environment and a large proportion of the average annual effective dose received by the population results from the environmental radiation what is called background radiation. Each member of the world population is exposed, on average, to 2.4 mSv of unavoidable ionizing radiation every year.

3 Radiation exposure Radiation exposure is a measure of the intensity of the radiation field Radiation exposure is a measure of the intensity of the radiation field. For X and gamma rays, exposure is precisely defined in terms of the amount of ionization produced in air by the radiation source. Some radiation passes through a volume of medium without interacting and, therefore, does no damage. Thus, only the radiation that interacts with the medium is measured. The SI unit for exposure is the coulomb per kilogram, or unit of charge generated per unit mass. References used in this module: 1.Perkins A.C. Nuclear Medicine Science and Safety. John Libbey&Company Ltd. London, 1995. 2. Early P.E. Radiation Measurement and Protection. In Principles and Practice of Nuclear Medicine. Mosby-Year Book, St. Luis, Missouri, 1994. 3. Pannsylvania University, Environmental Health and Radiation Safety. Training Program, (2001) 4. Moore M.M. Radiation Safety in Nuclear Medicine. In Nuclear Medicine Technology and Techniques. Eds.Bernier D.R., Christian P.E., Langan J.K. Mosby-Year Book, Inc. St. Louis, Missouri 1997. 5. Martin J.E. Physics for Radiation Protection, John Wiley & Sons, New York, 2000 For X and gamma rays, exposure is precisely defined in terms of the amount of ionization produced in air by the radiation source

4 coulombs per kilogram (C/kg)
Units of exposed dose The SI unit: coulombs per kilogram (C/kg) Traditional (old) unit: Roentgen (R) 1 R = 2.58 x 10-4 coulomb/kg Radiation exposure is measured in units of coulombs per kilogram (C/kg) of air at NTP, and is directly related to the radiation fluence. The old unit for exposure is the roentgen (R). The roentgen (R) was originally defined as the amount of X radiation that produced 1 electrostatic unit (esu) of charge as a result of interactions in 1cc of dry air at NTP. 1R=2.58x10-4C/kg

5 Absorbed dose (D) Energy imparted to matter from any type of radiation
D = E/m Because the roentgen is only defined for ionization in air caused by X or gamma radiation, a term is needed to quantify the amount of energy imparted to matter from any type of radiation. To look at biological effects, we must measure how much energy is deposited per unit mass of the medium with which the radiation is interacting. This quantity is known as the absorbed dose (D) which is defined as the quotient of E/m, where E is the energy absorbed by material of mass m: D=E/m D - absorbed dose, E - energy absorbed by material of mass ‘m’

6 joule/kilogram or gray (Gy)
Units of absorbed dose The SI unit: joule/kilogram or gray (Gy) 1 Gy = 1 J/kg Traditional (old) unit: rad (radiation absorbed dose) 1 Gy=100 rad The international unit (SI) of measure for absorbed dose is the gray (Gy), which is defined as 1 joule of energy deposited per 1 kilogram of medium. The old unit of measure for this is the rad, which stands for "radiation absorbed dose." One Gray is equal to 100 rads. Not all kinds of ionizing radiation are equally damaging. How damaging any given radiation is depends on many factors. Two of the most important factors are (1) how much energy is deposited and (2) how quickly the energy is deposited.

7 Variants of radiation exposure
External irradiation Internal irradiation Local irradiation Total irradiation Acute irradiation Chronic irradiation Prolonged irradiation Fractioned irradiation

8 HT = WR x D Equivalent dose (HT) Accounts for biological effect
per unit dose radiation weighting absorbed factor ( WR ) dose (D) HT = WR x D X Equivalent dose is a quantity which takes into account the relative biological damage produced in tissue by different types of radiation. Even when the energy deposition is equal at a macroscopic level (that is, the absorbed dose is the same), different types and energies of radiation will produce different amounts of biological damage. The actual damage produced per Gy will depend on the linear energy transfer (LET) of the radiation, or density of ionization produced at a microscopic level by each radiation particle as it traverses through tissue. For the purpose of comparing the biological effects of different types of radiation, a radiation weighting factor WR, which takes account of the relative biological effectiveness (RBE) of each type of radiation, is introduced. The average absorbed dose in a tissue or organ T in Gy is mutiplied by this factor to give the equivalent dose,HT . This is given by HT = WR x DTR  where DTR is the absorbed dose in tissue or organ T from radiation R and WR is the appropriate radiation weighting factor. When the radiation source consists of various types and energies with different values of WR, the total equivalent dose HT is given by HT = R WR x DTR

9 Radiation weighting factors (WR)
To account for differences in LET when measuring the effect of radiation, each type of radiation has been assigned a radiation weighting factor (WR). This was done by measuring how much of each radiation type it took to produce the same biological effect as 200-keV X rays. As shown, all photons, beta particles, and electrons do the same amount of damage. Thermal neutrons do somewhat more damage, and fast neutrons and alpha particles are extremely damaging. Indeed, of the radiation types that we deal with, alpha particles and high-energy neutrons are the most damaging.

10 Unit of equivalent dose
The SI unit: sievert (Sv) HT (Sv) = WR x D (Gy) Traditional (old) unit: rem (roentgen equivalent man) HT (rem) = WR x D (rad) 1 Sv = 100 rem The unit of equivalent dose is the sievert (Sv) named after Rolf M Sievert, the Swedish physicist who laid the foundations of modern radiation physics. The old unit of equivalent dose is the rem, which is equal to the absorbed dose, rad, multiplied by the radiation-weighting factor. Also, just as 1 Gy is 100 rads, 1 Sv is 100 rems.

11 E = ΣT (WT x HT) Effective dose (E)
Risk related parameter, taking relative radiosensitivity of each organ and tissue into account E = ΣT (WT x HT) WT - tissue weighting factor for organ T HT - equivalent dose received by organ or tissue T The SI unit of effective dose: sievert (Sv) It is now understood that different organs of the body vary in their sensitivity to absorbed doses of radiation. The ICRP has introduced a quantity, the effective dose equivalent, which reflects not only specific organ doses but also the relative radiosensitivity of the organs. The calculation of effective dose equivalent required knowledge of the radiation doses to individual organs. These were then multiplied by “tissue weighting factors”(WT) to take account of the relative sensitivity of each type of tissue to radiation. This is a weighted sum of doses to individual organs where the value of the tissue weighting factors is based upon the estimates of the relative risk of stochastic effects from the irradiation of the different tissues. E(Sv)= ΣT WT x HT WT :Tissue weighting factor for organ T HT : Equivalent dose received by organ or tissue T Effective dose is expressed in sieverts (Sv). Use of this concept enables comparison between situations where the whole body is irradiated uniformly and where individual organs receive relatively higher doses.

12 Tissue weighting factors (WT)
These are multipliers used for radiation protection purposes to account for the different sensitivities of the organs and tissues to the induction of stochastic effects of radiation. The relationship between the probability of the stochastic effect and equivalent dose varies with the tissue irradiated. Tissues which are at higher risk from radiation will have higher weighting factors (WT) The sum of the tissue weighting factors is equal to 1.

13 Collective effective dose (S)
Total radiation dose incurred by population S = Σi (Ei x Ni) Ei - average effective dose in the population subgroup i Ni - number of individuals in subgroup i The SI unit of collective effective dose: man-sievert (man-Sv) Collective effective dose accounts for the number of people exposed to a source by multiplying the average effective dose to the exposed group from the source by the number of individuals in the group. Unit: man sievert (man Sv). 

14 Conversion between units used in radiation protection
The basic information to be remembered: 1 Bq = 1 decay/sec 1 Ci = 3.7 x 1010 Bq 1 Gy = 100 rad, 1 Sv = 100 rem

15 Sources and levels of radiation exposure to population
Radiation is present throughout the environment and a large proportion of the average annual effective dose received by the population results from the environmental radiation what is called background radiation. Each member of the world population is exposed, on average, to 2.4 mSv of unavoidable ionizing radiation every year.

16 Sources of radiation exposure to people population
We all live with exposure to radiation on a daily basis. Shown here are some typical sources of radiation exposure.You can see that the largest contribution is made by natural sources (85%). An additional 15% of the average annual exposure is man-made, consisting of 14% from medical examinations (10% from diagnostic X rays and 4% from nuclear medicine procedures) and 1% from miscellaneous sources such as nuclear discharges, consumer goods, fallout and occupational exposure.

17 Background radiation Terrestrial radioactivity Cosmic radiation
Internal radioactivity Humans have always been exposed to background levels of ionizing radiation caused by: 1. Terrestrial radiation from the presence of naturally ocurring radioactivity in the soil, primarily due to uranium and its by-products. 2. Cosmic radiation that results from the interaction of particles from outer space with the atmosphere and high energy photons from outher space. 3. Internal radioactivity due to naturally occurring radioactivity deposited in the body.

18 Terrestrial radiation: external and internal exposure
Radioactivity is present throughout the earth’s crust. Uranium-238 is the parent of a long series of radionuclides, including radon-222 which escapes as a gas. Thorium-232 is also a parent of another radioactive series which in turn produces the gas radon-220. The radon gases seep up through the rocks and soil and can lead to high levels in dwellings, especially where there is little air flow. U Ra-222 Th Ra-220

19 High background areas The annual effective radiation dose from natural and man-made sources for the world's population is about 3 mSv, which includes exposure to alpha radiation from radon and its progeny nuclides. Nearly 80% of this dose (2.4 mSv) comes from natural background radiation, although levels of natural radiation can vary greatly. Ramsar, a northern coastal city in Iran, has areas with some of the highest levels of natural radiation measured to date. The effective dose equivalents in very high background radiation areas of Ramsar in particular in Talesh Mahalleh, are a few times higher than the ICRP-recommended radiation dose limits for radiation workers.

20 Cosmic radiation Cosmic rays are extremely energetic particles, primarily protons, which originate in the sun, other stars and from violent cataclysms in the far reaches of space.  Cosmic ray particles interact with the upper atmosphere of the earth and produce showers of lower energy particles. Many of these lower energy particles are absorbed by the earth's atmosphere.  At sea level, cosmic radiation  is composed mainly of muons, with some gamma rays, neutrons and electrons. Because the earth's atmosphere acts as a shield, the exposure of an individual to cosmic rays is greater at higher elevations than at sea level.

21 Internal radioactivity
in diet potassium-40 lead-210 polonium-210 Natural radioactivity in the body Radioactivity in air, food and water enter the body, irradiating internal organs and tissues. Potassium-40 is present everywhere in a stable ratio where potassium occurs. It is the most important natural radionuclide permanently present in our body. Decay products from uranium and thorium such as lead-210 and polonium-210 are two of the main natural radionuclides, besides potassium-40, also in ingested sources.

22 Background radiation Air Radon - 2 mSv Cosmic - 0.3 mSv Food - 0.4 mSv
Non-occupational exposures can be divided into one of two categories: those originating from natural sources and those resulting from human-made sources. All individuals are continuously exposed to ionizing radiation from various natural sources. These sources include cosmic radiation and naturally occurring radionuclides within the environment and within the human body. The radiation levels resulting from natural sources are collectively called "natural background." Natural background (and the associated dose it imparts) varies considerably from one location to another. Food mSv Terrestrial mSv

23 Natural background radiation doses in Europe
Naturally occuring background levels of radiation can typically range from 2.0 to 4.0 mSv a year Naturally occuring background levels of radiation can typically range from 1.0 to 3.5 mSv a year and in some places can be much higher. The highest known level of background radiation is in Kerala and Madras States in India where a population of over 100,000 people receive an annual dose rate which averages 13 millisieverts. As shown in this slide, the average doses from natural sources of radiation vary throughout Europe. Radiation doses in the United Kingdom and the Netherlands are the lowest at around 2 to 3 mSv per year whereas in Sweden and Finland the annual doses are around 6 to 7 mSv.

24 Artificial sources of ionizing radiation
Radioactive sources Electric generators of ionizing radiation Activities using nuclear energy: nuclear weapons nuclear reactors Radiological and nuclear risks are everywhere in society. In fact, ionizing radiation is encountered in a variety of spheres, sometimes unsuspected. We can differentiate between the sources of radioactivity, viz. electrical generators and activities using nuclear energy.

25 Radioactive sources Radioactive sources are present in the sealed (normally non spreadable) and unsealed form (spreadable): Gammagraphy essentially uses as sources iridium-192 and sometimes cobalt-60 Neutrongraphy uses sources of neutrons like californium-252 or an americium/beryllium couple. Betagraphy uses beta sources like carbon-14. Chemical and biological radiation-treatment uses gamma radiation sources cobalt-60 or caesium-137. Radioactive sources are present in the sealed (normally non spreadable) and unsealed form (spreadable). Industrial applications of sealed sources comprise essentially radiography, radiometric measuring instruments and radiation-treatment. Research laboratories use the majority of available radioactive sources which are associated with unusual radio-elements by function of their specific activity. Non-destructive control sources are used to produce radiographs of materials. Gammagraphy essentially uses as sources iridium 192 and sometimes cobalt 60.The activity of the most usual sources is significant, the order of 3,000 gigabecquerels (GBq). Gammagraphs are widely spread pieces of equipment (there are more than 600 in circulation in France). The source in a grammagraph is a small steel cylinder measuring about 2cm long with a diameter of 5mm. These small dimensions lead to underestimation of the potential dangers that they represent when handled by persons who have not had prior warning of the danger. They can be the source of serious irradiation accidents. Neutrongraphy uses sources of neutrons like californium 252 or an americium/beryllium couple. Neutrongraphy is used to radiograph hydrogen containing materials. Betagraphy, using beta sources like carbon 14, is cited to be remembered. Radiation meters use a radioactive source/detector pair. By measuring the absorption of ionizing radiation by a material, you can measure the value of a parameter. Meters to measure thickness and density exist, the sources of which have an average activity of the order of 30GBq. Humidity meters, for research into very light elements like water or hydrocarbons in geological prospecting use portable neutron sources of the same type as those used in neutrongraphy. Chemical and biological radiation-treatment uses gamma radiation. Chemistry under ionizing radiation employs very strong sources (cobalt 60 or cesium 137), in excess of 37,000 GBq for the treatment of some plastics or for the radio-sterilization of medical products, foodstuffs or cosmetics. These sources must conform to special legislation for their safe use. Sealed sources can also be found in other uses, for example in old lightning conductors, electrostatic charge elimination, or yet still, in some smoke detectors. These sources always have very low activity. Non-sealed sources are not frequently found in industrial sectors. These are essentially used as tracers in hydrological studies, inspection of wear of machine parts, searching for leaks and the manufacture of radio-luminescent objects. In the medical sphere, sealed radioactive sources are used in radiotherapy to carry out treatment in situ (Brach therapy) or remotely (external radiotherapy). In Europe the sources for brachytherapy are iridium or caesium, both being gamma emitters. These sources have activities below 37GBq. For external radiotherapy cobalt 60 has replaced caesium 137. These are physically very small sources (a few centimeters) having major activities above 37,000GBq (several thousand curies).

26 Radioactive sources in medicine
In medicine there are three uses for non-sealed radioactive nuclides: Biological analyses: radio-markers have been replaced progressively by non-radioactive markers. Medical imaging: nuclear medicine department use radio-pharmaceuticals for diagnostics, which are ingested by the patient to obtain an image of the tissue or organ while it is functioning. Therapy: radio-pharmaceuticals can constitute the treatment itself, for example iodine 131 for the treatment of thyroid cancer. In medicine there are three uses for non-sealed radio-elements. Biological analyses: radio-markers have been replaced progressively by non-radioactive markers. The radio-elements used are very varied. The quantities generally employed are small to limit the risks. Medical imaging: nuclear medicine department use radio-pharmaceuticals for diagnostics, which are ingested by the patient to obtain an image of the tissue or organ while it is functioning. Therapy: radio-pharmaceuticals can constitute the treatment itself, for example iodine 131 for the treatment of thyroid cancer. The quantities of radio-elements in the non-sealed form employed by the nuclear medicine service can be significant: to treat thyroid cancer you use about 3.7 GBq per patient.

27 Electric generators of ionizing radiation
The industrial applications of electric generators of ionizing radiation are neighbors of radioactive sources. Medical applications comprise radio-diagnostics and radiotherapy: Medical radio-diagnostics is man’s largest source of exposure to ionizing radiation. It uses standard radiography equipment and X-scanners. The electric generators used in radiotherapy are electron accelerators of medium energy (20 million volts) which enable a beam of electrons or X-rays to be obtained. In the research sector the large accelerators and scientific instruments are used to study the fine structure of matter. The industrial applications of electric generators of ionizing radiation are neighbors of radioactive sources. The principal difference lies in the fact that this equipment requires an electricity supply which can be switched off at any time, which then interrupts the emission of ionizing radiation. Medical applications comprise radio-diagnostics and radiotherapy. Medical radio-diagnostics is man’s largest source of exposure to ionizing radiation. It uses standard radiography equipment and X-scanners. The electric generators used in radiotherapy are electron accelerators of medium energy (20 million volts) which enable a beam of electrons or X-rays to be obtained. In the research sector the large accelerators and scientific instruments are used to study the fine structure of matter. This induces very variable risks. All types of ionizing radiation can be encountered there. Certain plants use the activation phenomenon which leaves behind a persistent radiological risk, even after the plant has stopped operating.

28 Effective doses from medical exposure
Effective dose (mSv) Equivalent period of natural radiation Radiography Chest 0.02 3 days Pelvis 1.0 6 months IVP 4.6 2.5 years Barium studies 9.0 4.5 years CT (Chest, Abdomen) 8.0 4 years Nuclear Medicine Thyroid imaging Bone imaging 3.6 1.8 years The effective dose of X-ray and nuclear medicine investigations mainly lies between 0.5 mSv and 10 mSv. In general, doses from individual radiological investigations are seldom greater than 10 mSv, most being of the order of 2-3 mSv, which is comparable with individual doses received from natural sources over one year. The X-ray investigations with the highest effective dose are CT of the chest and abdomen, and barium enema (approximately 8 mSv). X-ray fluoroscopy is another procedure which can result in comparatively large radiation exposure to both patients and staff. In nuclear medicine the most commonly used procedure, the Tc-99m bone scan, results in an effective dose of less than 4 mSv.

29 Nuclear weapons nuclear fission or nuclear fusion:
Nuclear weapons can function by two very different modes – nuclear fission or nuclear fusion: Fission arms employ the principle of an uncontrolled chain reaction, i.e. each fission reaction leads to several further fission reactions Fusion arms (thermonuclear) use the fact that the union of deuterium and tritium to form a single nucleus of helium liberates a very large amount of energy Nuclear weapons can function by two very different modes – nuclear fission or nuclear fusion: Fission arms employ the principle of an uncontrolled chain reaction, i.e. each fission reaction leads to several further fission reactions Fusion arms (thermonuclear) use the fact that the union of deuterium and tritium to form a single nucleus of helium liberates a very large amount of energy

30 Summary number of explosions of nuclear weapons from 1945 to 1998
Country Years Number of explosions USA 1945 – 1992 1030 Russia 1949 – 1991 716 France 1960 – 1997 210 Great Britain 1950 – 1960 44 China 1964 – 1996 45 India 1974, 1998 6 Pakistan 1998 5 США (Невада – 935, Нью-Мексико – 3, Миссисипи –2, Колорадо – 2, Аляска – 3); РОССИЯ (в том числе на Новой Земле - 132); Казахстан – 496; Украина – 2; Узбекистан – 2; Туркменистан – 1; Китай (на полигоне Лобнор, штат Синьцзян) – 45; Алжир –17; Австралия – 12; Индия (на площадке Покхаране ) – 6; Пакистан (горный район Чагаи, провинция Белуджистан ) - 5, на атоллах: Муруроа – 175, Эниветок – 43; на островах: Рождества – 30, Бикини – 23, Джонстон – 12, Фангатофа –12, Молден –3; в Тихом океане – 4; в Южной Атлантике – 3.

31 Summary number of nuclear explosions in atmosphere
% USA Russia France China Britain

32 Nuclear explosions in atmosphere in various years
France

33 Ecological consequences of nuclear explosions and radiation accident
Summary activity, x 1016 Bq Contamination areas, km2 Nuclear explosions in atmospheres 510 x 1016 Chernobyl accident, 1986 185 250 x 106 River Techa accident, 1950 10,2 2 x 102 Kyshtym accident, 1957 7,4 23 x 103 Wind scale accident, 1957 1,1 3 x 102 Lake Karachay accident, 1967 0,003 Ecological consequences of nuclear explosions and radiation accident you can show in table.

34 Effective doses received during various types of work
‘Non-coal’ mining 16.3 milisieverts The average effective dose due to occupational exposure to all radiation workers is 1.4 mSv per year. Non-coal mining activities resulting in the highest occupational doses (16.3 mSv/yr). A dose of 1 mSv would result from flying above feet for approximately 200 h. This is equivalent to about 30 transatlantic flights as evident from the radiation doses received by air crews. (Obtained from the UK National Radiological Protection Board) Paints for luminous watch faces This unfortunate experience illustrates well the risk of internal contamination . In the 1920s and 1930s the clock making industry used radium 226 and 228 in radio-luminescent paint for watches. At this time, the risk from alpha emitting radio-elements was almost unknown. The workers who painted the luminous faces had the bad habit of tapering their brushes with their lips. Every time they did this they ingested several becquerels of radium. The fact that radium and calcium are chemical homologues, resulted in rare bone cancers appearing starting from the 20s, in the form of carcinoma of the sinus of the face. An epidemiological enquiry demonstrated the link between exposure to radium and the risk of bone cancer in 2,403 workers, whose ingestion of quantities of radium could be evaluated. 64 were suffering from osteosarcoma whereas 2 cases of this type of cancer would have been expected statistically. Dose in milisieverts

35 Comparison of radiation doses from any sources
0.1 mSv: dental X-ray or return flight across Atlantic 1 mSv: average yearly dose from natural radiation excluding radon  20 mSv: In many countries, the highest allowable yearly dose for people working with radioactivity A few 100 mSv/year: lower limit for deterministic effects from prolonged exposure 1000 to few 1000 mSv: thresholds for different deterministic effects at acute exposures mSv: will kill most people and higher animals after acute exposure 0.1 millisievert: Dental x-ray or a return flight across the Atlantic. 1 millisievert: The average yearly dose from natural radiation (from the ground, cosmic radiation, and naturally radioactive substances within the body), excluding radon. In regulating nuclear activities, 1 millisievert is used as the yearly dose limit for all man-made radioactivity to which the general public can be exposed. It corresponds to an increased risk of fatal cancer for 1 person out of 20 millisieverts: In many countries, the highest allowable yearly dose for people working with radioactivity. A few hundred millisieverts per year: the lower limit for deterministic effects from chronic exposure. One thousand to a few thousand millisieverts: thresholds for different deterministic effects at acute exposures. millisieverts: will kill most people and higher animals after acute exposure.

36 Dose limits recomended by ICRP (1991) whole body
Occupational exposure Public exposure 50 mSv maximum in any 1 year 100 mSv in 5 years 5 mSv in any 5 consecutive years Working figure 20 mSv per year 1 mSv per year Radiation dose limitation  The benefits of the use of radiation have been recognized for over a century. The potential for harm was also recognized shortly after radiation was first used for medical and therapeutic uses. Various advisory groups exist to review the use of radiation, evaluate the risk, and make recommendations on safe use, including exposure levels for personnel and the general population. The most prominent international organization is the International Commission on Radiological Protection (ICRP). According to ICRP recommendations, occupational exposure to radiation should not be higher than 50 mSv in any one year, and the annual average dose over five years must not exceed 20 mSv. The dose limits for the general public are lower than those for workers. The ICRP recommends that the public should not be exposed to more than an average of 1 mSv per year. Special limits are needed for women workers who become pregnant. It is important that a woman declare her pregnancy as early as possible; the ICRP recommends that the embryo or foetus should be protected by applying a more restrictive dose limit for the remaining time of the pregnancy. The objective of management once a pregnancy is declared is to ensure that the embryo or foetus is afforded the same broad level of protection as is required for members of the public.

37 Dose limits recomended by ICRP (1991) tissues
Annual doses to tissues Occupational Public Lens of the eye 150 mSv 15 mSv Skin (1 cm2) 500 mSv 50 mSv Hands and feet or individual organ The recommended annual equivalent dose limit for the lens of eye is 150 mSv. The recommended annual equivalent dose limit for the skin is 500 mSv, taken as an average over 1 cm2 of the most highly irradiated area of the skin. The nominal depth is considered to be 70 m (the depth of basal layer of the epidermis.

38 Modalities of irradiation and risk of radiation exposure
Radiation is present throughout the environment and a large proportion of the average annual effective dose received by the population results from the environmental radiation what is called background radiation. Each member of the world population is exposed, on average, to 2.4 mSv of unavoidable ionizing radiation every year.

39 Risk due to radiation exposure
Exposure to ionizing radiation can take three distinct forms, which can sometimes be combined: external exposure (or external irradiation), external contamination and internal contamination

40 External exposure The risks associated with external exposure depend on the type of incident radiation: Alpha radiation does not present any risk by external exposure Beta radiation can be hazard at the site of exposure on the skin and deep derma Neutrons entail the same risks as gamma radiation Gamma radiation reaches the skin, the derma and all deep tissues External exposure Ionizing radiation emitted by a remote source from the organism can reach the latter either directly or indirectly after it has diffused towards the objects situated in the radiation field. When the organism is no longer exposed to the source, the external irradiation immediately stops. The risks associated with external exposure depend on the type of incident radiation. Alpha radiation has a pathway (depth of penetration or distance traveled in a given medium) in air of several centimeters and is stopped by the horny layer of the skin, which is composed of dead cells. Therefore, it does not present any risk by external exposure. Beta radiation has a pathway of the order of a meter in air and several millimeters in living tissue. It can therefore be at the site of exposure on the skin and deep derma. Having high energy, they can cause profound exposure due to the radioactive energy loss. Neutrons have a pathway of the order of a kilometer in air and a meter in living tissue. They entail the same risks as gamma radiation. Gamma radiation has a path of several kilometers in air and several meters in living tissue: it reaches the skin, the derma and all deep tissues.

41 The San Salvador accident in February 1989
Three employees at an industrial sterilization plant in San Salvador were using a very significant Co-60 source of 600 TBq (more than 15,000 Ci). They were seriously irradiated due to obsolete plant and their not being aware of the risks. As a result of their position and the time they spent near the source, the whole body exposure doses they received have been estimated at 8 Gy, 4 Gy and 3 Gy, respectively. Vomiting appeared less than two hours after exposure. The three victims were referred to the nearest hospital because they felt very tired and could not stop vomiting. They did not present any other sign of acute exposure. Although they had mentioned their work in a plant using ionizing radiation, they were diagnosed as having food poisoning. Acute irradiation syndrome was only recognized three days later when another patient presented with erythema, skin burns, nausea and vomiting and told them that there had been a technical accident at an irradiation plant. The San Salvador accident This accident occurred in San Salvador in February 1989 and typifies external exposure. Three employees at an industrial sterilization plant in San Salvador were using a very significant cobalt 60 source of 600 TBq ie. more than 15,000 curies. They were seriously irradiated due to obsolete plant and their not being aware of the risks. As a result of their position and the time they spent near the source, the whole body exposure doses they received have been estimated at 8 Gy, 4 Gy and 3 Gy, respectively. Vomiting appeared less than two hours after exposure. The three victims were referred to the nearest hospital because they felt very tired and could not stop vomiting. They did not present any other sign of acute exposure. Although they had mentioned their work in a plant using ionizing radiation, they were diagnosed as having food poisoning. Acute irradiation syndrome was only recognized three days later when another patient presented with erythema, skin burns, nausea and vomiting and told them that there had been a technical accident at an irradiation plant. This example shows how difficult diagnosis of acute irradiation can be, especially when it has not been established that a radiological accident has occurred.

42 External contamination
The risks linked to external exposure of the skin differ according to the type of radiation: alpha emitting radio-elements do not a priori present any risk by external contamination, beta emitting radio-elements do present a special risk because they entail exposure which is almost exclusively of the skin, gamma emitting radio-elements pose the same problems by external contamination as in external exposure, external contamination by a neutron emitting radio-element is impossible. External contamination reveals a secondary potential risk of internal contamination by inhalation, ingestion or breaking and penetration of the skin. External contamination Every deposition of radio-elements on the skin or its secondary features (hair, nails, etc), following fall-out or direct contact with radio-elements from a non sealed source, constitutes external contamination or external skin exposure. Consecutive irradiation is continuous when external decontamination has not been carried out, even when the person is no longer exposed to the source of contamination. The risks linked to external exposure of the skin differ according to the type of radiation: alpha emitting radio-elements do not a priori present any risk by external contamination, beta emitting radio-elements do present a special risk because they entail exposure which is almost exclusively of the skin, gamma emitting radio-elements pose the same problems by external contamination as in external exposure, external contamination by a neutron emitting radio-element is impossible. External contamination reveals a secondary potential risk of internal contamination by inhalation, ingestion or breaking and penetration of the skin.

43 People involved in the Chernobyl accident in 1986
The Chernobyl accident, 26 April 1986, involved the very serious irradiation and contamination of a number of people working in the power station and those who immediately intervened, it provides a good example of external contamination. More than 200 patients were hospitalized in the hours following the catastrophe. Before this massive flood of victims, the initial efforts to manage the situation were limited to treatment of the symptoms a full assessment of lesions, treatment of traumatic lesions and summary external decontamination. The latter fact was revealed to be particularly damaging as all the patients had external contamination by fission products, such as Cs-137, Sr-90, or I-131, all of them being beta and some gamma emitters. Beta emitters on the skin caused severe radiological burns with complex development. It is estimated that 5 of the 28 premature deaths following the accident were attributable in part to radiological burns. These 5 deaths, and perhaps others, could doubtless have been avoided if good external decontamination of all the exposed subjects had been carried out in the shortest time. People involved in the Chernobyl accident The Chernobyl accident, 26 April 1986, involved the very serious irradiation and contamination of a number of people working in the power station and those who immediately intervened, it provides a good example of external contamination. More than 200 patients were hospitalized in the hours following the catastrophe. Before this massive flood of victims, the initial efforts to manage the situation were limited to treatment of the symptoms (anti-emetics, sedatives and potassium iodide), a full assessment of lesions, treatment of traumatic lesions and summary external decontamination. The latter fact was revealed to be particularly damaging as all the patients had external contamination by fission products, such as caesium 137, strontium 90, or iodine 131, all of them being beta and some gamma emitters. Beta emitters on the skin caused severe radiological burns with complex development. It is estimated that 5 of the 28 premature deaths following the accident were attributable in part to radiological burns. These 5 deaths, and perhaps others, could doubtless have been avoided if good external decontamination of all the exposed subjects had been carried out in the shortest time.

44 Internal contamination
When radioactive nuclides enter an organism it is still called internal exposure. Incorporation can occur via different pathways: respiratory, digestive, transcutaneous or through breaking and penetration of the skin. The most frequent points of entry are by inhalation and wounds. In internal contamination the radio-elements are in contact with living cells. This position does not much alter the risk induced by beta or X radiation. By contrast, the risk associated with alpha radiation, which did not exist for the other modes of exposure, is major here. The presence of radio-elements in an organism is not always pathological, a certain number of atoms, of which the organism is constructed, are radio-elements (example: K-40). Internal contamination When radio-elements enter an organism it is still called internal exposure. Such incorporation can occur via different pathways: respiratory, digestive, transcutaneous (iodine and tritium essentially) or through breaking and penetration of the skin. The most frequent points of entry are by inhalation and wounds. Even when the subject is no longer exposed to the source of contamination, irradiation due to the continuing incorporation of radio-elements as contamination has not been eliminated. This occurs either spontaneously or after specific treatment suited to the contaminant. In internal contamination the radio-elements are in contact with living cells. This position does not much alter the risk induced by beta or X radiation. By contrast, the risk associated with alpha radiation, which did not exist for the other modes of exposure, is major here. In fact, no screen exists which can separate living cells from an alpha emitter and the deposition of energy from alpha particles, which have a very short pathway, induce very significant cell lesions. The presence of radio-elements in an organism is not always pathological, a certain number of atoms, of which the organism is constructed, are radio-elements. Thus, only potassium 40 is radioactive out of the three natural isotopes of potassium. It only represents % of the potassium stored in an organism, ie. about 7,000 Bq for an adult man.

45 Paints for luminous watch faces
In the 1920s and 1930s the clock making industry used radium 226 and 228 in radio-luminescent paint for watches. At this time, the risk from alpha emitting radio-elements was almost unknown. The workers who painted the luminous faces had the bad habit of tapering their brushes with their lips. Every time they did this they ingested several becquerels of radium. The fact that radium and calcium are chemical homologues, resulted in rare bone cancers appearing starting from the 20s, in the form of carcinoma of the sinus of the face. An epidemiological enquiry demonstrated the link between exposure to radium and the risk of bone cancer in 2,403 workers, whose ingestion of quantities of radium could be evaluated. 64 were suffering from osteosarcoma whereas 2 cases of this type of cancer would have been expected statistically. Paints for luminous watch faces This unfortunate experience illustrates well the risk of internal contamination . In the 1920s and 1930s the clock making industry used radium 226 and 228 in radio-luminescent paint for watches. At this time, the risk from alpha emitting radio-elements was almost unknown. The workers who painted the luminous faces had the bad habit of tapering their brushes with their lips. Every time they did this they ingested several becquerels of radium. The fact that radium and calcium are chemical homologues, resulted in rare bone cancers appearing starting from the 20s, in the form of carcinoma of the sinus of the face. An epidemiological enquiry demonstrated the link between exposure to radium and the risk of bone cancer in 2,403 workers, whose ingestion of quantities of radium could be evaluated. 64 were suffering from osteosarcoma whereas 2 cases of this type of cancer would have been expected statistically.

46 Common risks Approximately 1 in 10,000 will die from
Working one year in a safe industry Receiving 50 mSv whole body Smoking 10 packs of cigarettes Living with a smoker for 15 years Drinking 50 bottles of wine Taking a 1,000 mile bike ride Traveling 30,000 miles by car 10,000 hours flying time It is difficult to estimate risks from radiation, for most of the radiation exposures that humans receive are very close to background levels. In most cases, the effects from radiation are not distinguishable from normal levels of those same effects. With the beginning of radiation use in the early part of the century, the early researchers and users of radiation were not as careful as we are today though. The information from medical uses and from the survivors of the atomic bombs (ABS) in Japan, have given us most of what we know about radiation and its effects on humans. Risk estimates have their limitations: The doses from which risk estimates are derived were much higher than the regulated dose levels of today; The dose rates were much higher than normally received; The actual doses received by the ABS group and some of the medical treatment cases have had to be estimated and are not known precisely; Many other factors like ethnic origin, natural levels of cancers, diet, smoking, stress and bias effect the estimates.

47 Summary of lecture Becquerel (Bq), coulomb per kilogram (C/kg), gray (Gy) and sievert (Sv) are part of International System of Units (SI) Absorbed dose of radiation in SI units is expressed in gray (Gy) Ability of some types of radiation to cause more significant levels of biological damage taken into account with radiation weighting factor used to determine equivalent dose, expressed in sieverts (Sv) Effective dose, expressed in sieverts (Sv), is based upon the estimates of the relative risk of stochastic effects from the irradiation of the different tissues Natural sources of radiation is made 85 % of effective doses received people from various sources of radiation Becquerel (Bq), coulomb per kilogram (C/kg), gray (Gy) and sievert (Sv) are part of International System of Units (SI) Absorbed dose of radiation in SI units is expressed in gray (Gy) Ability of some types of radiation to cause more significant levels of biological damage taken into account with radiation weighting factor used to determine equivalent dose, expressed in sieverts (Sv) Effective dose, expressed in sieverts (Sv), is based upon the estimates of the relative risk of stochastic effects from the irradiation of the different tissues Natural sources of radiation is made 85 % of effective doses received people from various sources of radiation

48 kindly given by doctor Elena Buglova, were used
Lecture is ended THANKS FOR ATTENTION Quiz 1) In what old and SI units are biological effects of radiation measured? a) rad only b) rem only c) gray only d) rad and sievert e) rem and gray 2) Which of these units of measure are not SI units? a) gray only b) rem and roentgen c) rem only d) roentgen only 3) Naturally occurring background levels of radiation can typically range from a)1.0 to 3.5 mSv/year b)10 to 50 mSv/year c) 1.0 to 5 Sv/year d) 1.0 to 3.5 Sv/year 4) According to ICRP recommendations, occupational exposure to radiation should not be higher than a) 100 mSv in any one year, and the annual average dose over five years must not exceed 50 mSv. b) 10 mSv in any one year, and the annual average dose over five years must not exceed 5 mSv. c) 50 mSv in any one year, and the annual average dose over five years must not exceed 20 mSv. d) 50 Sv in any one year, and the annual average dose over five years must not exceed 20 Sv. 5) 1 mSv increases fatal cancer risk a) 50 in a million b) 500 in a million c) 5000 in a million d) 0.1 in a million In lecture materials of the International Atomic Energy Agency (IAEA), kindly given by doctor Elena Buglova, were used


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