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100-495: Khushab Nuclear Complex is a plutonium production nuclear reactor and heavy water complex situated 30 kilometres (19 mi) south of the town of Jauharabad in Khushab District , Punjab , Pakistan . The heavy water and natural uranium reactors at Khushab are a central element of Pakistan's program to produce plutonium and tritium for use in compact nuclear warheads . Khushab Nuclear Complex, like that at Kahuta ,

200-470: A Patlak plot . Radionuclide therapy can be used to treat conditions such as hyperthyroidism , thyroid cancer , skin cancer and blood disorders. In nuclear medicine therapy, the radiation treatment dose is administered internally (e.g. intravenous or oral routes) or externally direct above the area to treat in form of a compound (e.g. in case of skin cancer). The radiopharmaceuticals used in nuclear medicine therapy emit ionizing radiation that travels only

300-475: A nuclear proliferation risk as they can be configured to produce plutonium , as well as tritium gas used in boosted fission weapons . Reactor spent fuel can be reprocessed to yield up to 25% more nuclear fuel, which can be used in reactors again. Reprocessing can also significantly reduce the volume of nuclear waste, and has been practiced in Europe, Russia, India and Japan. Due to concerns of proliferation risks,

400-523: A radionuclide into the body by intravenous injection in liquid or aggregate form, ingestion while combined with food, inhalation as a gas or aerosol, or rarely, injection of a radionuclide that has undergone micro-encapsulation . Some studies require the labeling of a patient's own blood cells with a radionuclide ( leukocyte scintigraphy and red blood cell scintigraphy). Most diagnostic radionuclides emit gamma rays either directly from their decay or indirectly through electron–positron annihilation , while

500-553: A " neutron howitzer ") produced a barium residue, which they reasoned was created by fission of the uranium nuclei. In their second publication on nuclear fission in February 1939, Hahn and Strassmann predicted the existence and liberation of additional neutrons during the fission process, opening the possibility of a nuclear chain reaction . Subsequent studies in early 1939 (one of them by Szilárd and Fermi), revealed that several neutrons were indeed released during fission, making available

600-745: A ceremony at the Khushab complex for what is believed to be the completion of the second reactor. There has been little to no government comment on the complex or other aspects of the nuclear weapons program since the late 1990s. Judging by external appearance all but the first reactor are similar or identical in design. The heavy water plant is estimated to be able to produce between 50 and 100 tonnes (49 and 98 long tons; 55 and 110 short tons) of heavy water per year. See also: Military equipment manufactured in Pakistan & List of missiles of Pakistan Nuclear reactor Nuclear reactors have their origins in

700-441: A crucial role in generating large amounts of electricity with low carbon emissions, contributing significantly to the global energy mix. Just as conventional thermal power stations generate electricity by harnessing the thermal energy released from burning fossil fuels , nuclear reactors convert the energy released by controlled nuclear fission into thermal energy for further conversion to mechanical or electrical forms. When

800-445: A gas or a liquid metal (like liquid sodium or lead) or molten salt – is circulated past the reactor core to absorb the heat that it generates. The heat is carried away from the reactor and is then used to generate steam. Most reactor systems employ a cooling system that is physically separated from the water that will be boiled to produce pressurized steam for the turbines , like the pressurized water reactor . However, in some reactors

900-435: A higher Rem or Sv value, due to its much higher Relative Biological Effectiveness (RBE). Alpha emitters are nowadays rarely used in nuclear medicine, but were used extensively before the advent of nuclear reactor and accelerator produced radionuclides. The concepts involved in radiation exposure to humans are covered by the field of Health Physics ; the development and practice of safe and effective nuclear medicinal techniques

1000-442: A large fissile atomic nucleus such as uranium-235 , uranium-233 , or plutonium-239 absorbs a neutron, it may undergo nuclear fission. The heavy nucleus splits into two or more lighter nuclei, (the fission products ), releasing kinetic energy , gamma radiation , and free neutrons . A portion of these neutrons may be absorbed by other fissile atoms and trigger further fission events, which release more neutrons, and so on. This

1100-424: A less effective moderator. In other reactors, the coolant acts as a poison by absorbing neutrons in the same way that the control rods do. In these reactors, power output can be increased by heating the coolant, which makes it a less dense poison. Nuclear reactors generally have automatic and manual systems to scram the reactor in an emergency shut down. These systems insert large amounts of poison (often boron in

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1200-418: A nuclear medicine procedure will receive a radiation dose . Under present international guidelines it is assumed that any radiation dose, however small, presents a risk. The radiation dose delivered to a patient in a nuclear medicine investigation, though unproven, is generally accepted to present a very small risk of inducing cancer. In this respect it is similar to the risk from X-ray investigations except that

1300-570: A number of ways: A kilogram of uranium-235 (U-235) converted via nuclear processes releases approximately three million times more energy than a kilogram of coal burned conventionally (7.2 × 10 joules per kilogram of uranium-235 versus 2.4 × 10 joules per kilogram of coal). The fission of one kilogram of uranium-235 releases about 19 billion kilocalories , so the energy released by 1 kg of uranium-235 corresponds to that released by burning 2.7 million kg of coal. A nuclear reactor coolant – usually water but sometimes

1400-468: A particular section of the body (e.g.: chest X-ray, abdomen/pelvis CT scan, head CT scan, etc.). In addition, there are nuclear medicine studies that allow imaging of the whole body based on certain cellular receptors or functions. Examples are whole body PET scans or PET/CT scans, gallium scans , indium white blood cell scans , MIBG and octreotide scans . While the ability of nuclear metabolism to image disease processes from differences in metabolism

1500-461: A patent on reactors on 19 December 1944. Its issuance was delayed for 10 years because of wartime secrecy. "World's first nuclear power plant" is the claim made by signs at the site of the EBR-I , which is now a museum near Arco, Idaho . Originally called "Chicago Pile-4", it was carried out under the direction of Walter Zinn for Argonne National Laboratory . This experimental LMFBR operated by

1600-737: A pile (hence the name) of graphite blocks, embedded in which was natural uranium oxide 'pseudospheres' or 'briquettes'. Soon after the Chicago Pile, the Metallurgical Laboratory developed a number of nuclear reactors for the Manhattan Project starting in 1943. The primary purpose for the largest reactors (located at the Hanford Site in Washington ), was the mass production of plutonium for nuclear weapons. Fermi and Szilard applied for

1700-407: A planned typical lifetime of 30–40 years, though many of those have received renovations and life extensions of 15–20 years. Some believe nuclear power plants can operate for as long as 80 years or longer with proper maintenance and management. While most components of a nuclear power plant, such as steam generators, are replaced when they reach the end of their useful lifetime, the overall lifetime of

1800-471: A reactor. One such process is delayed neutron emission by a number of neutron-rich fission isotopes. These delayed neutrons account for about 0.65% of the total neutrons produced in fission, with the remainder (termed " prompt neutrons ") released immediately upon fission. The fission products which produce delayed neutrons have half-lives for their decay by neutron emission that range from milliseconds to as long as several minutes, and so considerable time

1900-558: A rotating gamma-camera are reconstructed to produce an image of a "slice" through the patient at a particular position. A collection of parallel slices form a slice-stack, a three-dimensional representation of the distribution of radionuclide in the patient. The nuclear medicine computer may require millions of lines of source code to provide quantitative analysis packages for each of the specific imaging techniques available in nuclear medicine. Time sequences can be further analysed using kinetic models such as multi-compartment models or

2000-518: A set of theoretical nuclear reactor designs. These are generally not expected to be available for commercial use before 2040–2050, although the World Nuclear Association suggested that some might enter commercial operation before 2030. Current reactors in operation around the world are generally considered second- or third-generation systems, with the first-generation systems having been retired some time ago. Research into these reactor types

2100-706: A short distance, thereby minimizing unwanted side effects and damage to noninvolved organs or nearby structures. Most nuclear medicine therapies can be performed as outpatient procedures since there are few side effects from the treatment and the radiation exposure to the general public can be kept within a safe limit. In some centers the nuclear medicine department may also use implanted capsules of isotopes ( brachytherapy ) to treat cancer. The history of nuclear medicine contains contributions from scientists across different disciplines in physics, chemistry, engineering, and medicine. The multidisciplinary nature of nuclear medicine makes it difficult for medical historians to determine

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2200-472: A sufficient amount of the procedure to achieve a diagnosis, then it would be inappropriate to proceed with injecting the patient with the radioactive tracer. When the benefit does justify the procedure, then the radiation exposure (the amount of radiation given to the patient) should also be kept "ALARP". This means that the images produced in nuclear medicine should never be better than required for confident diagnosis. Giving larger radiation exposures can reduce

2300-679: Is a key focus of Medical Physics . Different countries around the world maintain regulatory frameworks that are responsible for the management and use of radionuclides in different medical settings. For example, in the US, the Nuclear Regulatory Commission (NRC) and the Food and Drug Administration (FDA) have guidelines in place for hospitals to follow. With the NRC, if radioactive materials aren't involved, like X-rays for example, they are not regulated by

2400-417: Is called a physiological imaging modality . Single photon emission computed tomography (SPECT) and positron emission tomography (PET) scans are the two most common imaging modalities in nuclear medicine. In nuclear medicine imaging, radiopharmaceuticals are taken internally, for example, through inhalation, intravenously, or orally. Then, external detectors ( gamma cameras ) capture and form images from

2500-509: Is disease or pathology present. The radionuclide introduced into the body is often chemically bound to a complex that acts characteristically within the body; this is commonly known as a tracer . In the presence of disease, a tracer will often be distributed around the body and/or processed differently. For example, the ligand methylene-diphosphonate ( MDP ) can be preferentially taken up by bone. By chemically attaching technetium-99m to MDP, radioactivity can be transported and attached to bone via

2600-515: Is extracted. The F is then typically used to make FDG . Z = atomic number, the number of protons T 1/2 = half-life decay = mode of decay photons = principal photon energies in kilo-electron volts, keV , (abundance/decay) β = beta maximum energy in kilo-electron volts, keV , (abundance/decay) β = β decay ; β = β decay ; IT = isomeric transition ; ec = electron capture * X-rays from progeny, mercury , Hg A typical nuclear medicine study involves administration of

2700-413: Is inserted deeper into the reactor, it absorbs more neutrons than the material it displaces – often the moderator. This action results in fewer neutrons available to cause fission and reduces the reactor's power output. Conversely, extracting the control rod will result in an increase in the rate of fission events and an increase in power. The physics of radioactive decay also affects neutron populations in

2800-428: Is known as a nuclear chain reaction . To control such a nuclear chain reaction, control rods containing neutron poisons and neutron moderators are able to change the portion of neutrons that will go on to cause more fission. Nuclear reactors generally have automatic and manual systems to shut the fission reaction down if monitoring or instrumentation detects unsafe conditions. The reactor core generates heat in

2900-405: Is mined, processed, enriched, used, possibly reprocessed and disposed of is known as the nuclear fuel cycle . Under 1% of the uranium found in nature is the easily fissionable U-235 isotope and as a result most reactor designs require enriched fuel. Enrichment involves increasing the percentage of U-235 and is usually done by means of gaseous diffusion or gas centrifuge . The enriched result

3000-489: Is not subject to International Atomic Energy Agency inspections. Four currently operating reactors have capacities variously reported at between 40  MWth to 50 MWth, and as high as 70 MWth. In total, they are estimated to be capable of producing 44 kilograms (97 lb) of weapons grade plutonium annually. Plutonium production and nuclear reprocessing facilities are being expanded at Khushab, New Labs and Chashma. Pakistan's first indigenous nuclear reactor

3100-401: Is produced. Fission also produces iodine-135 , which in turn decays (with a half-life of 6.57 hours) to new xenon-135. When the reactor is shut down, iodine-135 continues to decay to xenon-135, making restarting the reactor more difficult for a day or two, as the xenon-135 decays into cesium-135, which is not nearly as poisonous as xenon-135, with a half-life of 9.2 hours. This temporary state is

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3200-448: Is reaching or crossing their design lifetimes of 30 or 40 years. In 2014, Greenpeace warned that the lifetime extension of ageing nuclear power plants amounts to entering a new era of risk. It estimated the current European nuclear liability coverage in average to be too low by a factor of between 100 and 1,000 to cover the likely costs, while at the same time, the likelihood of a serious accident happening in Europe continues to increase as

3300-416: Is required to determine exactly when a reactor reaches the critical point. Keeping the reactor in the zone of chain reactivity where delayed neutrons are necessary to achieve a critical mass state allows mechanical devices or human operators to control a chain reaction in "real time"; otherwise the time between achievement of criticality and nuclear meltdown as a result of an exponential power surge from

3400-402: Is then converted into uranium dioxide powder, which is pressed and fired into pellet form. These pellets are stacked into tubes which are then sealed and called fuel rods . Many of these fuel rods are used in each nuclear reactor. Nuclear medicine Nuclear medicine ( nuclear radiology , nucleology ), is a medical specialty involving the application of radioactive substances in

3500-423: Is unsurpassed, it is not unique. Certain techniques such as fMRI image tissues (particularly cerebral tissues) by blood flow and thus show metabolism. Also, contrast-enhancement techniques in both CT and MRI show regions of tissue that are handling pharmaceuticals differently, due to an inflammatory process. Diagnostic tests in nuclear medicine exploit the way that the body handles substances differently when there

3600-484: The Manhattan Project . Eventually, the first artificial nuclear reactor, Chicago Pile-1 , was constructed at the University of Chicago , by a team led by Italian physicist Enrico Fermi, in late 1942. By this time, the program had been pressured for a year by U.S. entry into the war. The Chicago Pile achieved criticality on 2 December 1942 at 3:25 PM. The reactor support structure was made of wood, which supported

3700-514: The PWR , BWR and PHWR designs above, and some are more radical departures. The former include the advanced boiling water reactor (ABWR), two of which are now operating with others under construction, and the planned passively safe Economic Simplified Boiling Water Reactor (ESBWR) and AP1000 units (see Nuclear Power 2010 Program ). Rolls-Royce aims to sell nuclear reactors for the production of synfuel for aircraft. Generation IV reactors are

3800-515: The U.S. Atomic Energy Commission produced 0.8 kW in a test on 20 December 1951 and 100 kW (electrical) the following day, having a design output of 200 kW (electrical). Besides the military uses of nuclear reactors, there were political reasons to pursue civilian use of atomic energy. U.S. President Dwight Eisenhower made his famous Atoms for Peace speech to the UN General Assembly on 8 December 1953. This diplomacy led to

3900-679: The Washington University School of Medicine . These innovations led to fusion imaging with SPECT and CT by Bruce Hasegawa from University of California, San Francisco (UCSF), and the first PET/CT prototype by D. W. Townsend from University of Pittsburgh in 1998. PET and PET/CT imaging experienced slower growth in its early years owing to the cost of the modality and the requirement for an on-site or nearby cyclotron. However, an administrative decision to approve medical reimbursement of limited PET and PET/CT applications in oncology has led to phenomenal growth and widespread acceptance over

4000-477: The coolant also acts as a neutron moderator . A moderator increases the power of the reactor by causing the fast neutrons that are released from fission to lose energy and become thermal neutrons. Thermal neutrons are more likely than fast neutrons to cause fission. If the coolant is a moderator, then temperature changes can affect the density of the coolant/moderator and therefore change power output. A higher temperature coolant would be less dense, and therefore

4100-421: The diagnosis and treatment of disease . Nuclear imaging is, in a sense, radiology done inside out , because it records radiation emitted from within the body rather than radiation that is transmitted through the body from external sources like X-ray generators . In addition, nuclear medicine scans differ from radiology, as the emphasis is not on imaging anatomy, but on the function. For such reason, it

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4200-629: The physical properties of the radiopharmaceutical used, its distribution in the body and its rate of clearance from the body. Effective doses can range from 6 μSv (0.006 mSv) for a 3 MBq chromium -51 EDTA measurement of glomerular filtration rate to 11.2 mSv (11,200 μSv) for an 80 MBq thallium -201 myocardial imaging procedure. The common bone scan with 600 MBq of technetium-99m MDP has an effective dose of approximately 2.9 mSv (2,900 μSv). Formerly, units of measurement were: The rad and rem are essentially equivalent for almost all nuclear medicine procedures, and only alpha radiation will produce

4300-545: The tracer principle. Possibly, the genesis of this medical field took place in 1936, when John Lawrence , known as "the father of nuclear medicine", took a leave of absence from his faculty position at Yale Medical School , to visit his brother Ernest Lawrence at his new radiation laboratory (now known as the Lawrence Berkeley National Laboratory ) in Berkeley , California . Later on, John Lawrence made

4400-402: The "iodine pit." If the reactor has sufficient extra reactivity capacity, it can be restarted. As the extra xenon-135 is transmuted to xenon-136, which is much less a neutron poison, within a few hours the reactor experiences a "xenon burnoff (power) transient". Control rods must be further inserted to replace the neutron absorption of the lost xenon-135. Failure to properly follow such a procedure

4500-590: The 1930s. The history of nuclear medicine will not be complete without mentioning these early pioneers. Nuclear medicine gained public recognition as a potential specialty when on May 11, 1946, an article in the Journal of the American Medical Association (JAMA) by Massachusetts General Hospital's Dr. Saul Hertz and Massachusetts Institute of Technology's Dr. Arthur Roberts, described the successful use of treating Graves' Disease with radioactive iodine (RAI)

4600-453: The 1960s became a practical method for medical use. Today, Technetium-99m is the most utilized element in nuclear medicine and is employed in a wide variety of nuclear medicine imaging studies. Widespread clinical use of nuclear medicine began in the early 1950s, as knowledge expanded about radionuclides, detection of radioactivity, and using certain radionuclides to trace biochemical processes. Pioneering works by Benedict Cassen in developing

4700-566: The 1986 Chernobyl disaster and 2011 Fukushima disaster . As of 2022 , the International Atomic Energy Agency reported there are 422 nuclear power reactors and 223 nuclear research reactors in operation around the world. The US Department of Energy classes reactors into generations, with the majority of the global fleet being Generation II reactors constructed from the 1960s to 1990s, and Generation IV reactors currently in development. Reactors can also be grouped by

4800-708: The U.S. military sought other uses for nuclear reactor technology. Research by the Army led to the power stations for Camp Century, Greenland and McMurdo Station, Antarctica Army Nuclear Power Program . The Air Force Nuclear Bomber project resulted in the Molten-Salt Reactor Experiment . The U.S. Navy succeeded when they steamed the USS Nautilus (SSN-571) on nuclear power 17 January 1955. The first commercial nuclear power station, Calder Hall in Sellafield , England

4900-528: The United States does not engage in or encourage reprocessing. Reactors are also used in nuclear propulsion of vehicles. Nuclear marine propulsion of ships and submarines is largely restricted to naval use. Reactors have also been tested for nuclear aircraft propulsion and spacecraft propulsion . Reactor safety is maintained through various systems that control the rate of fission. The insertion of control rods, which absorb neutrons, can rapidly decrease

5000-546: The World War II Allied Manhattan Project . The world's first artificial nuclear reactor, Chicago Pile-1, achieved criticality on 2 December 1942. Early reactor designs sought to produce weapons-grade plutonium for fission bombs , later incorporating grid electricity production in addition. In 1957, Shippingport Atomic Power Station became the first reactor dedicated to peaceful use; in Russia, in 1954,

5100-554: The agency and instead are regulated by the individual states. International organizations, such as the International Atomic Energy Agency (IAEA), have regularly published different articles and guidelines for best practices in nuclear medicine as well as reporting on emerging technologies in nuclear medicine. Other factors that are considered in nuclear medicine include a patient's medical history as well as post-treatment management. Groups like International Commission on Radiological Protection have published information on how to manage

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5200-458: The anatomy and function, which would otherwise be unavailable or would require a more invasive procedure or surgery. Although the risks of low-level radiation exposures are not well understood, a cautious approach has been universally adopted that all human radiation exposures should be kept As Low As Reasonably Practicable , "ALARP". (Originally, this was known as "As Low As Reasonably Achievable" (ALARA), but this has changed in modern draftings of

5300-561: The appearance of a "cold spot". Many tracer complexes have been developed to image or treat many different organs, glands, and physiological processes. In some centers, the nuclear medicine scans can be superimposed, using software or hybrid cameras, on images from modalities such as CT or MRI to highlight the part of the body in which the radiopharmaceutical is concentrated. This practice is often referred to as image fusion or co-registration, for example SPECT/CT and PET/CT. The fusion imaging technique in nuclear medicine provides information about

5400-565: The area was contaminated, like Fukushima, Three Mile Island, Sellafield, and Chernobyl. The British branch of the French concern EDF Energy , for example, extended the operating lives of its Advanced Gas-cooled Reactors (AGR) with only between 3 and 10 years. All seven AGR plants were expected to be shut down in 2022 and in decommissioning by 2028. Hinkley Point B was extended from 40 to 46 years, and closed. The same happened with Hunterston B , also after 46 years. An increasing number of reactors

5500-770: The beginning of his quest to produce the Einstein-Szilárd letter to alert the U.S. government. Shortly after, Nazi Germany invaded Poland in 1939, starting World War II in Europe. The U.S. was not yet officially at war, but in October, when the Einstein-Szilárd letter was delivered to him, Roosevelt commented that the purpose of doing the research was to make sure "the Nazis don't blow us up." The U.S. nuclear project followed, although with some delay as there remained skepticism (some of it from Enrico Fermi ) and also little action from

5600-529: The birthdate of nuclear medicine. This can probably be best placed between the discovery of artificial radioactivity in 1934 and the production of radionuclides by Oak Ridge National Laboratory for medicine-related use, in 1946. The origins of this medical idea date back as far as the mid-1920s in Freiburg , Germany, when George de Hevesy made experiments with radionuclides administered to rats, thus displaying metabolic pathways of these substances and establishing

5700-778: The cell-damaging properties of beta particles are used in therapeutic applications. Refined radionuclides for use in nuclear medicine are derived from fission or fusion processes in nuclear reactors , which produce radionuclides with longer half-lives, or cyclotrons , which produce radionuclides with shorter half-lives, or take advantage of natural decay processes in dedicated generators, i.e. molybdenum/technetium or strontium/rubidium. The most commonly used intravenous radionuclides are technetium-99m, iodine-123, iodine-131, thallium-201, gallium-67, fluorine-18 fluorodeoxyglucose , and indium-111 labeled leukocytes . The most commonly used gaseous/aerosol radionuclides are xenon-133, krypton-81m, ( aerosolised ) technetium-99m. A patient undergoing

5800-458: The choices of coolant and moderator. Almost 90% of global nuclear energy comes from pressurized water reactors and boiling water reactors , which use water as a coolant and moderator. Other designs include heavy water reactors , gas-cooled reactors , and fast breeder reactors , variously optimizing efficiency, safety, and fuel type , enrichment , and burnup . Small modular reactors are also an area of current development. These reactors play

5900-467: The complexities of handling actinides , but significant scientific and technical obstacles remain. Despite research having started in the 1950s, no commercial fusion reactor is expected before 2050. The ITER project is currently leading the effort to harness fusion power. Thermal reactors generally depend on refined and enriched uranium . Some nuclear reactors can operate with a mixture of plutonium and uranium (see MOX ). The process by which uranium ore

6000-660: The dissemination of reactor technology to U.S. institutions and worldwide. The first nuclear power plant built for civil purposes was the AM-1 Obninsk Nuclear Power Plant , launched on 27 June 1954 in the Soviet Union . It produced around 5 MW (electrical). It was built after the F-1 (nuclear reactor) which was the first reactor to go critical in Europe, and was also built by the Soviet Union. After World War II,

6100-465: The dose is delivered internally rather than from an external source such as an X-ray machine, and dosage amounts are typically significantly higher than those of X-rays. The radiation dose from a nuclear medicine investigation is expressed as an effective dose with units of sieverts (usually given in millisieverts, mSv). The effective dose resulting from an investigation is influenced by the amount of radioactivity administered in mega becquerels (MBq),

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6200-485: The energy of the neutrons that sustain the fission chain reaction : In principle, fusion power could be produced by nuclear fusion of elements such as the deuterium isotope of hydrogen . While an ongoing rich research topic since at least the 1940s, no self-sustaining fusion reactor for any purpose has ever been built. Used by thermal reactors: In 2003, the French Commissariat à l'Énergie Atomique (CEA)

6300-448: The first rectilinear scanner and Hal O. Anger 's scintillation camera ( Anger camera ) broadened the young discipline of nuclear medicine into a full-fledged medical imaging specialty. By the early 1960s, in southern Scandinavia , Niels A. Lassen , David H. Ingvar , and Erik Skinhøj developed techniques that provided the first blood flow maps of the brain, which initially involved xenon-133 inhalation; an intra-arterial equivalent

6400-402: The first application in patients of an artificial radionuclide when he used phosphorus-32 to treat leukemia . Many historians consider the discovery of artificially produced radionuclides by Frédéric Joliot-Curie and Irène Joliot-Curie in 1934 as the most significant milestone in nuclear medicine. In February 1934, they reported the first artificial production of radioactive material in

6500-524: The first small nuclear power reactor APS-1 OBNINSK reached criticality. Other countries followed suit. Heat from nuclear fission is passed to a working fluid coolant (water or gas), which in turn runs through turbines . In commercial reactors, turbines drive electrical generator shafts. The heat can also be used for district heating , and industrial applications including desalination and hydrogen production . Some reactors are used to produce isotopes for medical and industrial use. Reactors pose

6600-407: The fission process generates heat, some of which can be converted into usable energy. A common method of harnessing this thermal energy is to use it to boil water to produce pressurized steam which will then drive a steam turbine that turns an alternator and generates electricity. Modern nuclear power plants are typically designed for a lifetime of 60 years, while older reactors were built with

6700-529: The form of boric acid ) into the reactor to shut the fission reaction down if unsafe conditions are detected or anticipated. Most types of reactors are sensitive to a process variously known as xenon poisoning, or the iodine pit . The common fission product Xenon-135 produced in the fission process acts as a neutron poison that absorbs neutrons and therefore tends to shut the reactor down. Xenon-135 accumulation can be controlled by keeping power levels high enough to destroy it by neutron absorption as fast as it

6800-424: The fuel rods. This allows the reactor to be constructed with an excess of fissionable material, which is nevertheless made relatively safe early in the reactor's fuel burn cycle by the presence of the neutron-absorbing material which is later replaced by normally produced long-lived neutron poisons (far longer-lived than xenon-135) which gradually accumulate over the fuel load's operating life. The energy released in

6900-421: The hydroxyapatite for imaging. Any increased physiological function, such as due to a fracture in the bone, will usually mean increased concentration of the tracer. This often results in the appearance of a "hot spot", which is a focal increase in radio accumulation or a general increase in radio accumulation throughout the physiological system. Some disease processes result in the exclusion of a tracer, resulting in

7000-447: The idea of nuclear fission as a neutron source, since that process was not yet discovered. Szilárd's ideas for nuclear reactors using neutron-mediated nuclear chain reactions in light elements proved unworkable. Inspiration for a new type of reactor using uranium came from the discovery by Otto Hahn , Lise Meitner , and Fritz Strassmann in 1938 that bombardment of uranium with neutrons (provided by an alpha-on-beryllium fusion reaction,

7100-494: The invention of the first positron emission tomography scanner ( PET ). The concept of emission and transmission tomography, later developed into single photon emission computed tomography (SPECT), was introduced by David E. Kuhl and Roy Edwards in the late 1950s. Their work led to the design and construction of several tomographic instruments at the University of Pennsylvania. Tomographic imaging techniques were further developed at

7200-440: The journal Nature , after discovering radioactivity in aluminum foil that was irradiated with a polonium preparation. Their work built upon earlier discoveries by Wilhelm Konrad Roentgen for X-ray, Henri Becquerel for radioactive uranium salts, and Marie Curie (mother of Irène Curie) for radioactive thorium, polonium and coining the term "radioactivity." Taro Takemi studied the application of nuclear physics to medicine in

7300-411: The last few years, which also was facilitated by establishing 18F-labelled tracers for standard procedures, allowing work at non-cyclotron-equipped sites. PET/CT imaging is now an integral part of oncology for diagnosis, staging and treatment monitoring. A fully integrated MRI/PET scanner is on the market from early 2011. Tc is normally supplied to hospitals through a radionuclide generator containing

7400-456: The legislation to add more emphasis on the "Reasonably" and less on the "Achievable".) Working with the ALARP principle, before a patient is exposed for a nuclear medicine examination, the benefit of the examination must be identified. This needs to take into account the particular circumstances of the patient in question, where appropriate. For instance, if a patient is unlikely to be able to tolerate

7500-476: The noise in an image and make it more photographically appealing, but if the clinical question can be answered without this level of detail, then this is inappropriate. As a result, the radiation dose from nuclear medicine imaging varies greatly depending on the type of study. The effective radiation dose can be lower than or comparable to or can far exceed the general day-to-day environmental annual background radiation dose. Likewise, it can also be less than, in

7600-449: The normal nuclear chain reaction, would be too short to allow for intervention. This last stage, where delayed neutrons are no longer required to maintain criticality, is known as the prompt critical point. There is a scale for describing criticality in numerical form, in which bare criticality is known as zero dollars and the prompt critical point is one dollar , and other points in the process interpolated in cents. In some reactors,

7700-417: The nuclear medicine imaging process is a dataset comprising one or more images. In multi-image datasets the array of images may represent a time sequence (i.e. cine or movie) often called a "dynamic" dataset, a cardiac gated time sequence, or a spatial sequence where the gamma-camera is moved relative to the patient. SPECT (single photon emission computed tomography) is the process by which images acquired from

7800-581: The opportunity for the nuclear chain reaction that Szilárd had envisioned six years previously. On 2 August 1939, Albert Einstein signed a letter to President Franklin D. Roosevelt (written by Szilárd) suggesting that the discovery of uranium's fission could lead to the development of "extremely powerful bombs of a new type", giving impetus to the study of reactors and fission. Szilárd and Einstein knew each other well and had worked together years previously, but Einstein had never thought about this possibility for nuclear energy until Szilard reported it to him, at

7900-538: The parent radionuclide molybdenum-99 . Mo is typically obtained as a fission product of U in nuclear reactors, however global supply shortages have led to the exploration of other methods of production . About a third of the world's supply, and most of Europe's supply, of medical isotopes is produced at the Petten nuclear reactor in the Netherlands . Another third of the world's supply, and most of North America's supply,

8000-406: The physics of radioactive decay and are simply accounted for during the reactor's operation, while others are mechanisms engineered into the reactor design for a distinct purpose. The fastest method for adjusting levels of fission-inducing neutrons in a reactor is via movement of the control rods . Control rods are made of so-called neutron poisons and therefore absorb neutrons. When a control rod

8100-415: The power plant is limited by the life of components that cannot be replaced when aged by wear and neutron embrittlement , such as the reactor pressure vessel. At the end of their planned life span, plants may get an extension of the operating license for some 20 years and in the US even a "subsequent license renewal" (SLR) for an additional 20 years. Even when a license is extended, it does not guarantee

8200-701: The radiation emitted by the radiopharmaceuticals. This process is unlike a diagnostic X-ray, where external radiation is passed through the body to form an image. There are several techniques of diagnostic nuclear medicine. Nuclear medicine tests differ from most other imaging modalities in that nuclear medicine scans primarily show the physiological function of the system being investigated as opposed to traditional anatomical imaging such as CT or MRI. Nuclear medicine imaging studies are generally more organ-, tissue- or disease-specific (e.g.: lungs scan, heart scan, bone scan, brain scan, tumor, infection, Parkinson etc.) than those in conventional radiology imaging, which focus on

8300-408: The range of, or higher than the radiation dose from an abdomen/pelvis CT scan. Some nuclear medicine procedures require special patient preparation before the study to obtain the most accurate result. Pre-imaging preparations may include dietary preparation or the withholding of certain medications. Patients are encouraged to consult with the nuclear medicine department prior to a scan. The result of

8400-407: The reactor and the heavy water plant respectively. According to a Pakistani press report this reactor began operating in early 1998. Based on the success of these projects and the experience and capability gained during their construction, onsite construction work on the second unit began around 2001 or 2002. In February 2010 Prime Minister Yousaf Raza Gillani and senior military officers attended

8500-563: The reactor fleet grows older. The neutron was discovered in 1932 by British physicist James Chadwick . The concept of a nuclear chain reaction brought about by nuclear reactions mediated by neutrons was first realized shortly thereafter, by Hungarian scientist Leó Szilárd , in 1933. He filed a patent for his idea of a simple reactor the following year while working at the Admiralty in London, England. However, Szilárd's idea did not incorporate

8600-416: The reactor will continue to operate, particularly in the face of safety concerns or incident. Many reactors are closed long before their license or design life expired and are decommissioned . The costs for replacements or improvements required for continued safe operation may be so high that they are not cost-effective. Or they may be shut down due to technical failure. Other ones have been shut down because

8700-437: The reactor's output, while other systems automatically shut down the reactor in the event of unsafe conditions. The buildup of neutron-absorbing fission products like xenon-135 can influence reactor behavior, requiring careful management to prevent issues such as the iodine pit , which can complicate reactor restarts. There have been two reactor accidents classed as an International Nuclear Event Scale Level 7 "major accident":

8800-637: The small number of officials in the government who were initially charged with moving the project forward. The following year, the U.S. Government received the Frisch–Peierls memorandum from the UK, which stated that the amount of uranium needed for a chain reaction was far lower than had previously been thought. The memorandum was a product of the MAUD Committee , which was working on the UK atomic bomb project, known as Tube Alloys , later to be subsumed within

8900-492: The thyroid gland, quantification of the thyroid function, and therapy for hyperthyroidism. Among the many radionuclides that were discovered for medical-use, none were as important as the discovery and development of Technetium-99m . It was first discovered in 1937 by C. Perrier and E. Segre as an artificial element to fill space number 43 in the Periodic Table. The development of a generator system to produce Technetium-99m in

9000-424: The water for the steam turbines is boiled directly by the reactor core ; for example the boiling water reactor . The rate of fission reactions within a reactor core can be adjusted by controlling the quantity of neutrons that are able to induce further fission events. Nuclear reactors typically employ several methods of neutron control to adjust the reactor's power output. Some of these methods arise naturally from

9100-476: Was a key step in the Chernobyl disaster . Reactors used in nuclear marine propulsion (especially nuclear submarines ) often cannot be run at continuous power around the clock in the same way that land-based power reactors are normally run, and in addition often need to have a very long core life without refueling . For this reason many designs use highly enriched uranium but incorporate burnable neutron poison in

9200-572: Was also used to investigate, e.g., imagined sequential movements, mental calculation and mental spatial navigation. By the 1970s most organs of the body could be visualized using nuclear medicine procedures. In 1971, American Medical Association officially recognized nuclear medicine as a medical specialty. In 1972, the American Board of Nuclear Medicine was established, and in 1974, the American Osteopathic Board of Nuclear Medicine

9300-688: Was commissioned at Khushab in March ;1996. The Khushab Nuclear Complex was conceived and planned by the then chairman of the Pakistan Atomic Energy Commission (PAEC), Munir Ahmad Khan , who began work on the 50 MWth Khushab-I reactor and heavy water plant in 1986. He appointed nuclear engineer Sultan Bashiruddin Mahmood and Dr. N.A. Javed, both from the PAEC , as the Project-Directors for

9400-432: Was developed soon after, enabling measurement of the local distribution of cerebral activity for patients with neuropsychiatric disorders such as schizophrenia. Later versions would have 254 scintillators so a two-dimensional image could be produced on a color monitor. It allowed them to construct images reflecting brain activation from speaking, reading, visual or auditory perception and voluntary movement. The technique

9500-424: Was established, cementing nuclear medicine as a stand-alone medical specialty. In the 1980s, radiopharmaceuticals were designed for use in diagnosis of heart disease. The development of single photon emission computed tomography (SPECT), around the same time, led to three-dimensional reconstruction of the heart and establishment of the field of nuclear cardiology. More recent developments in nuclear medicine include

9600-781: Was officially started by the Generation ;IV International Forum (GIF) based on eight technology goals. The primary goals being to improve nuclear safety, improve proliferation resistance, minimize waste and natural resource utilization, and to decrease the cost to build and run such plants. Generation V reactors are designs which are theoretically possible, but which are not being actively considered or researched at present. Though some generation V reactors could potentially be built with current or near term technology, they trigger little interest for reasons of economics, practicality, or safety. Controlled nuclear fusion could in principle be used in fusion power plants to produce power without

9700-463: Was opened in 1956 with an initial capacity of 50 MW (later 200 MW). The first portable nuclear reactor "Alco PM-2A" was used to generate electrical power (2 MW) for Camp Century from 1960 to 1963. All commercial power reactors are based on nuclear fission . They generally use uranium and its product plutonium as nuclear fuel , though a thorium fuel cycle is also possible. Fission reactors can be divided roughly into two classes, depending on

9800-621: Was produced at the Chalk River Laboratories in Chalk River , Ontario , Canada until its permanent shutdown in 2018. The most commonly used radioisotope in PET, F , is not produced in a nuclear reactor, but rather in a circular accelerator called a cyclotron . The cyclotron is used to accelerate protons to bombard the stable heavy isotope of oxygen O . The O constitutes about 0.20% of ordinary oxygen (mostly oxygen-16 ), from which it

9900-436: Was published. Additionally, Sam Seidlin . brought further development in the field describing a successful treatment of a patient with thyroid cancer metastases using radioiodine ( I-131 ). These articles are considered by many historians as the most important articles ever published in nuclear medicine. Although the earliest use of I-131 was devoted to therapy of thyroid cancer, its use was later expanded to include imaging of

10000-619: Was the first to refer to "Gen II" types in Nucleonics Week . The first mention of "Gen III" was in 2000, in conjunction with the launch of the Generation IV International Forum (GIF) plans. "Gen IV" was named in 2000, by the United States Department of Energy (DOE), for developing new plant types. More than a dozen advanced reactor designs are in various stages of development. Some are evolutionary from

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