Radioactive nucleonic

There are four modes of radioactive decay that are common and that are exhibited by the decay of naturally occurring radionucHdes. These four are a-decay, j3 -decay, electron capture and j3 -decay, and isomeric or y-decay. In the first three of these, the atom is changed from one chemical element to another in the fourth, the atom is unchanged. In addition, there are three modes of decay that occur almost exclusively in synthetic radionucHdes. These are spontaneous fission, delayed-proton emission, and delayed-neutron emission. Lasdy, there are two exotic, and very long-Hved, decay modes. These are cluster emission and double P-decay. In all of these processes, the energy, spin and parity, nucleon number, and lepton number are conserved. Methods of measuring the associated radiations are discussed in Reference 2 specific methods for y-rays are discussed in Reference 1. 

Since the radioactive half-lives of the known transuranium elements and their resistance to spontaneous fission decrease with increase in atomic number, the outlook for the synthesis of further elements might appear increasingly bleak. However, theoretical calculations of nuclear stabilities, based on the concept of closed nucleon shells (p. 13) suggest the existence of an island of stability around Z= 114 and N= 184. Attention has therefore been directed towards the synthesis of element 114 (a congenor of Pb in Group 14 and adjacent superheavy elements, by bombardment of heavy nuclides with a wide range of heavy ions, but so far without success. 

The discoveries of Becquerel, Curie, and Rutherford and Rutherford s later development of the nuclear model of the atom (Section B) showed that radioactivity is produced by nuclear decay, the partial breakup of a nucleus. The change in the composition of a nucleus is called a nuclear reaction. Recall from Section B that nuclei are composed of protons and neutrons that are collectively called nucleons a specific nucleus with a given atomic number and mass number is called a nuclide. Thus, H, 2H, and lhO are three different nuclides the first two being isotopes of the same element. Nuclei that change their structure spontaneously and emit radiation are called radioactive. Often the result is a different nuclide. 

The alpha particle is a helium nucleus produced from the radioactive decay of heavy metals and some nuclear reactions. Alpha decay often occurs among nuclei that have a favorable neutron/proton ratio, but contain too many nucleons for stability. The alpha particle is a massive particle consisting of an assembly of two protons and two neutrons and a resultant charge of +2. 

There are at present 116 known chemical elements. However, there are well over 2000 known nuclear species as a result of several isotopes being known for each element. About three-fourths of the nuclear species are unstable and undergo radioactive decay. Protons and neutrons are the particles which are found in the nucleus. For many purposes, it is desirable to describe the total number of nuclear particles without regard to whether they are protons or neutrons. The term nucleon is used to denote both of these types of nuclear particles. In general, the radii of nuclides increase as the mass number increases with the usual relationship being expressed as... 

Radiative deactivation of an excited state of a molecular entity. 2. The release of a nucleon (usually an electron, neutron, or photon) during radioactive decay. 

Sample Problem 1.2 Because of the conservation of the number of nucleons in the nucleus and conservation of charge during radioactive decay (Table 1.1),... 

Note how the nuclear equation for the radioactive decay of uranium-238 is written. The equation is not balanced in the usual chemical sense because the kinds of nuclei are not the same on both sides of the arrow. Instead, a nuclear equation is balanced when the sums of the nucleons are the same on both sides of the equation and when the sums of the charges on the nuclei and any elementary particles (protons, neutrons, and electrons) are the same on both sides. In the decay of 2 U to give He and 2 oTh, for example, there are 238 nucleons and 92 nuclear charges on both sides of the nuclear equation. 

Helium-6 is a radioactive isotope with fj/2 = 0.861 s. Calculate the mass defect (in g/mol) for the formation of a 6He nucleus, and calculate the binding energy in MeV/nucleon. Is a 6He nucleus more stable or less stable than a 4He nucleus (The mass of a 6He atom is 6.018 89 amu.)... 

The binding energy of a radioactive 6He nucleus is 4.89 MeV/nucleon, making it less stable than a 4He nucleus, whose binding energy is 7.08 MeV/nucleon. 

Hall, T. A. Chemical Element Analysis of Radioactive Mixtures in Biological Materials. Nucleonics 12, No. 3, 34 (1954). 

The nucleons inside a radioactive nucleus contained in a molecule interact with the electron-neutrino field and undergo the / transition—a transformation of a neutron into a proton accompanied by the emission of a / electron and a neutrino.5 The weak interaction does not affect the electron shell and the other nuclei of the molecule. For them the / decay is an instantaneous change (a jump) in the charge of the radioactive nucleus by unity. Besides this, the nucleus obtains a recoil momentum due to the emission... 

In order to use the perturbation theory it is necessary that the state vectors in the matrix element Eq. (8) belong to the spectrum of the unperturbed Hamiltonian H0 only. However, this is usually not so, since, in p decay, the initial particles are not the same as the final products of the reaction the initial molecule containing the radioactive atom transforms into a different molecule besides, the ft electron and the neutrino appear. One of the ways to describe the initial and final states using only the H0 Hamiltonian is to use the isotopic spin formalism for both the nucleons and the leptons (/ electron and neutrino). In the appendix (Section V) we present the wave functions of the initial and the final states together with the necessary transformations, which one can use to factorize the initial matrix element Eq. (8) into the intranuclear and the molecular parts. Here we briefly discuss only the approximations necessary for performing such a factorization. 

The various decay modes are listed in Table 5.1. Unstable, radioactive nuclei may be transformed by emission of nucleons (a decay and, very rarely, emission of protons or neutrons) or by emission of electrons or positrons and decay, respectively). Alternatively to the emission of a positron, the unstable nucleus may capture an electron of the electron shell of the atom (symbol e). 

The isotopes of a particular element have the same number of protons in the nucleus but a different number of neutrons, giving them the same proton number (atomic number) but a different nucleon number (mass number, i.e. number of protons + number of neutrons). Isotopes may be stable or radioactive. Radioactive isotopes (radioisotopes) disintegrate spontaneously at random to yield radiation and a decay product. 

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