Krypton is a chemical element with symbol Kr and atomic number 36. Krypton is a colorless, odorless, tasteless gas. It was discovered by the Scottish chemist Sir William Ramsey in 1898. He discovered a series of noble gases by examining the residue left over from evaporating liquefied air.

           Krypton is one of the noble gases in Group 18 of the periodic table along with helium, neon, argon, xenon and radon. Because their outer shell of electrons is full, the nobles gases are very non-reactive and form few compounds with other elements. The melting point and boiling point of krypton are very close at -157° C and -153° C.

            Krypton has 33 known isotopes that vary in atomic weight from 69 to 101. There are 6 stable isotopes and 27 radioactive isotopes.. Kr-83,84,85,and 86 are fission products produced by uranium decay. Small amounts of some krypton isotopes are generated by cosmic rays hitting the atmosphere. The radioisotopes have half-lives that vary from 154 billionths of a second for Kr-83m1 to 225,000 years for Kr-81. Most of the isotopes of krypton are short lived The primary decay mode of isotopes lighter than atomic weight 82 is emission of a positron (anti-electron)  to become bromine. Above atomic weight 84, krypton decay emits an electron to become rubidium.  Kr-71 and Kr-73 emit protons is a small number of decays and become selenium. Metastable states of Kr-83 and Kr-85 emit gamma rays when they decay. A few krypton isotopes emit gamma rays when they decay. Kr-92, Kr-93, Kr-94, Kr-97 and Kr-101 emit neutrons during decay.

           Krypton is present on Earth mainly as a minor constituent of the atmosphere. It is also present in gas emitted from underwater thermal vents and from volcanoes. Krypton is the second rarest stable element on Earth.

          Krypton is used to make bright white lights for photography. Powerful lasers have been developed utilizing krypton. Krypton-81 can be used to date old groundwater up to 800,000 years old. Krypton-83 is used in magnetic resonance imaging of respiratory system.  It may also be useful in computer tomography imaging in a mixture of gases including xenon. Krypton-85 with a half-life of about 10 years is used indicator lights in home appliances and consumer electronics, to gauge thickness of plastics, sheet metal, rubber and paper, to measure dust and pollutant levels, to detect explosives, in voltage regulators and surge protectors, and in laboratory gas chromatography equipment. Kr-85 is released when nuclear fuel rods are reprocessed and can be used to detect clandestine reprocessing plants.

          Krypton has no known biological function and is considered harmless with regard to health. Krypton could cause asphyxiation if present in sufficient quantities to displace oxygen in the air being breathed. The radioisotopes are very short lived and their beta emission are easily blocked.  

Wicked Lasers S3 krypton laser:

 

           Promethium is a chemical element with the symbol Pm and atomic number 61. A gap in the periodic table was pointed out between neodymium at 60 and samarium at 62 by Bohuslav Brauner. After two false claims of discovery in 1926, in 1938 a few atoms of promethium were created but intentional production and chemical proof did not happen until 1945 at Ohio State University when promethium was extracted from irradiated uranium fuel. A sample of the metal was only produced in 1963. Promethium was named for “Prometheus,” the Titan in Greek mythology who stole fire from the god and gave it to humanity.

            Promethium is a metallic member of the cerium group of the lanthanide series. It forms salts with oxygen, water, chloride, nitrogen and sulfur.

           Promethium has no stable isotopes; all of its thirty eight isotopes are radioactive. They vary in atomic weight from 126 to 163. They have half-lives that range from around 200 billionths of a second for Pm-129 to 17.7 years for Pm-145. Most of the isotopes of promethium decay by emission of positrons (anti-electrons). Pm-145 also emits protons.

           Promethium is extremely rare in nature, minute quantities being produced in uranium ores by the spontaneous fission of uranium-238. This process has contributed about half a kilogram of promethium to the curst of the Earth. Pm-150 can be produced by rare beta decay of neodymium and europium decay can produce Pm-147 via an alpha particle. Europium decay has produced about 12 grams of promethium in the history of the Earth. Promethium has been found in the spectra of some stars.

            Promethium-147 is the only isotope of promethium that has industrial applications. It is produced by bombardment of unranium-235 with thermal neutrons, bombardment of uranium-238 with fast neutrons to trigger fast fission, and by decay of artificially produced neodymium-146. Pm-147 has a relatively long half-life with radiation that has a shallow penetration and it produces no gamma rays. Glowing hands and numbers for watches and gauges contain a phosphor activated by Pm-147 which causes it to emits light. Because beta emission does not cause the phosphor to age, such applications have years of stable light release. Atomic batteries utilize a sandwich of semiconductor material and Pm0147 and has about a 5 year useful lifespan. It is also used in batteries that convert light to electricity for use in watches, calculators, radios, etc. Pm-147 is used as a starter in the new compact fluorescent lamps. It can also be used to measure the thickness of materials such as plastic, sheet metal, rubber, textiles and paper. It is used in electric blanket thermostats.

          Promethium has no biological function but it is dangerous to living systems due to x-rays emitted during beta decay. Sealed devices containing promethium are safe but if the seal is broken, precautions should be taken when handling the device.

Seiko watches with promethium:

          Californium is a chemical element with the symbol Cf and atomic number 98. It is a silvery white actinide metal element that was first synthesized by bombardment of curium with alpha particles by a team at the University of California, Berkeley in 1950 and named for the state of California.

          Californium is melting point of 900° C and a boiling point of 1745° C. It is a soft malleable metal that is easily cut with a knife. It can form alloys with lanthanide metals. When heated, it reacts with hydrogen, nitrogen and oxygen. It forms salts with nitrogen, and sulfur as wells as the halogen family of elements which include fluorine, chlorine,  bromine, iodine, and astatine.  

            Californium has no stable isotopes. All of its 20 isotopes are radioactive. They vary in atomic weight from 237 to 256 with half-lives ranging from 45 millionths of a second to Cf-251with a half-life of 900 years. Cf-251 and Cf-252 emit gamma radiation. Most isotopes of californium decay by emission of alpha particles to curium or by emission of beta particles to berkelium. A few isotopes can decay to fermium and einsteinium.

           Californium is the heaviest element that exists in nature. It is generated by neutron capture and beta decay in rich deposits of uranium ore. It is not very soluble in water and will be present in much larger quantities in soil than in water. There is a small amount of californium created by nuclear explosion and present in nuclear fallout.

           Californium-250 is produced by bombarding berkelium-249 with neutrons. Cf-251 and Cf-252 are generated by bombarding Cf-250 with neutrons. Cf-252 has many applications because it is a strong neutron emitter. One fresh microgram of californium will generate 139 million neutrons per minute. Cf-252 used to be mainly used for reactor startup but that use has declined in recent years. It is used to treat some forms of cervical and brain cancer. It is used by universities for educational purposes. It is used inline to analyze bulk materials such as coal. Neutron penetrate into various materials and can be used to image such things as thickness, integrity and other useful physical properties of nuclear fuel rods, airplane parts, and corrosion, bad welds, cracks and trapped moisture in pipelines. Neutrons moisture gauges are used in the oil industry, in gold and sliver prospecting, and to detect groundwater movement.  Californium-249 has been used to create a few atoms of ununoctium, element 118, the heaviest element ever synthesized. Bombardment of californium has also been used to synthesized other transuranic elements such as lawrencium, element 103.

          Californium has no natural biological function due to its scarcity and high radioactivity. If it enters the body through consuming food, drinking fluids or breathing air contaminated by particles of californium, about two third will be deposited in the skeleton and a quarter in the liver. Californium in the skeletal tissue can interfere with the body’s ability to produce red blood cells. Gamma radiation from Cf-251 and Cf-251can cause bone and/or liver cancer when present in the body.

Toy train with californium-252 used for calibration at Princeton Plasma Physics Laboratory:

          Technetium is a chemical element with the symbol Tc and atomic number 43. It is a silvery gray, crystalline transition metal in the same column of the periodic table as manganese, rhenium and bohrium. Early forms of Mendeleyev’s periodic table showed a gap above manganese and Mendeleyev predicted many of its properties from its position in the table in 1871. Chemists searched for the missing element and there were a number of false announcements before its documented discovery at the University of Palermo in Italy by Carol Perrier and Emilio Sergre in 1943.

         Solid technetium has an appearance similar to platinum but is usually produced as a gray powder. It becomes a superconductor when cooled near absolute zero. Technetium is reacts weakly with other elements and compounds. It forms compounds with hydrogen, oxygen, sulfur, sulfides, selenides and carbon.

          Technetium is the lowest atomic weight element that has no stable isotopes. All of 56 of its isotopes are radioactive. They range in weight from 85 to 118 with numerous metastable states with excited nucleons. Their half-lives vary from Tc-85 with a half-life of less than 110 billionth of a second to Tc-98 with a half-life of 4.2 million years. The heavier isotopes decay by electron capture and become molybdenum-42 with emission of gamma rays from the metastable states. The lighter isotopes decay by beta emission of an electron or positron and gamma radiation.  Gamma rays are also emitted in the metastable state.

          Technetium-99 is a natural product of uranium fission and is found in minute quantities in uranium ore and in some red giant stars known as technetium stars. Tc-99 is produced in nuclear explosions and is present in fallout. Tc-99 is produced in fission reactors at a rate of about 6% from U-235, U-238 and Pu-239. A small amount is extracted for commercial purposes. Its long half-life, low energy beta emission, lack of gamma emission and ease of extraction from nuclear waste make it a standard beta emitter used for equipment calibration.

          Technetium-99m is the most commonly used radioisotope in nuclear medicine. Tc-99m which decays to Tc-99 with a half-life of 6 hours.It is produced by bombardment of enriched uranium to produce molybdenum-99 which has a half-life of 67 hours and decays to Tc-99m. The Mo-99 is transported to medical facilities where the Tc-99m which is being constantly produced is chemically extracted. The short half-life and the distinctive gamma radiation produced by Tc-99 make it very useful for radiopharmaceutical imaging and functional studies of brain, thyroid, lungs, liver, gallbladder, kidneys, bones, blood and tumors.

         Technetium-95m, a metastable state of Tc-95, has a half-life of 61 days and is used to trace movement of materials in plants, animals and the environment.

         Technetium has no biological role and is not usually found in the human body. It has low chemical toxicity in living systems. As always, inhalation of particles of technetium can pose a cancer risk to the lungs. Tc-99 generated by nuclear fuel reprocessing is one of the main isotopes that poses a major problem for long term disposal.

 

 Carbon is a chemical element with the symbol C and the atomic number 6. It has been known since ancient times. Graphite was named in 1594 by D.L.G. Harsten and A.G. Werner. Carbon was named by A.L. Lavoisier in 1789. It is a member of the non-metallic tetravalent (having 4 valence electrons) Group 14 in the periodic table which also includes silicon, germanium, tin, lead and flervium. Nine different structural forms of carbon have been identified including diamond, graphite, Lonsdaleite, Buckminsterfullerene, C-70, amorphous carbon, carbon nanotubes and grapheme. The physical properties of color, transparency, thermal conductivity, electrical conductivity, hardness vary considerablely between the different allotropes.

         Carbon is a very common element found throughout the universe, solar system and the natural environment on earth. It is the 4^th most abundant element by weight in the universe and the 15^th most abundant element in the Earth’s crust. Carbon is extracted from deposits of coal and processed for a wide variety of commercial applications. Diamonds are a hard form of carbon created by volcanic activity.

         Carbon is the stuff of life. Its four valence electrons allow it to form a wide variety of molecular structures. The DNA and RNA in the nucleus of every living cell on Earth contains carbon along with oxygen, hydrogen, nitrogen and phosphorus. The proteins that make up living creatures all contain carbon, hydrogen and nitrogen. Many compounds of carbon and hydrogen are created and utilized by plants and animals.

          Carbon has 16 known isotopes which range in atomic weight from 8 to 23. C-12 and C-13 are stable naturally occurring isotopes and the rest are radioisotopes. Half-lives of the radioactive isotopes of carbon vary from C-21 with a half-life of less than 30 billionths of a second to C-14 with a half-life of 5700 years. Carbon-14 is produced by the action of cosmic rays on the Earth’s atmosphere.

          Carbon-14 was discovered Carbon-14 is absorbed by all living things. When they die, they stop absorbing C-14. Therefore, the amount of C-14 found in the remains of plants and animals can be used to date them.  C-14 is one of the primary tools of archeology.  Some of the limitations of C-14 dating include restriction to things that were once alive, distribution throughout the sample, changes in the atmosphere that affect C-14 generation and inability to date objects older than 60,000 years which excludes the vast majority of fossils.

          Carbon-11 has a half-life of about 20 minutes and it decays by positron emission to Boron-11. It is produced by proton bombardment of Nitrogen-14. C-11 accumulates preferentially in tumors. Tumors create many new proteins and C-11 absorption is an indicator of tumor growth. C-11 is useful for positron emission tomography for the early diagnosis of cancer, monitoring therapeutic response to cancer treatment and for the investigation of the biological action of anti-cancer drugs. Because of its short half-life, utilization of C-11 is dependent on the fast generation of C-11 and the compounds that contain it followed by rapid application.

          Strontium is a chemical element with symbol Sr and atomic number 38. It was discovered in 1790 by Adair Crawford, a physician, in ore taken from lead mines in the village of Strontian, Scotland and named after the village.

         Strontium is a soft silvery-white alkaline earth metal. The family of alkaline earth metals also includes beryllium, magnesium, calcium, barium and radium. Like other members of the family, strontium is highly reactive.  Finely powdered strontium is pyrophoric and will burn spontaneously in when exposed to the air.

          Strontium is the 15^th most abundant element on earth. It is most often found in sedimentary deposits of the sulfate celestite and the carbonate strontianite.  The strontianite is preferable but the best deposits for mining are celestite. It is produced by electrolysis of melted strontium chloride mixed with potassium chloride. China produces two thirds of the world’s strontium. It is also mined in Spain, Mexico, Turkey, Argentina and Iran.

          There are thirty nine isotopes of strontium which vary in atomic weight from 73 to 105. There are four  stable isotopes of strontium, Sr-84, Sr-86, Sr-87, Sr-88. Sr-87 is radiogenic meaning that it can be produced by the radioactive decay of Rubidium-878 as well as primordial nucleosynthesis in stars. There are thirty five unstable radioisotopes of strontium. Their half-lives range from Sr-97m1 at 170 billionths of a second to Sr-90 at 28.90 years.

         Strontium found its first major use in the form of strontium hydroxide which was used in huge quantities to extract sugar from sugar beets. Strontium burns with a bright red color and is used in fireworks. It is also used in the creation of ferrite magnets, refining zinc, optical applications in the form of strontium titanate, in strontium aluminate for phosphorescence, in strontium chloride in toothpaste, as strontium oxide to improve potter glazes, strontium ranelate is use to treat osteoporosis and in chemical reagents for laboratory use. 

          Strontium-89 is the active ingredient in a strontium chloride compound that is used to treat bone cancer because, as a relative of calcium, strontium is taken up by the bones. Sr-90 is a product of nuclear fission. It is produced by nuclear explosions and nuclear reactors. It has been used in radioisotope thermoelectric generators because, even though it has a shorter half life than plutonium-238 which is also used, it is cheap and can be extracted from nuclear waste. The old Soviet Union installed many generators powered by Sr-90. Sr-90 is also used for cancer therapy. Sr-89 and Sr-90 are used as radioactive tracers in medicine.

          Sr-90 is the most dangerous radioisotope from nuclear explosions. It is less volatile than cesium and less likely to be released in nuclear accidents.  Improper disposal of Sr-90 devices can result in contamination of steel made from scrap metal. Dispersed in the natural environment it poses a threat to human health. Entering the body through consumption of contaminated food and water, it is taken up by the bones and can cause bone cancer, cancer of nearby tissues and leukemia.

Abandoned radioisotope thermoelectric generator from Soviet era. Picture from Finmark regional government:            

          Cesium is chemical element with the symbol Cs and an atomic weight of 55. It was discovered in 1860 by Robert Bunsen and Gustav Kirchhoff with the new flame spectroscopy method. It is a soft, silvery gold alkali metal with a melting point of 28° C or 82° F and is one of only five elemental metals that is liquid near room temperature. It is highly reactive and pyrophoric. In open air, it will burst into flames and it reacts explosively with water. Cesium can form compounds with many other metals. It readily forms phosphate, acetate, carbonate, halide, oxide, nitrate and sulfate salts.

          Cesium is a relatively rare element at 45^th in abundance. Because of its structure, it crystallizes last when magma cools and is found mostly in zone deposits of granite. The only commercial ore is pollucite which in a mineral of cesium, aluminum, silicon and oxygen. Two thirds of the worlds reserves are found in high grade ore in Manitoba, Canada. There are also deposits in Zimbabwe and Namibia in Africa.

          Cesium has 40 isotopes from atomic weight of 112 to 151 with only Cs-133 being stable. All the rest are radioactive with half-lives ranging from Cs-122m1 and Cs-126m1 at less than one millionths of a second to Cs-135 with a half-life of 2.3 million years. Almost all radioisotopes of cesium are produced in nuclear explosions or nuclear reactors by fission processes or by decay of fission products. Cs-137 with a half-life of 30 years accounts for most of the radioactivity in spent nuclear fuel for several hundred years. Because isotopes of cesium are created by decay of isotopes of radioactive xenon gas, if there is a release of radioactive materials from a nuclear accident, Cs-137 can be produced far from the site of the accident. Decay of Cs generates beta particles and gamma rays.

          Commercial uses of non-radioactive cesium include use in photoelectric and solar cells due the fact that light can free electrons from the cesium atom. Its high reactivity makes it useful for clearing out the remaining gases in the manufacture of light bulbs. It is also used as a catalyst for the hydrogenation of a few organic compounds. Ion propulsion systems for space craft have been created using cesium which is 140 times more efficient than burning any other know liquid or solid.

          Cesium-137 is recovered by reprocessing spent nuclear fuel. Atomic clocks are constructed by exciting Cs-137 with a beam of energy and measuring the radiation of the outer electrons in the electron shell. It can be used to calibrate radiation detection equipment. The gamma radiation emitted by Cs-137 is used in industry for density measurements of fluid flow and thickness of materials. It is sometimes used in cancer therapy. Because Cs-137 is entirely man-made and only entered the environment after the detonation of nuclear bombs, it can be used to determine if a sealed container was made before or after the start of the atomic age in the 1940s. Mishandling of Cs-137 has resulted in radioactive contamination of steel produced by recycling scrap metal. Cs-137 is dangerous and ingestion of less than one thousandth of a gram per kilogram is lethal within weeks.

          Iodine is a chemical element with the symbol I and atomic number 53. It was discovered in 1811 by Frenchman Bernard Courtis in one of those luck accidents when he added too much sulfuric acid to ashes of seaweed that he was processing. The purple vapor that was given off crystallized out on nearby surfaces and was eventually given the name “iodine” derived from the Greek word for purple.

          Iodine is a non-metallic element of the halogen family in the periodic table which also includes fluorine, chlorine, bromine and astatine. It is a bluish black solid under normal conditions but it does sublimate into purple vapor. It melts at 113.7 °C but also gives off the purple gas as it melts. It dissolves easily in most organic solvents but does not dissolve very well in water unless it is in the presence of potassium. Iodine is a relatively rare element which is found in greater concentrations in free ions of iodine salts in ocean water than in rocks. It is rare in soils and is leached out by rainwater and carried to the ocean.

        Iodine is the heaviest of the essential mineral elements and was probably incorporated into biological functioning because of its presence in the oceans where life originated. Iodine assists in the synthesis of thyroid hormones and it is absorbed by the thyroid when it enters the body. Because of its rarity in soil, especially away from the ocean, about two billion people on earth have iodine deficiency which can lead to intellectual disabilities.

         Iodine has 37 isotopes from atomic weight of I-108 to I-144. Only one of the isotopes, I-127 is stable and the rest are radioactive. The half-lives vary from I-130m2 with a half-life of 133 billionths of a second to I-129 with a half-life of 15.7 million years. All the rest of the radioisotopes of iodine have half-lives of less than 60 days. All most all of the Iodine on earth occurs is in the form of the stable isotope. The tiny amount of I-129 on earth results mostly from nuclear explosions and nuclear accidents. Other isotopes rapidly vanish after their creation.

            I-135 is produced in nuclear reactors and decays to xenon-135 which “poisons” nuclear fuel by reducing the neutron flux and slowing fission reactions. Large amounts of Xe-135 can temporarily interfere with restarting a shut-down reactor.

          I-131 is one of the primary by-products of nuclear fission and is produced in nuclear reactors. It emits highly energetic beta particles and is the most carcinogenic of all the isotopes of iodine. When it escapes into the natural environment by nuclear explosions or severe nuclear accidents, it poses a very serious but short term health danger. Nonradioactive iodine in the form of potassium iodine tablets is given to people who may be exposed to I-131 because it will saturate the thyroid gland and prevent the I-131 from being absorbed.

         Four of the isotopes of iodine are produced commercially for medical use. The beta radiation emitted by I-131 is used to kill thyroid tissue to prevent it from becoming cancerous. Isotopes I-123 and I-125 emit gamma rays which are useful as tracers which help image the structure and functioning of the thyroid gland. I-125 can also be implanted in a small capsule to irradiate cancerous tissue in the lungs. I-124 emits protons which is useful for positron emission tomography (PET) for direct imaging of the thyroid gland or tracer imaging. 

Iodine crystals:

          Americium is alkaline metal element with the symbol Am and atomic number 95. It is above uranium in the periodic table and is referred to as a transuranic element. Silvery in color, Americium is a soft radioactive metal. It was first synthesized in 1944 by Glenn T. Seaborg at the University of California, Berkeley. The name was taken from America.

          Americium oxidizes easily and dissolves well in acids. It forms compounds with halogen gases, sulfur., selenium, phosphorus, arsenic, antimony, bismuth and silicon. The metallic form is malleable and has a relatively high melting point of 1173 C°

          Americium has 19 isotopes, all of them radioactive. The atomic weights vary from Am-231 to Am-249. The half-lives vary from Am-239m at 163 billionths of a second to Am-243 at 7,370 years. Americium is produced by the bombardment of uranium, plutonium or existing Americium with slow neutrons. A tiny amount is produced in nuclear reactors and in nuclear explosions.  Am-241 with a half-life of 432 years is the most plentiful isotope in radioactive waste. It decays by alpha emission with gamma ray production.

          Commercial production of americium consists of dissolving the uranium and plutonium out of spent mixed oxide nuclear fuel. This leaves a mixture of oxides of actinide and lanthanide isotopes. Using various solvents along with chromatography and centrifuges, the Am-241 is extracted. The Am-241 can then be used to create other isotopes of americium if desired.

         The most common use of americium is in home smoke detectors. It is a source of ionizing radiation in the form of alpha particles but it emits much less gamma radiation and is preferred over radium-228. About one quarter of a millionth of a gram of americium is used in a typical smoke detector. The americium ionizes the air between two electrodes allowing a small current to flow. When smoke enters the alarm, it reduces the ionization which lowers the current and triggers the alarm. These alarms are more sensitive but more prone to false alarms than optical smoke detectors.

         Americium combined with beryllium is used as a source of neutrons in devices that measure the water content of soil, neutron radiography, tomography, and other applications that require neutrons.

          Use of americium in radioisotope thermoelectric generators has been suggested. It has five times the half life of the plutonium which is currently used in such generators. Americium may also find use as part of a propulsion system for spacecraft. The fission products of americium could be used to directly drive the craft or it could be used to heat a thrusting gas or liquid. Efficient nuclear batteries based on the charge properties of americium have also been proposed. The main impediment to these new applications lies in the high cost and low availability of americium.

        As with other transuranics, americium has no biological function. It mainly emits alpha particles which can be easily blocked but are dangerous if inhaled or consumed. Inside the body, the americium finds it way to the bones, the liver and the testicles or ovaries and can cause cancer. Daughter products from americium decay produce dangerous gamma rays and neutrons. There are few regulations about disposure of smoke detectors which is the main way that americium enters the environment.

Inside a smoke detector:

 

          Cobalt is a chemical element with the symbol Co and the atomic number 27. It readily forms compounds with other elements and compounds. When it is extracted from naturally occurring compounds via reductive smelting, it is a hard, shiny, sliver-gray metal.

         The name comes from the German word “kobold” which mean “goblin.” Miners were familiar with ores that were poor in metals that they called goblin ore partly because of the deadly arsenic fumes given off when heated.  The minerals in such ores were used since ancient times as a pigment for blue paint. Most of the cobalt ore mined in the world today is a byproduct of copper and nickel mining in the Democratic Republic of Congo and Zambia in Africa.

       Today cobalt is used to create high-strength alloys which are wear-resistant and magnetic. Silicate and aluminate compounds of cobalt are used to impart a deep blue color to glass, ceramics, inks, paints and varnishes.

       Cobalt is present in living cells. The cobalt atom forms the active center of certain coenzymes called cobalamins. The vitamin B₁₂ is an example of such cobalamins. Cobalt is a necessary trace dietary mineral for all living creatures.

       Naturally occurring cobalt contains the stable isotope with an atomic weight of 59 which is the only stable isotope. There are a total of 28 radioactive isotopes that range from atomic weight of 47 to 73. They vary Co-51 with a half-life of 200 billionth of a second to Co-60 with a half-life of 5.27 years.

      Cobalt-60 is created by bombarding the stable Co-59 with slow neutrons in CANDU reactors or from californium-252. It undergoes beta decay to Nickel-70 which then gives off gamma radiation to achieve a stable state. It is the emission of gamma rays that makes Co-60 a useful isotope. It is used as a tracer for chemical reactions, sterilization of medical equipment, a source of radiation for medical radiotherapy, a radiation source for industrial radiography, a radiation source for leveling devices and thickness gauges, a radiation source to sterilize food and blood and a radiation source for general laboratory use.

       One of the problems with the use of Co-60 is the fact that the solid form can disintegrate into a powder which can be inhaled and cause biological damage. This makes the handling of devices employing Co-60 more dangerous. Its use in many applications as a gamma ray source has been declining. Improper disposal of medical equipment containing Co-60 as scrap metal led to radioactivity appearing in iron produced by smelting the contaminated scrap.

       Cobalt-57 is made in cyclotrons by the irradiation of iron. It has a half-life of 271 days and it decays by electron capture to Iron-57 which emits gamma radiation to achieve a stable state. It is used in medicine as a tracer for the metabolization  of vitamin B_12.

Cobalt 60 cancer therapy machine: