Nuclear reactors, radium

In some nuclear reactors, radium provides alpha particles that can interact with beryllium to produce neutrons via the following reaction. 

Argon-40 [7440-37-1] is created by the decay of potassium-40. The various isotopes of radon, all having short half-Hves, are formed by the radioactive decay of radium, actinium, and thorium. Krypton and xenon are products of uranium and plutonium fission, and appreciable quantities of both are evolved during the reprocessing of spent fuel elements from nuclear reactors (qv) (see Radioactive tracers). 

The radioactive element is a silvery, shiny, soft metal that is chemically similar to calcium and barium. It is found in tiny amounts in uranium ores. Its radioactivity is a million times stronger that that of uranium. Famous history of discovery (in a shed). Initially used in cancer therapy. Fatal side effects. Small amounts are used in luminous dyes. Radium was of utmost importance for research into the atom. Today its reputation is rather shaky as its decay gives rise to the unpleasant radon (see earlier). In nuclear reactors, tiny amounts of actinium are formed from radium. 

Uses. The main use of radium is the preparation of 227Ac, via neutron capture in a nuclear reactor. 

Actinium is a rare element that is found in very small amounts in uranium ore (pitchblende), making it difficult and expensive to extract even a small quantity. It is less expensive and easier to produce small amounts by bombarding the element radium with neutrons in a nuclear reactor. Actinium has few commercial uses. 

The rarity of polonium is evident from a calculation (1) which shows that the outermost mile of the earth s crust contains only 4000 tons of the element, whereas radium, usually classed as rare, is present to the extent of 1.8 X 107 tons. The abundance of polonium in uranium ores is only about 100 Mg per ton and hence separation of the element from such mineral sources cannot seriously be considered. However, radium, at equilibrium with its daughters, contains 0.02 wt % of polonium and, until recently, most of the element was obtained either from radium itself or, more usually, from expended radon ampoules which, after the radon decay is complete, contain radium-D and its daughters. Fortunately, however, the parent of polonium in these sources, bismuth-210, can be synthesized by neutron bombardment of natural bismuth [Bi209 (n,y) Bi210] and with the advent of the nuclear reactor it has become practicable to prepare milligram amounts of polonium. Almost all of the chemistry of the element recorded in the recent literature has been the result of studies carried out with polonium-210 prepared in this way. 

An important reaction used quite widely for this purpose is irradiation by neutrons and measurement of die energies of radiations emitted. The source of the neutrons may be a nuclear reactor, a particle accelerator, or an isotopic source, that is, a sealed container in which neutrons are produced by alpha rays emitted by a source such as radium, sodium-24(24Na), yttrium-88f8sY), etc., and arranged so that the alpha rays react-with a substance such as beryllium which in turn emits neutrons. The neutrons react with stable nuclides in the sample to produce radioactive ones. Thus... 

The isotopes of thorium include mass numbers 223-234. 232Th has a half-life of 1.39 x 1010 years, See also Radioactivity. It emits an alpha-particle and forms meso-thorium 1 (radium-228), which is also radioactive, having a half-life of 6.7 years, emitting a beta-particle. Since 2 2Th captures slow neutions to form, by a series of nuclear reactions, >>U which is fissionable, thorium can be used as a fuel for nuclear reactors of the breeder type. Thorium occurs in earth minerals, an average content estimated at about 12 ppm. Findings of hc Apollo 11 space flight indicated that thorium concentrations in some lunar rocks are about the same as the concentrations in terrestrial basalts. 

The curie is a huge unit of radioactivity and is approximately equal to the activity of one gram of radium. The inventories of radioactivity in a nuclear reactor upon shutdown are typically 109 Ci, whereas radiation sources used in tracer experiments have activities of p.Ci and the environmental levels of radioactivity are nCi or pCi. 

All isotopes of radium are radioactive, the longest-lived isotope being 226Ra (a —1600 years). This isotope is formed in the natural decay series of 238U and was first isolated by Pierre and Marie Curie from pitchblende. Once widely used in radiotherapy, it has largely been supplanted by radioisotopes made in nuclear reactors. 

Early studies (1936-1950) of neutron scattering used radium-beryllium neutron sources but their low neutron flux prevented exploitation of neutron scattering as a spectroscopic technique [4]. Today neutrons are either extracted from a nuclear reactor or generated at a pulsed, accelerator-based spallation source. The exploitation of neutrons from nuclear reactors in structural studies and spectroscopy dates from the 1950s and from pulsed sources from the 1970s. A useful summary of the development of neutron sources is given in [5]. 

Radon has been produced commercially for use in radiation therapy but for the most part has been replaced by radionuclides made in accelerators and nuclear reactors. Radiopharmaceutical companies and a few hospitals pump the radon from a radium source into tubes called "seeds" or "needles" which may be implanted in patients (Cohen 1979). Research laboratories and universities produce radon for experimental studies. 

Radium was also utilized in self-luminous paints for watch, clock and instrument dials and for emission in automatic control systems. Safer radioisotopes for technical properties, such as cobalt-60 and cesium-137, can nowadays be tailored in nuclear reactors and have entirely replaced radium. This has released us from the need for radium, which is a great advantage, as radium is so difficult to handle from an environmental point of view. It forms gaseous radon, affecting its surroundings. And the problem remains for a long time, as the most usual radidum isotope, Ra, has a half-life of 1600 years. Nowadays the use of radium has ceased. The annual amount manufactured is only round 100 g. 

A notable feature of this agreement was Eldorado s undertaking to sell reactor-produced radioisotopes on behalf of U.S. Radium, if and when they became available fiom U.S. atomic reactors. These were radioactive substances that, unlike radium, were human-made. Before the war they had been produced experimentally in small quantities, but as nuclear reactors spawned by wartime atomic research came onstream, commercial production seemed just around the corner. In this part of the deal, Bennett was anticipating one of the many possible directions that the business might take in the future. It was much more likely, however, that Eldorado would sell instead isotopes that would be produced by the NRC s establishment at Chalk River, which was scheduled to have its first reactor in service the following year. Eldorado and the Chalk River labs were complemencny parts of the government s atomic-research enterprise supervised by CD. Howe. 

The United States Navy turned to CPD to provide radium-beryllium neutron sources to start the small nuclear reactors in the world s first two nuclear submarines, the Nautilus (shown here) and theSVaxe. CPD had to file daily progress reports and field personal phone calls fiom Admiral Rickover. Over the next fiw years, CPD would make start-up sources for more than 15 nuclear subs. 

Successful in selling radium. Errington s department (renamed Commercial Products) wins the right to sell isotopes produced by Canada s fledgling nuclear reactor program. Commercial Products becomes part of a new crown corporation. Atomic Energy of Canada Limited (AECL), in 1952. 

MDS Nordion began in 1946 as the radium sales department of Eldorado Mining and Refining (1944) Ltd., an Ottawa-based crown corporation that mined uranium ore, from which radium, a naturally occurring radioactive element, was extracted and refined. Radium was employed extensively in cancer therapy at the time, and Eldorado sold it around the world. In 1947 the Canadian government s nuclear research establishment at Chalk River, Ontario completed a nuclear reactor that began to produce radioisotopes. Since there was a potential market in the medical field for many... 

It is at present somewhat uncertain if very low levels of radiatirm are harmful. We cannot avoid all radiation since there is a natural radiation background (with approximate yearly exposure) due to, for example, the cosmic rays (40 millirem at sea level, 250 Rem at 500 m elevation) radium and radon in ground and building material (40 Rem) and potassium 40 (18 Rem). In addition, we can add some man-made radiation sources such as one chest X-ray (40 Rem), one dental X-ray (20 Rem), fallout from nuclear explosions (5 Rem), as well as miscellaneous sources such as TV, CRT, etc., all of which total to 163 Rem/year (for sea level). The average annual radiadmi dose to a nuclear reactor worker in Ontario is 0.68 Rem with an annual limit of 5 Rem set by radiation protection regulations. 

Significant health hazards have resulted from exposure to radioisotopes in the mining of uranium used as nuclear reactor fuel. The main hazards are from inhalation of radioactive uranium decay products. The most significant of these are radium-226 and radon-226. The radium is carried by dust... 

Actinium and protactinium are decay products of the naturally occurring uranium isotope U and are present in uranium minerals in such low concentration that recovery from natural sources is a very difficult and unrewaidii task. By comparison, it is relatively straightforward to obtain actinium, protactinium, and most of the remaining transuranium elements by neutron irradiation of elements of lower atomic number in nuclear reactors [2-4]. Thus, actinium has been produced in multigram quantities by the transmutation of radium with neutrons produced in a high-flux nuclear reactor ... 

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