Marie Curie and Irène Curie on radium

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Introduction
RADIUM
- CHEMICAL PROPERTIES
- RADIOACTIVE PROPERTIES
- DISCOVERY OF RADIUM
- INDUSTRIAL PRODUCTION OF RADIUM
- MEASUREMENTS
- APPLICATIONS OF RADIUM

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APPLICATIONS OF RADIUM

in Marie Curie and Irène Curie on radium in RADIUM

Written by Marie Curie, Irène Curie•All

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The principal application of radium is the use for therapeutic purposes of the biological action of the rays (see RADIOTHERAPY; THERAPEUTICS). The biological action is a selective destruction of certain cells and can have very dangerous consequences, but can also be directed against nocive tissue, as for instance in the case of cancer. For medical use radium is put into tubes of glass or in platinum needles, sometimes also on flat surfaces recovered by a varnish, for the irradiation of the skin. Another form of use is to keep radium in solution and to extract from time to time the accumulated radon which, introduced into small tubes, has the same efficiency as radium till its activity has disappeared. The use of radium for pharmaceutical preparations has been frequently tried. The scientific basis, however, in this case is far from being well established. Experimentation on the improvement of the soil by small quantities of radium has been till now very limited and some favourable results in this direction have been claimed.

By incorporating radium with phosphorescent zinc sulphide it is possible to obtain luminous paints giving a weak light visible in darkness. The most important use of this paint is for watches. The quantity necessary is of the order of one-tenth of a milligramme per gramme of zinc sulphide. After several years, the phosphorescent product is altered by the action of the rays and becomes less luminous, though the quantity of radium has not changed appreciably.

Radium in Nature.—Radium exists in minute proportion in every kind of soil and water; the extraordinary sensitiveness of the methods of analysis has made it possible to ascertain this fact. If some inactive element is present in the same proportions, we are not able to detect it. The quantity of radium contained in the ordinary soil is of the order of 10^-12 or 10^-11 gr. of radium per gramme while a good radioactive ore contains about 10^-7 gr. of radium per gramme of mineral.

Radium existing in the depths of the earth is sometimes dissolved by water and affects springs. Other springs dissolve principally the radon liberated by the radium and their activity dies out with the radon. This would explain why certain mineral waters are reputed to be efficient for curative effect only when used directly at the source. Some radio-active waters contain amounts of radium up to 10^-10 gr. per litre; the amount of radon can attain 10^-7 curies per litre.

The radium in the soil is the origin of the small quantity of radon present in the air and is partly responsible for the natural ionisation of the air which is known to be an important factor in the meteorological conditions of the atmosphere. Radium and radioactive elements in general have played an important part in the evolution of terrestrial heat. It is not improbable that the radium present at the surface of the earth in a very dilute state has some connection with the evolution of life on our planet (see Mme. Curie, Traité de Radioactivité, 2 vol. (1910)).

Marie Curie Irène Curie

radioactivity

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Figure 4: The decay of a particle of mass M into two particles the sum of whose rest masses is less than M (see text).

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radioactivity summary

radioactivity

Also known as: disintegration, nuclear disintegration, radioactive decay

Written by John O. Rasmussen, Ellis P. Steinberg•All

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Article History

Key People:: Frédéric Joliot-Curie; Irène Joliot-Curie; Ernest Rutherford; Enrico Fermi; Marie Curie

Related Topics:: decay rate; disintegration energy; radioactive heat; stability; Geiger-Nuttall law

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radioactivity, property exhibited by certain types of matter of emitting energy and subatomic particles spontaneously. It is, in essence, an attribute of individual atomic nuclei.

An unstable nucleus will decompose spontaneously, or decay, into a more stable configuration but will do so only in a few specific ways by emitting certain particles or certain forms of electromagnetic energy. Radioactive decay is a property of several naturally occurring elements as well as of artificially produced isotopes of the elements. The rate at which a radioactive element decays is expressed in terms of its half-life; i.e., the time required for one-half of any given quantity of the isotope to decay. Half-lives range from more than 10²⁴ years for some nuclei to less than 10⁻²³ second (see below Rates of radioactive transitions). The product of a radioactive decay process—called the daughter of the parent isotope—may itself be unstable, in which case it, too, will decay. The process continues until a stable nuclide has been formed.

The nature of radioactive emissions

The emissions of the most common forms of spontaneous radioactive decay are the alpha (α) particle, the beta (β) particle, the gamma (γ) ray, and the neutrino. The alpha particle is actually the nucleus of a helium-4 atom, with two positive charges 4/2He. Such charged atoms are called ions. The neutral helium atom has two electrons outside its nucleus balancing these two charges. Beta particles may be negatively charged (beta minus, symbol e⁻), or positively charged (beta plus, symbol e⁺). The beta minus [β⁻] particle is actually an electron created in the nucleus during beta decay without any relationship to the orbital electron cloud of the atom. The beta plus particle, also called the positron, is the antiparticle of the electron; when brought together, two such particles will mutually annihilate each other. Gamma rays are electromagnetic radiations such as radio waves, light, and X-rays. Beta radioactivity also produces the neutrino and antineutrino, particles that have no charge and very little mass, symbolized by ν and ν, respectively.

In the less common forms of radioactivity, fission fragments, neutrons, or protons may be emitted. Fission fragments are themselves complex nuclei with usually between one-third and two-thirds the charge Z and mass A of the parent nucleus. Neutrons and protons are, of course, the basic building blocks of complex nuclei, having approximately unit mass on the atomic scale and having zero charge or unit positive charge, respectively. The neutron cannot long exist in the free state. It is rapidly captured by nuclei in matter; otherwise, in free space it will undergo beta-minus decay to a proton, an electron, and an antineutrino with a half-life of 12.8 minutes. The proton is the nucleus of ordinary hydrogen and is stable.

Types of radioactivity

The early work on natural radioactivity associated with uranium and thorium ores identified two distinct types of radioactivity: alpha and beta decay.

Alpha decay

In alpha decay, an energetic helium ion (alpha particle) is ejected, leaving a daughter nucleus of atomic number two less than the parent and of atomic mass number four less than the parent. An example is the decay (symbolized by an arrow) of the abundant isotope of uranium, ²³⁸U, to a thorium daughter plus an alpha particle: Depiction of the products of a radioactive decay.

Given for this and subsequent reactions are the energy released (Q) in millions of electron volts (MeV) and the half-life (t_1⁄2). It should be noted that in alpha decays the charges, or number of protons, shown in subscript are in balance on both sides of the arrow, as are the atomic masses, shown in superscript.

Beta-minus decay

In beta-minus decay, an energetic negative electron is emitted, producing a daughter nucleus of one higher atomic number and the same mass number. An example is the decay of the uranium daughter product thorium-234 into protactinium-234: Depiction of the products of a radioactive decay.

In the above reaction for beta decay, ν represents the antineutrino. Here, the number of protons is increased by one in the reaction, but the total charge remains the same, because an electron, with negative charge, is also created.