From Big Medical Encyclopedia

ALPHA DECAY — the radioactive transformation of a kernel which is followed by emission of alpha particles. At any And. - the river with mass number And (number of particles in a kernel) and atomic number of Z (number of protons in a kernel) is formed of an initial kernel of X a new kernel At with mass number And — 4 and atomic number Z — 2 (see. Radioactivity , atomic nucleus ): , where - alpha particle (yadroizotop of helium). At And. - the river occurs formation of kernels of the new element displaced in D. I. Mendeleyev's table is two sections more left than an initial kernel. Such spontaneous transformations of atomic nuclei are followed by allocation of rather large amounts of energy, do not depend on external conditions and are caused only by internal structure of the breaking-up atomic nuclei.

For the first time patterns And. - rubles were established by overseeing by disintegration radium (see) — which lets out alpha particles and turns into new radioactive elementary gas radon (cm.) - . Measurements of atomic weight of radon confirmed such transformation.

All heavy-nuclei of atoms with Z more than 82 are radioactive kernels; among these elements there are alpha-active isotopes. These unstable isotopes undergo chains alpha and beta decays until turn into stable isotopes of lead (see. Radioactivity ). Heavy-nuclei are the least steady since with increase in Z Coulomb forces of pushing away of protons increase. There are also easier alpha-active kernels: isotopes of samarium — Sm 146, 147, 152 , tungsten — , neodymium - and - platinum — . The kernel is less steady, the it breaks up quicker and lets out alpha particles with greater energy — E. For various alpha-active kernels E = 2 — 10 Mev, and half-life of T changes in very wide limits: from 3,04⋅10 - 7 sec. to 2,2⋅10 17 years . At And. - the river is usually formed of an unexcited maternal kernel an unexcited affiliated kernel. At the same time alpha particles of identical energy are let out, and the kernel experiences return. Energy of a kernel of return and an alpha particle are inversely proportional to their masses. Also isotopes which kernels, letting out alpha particles, turn into the kernels which are in various power states (normal and excited) meet. In this case not only alpha particles, but also gamma quanta of several energy are let out. At some isotopes with small half-lives (Ro 211, 212, 214 ) transitions from excited states with emission of alpha particles considerably of bigger energy are observed, than upon transition from an unexcited state. Such long-range particles are not enough.

In medicine and radiobiology alpha-active isotopes find broad application for treatment (see. Radiation therapy , Radium , Radon ) and diagnoses. In recent years alpha-active isotopes are strenuously studied by radio biologists and toxicologists since they are applied in the atomic industry and the atomic equipment. See also Alpha radiation , Alpha therapy .

Bibliography: Belousova I. M. and Shtukkenberg Yu. M. Natural radioactivity, M., 1961; M. Radioaktivnost's Curie, the lane with fr., M., 1960; Shpolsky E. V. Atomic physics, t. 2, S; 516, M. — L., 1951.

Yu. M. Shtukkenberg.