radium

Chemical Properties

Radium (Ra) is a radioactive element, found naturally occurring in the environment. Ra is a silvery- white-metallic solid @ 25℃; it tarnishes black when exposed to air. It is an alkaline earth metal; there are 33 isotopes, all of them are unstable. Radium is commonly available as radium bromide (RaBr2 ) or radium chloride (RaCl2 ).

Physical properties

Radium is the last element in group 2 and is very similar to the other alkali earth metals,which makes it the largest and heaviest element in the group. It particularly resembles barium,which is just above it in group 2 of the periodic table. Radium is a bright white radioactiveluminescent alkali earth metal that turns black when exposed to air. Its melting point is700°C, its boiling point is 1,140°C, and its density is approximately 5.0 g/cm³.

Isotopes

There are no stable isotopes of radium. Radium has 25 known radioisotopes,ranging from Ra-206 to Ra-230. Their half-lives range from a fraction of a second tohundreds of years. Radium-226 was discovered by the Curies and has a half-life ofabout 1630 years. Ra-226 is the most abundant isotope, and thus, Ra-226 is used todetermine radium’s atomic mass.Various radium isotopes are derived through a series of radioactive decay processes. Forexample, Ra-223 is derived from the decay of actinium. Ra-228 and Ra-224 are the resultof the series of thorium decays, and Ra-226 is a result of the decay of the uranium series.

Origin of Name

Radium’s name is derived from the Latin word radius, which means “ray.

Occurrence

Radium is the 85th most abundant element found in the Earth’s crust. Radium is found inthe uranium ores pitchblende and chalcolite, which are both very radioactive. Radium metalexists to the extent of only one part to every three million parts of the uranium ore (pitchblende). Only about one gram of radium is found in every seven or eight tons of uraniumore. This scarcity seems to be the reason that only about five pounds of uranium are producedeach year in the entire world. Uranium ores are found in the states of Utah, New Mexico, andColorado in the United States and in Canada, the Czech Republic, Slovakia, Russia, Zaire,and France.

Characteristics

Radium is extremely radioactive. It glows in the dark with a faint bluish light. Radium’sradioisotopes undergo a series of four decay processes; each decay process ends with a stableisotope of lead. Radium-223 decays to Pb-207; radium-224 and radium-228decay to Pb-208;radium-226 decays to Pb-206; and radium-225 decays to Pb-209. During the decay processesthree types of radiation—alpha (α), beta (β), and gamma (γ)—are emitted.In addition to being radioactive, radium is extremely chemically reactive and forms manycompounds. These radium compounds are not only radioactive but also toxic and should behandled by experienced personnel.

History

Curie in the pitchblende or uraninite of North Bohemia (Czech Republic), where it occurs. There is about 1 g of radium in 7 tons of pitchblende. Radium was discovered by Marie and Pierre Curie in December 1898, after they found that the ore pitchblende was more radioactive than pure uranium, indicating the presence of a new, highly radioactive element. The element was isolated in 1911 by Mme. Curie and Debierne by the electrolysis of a solution of pure radium chloride, employing a mercury cathode; on distillation in an atmosphere of hydrogen this amalgam yielded the pure metal. Originally, radium was obtained from the rich pitchblende ore found at Joachimsthal, Bohemia. The carnotite sands of Colorado furnish some radium, but richer ores are found in the Republic of Congo-Kinshasa and the Great Bear Lake region of Canada. Radium is present in all uranium minerals, and could be extracted, if desired, from the extensive wastes of uranium processing. Large uranium deposits are located in Ontario, New Mexico, Utah, Australia, and elsewhere. Radium is obtained commercially as the bromide or chloride; it is doubtful if any appreciable stock of the isolated element now exists. The pure metal is brilliant white when freshly prepared, but blackens on exposure to air, probably due to formation of the nitride. It exhibits luminescence, as do its salts; it decomposes in water and is somewhat more volatile than barium. It is a member of the alkaline-earth group of metals. Radium imparts a carmine red color to a flame. Radium emits alpha, beta, and gamma rays and when mixed with beryllium produce neutrons. One gram of ²²⁶Ra undergoes 3.7 × 1010 disintegrations per s. The curie (Ci) is defined as that amount of radioactivity which has the same disintegration rate as 1 g of 226Ra. Thirty-six isotopes are now known; radium 226, the common isotope, has a half-life of 1599 years. One gram of radium produces about 0.0001 mL (stp) of emanation, or radon gas, per day. This is pumped from the radium and sealed in minute tubes, which are used in the treatment of cancer and other diseases. One gram of radium yields about 4186 kJ per year. Radium is used in producing self-luminous paints, neutron sources, and in medicine for the treatment of cancer. Some of the more recently discovered radioisotopes, such as 60Co, are now being used in place of radium. Some of these sources are much more powerful, and others are safer to use. Radium loses about 1% of its activity in 25 years, being transformed into elements of lower atomic weight. Lead is a final product of disintegration. Stored radium should be ventilated to prevent build-up of radon. Inhalation, injection, or body exposure to radium can cause cancer and other body disorders. The maximum permissible burden in the total body for ²²⁶Ra is 7400 becquerel.

Uses

Radium’s most important use is as a source of radiation in industry, medicine, and laboratories. The isotope radium-226, which is the most abundant of all the 25 isotopes and has ahalf-life of 1630 years, is the only useful form of the element. It is used in the medical treatment of malignant cancer growth. It kills cancer cells that have spread throughout the body.Other uses are to produce phosphorescence and fluorescence in organic compounds andfor scintillation screens on instruments used to detect radiation. Radium salts were used in thepast to paint the dials of luminous clock faces that glow in the dark.

Definition

A white radioactive luminescent metallic element of the alkaline- earth group. It has several short-lived radioisotopes and one long-lived isotope, radium-226 (half-life 1602 years). Radium is found in uranium ores, such as the oxides pitchblende and carnotite. It was formerly used in luminous paints and radiotherapy. Symbol: Ra; m.p. 700°C; b.p. 1140°C; r.d. 5 (approx. 20°C); p.n. 88; r.a.m. 226.0254 (²²⁶Ra).

Hazard

Because radium energetically emits three types of radiation, it poses great danger to anyone handling it. In addition, it is toxic. If it is ingested in even small amounts, it replaces bone tissue, which can result in radiation sickness and death.
One of the decay products of radium is the gas radon, which can seep up through the Earth s crust into basements and slab level homes. Good ventilation assures that the radon does not accumulate to the extent that would be harmful.
At one time, women painted clock and watch dials with luminous radium paint that was a mixture of radium salts and zinc sulfide. They would place the small brushes between their lips and tongue to make the bristles more pointed, in order to paint fine lines with the radium paint. Over the years, they developed cancers that resulted in badly eaten-away and disfigured lips and jaws. Once the danger was known, luminous radium paint was banned for this use. Today, promethium (Pm-147), with a half-life of 2.4 years, is used for this purpose.

Carcinogenicity

The U.S. EPA has classified radium as a class A carcinogen, meaning that there are sufficient data to support a link between exposure to radium and the development of human cancer. The α-particle radiation associated with radium is recognized as the causative agent for sarcomas of the bone and carcinomas of the paranasal sinuses in humans. A study attempting to ascertain the dose–incidence relationship for induction of these tumors examined 1474 women employed in the U.S. radium dial painting industry before 1930. This population exhibited 61 known cases of bone sarcoma and 21 cases of carcinoma of the paranasal sinuses or the mastoid air cells. Of these individuals, the radium body burden was known for 759, among whom there were 38 cases of bone sarcoma and 17 head carcinomas.

Environmental Fate

Radium is released to the environment from a variety of sources, including milling and mining operations focused on phosphates and uranium, waste streams from factories used to produce products containing radium, or waste byproducts from production, such as phosphate fertilizers. The most important route of radium release into the environment is the combustion of coal, and released radium is estimated at 150 Ci per year (or 5.55×10¹² Bq). Radium released into the atmosphere will remain in particulate form until wet or dry deposition. Radium adsorbs to soils, and is not expected to volatize from soils or water due to its ionic nature. In water, radium exists as Ra⁺² and can interact with sediments and dissolve in water, and therefore generally adsorbs to sediments at the emission site and is not transported. Some isotopes of radium are very short lived, but radium-226 has a half-life of 1600 years, making long-range transport more likely, though generally only through an atmospheric route. Radium’s ionic nature makes bioaccumulation or biomagnification unlikely.

Shipping

UN3323(does not appear in the 49CFR hazard materials tables ) Radioactive material, Type C package, nonfissile or fissile excepted. UN2915 Radioactive mate- rial, Type A package nonspecial form, nonfissile or fissile- excepted, Hazard class: 7-Radioactive material; Labels: None. A1 and A2 values for Radium- 226 taken from y173.435 (see also Table A-1 in 10CFR71(Appendix A): A1 (SpecialForm * ) 0.3 TBq (8.11Ci); A2 (NormalForm) 0.02TBq (0.541Ci))

Incompatibilities

Metallic radium is highly chemically reactive. It forms compounds that are very similar to barium compounds, making separation of the two elements difficult. On contact with water, radium forms flammable hydrogen gas.

Waste Disposal

Radioactive material consid- ered waste and must be retained in containers for disposi- tion by the authorizing institution. Drain disposal is prohibited. It is the responsibility of the operating institu- tion to arrange for the proper disposal of all forms of any radioisotopes. The use, storage, transportation, labeling, and disposal of radioactive material are regulated through the Nuclear Regulatory Commission (NRC) using 10 CFR (Code of Federal Regulations) as the regulatory basis and 49 CFR (Transportation).

Raw materials

Preparation Products