Radiation Physics Past Paper PDF

Radiation Physics (46351) Radiation and Environment (42341) Chapter 3 RADIOACTIVITY SOURCES AND DECAY CHAINS Prof. Dr. Khalil Thabayneh Hebron University Palestine  INTRODUCTION The earth‘s environment contains Natural Occurring Radioactive Materials (NOR...

Radiation Physics (46351) Radiation and Environment (42341) Chapter 3 RADIOACTIVITY SOURCES AND DECAY CHAINS Prof. Dr. Khalil Thabayneh Hebron University Palestine  INTRODUCTION The earth‘s environment contains Natural Occurring Radioactive Materials (NORMs) which are widely spread and exist in different geological formations such as water, rocks, and air. The environment contains food, air, building and many more elements around us that are radioactive and contain many radionuclides. These can be regarded as radioactive although they are considered as background level and do not harm humans ‫ ﻻ ﺗﺆذي اﻟﺒﺸﺮ‬and living things within this level except if there is an environmental effect caused by man-made activities involving radionuclides. We are continuously exposed to radiation from many sources. All species on Earth have existed and evolved in environments where they have been exposed to radiation from the natural background. Where does radiation come from? More recently‫ﻓﻲ اﻵوﻧﺔ اﻷﺧﯿﺮة‬, humans and other organisms have also been exposed to artificial sources developed over the past century or so. Over 80 per cent of our exposure is from natural sources and only 20 per cent is human made from artificial sources-mainly from radiation applications used in medicine. Another way to categorize radiation exposure is how it irradiates us. Radioactive substances and radiation in the environment may irradiate our body from the externally. Or we may inhale the substances in air, swallow them in food and water or absorb them through skin and wounds ‫اﻟﺠﺮوح‬, and then they irradiate us from inside—internally. Considered globally, doses from internal and external  NATURAL SOURCES Since the creation of the Earth‫ ﻣﻨﺬ ﻧﺸﺄة اﻷرض‬, its environment has been exposed to radiation both from outer space and from radioactive material in its crust and core. There is no way to avoid ‫ ﻟﺘﺠﻨﺐ‬being exposed to these natural sources, which, in fact, cause most of the radiation exposure of the world’s population. The global average effective dose per person is about 2.4 mSv and ranges from about 1 to more than 10 mSv depending on where people live. Buildings may trap‫ ﺗﺤﺒﺲ‬a particular radioactive gas, called radon, or the building material itself may contain radionuclides that increase radiation exposure. Although the sources are natural, our exposure can be modified by choices we make, such as how and where we live or what we eat and drink. ‫ﯾﻤﻜﻦ ﺗﻌﺪﯾﻞ ﺗﻌﺮﺿﻨﺎ ﻣﻦ ﺧﻼل اﻟﺨﯿﺎرات اﻟﺘﻲ ﻧﺘﺨﺬھﺎ‬ ‫ ﻣﺜﻞ ﻛﯿﻒ وأﯾﻦ ﻧﻌﯿﺶ أو ﻣﺎذا ﻧﺄﻛﻞ وﻧﺸﺮب‬،. (a) Cosmogenic Radiation Primary radiation (protons and other heavier nuclei), originating from outer space, called cosmic rays continuously bombard stable atoms in the atmosphere and create radionuclides (e.g. 22Na, 7Be and 14C). When cosmic rays strike the atmosphere, they produce a nuclear cascade ‫ﺷﻼﻻ ﻧﻮوﯾﺎ‬ of secondary particles. Most of these are eventually ‫ﻧﮭﺎﯾﺔ اﻟﻤﻄﺎف‬ stopped before they reach the surface of the earth except for energetic muons ‫(اﻟﻤﯿﻮﻧﺎت اﻟﻨﺸﻄﺔ‬µ), and neutrons (n), which may penetrate all the way into the earth. There are two important cosmogenic radionuclides that are produced during the thermal neutron reaction: 14C by the (n, p) reaction on 14N has half-life (t1/2= 5,730 years) and 81Kr by the (n, γ) has half life (t1/2= 210,000 years).  Most of these rays originate from deep in interstellar space; some are released from the sun during solar flares. They irradiate the Earth directly, and interact with the atmosphere, producing different types of radiation and radioactive material. The Earth’s atmosphere and magnetic field considerably reduce cosmic radiation, some parts of the earth are more exposed than others. As cosmic radiation is deflected by the magnetic field to the North and South Poles, they receive more than the equatorial regions. ‫ﺑﺴﺒﺐ أن اﻟﻤﺠﺎل اﻟﻤﻐﻨﺎطﯿﺴﻲ ﯾﺤﺮف اﻹﺷﻌﺎع‬ ‫ ﻓﺈﻧﮭﻢ ﯾﺘﻠﻘﻮن أﻛﺜﺮ ﻣﻦ اﻟﻤﻨﺎطﻖ اﻻﺳﺘﻮاﺋﯿﺔ‬، ‫اﻟﻜﻮﻧﻲ إﻟﻰ اﻟﻘﻄﺒﯿﻦ اﻟﺸﻤﺎﻟﻲ واﻟﺠﻨﻮﺑﻲ‬. Moreover, the level of exposure increases with altitude because there is less air overhead to act as a shield. Thus, people living at sea level receive, on average, an effective dose of about 0.3 mSv annually from cosmic sources of radiation, or roughly 10–15% of their total dose from natural sources.  Those who live above 2000 m receive several times this dose. Airplane passengers might be exposed to even higher doses as the radiation exposure from cosmic sources depends not only on the altitude but also on the length of flights. For instance, at cruising altitudes‫ اﻟﻄﯿﺮان اﻟﻤﺮﺗﻔﻊ‬, the average effective dose is 0.03–0.08 mSv for a 10 hour flight. In other words, a New York–Paris round trip flight would expose a person to about 0.05 mSv. This is approximately equal to the effective dose a patient would receive from a routine chest X-ray examination. Although the estimated effective doses received by individual passengers during a flight are low, the collective doses may be quite high because of the large number of passengers and flights worldwide. ‫ﻋﻠﻰ اﻟﺮﻏﻢ ﻣﻦ أن اﻟﺠﺮﻋﺎت اﻟﻔﻌﺎﻟﺔ اﻟﻤﻘﺪرة اﻟﺘﻲ ﯾﺘﻠﻘﺎھﺎ اﻟﺮﻛﺎب‬ ‫ إﻻ أن اﻟﺠﺮﻋﺎت اﻟﺠﻤﺎﻋﯿﺔ ﻗﺪ ﺗﻜﻮن ﻋﺎﻟﯿﺔ ﺟﺪًا ﺑﺴﺒﺐ‬، ‫اﻷﻓﺮاد أﺛﻨﺎء اﻟﺮﺣﻠﺔ ﻣﻨﺨﻔﻀﺔ‬ ‫اﻟﻌﺪد اﻟﻜﺒﯿﺮ ﻣﻦ اﻟﺮﻛﺎب واﻟﺮﺣﻼت اﻟﺠﻮﯾﺔ ﻓﻲ ﺟﻤﯿﻊ أﻧﺤﺎء اﻟﻌﺎﻟﻢ‬. ‫ﺧدﻣﺔ اﻟﻧﻘل‬ (b)Terrestrial Radiation Terrestrial NORM comes out of the mantle and earth’s crust which consists of radioactive material and exploration of the earth crust by humans that have resulted to increased radiological exposure. The most important terrestrial NORM natural radionuclides originate from 232Th, 238U, 235U and 40K. these radionuclides decay- such as 226Ra and 222Rn - have been emitting radiation since before the Earth took its current shape. There are two main important chains which provide nuclides of significance in NORM; they are the thorium series and the uranium series. These radionuclides (NORM) in the Earth’s crust have very long half-lives as they have been in existence earth’s formation. The radionuclides in nature are approximately in a state of secular equilibrium and the activities of all radionuclides, within each series, are almost equal.  UNSCEAR calculates that every person worldwide receives, on average, an effective dose of about 0.48 mSv annually as external exposure from terrestrial sources. External exposure varies considerably from one location to another. Studies in France, Germany, Italy, Japan and the United States, for example, suggest that about 95 per cent of their populations live in areas where the average annual dose outdoors varies from 0.3 to 0.6 mSv. However, in some places in these countries people can receive doses higher than 1 mSv annually. There are other places in the world where radiation exposure from terrestrial sources is higher still. For example, on the southwest coast of Kerala, India, a densely populated 55-kilometre long strip of land contains thorium-rich sands, where people receive, on average, 3.8 mSv annually. Other regions with high levels of natural terrestrial sources of radiation are known to exist in Palestine, Brazil, China, the Islamic Republic of Iran, Madagascar, and Nigeria.  Radon Radon-222 (222Rn) is the most stable isotope of radon, with a half-life of 3.82 days. It is transient in the decay chain of primordial uranium-238 and is the immediate decay product of radium-226 (226Ra). Owing to its gaseous nature and high radioactivity, 222Rn is one of the leading causes of lung cancer. Radon-222 is generated in the uranium series from the alpha decay of 226Ra, which has a half-life of 1600 years. 222Rn itself alpha decays to polonium-218 with a half-life of 3.82 days, making it the most stable isotope of radon. Radon-222 is especially dangerous because its longer half-life allows it to permeate soil and rocks, where it is produced in trace quantities from decays of uranium-238, and concentrate in buildings and uranium mines.  When inhaled, some of radon’s short-lived decay products - mainly 218Po and 214Po - are retained in the lungs and irradiate cells in the respiratory tract with alpha particles. Radon is, hence, a primary cause of lung cancer in both smokers and non-smokers; however, smokers are far more vulnerable because of a strong interaction between smoking and radon exposure. Thus, 222Rn is a carcinogen ‫ ;ﻣﺎدة ﻣﺴﺮطﻨﺔ‬in fact, it is the second leading cause of lung cancer in the world after cigarette smoking, with millions deaths per year attributed to radon-induced lung cancer. Radon is present in the atmosphere everywhere, and can seep directly into buildings through cellars and floors, where its concentration – the amount of activity in terms of decays per time in a volume of air - can build up.  Mainly when homes are heated, warm air rises and escapes at the top of the house through windows or leakages, which creates low pressure in the ground floor and basement. This, in turn, causes active suction of radon from the subsoil through cracks and leakages (e.g. around service pipe entries) at the bottom of the house. The worldwide-average concentration of indoor radon is about 50 Bq/m3. The permissible concentration according to the World Health Organization is (WHO)100 Bq/m3.However, this average hides the great variability from place to place. In general, national average concentrations vary widely, ranging from less than 10 Bq/ m3 in Cyprus, Egypt and Cuba to more than 100 Bq/m3 in the Czech Republic, Finland and Luxembourg. In some countries such as Canada, Sweden and Switzerland there are houses with radon concentrations of between 1 000 and 10 000 Bq/m3.  Nevertheless, the proportion ‫ ﻧﺴﺒﺔ‬of houses with such high-level concentrations is rare ‫ﻧﺎدرة‬. Some of the factors that cause this variation are the local geology, the permeability‫ﻧﻔﺎذﯾﺔ‬ of the soil, the construction material and ventilation of buildings. In particular, ventilation, which depends on the climate, is a key factor. If buildings are well ventilated, such as in a tropical climate‫ اﻟﻤﻨﺎخ اﻻﺳﺘﻮاﺋﻲ‬, the accumulation of radon is unlikely to be substantial ‫ﻣﻦ ﻏﯿﺮ اﻟﻤﺤﺘﻤﻞ أن ﯾﻜﻮن ﺗﺮاﻛﻢ اﻟﺮادون ﻛﺒﯿﺮًا‬. However, in temperate or cold climates, where places tend to be less ventilated, the concentrations of radon can build up considerably‫إﻟﻰ ﺣﺪ ﻛﺒﯿﺮ‬. Extensive measurement programs have been conducted in many countries and have formed the basis for implementing measures to reduce indoor radon concentrations. ‫ﺗﻢ إﺟﺮاء ﺑﺮاﻣﺞ‬ ‫ﻗﯿﺎس واﺳﻌﺔ اﻟﻨﻄﺎق ﻓﻲ اﻟﻌﺪﯾﺪ ﻣﻦ اﻟﺒﻠﺪان وﺷﻜﻠﺖ اﻷﺳﺎس ﻟﺘﻨﻔﯿﺬ ﺗﺪاﺑﯿﺮ ﻟﺘﻘﻠﯿﻞ‬  The level of radon in water is usually very low but some supplies - e.g. deep wells and hot springs, in several countries - have very high concentrations. Radon in water can contribute to an increase of the concentration of radon in the air - particularly in the bathroom when showering. However, UNSCEAR concludes that the dose contribution from radon ingested in drinking water is small in comparison with its inhalation. UNSCEAR estimates that the average annual effective dose from radon is 1.3 mSv, representing about half of what the public receives from all natural sources.  ‫ﻣﺳﺎم اﻷرض‬ ‫أﻧﺎﺑﯾب اﻟﺳﺑﺎﻛﺔ وﺗﺟﮭﯾزاﺗﮭﺎ‬  Exposure of Radon in Workplaces For certain workplaces, inhaling radon gas dominates ‫ ﯾﮭﯿﻤﻦ‬the radiation exposure of workers. Radon is the main source of radiation exposure in underground mines of all types. The annual average effective dose to a coal miner is about 2.4 mSv and for other miners about 3 mSv. In the nuclear industry, the annual average effective dose to a worker is about 1 mSv, mainly from radon exposure in uranium mining. (c) Internal Exposure Internal radiation exposure hazards result from radioactive material that gets inside the body when you breathe it or eat it or when it passes through your skin. It was mentioned that external radiation exposure is unlikely from alpha and beta particles. Internal exposure, however, can come from all types of radioactive materials if they are inside the body. Once inside, much of the radiation energy will get absorbed in cells, tissues, and organs. The extent of an internal radiation dose is related to the amount of material inside the body, where it goes in the body, how long it stays in the body, and the type of radiation it emits. ، ‫ﯾﺮﺗﺒﻂ ﻣﺪى ﺟﺮﻋﺔ اﻹﺷﻌﺎع اﻟﺪاﺧﻠﻲ ﺑﻜﻤﯿﺔ اﻟﻤﻮاد داﺧﻞ اﻟﺠﺴﻢ‬ ‫ وﻧﻮع اﻹﺷﻌﺎع اﻟﺬي ﺗﻨﺒﻌﺚ ﻣﻨﮫ‬، ‫ وﻛﻢ ﺗﺒﻘﻰ ﻓﻲ اﻟﺠﺴﻢ‬، ‫وأﯾﻦ ﺗﺬھﺐ ﻓﻲ اﻟﺠﺴﻢ‬. Food and drink may contain primordial and some other radionuclides, mainly from natural sources. Radionuclides can be transferred to plants and then to animals from rocks and minerals present in the soil and water.  Thus, the doses vary depending on the concentrations of radionuclides in food and water, and on local dietary habits. For example, fish and shellfish have relatively high levels of lead-210 and polonium-210 and so people eating large amounts of seafood might receive somewhat higher doses than the general population do. UNSCEAR estimates that the average effective dose from natural sources in food and drink is 0.3 mSv, due mainly to potassium-40 and to the uranium-238 and thorium-232 series radionuclides. Radionuclides from artificial sources can be present in foodstuffs in addition to radionuclides from natural sources. However, the dose contribution from the authorized discharges of these radionuclides to the environment is usually very small.  Artificial Radioactivity For about a century, humanity has been exposed to radiation sources other than those occurring naturally. These new sources are almost all for our benefit ‫ﻟﺼﺎﻟﺤﻨﺎ ﺗﻘﺮﯾﺒﺎ‬, such as medical uses, power generation, radioisotope production, scientific research and various industries. There is also an ugly face ‫ وﺟﮫ ﻗﺒﯿﺢ‬to nuclear industries, such as the production of nuclear weapons, nuclear tests, and radioactive leaks... Individual doses from artificial sources of radiation vary greatly ‫ﺑﺸﻜﻞ ﻛﺒﯿﺮ‬. Most people receive a relatively small dose from such sources but a few receive many times the average. Artificial sources of radiation are generally well controlled by radiation protection measures. (a) Medical Applications In large part, most of the ‘artificial’ rays in medicine are not the result of nuclear reactions. Instead, these are rays from the internal layers of the atom: known as X-rays. Despite their differing origins‫ ﻋﻠﻰ اﻟﺮﻏﻢ ﻣﻦ أﺻﻮﻟﮭﺎ اﻟﻤﺨﺘﻠﻔﺔ‬, X-rays and alpha/ beta/gamma rays all have similar effects on living tissue. As a result, they are often grouped together when discussing protection from overexposure. The use of radiation in medicine to diagnose and treat certain diseases plays such an important role that it is now by far the main artificial source of exposure in the world. On average, it accounts for 98 % of the radiation exposure from all artificial sources and, after natural sources, is the second largest contributor to the population exposure worldwide, representing approximately 20 % of the total.  Most of this exposure occurs in industrialized countries, where more resources for medical care are available and, therefore, radiology equipment is used much more extensively. In some countries, this has even resulted in an annual average effective dose from medical use that is similar to the one from natural sources. There are substantial and distinct differences between medical exposure and most other types of exposure. Medical exposure typically involves only a portion of the body, whereas other exposure often involves the whole body. Additionally, the distribution of patients’ ages normally covers an older age range than that of the general population. Moreover, doses resulting from medical exposure should be compared with those from other sources very carefully ‫ﺑﻌﻨﺎﯾﺔ ﻓﺎﺋﻘﺔ‬.  The population dose due to medical exposure continues to increase worldwide. UNSCEAR has been regularly collecting information on diagnostic and therapeutic procedures. According to its survey for the period 1997–2007, about 3.6 billion medical radiation procedures were performed annually worldwide, compared with 2.5 billion in the previous survey period covering 1991–1996, which is an increase of almost 50%. The main general categories of medical practice involving radiation are ‫اﻟﻔﺌﺎت اﻟﻌﺎﻣﺔ اﻟﺮﺋﯿﺴﯿﺔ ﻟﻠﻤﻤﺎرﺳﺔ اﻟﻄﺒﯿﺔ اﻟﺘﻲ ﺗﻨﻄﻮي ﻋﻠﻰ اﻟﻌﻼج‬ ‫ اﻹﺷﻌﺎﻋﻲ‬radiology , nuclear medicine and radiotherapy. Other uses not covered by UNSCEAR’s regular evaluations include health screening ‫ اﻟﻔﺤﺺ‬programs, and voluntary participation ‫اﻟﻤﺸﺎرﻛﺔ اﻟﻄﻮﻋﯿﺔ‬in medical, biomedical, diagnostic or therapeutic research programs. ► Diagnostic radiology is the analysis of images obtained using X-rays, such as in plain radiography (e.g. chest or dental X-rays), fluoroscopy (e.g. with barium meal) and computer tomography (CT). Imaging modalities ‫اﻷﺷﻌﺔ اﻟﺘﺸﺨﯿﺼﯿﺔ‬which use non-ionizing radiation, such as ultrasound or magnet resonance imaging (MRI), are not addressed ‫ ﻟﻢ ﯾﺘﻢ ﺗﻨﺎوﻟﮭﺎ‬by UNSCEAR. Because of the wider use of CT and the significant dose per examination, the global average effective dose from diagnostic radiological procedures nearly doubled from 0.35 mSv in 1988 to 0.62 mSv in 2007. According to UNSCEAR’s latest survey, CT scanning now accounts for 43% of the total collective dose due to radiology. These numbers vary from region to region. About 2/3 of all radiological procedures are received by the 25% of the world’s population living in industrialized countries. For the remaining 75% of the world’s population, the annual frequency of procedures has remained fairly constant. ► Nuclear medicine is the introduction of unsealed (i.e. soluble and not encapsulated) radioactive substances into the body, mostly to obtain images that provide information on either structure or organ function and less commonly to treat certain diseases, such as hyperthyroidism and thyroid cancer. Generally, a radionuclide is modified to form a radiopharmaceutical that is usually administered intravenously or orally. It then disperses in the body according to physical or chemical characteristics making a scan possible. Thus, the radiation emitted from the radionuclide within the body is analyzed to produce diagnostic images or is used to treat diseases. ‫ اﻟﻄﺐ اﻟﻨﻮوي ھﻮ إدﺧﺎل ﻏﯿﺮ ﻣﻐﻠﻒ )أي ﻗﺎﺑﻞ ﻟﻠﺬوﺑﺎن وﻟﯿﺲ ﻛﺒﺴﻮﻻت( اﻟﻤﻮاد اﻟﻤﺸﻌﺔ ﻓﻲ اﻟﺠﺴﻢ‬ ‫ ﻓﻲ اﻟﻐﺎﻟﺐ ﻟﻠﺤﺼﻮل ﻋﻠﻰ ﺻﻮر واﻟﺘﻲ ﺗﻮﻓﺮ ﻣﻌﻠﻮﻣﺎت ﻋﻦ اﻟﮭﯿﻜﻞ أو وظﯿﻔﺔ اﻟﻌﻀﻮ وأﻗﻞ‬، ‫ ﯾﺘﻢ ﺗﻌﺪﯾﻞ‬، ‫ ﺑﺸﻜﻞ ﻋﺎم‬.‫ ﻣﺜﻞ اﻟﺰﯾﺎدة ﻧﺸﺎط وﺳﺮطﺎن اﻟﻐﺪة اﻟﺪرﻗﯿﺔ‬، ‫ﺷﯿﻮﻋًﺎ ﻟﻌﻼج ﺑﻌﺾ اﻷﻣﺮاض‬ ‫ ﺛﻢ ﯾﻨﺘﺸﺮ ﻓﻲ‬.‫اﻟﻨﻮﯾﺪات اﻟﻤﺸﻌﺔ ﻟﺘﺸﻜﯿﻞ دواء إﺷﻌﺎﻋﻲ ﯾﺘﻢ إﻋﻄﺎؤه ﻋﺎدة ﻋﻦ طﺮﯾﻖ اﻟﻮرﯾﺪ أو اﻟﻔﻢ‬ ‫ ﯾﺘﻢ ﺗﺤﻠﯿﻞ‬، ‫ وﺑﺎﻟﺘﺎﻟﻲ‬.‫اﻟﺠﺴﻢ وﻓﻘًﺎ ﻟﻠﺨﺼﺎﺋﺺ اﻟﻔﯿﺰﯾﺎﺋﯿﺔ أو اﻟﻜﯿﻤﯿﺎﺋﯿﺔ ﻣﻤﺎ ﯾﺠﻌﻞ اﻟﻔﺤﺺ ﻣﻤﻜﻨًﺎ‬ ‫اﻹﺷﻌﺎع اﻟﻤﻨﺒﻌﺚ ﻣﻦ اﻟﻨﻮﯾﺪات اﻟﻤﺸﻌﺔ داﺧﻞ اﻟﺠﺴﻢ ﻹﻧﺘﺎج ﺻﻮر ﺗﺸﺨﯿﺼﯿﺔ أو ﯾﺴﺘﺨﺪم ﻟﻌﻼج‬  The number of diagnostic nuclear medicine procedures increased worldwide from about 24 million in 1988 to about 33 million in 2007. This resulted in a significant increase in the annual collective effective dose from 74 000 to 202 000 man Sv. Therapeutic applications ‫ اﻟﺘﻄﺒﯿﻘﺎت اﻟﻌﻼﺟﯿﺔ‬in modern nuclear medicine are also increasing, reaching about 0.9 million patients each year worldwide. ►Radiation Therapy (Radiotherapy) uses radiation to treat various diseases, usually cancer, but also benign ‫ ﺣﻤﯿﺪة‬tumors. External radiotherapy refers to patient treatment using a radiation source that is outside the patient’s body and is called teletherapy‫ اﻟﻌﻼج ﻋﻦ ﺑﻌﺪ‬. This uses a machine containing a highly radioactive source (usually cobalt-60) or a high-voltage machine that produces radiation (e.g. a linear accelerator). Treatment can also be performed by placing metallic or sealed radioactive sources, within the patient and this is called brachytherapy  Worldwide, an estimated 5.1 million patients were treated annually with radiotherapy during the period 1997–2007, up from an estimated 4.3 million in 1988. About 4.7 million were treated by teletherapy and 0.4 million by brachytherapy. The 25% of the population living in industrialized countries received 70% of the radiotherapy treatment worldwide and 40% of all brachytherapy procedures. Exposure in Workplaces Because the total number of medical radiological procedures has increased significantly in the past decades‫ ﻓﻲ اﻟﻌﻘﻮد اﻟﻤﺎﺿﯿﺔ‬, so has the number of health workers involved, passing 7 million with an average annual effective dose of about 0.5 mSv per worker. In interventional ‫ اﻟﺘﺪاﺧﻠﯿﺔ‬radiology and nuclear medicine, medical staff might receive higher than the average dose. ► Accidents ‫ اﻟﺤﻮادث‬in medical application Some medical applications of radiation (e.g. radiotherapy, interventional radiology and nuclear medicine) involve the delivery ‫ إﻋﻄﺎء‬of high doses to patients. When applied incorrectly, these can cause serious harm ‫ ﺿﺮر ﺟﺴﯿﻢ‬or even death. The people at risk include not only patients, but also physicians and other staff in the vicinity. Human error has been the most common cause of these accidents. Examples include giving a wrong dose because of treatment planning errors, failure to use equipment properly, and exposing the wrong organ or, occasionally, even the wrong patient. ‫اﻷﻣﺜﻠﺔ ﺗﺸﻤﻞ إﻋﻄﺎء ﺟﺮﻋﺔ‬ ‫ وﻛﺸﻒ‬، ‫ واﻟﻔﺸﻞ ﻓﻲ اﺳﺘﺨﺪام اﻟﻤﻌﺪات ﺑﺸﻜﻞ ﺻﺤﯿﺢ‬، ‫ﺧﺎطﺌﺔ ﺑﺴﺒﺐ أﺧﻄﺎء ﺗﺨﻄﯿﻂ اﻟﻌﻼج‬ ‫ أو ﺣﺘﻰ اﻟﻤﺮﯾﺾ اﻟﺨﻄﺄ ﻓﻲ ﺑﻌﺾ اﻷﺣﯿﺎن‬، ‫اﻟﻌﻀﻮ اﻟﺨﻄﺄ‬. Not only overexposure but underexposure might have serious consequences ‫ﻋﻮاﻗﺐ وﺧﯿﻤﺔ‬, when patients receive insufficient ‫ﻏﯿﺮ ﻛﺎﻓﯿﺔ‬ radiation dose to treat a life threatening disease ‫ﻣﺮض ﯾﮭﺪد اﻟﺤﯿﺎة‬. Quality assurance programs help to maintain high and consistent standards of practice in order to minimize the risk of such accidents. ‫ﺗﺴﺎﻋﺪ ﺑﺮاﻣﺞ ﺿﻤﺎن‬ ‫اﻟﺠﻮدة ﻓﻲ اﻟﺤﻔﺎظ ﻋﻠﻰ ﻣﻌﺎﯾﯿﺮ ﻣﻤﺎرﺳﺔ ﻋﺎﻟﯿﺔ وﻣﺘﺴﻘﺔ ﻣﻦ أﺟﻞ ﺗﻘﻠﯿﻞ ﻣﺨﺎطﺮ ﻣﺜﻞ ھﺬه اﻟﺤﻮادث‬. Global exposure from radiology (1988- 2008) Global exposure from nuclear medicine (1988- 2008) (b) Nuclear Weapon The involvement ‫إﺷﺮاك‬of nuclear power has made great impact on the global environment and has also contributed to the release of certain radionuclides into the atmosphere. We may assess and compared to the emissions from the nuclear weapons production and testing and the coal fuel cycle. In 1945 and 1980, countries like USA, France, UK, China and the Soviet Union have been involved in the past in testing nuclear weapons without any restriction‫ دون أي ﻗﯿﻮد‬, (in all, over 500 tests were conducted) releasing consequently radioactive materials into the atmosphere, such as 90Sr, 137Cs, and 131I, which have caused some effect on our environment. In response to concerns about the radiation exposure of humans and the environment, UNSCEAR was established in 1955. UNSCEAR ‫ ﺗﻢ إﻧﺸﺎء‬، ‫اﺳﺘﺠﺎﺑﺔً ﻟﻠﻤﺨﺎوف ﺑﺸﺄن ﺗﻌﺮض اﻹﻧﺴﺎن واﻟﺒﯿﺌﺔ ﻟﻺﺷﻌﺎع‬.1955 ‫ﻓﻲ ﻋﺎم‬  The estimated annual average effective dose due to global fallout from atmospheric nuclear weapons testing was highest in 1963, at 0.11 mSv, and subsequently fell to its present ‫ﺑﻌﺪ ذﻟﻚ اﻧﺨﻔﺾ‬ ‫ ﻻﺣﻘﺎ‬level of about 0.005 mSv. This exposure will decline ‫ﯾﮭﺒﻂ‬ only very slowly in the future because most of it is now due to the long-lived radionuclide carbon-14. As much as 50% of the total fallout produced by surface tests was deposited locally within about 100 km of the test site. People living near test sites were thus exposed mainly to local fallout. However, because the tests were conducted in relatively remote areas ‫أﺟﺮﯾﺖ ﻓﻲ ﻣﻨﺎطﻖ ﻧﺎﺋﯿﺔ ﻧﺴﺒﯿًﺎ‬, the local populations exposed were small and did not contribute significantly to the global collective dose. Nevertheless, people living downwind of the test sites received much higher doses than average. ‫ ﺗﻠﻘﻰ اﻷﺷﺨﺎص اﻟﺬﯾﻦ ﯾﻌﯿﺸﻮن ﻓﻲ اﺗﺠﺎه اﻟﺮﯾﺢ ﻓﻲ ﻣﻮاﻗﻊ اﻻﺧﺘﺒﺎر ﺟﺮﻋﺎت‬، ‫ وﻣﻊ ذﻟﻚ‬.‫أﻋﻠﻰ ﺑﻜﺜﯿﺮ ﻣﻦ اﻟﻤﺘﻮﺳﻂ‬  After the signature of this Partial Test Ban Treaty ‫ﻣﻌﺎھﺪة اﻟﺤﻈﺮ‬ ‫ اﻟﺠﺰﺋﻲ ﻟﻠﺘﺠﺎرب‬in 1963, about 50 tests were conducted underground annually until the 1990s; a few tests have also been conducted after that. Most of these tests had a much lower nuclear yield than the atmospheric tests, and any radioactive debris ‫ ﺣﻄﺎم‬was usually contained unless gases were vented or leaked ‫ ﺗﻨﻔﯿﺴﮭﺎ أو ﺗﺴﺮﺑﮭﺎ‬into the atmosphere. While the tests generated a very large quantity of radioactive residue ‫ﻣﺨﻠﻔﺎت ﻣﺸﻌﺔ‬, it is not expected to expose the public, because it is located deep underground and is essentially fused with the host rock ‫وﺗﻨﺼﮭﺮ‬ ‫أﺳﺎﺳًﺎ ﻣﻊ اﻟﺼﺨﻮر‬ ‫اﻟﻤﺨﺘﻠﻄﺔ ﻣﻌﮭﺎ‬ (c) Nuclear Reactors When certain isotopes of uranium or plutonium are hit by neutrons, the nucleus splits into two smaller nuclei by a process called nuclear fission, releasing energy and two or more neutrons. The neutrons released may also hit other uranium or plutonium nuclei and cause them to split, releasing more neutrons, which in turn can split more nuclei. This is called a chain reaction. These isotopes are normally used as the fuel in nuclear reactors, where the chain reaction is controlled to stop it going too fast. The energy released from fission in nuclear reactors can be used to produce electricity in nuclear power plants. However, there are also research reactors for testing nuclear fuel and various kinds of material, for investigations in nuclear physics and biology, and for the production of radionuclides to be used in medicine and industry. The work require industrial processes such as uranium mining and radioactive waste disposal ‫اﻟﺘﺨﻠﺺ ﻣﻦ اﻟﻨﻔﺎﯾﺎت اﻟﻤﺸﻌﺔ‬, which can give rise to occupational and public exposure. (d) Nuclear power plants The world’s first commercial nuclear power station on an industrial scale, was built in 1956 in the United Kingdom, and since then, the generation of electrical energy by nuclear power plants has grown considerably ‫ﻧﻤﺖ ﺑﺸﻜﻞ ﻛﺒﯿﺮ‬. Electrical energy production from nuclear sources continues to grow. By the end of 2010, around 440 power reactors were in operation in 29 countries, providing about 10% of global electricity generation, and 240 research reactors were widespread worldwide in 56 countries. The production of electricity by using nuclear power is in normal operation it contributes very little to global radiation exposure. Moreover, the radiation exposure levels vary widely from one type of facility to another, between different locations and over time. ► Exposure in Workplaces In the nuclear industry, the release of radon in underground uranium mines makes a substantial ‫ﺣﻘﯿﻘﻲ‬ contribution to occupational exposure. The extraction and processing of radioactive ores that may contain high levels of radionuclides is a widespread activity. The average annual effective dose per worker in the nuclear industry has gradually declined since the 1970s, from 4.4 mSv to 1 mSv at present. This is mainly because of significant reduction in uranium mining coupled with more advanced mining techniques and ventilation. ‫وﯾﺮﺟﻊ ذﻟﻚ أﺳﺎﺳًﺎ إﻟﻰ اﻻﻧﺨﻔﺎض اﻟﻜﺒﯿﺮ ﻓﻲ ﺗﻌﺪﯾﻦ اﻟﯿﻮراﻧﯿﻮم إﻟﻰ ﺟﺎﻧﺐ ﺗﻘﻨﯿﺎت‬.‫اﻟﺘﻌﺪﯾﻦ واﻟﺘﮭﻮﯾﺔ اﻷﻛﺜﺮ ﺗﻘﺪﻣًﺎ‬ ► Accidents at Nuclear Facilities ‫ﺣﻮادث ﻓﻲ اﻟﻤﻨﺸﺂت اﻟﻨﻮوﯾﺔ‬ The exposure levels during the normal operation of civil facilities of the nuclear industry are very low. However, there have been some serious accidents, which received extensive public attention and whose consequences have been reviewed by UNSCEAR. For examples: (1) The Vinca research facility in Yugoslavia in 1958, the three Mile Island nuclear power plant in the United States in 1979, and the fuel conversion facility at Tokai-Mura in Japan in 1999. (2) Severe ‫ ﺷﺪﯾﺪة‬radiation accidents in nuclear facilities between 1945 and 2007 resulted in tens employee deaths or serious injuries ‫إﺻﺎﺑﺎت ﺧﻄﯿﺮة‬, and seven caused off-site releases of radioactive material and detectable population exposure. There were other severe accidents in facilities related to nuclear weapon programs ‫ووﻗﻌﺖ ﺣﻮادث ﺧﻄﯿﺮة أﺧﺮى ﻓﻲ اﻟﻤﻨﺸﺂت ذات اﻟﺼﻠﺔ‬ ‫ﺑﺒﺮاﻣﺞ اﻷﺳﻠﺤﺔ اﻟﻨﻮوﯾﺔ‬.. (3) Chernobyl nuclear power plant accident The accident at the Chernobyl nuclear power plant on 26 April 1986 was not only the most severe in the history of civilian nuclear power, but also the most serious one in terms of exposure to radiation of the general population. The collective dose from the accident was many times greater than the combined collective dose from all other radiation accidents. The accident caused the largest uncontrolled radioactive release into the environment; large quantities of radioactive substances were released into the atmosphere. The radioactive cloud created by the accident dispersed over the entire northern hemisphere and deposited substantial amounts of radioactive material over large areas of the Soviet Union and other parts of Europe, and causing serious healthy, social and economic disruption to large segments of the population. ‫ﻛﻤﺎ أدى إﻟﻰ إﺣﺪاث اﺿﻄﺮاب ﺻﺤﻲ‬ ‫واﺟﺘﻤﺎﻋﻲ واﻗﺘﺼﺎدي ﺧﻄﯿﺮ ﻟﺸﺮاﺋﺢ واﺳﻌﺔ ﻣﻦ اﻟﺴﻜﺎن‬. (4) Fukushima-Daiichi nuclear power station accident After the great east-Japan earthquake of magnitude 9.0 and tsunami on the east coast of northern Japan on 11 March 2011, the Fukushima nuclear power station was severely damaged and radioactive material was released to the environment. The evacuated of residents around the nuclear power station greatly reduced the levels of exposure that would have been received by those affected. The consumption of water and certain foodstuffs was temporarily restricted to limit the radiation exposure of the public ‫ﺗﻢ ﺗﻘﯿﯿﺪ اﺳﺘﮭﻼك اﻟﻤﯿﺎه وﺑﻌﺾ اﻟﻤﻮاد‬ ‫اﻟﻐﺬاﺋﯿﺔ ﺑﺸﻜﻞ ﻣﺆﻗﺖ ﻟﻠﺤﺪ ﻣﻦ ﺗﻌﺮض اﻟﺠﻤﮭﻮر ﻟﻺﺷﻌﺎع‬.. (e) Industrial and other Applications Radiation sources are used in a broad spectrum of industrial applications. These include industrial irradiation used for sterilizing ‫ ﺗﻌﻘﯿﻢ‬medical and pharmaceutical products, preserving ‫ﺣﻔﻆ‬foodstuffs or eradicating insect infestation ‫اﻟﻘﻀﺎء ﻋﻠﻰ ﺗﻔﺸﻲ‬ ‫ ; اﻟﺤﺸﺮات‬industrial radiography used for examining welded metal joints for defects; alpha or beta emitters used in luminizing ‫ﻣﻀﯿﺌﺔ‬compounds in gun sights and as low-level light sources for exit signs and map illuminators ‫ ;إﺿﺎءة‬radioactive sources or X-ray machines used in well logging to measure geological characteristics in boreholes drilled‫ ﺣﻔﺮ اﻵﺑﺎر‬for mineral, oil or gas exploration; radioactive sources used in devices to measure thickness, moisture, density and levels of material; and other sealed radioactive sources used in research. these production are causes very low levels of exposure of the general public. ► Naturally occurring radioactive material There are several types of facilities around the world that, while unrelated to the use of nuclear energy, may expose the public to radiation because of increased concentrations of naturally occurring radioactive material (NORM) in their industrial products, by-products and waste. The most important of such facilities involve mining and mineral processing. Activities related to the extraction and processing of ores can also lead to increased levels of NORM. These activities include uranium mining and milling; metal mining and smelting; phosphate production; coal mining and power generation from coal burning; oil and gas drilling; rare earth and titanium oxide industries; zirconium and ceramic industries; and applications using naturally-occurring radionuclides (typically isotopes of radium and thorium). Coal, for example, contains traces of primordial radionuclides.  Geothermal energy generation is another source of radiation exposure of the general public. Underground reservoirs of steam and hot water are tapped to generate electricity or to heat buildings. Geothermal energy currently makes a relatively small contribution to the world’s energy production and thus to radiation exposure. A by-product of uranium enrichment is depleted uranium, which is less radioactive than natural uranium. Depleted uranium has been used for both civilian and military purposes for many years. Owing to its high density, it is used in radiation shielding or as counterweights in aircraft. Military use of depleted uranium, especially in armour-piercing munition ‫ﺧﺎﺻﺔ ﻓﻲ اﻟﺬﺧﯿﺮة اﻟﺨﺎرﻗﺔ‬ ‫ﻟﻠﺪروع‬, has raised concern about residual contamination. (f) Consumer Products ‫اﻟﻤﻨﺘﺠﺎت اﻟﻤﺴﺘﮭﻠﻜﺔ‬ A number of products bought for everyday use contain low levels of radionuclides, deliberately added in order to make use of their chemical or radioactive properties. Historically, the most significant radionuclide for use in luminous consumer products was radium-226. This use ended several decades ago, with radium being replaced by promethium-147 and hydrogen-3 (tritium), which are less radiotoxic. Even so, for clocks or watches containing tritium compounds, some leakage of tritium may have occurred, because it is very mobile. However, tritium emits only very weak beta particles that cannot penetrate the skin so it exposes people only if the tritium entered the body. Some modern smoke detectors consist of ionizing chambers with small foils of americium-241, which are emitters of alpha particles and produce a constant ion current. Ambient air is allowed to freely enter the detectors and if smoke enters the detector, it disrupts the current triggering an alarm.  Average Radiation Exposure to Public and Workers Generally, public exposure to radiation from natural sources dominates ‫ ﯾﮭﯿﻤﻦ‬the total exposure. UNSCEAR estimated the average annual effective dose to an individual at about 3 mSv. On average, the annual dose from natural sources is 2.4 mSv and 70% of it comes from radioactive substances in the air we breathe, the food we eat and the water we drink. The main source of exposure from artificial sources is radiation used in medicine, with an individual average annual effective dose of 0.62 mSv. Medical radiological exposure varies by region, country and health-care system ‫ﻧﻈﺎم اﻟﺮﻋﺎﯾﺔ اﻟﺼﺤﯿﺔ‬. UNSCEAR has estimated the average annual effective dose from medical applications of radiation in industrialized countries at 1.9 mSv and in non-industrialized countries at 0.32 mSv. However, these values might vary considerably (e.g. in the United States with 3 mSv or in Kenya with only 0.05 mSv).  Until the 1990, attention ‫ اﻻھﺘﻤﺎم‬concerning exposure of workers focused on artificial sources of radiation. Nowadays, however, it is realized that a very large number of workers are exposed to natural sources of radiation, mainly in the mining industry. For certain occupations ‫ﺑﻌﺾ اﻟﻤﮭﻦ‬in the mining sector, inhaling radon gas dominates ‫ ﯾﺴﯿﻄﺮ‬radiation exposure at work. While the release of radon in underground uranium mines makes a substantial contribution ‫ ﻣﺴﺎھﻤﺔ ﺟﻮھﺮﯾﺔ‬to occupational exposure on the part of the nuclear industry, the annual average effective dose to a worker in the nuclear industry overall has decreased from 4.4 mSv in the 1970 to about 1 mSv today. However, the annual average effective dose to a coal miner is still about 2.4 mSv and for other miners about 3 mSv. Three out of four workers exposed to artificial sources work in the medical sector, with an annual effective dose per worker of 0.5 mSv. Evaluation of the trends of the average annual effective dose per worker shows an increase in exposure from natural sources mainly due to mining and a decrease in exposure from artificial sources mainly because of the successful implementation of radiation ‫اﻟطﺎﻗم اﻟﺟوي‬ ‫ﻣﺗﻧوع‬  The Decay Chains of Radionuclides In nuclear science, the decay chain refers to a series of radioactive decays of different radioactive decay products as a sequential series of transformations. It is also known as a "radioactive cascade‫"ﺷﻼل‬. Most radioisotopes do not decay directly to a stable state, but rather undergo a series of decays until eventually a stable isotope is reached. A parent isotope is one that undergoes decay to form a daughter isotope. One example of this is uranium (atomic number 92) decaying into thorium (atomic number 90). The daughter isotope may be stable or it may decay to form a daughter isotope of its own. The daughter of a daughter isotope is sometimes called a granddaughter ‫اﺑﻨﺔ اﻻﺑﻨﺔ‬ isotope.  238 (1) U - Decay Series The 4n+2 chain of Uranium-238 is called the “Uranium Series" or “Radium Series". Beginning with naturally occurring Uranium-238 (half-life = 4.5×109 year), this series includes the following elements: Astatine, bismuth, lead, polonium, protactinium, radium, radon, thallium, and thorium. All are present, at least transiently, in any natural uranium-containing sample, whether metal, compound, or mineral. The series terminates with Lead-206 (Stable). The total energy released from uranium-238 to lead-206, including the energy lost to neutrinos, is 51.7 MeV. Note: A = 4n +m where n = natural number, m = 0, 1, 2, 3. Ex.: for 238U , A = 4n +m = 4(59) + 2  (2) 232Th - Decay Series The 4n chain of Th-232 is commonly called the “Thorium Series". Beginning with naturally occurring Thorium-232 (half-life = 1.405×1010 year), this series includes the following elements: Actinium, bismuth, lead, polonium, radium, radon and thallium. All are present, at least transiently ‫ﺑﺸﻜﻞ ﻋﺎﺑﺮ‬, in any natural thorium-containing sample, whether metal, compound, or mineral. The series terminates with Lead-208 (Stable). The total energy released from thorium-232 to lead-208, including the energy lost to neutrinos, is 42.6 MeV. (3) Actinium (235U) -Decay Series The 4n+3 chain of Uranium-235 is commonly called the “Actinium Series". Beginning with the naturally-occurring isotope U-235 (half-life = 7.04×108 year), this decay series includes the following elements: Actinium, astatine, bismuth, francium, lead, polonium, protactinium, radium, radon, thallium, and thorium. All are present, at least transiently, in any sample containing uranium-235, whether metal, compound, ore, or mineral. This series terminates with the stable isotope Lead-207 (Stable). The total energy released from uranium-235 to lead-207, including the energy lost to neutrinos, is 46.4 MeV. (4) Neptunium (237Np) - Decay Series The 4n+1 chain of 237Np is commonly called the “Neptunium Series". In this series, only two of the isotopes involved are found naturally in significant quantities, namely the final two: Bismuth-209 and thallium - 205. This series terminates with the stable isotope thallium-205 (Stable). The total energy released from californium-249 to thallium-205, including the energy lost to neutrinos, is 66.8 MeV.