Compound nucleus ground state

Mosshauer effect The resonance fluorescence by y-radiation of an atomic nucleus, returning from an excited state to the ground state. The resonance energy is characteristic of the chemical environment of the nucleus and Mossbauer spectroscopy may be used to yield information about this chemical environment. Used particularly in the study of Fe. Sn and Sb compounds. 

The isomer shift, S, is the consequence of the Coulomb interaction between the positively charged nucleus and the negatively charged s-electrons. Since the size of the nucleus in the excited state differs from that in the ground state, the Coulomb interaction energies are different as well. The isomer shift is therefore a measure of the s-electron density at the nucleus, and yields useful information on the oxidation state of the iron in the absorber. Isomer shift values are expressed in velocity units, mm/s, and are usually given with respect to the peak position of a reference such as metallic iron. Table 5.2 lists a few isomer shift values of common iron compounds. 

As distinct from photochromic spiropyrans and spirooxazines, [2//J-chro-menes do not contain a heterocyclic fragment such as an indoline nucleus. Consequently, in such compounds there are no specific n-a orbital interactions that elongate and weaken the C, iro—O bond, the ruptures of this bond in the excited and ground states being responsible for the photo- or thermochromic properties of spiropyrans and spirooxazines as well as [2// -chromcncs. 

The Eo Coulombic interaction alters the energy separation between the ground state and the excited state of the nucleus, thereby causing a slight shift in the position of the observed resonance line. The shift will be different in various chemical compounds, and for this reason is generally known as the chemical isomer shift. It is also frequently referred to as the isomer shift or chemical shift, but in view of the earlier use of these terms in optical spectroscopy and nuclear magnetic resonance spectroscopy respectively, the longer expression is preferred. A less frequently used synonym is centre shift. 

FIGURE 32-6 Overview of the neutron activation process. The incident neutron is captured by the target nucleus to produce an excited compound nucleus, which de-excites with emission of a prompt gamma ray. The radioactive nucleus formed decays by emitting a beta particle. If an excited product nucleus is formed, a delayed gamma ray can be emitted. If decay is directly to the ground state of the product nucleus, no gamma ray is emitted. 

The nuclear reactions are described as taking place in two steps (1) the formation of a compound nucleus in a highly excited virtual level, and (2) the dissociation of this compound nucleus leading to a state of high excitation of the product nucleus. The product nucleus, which decays promptly by electromagnetic transitions, ends up in the ground state or in some low-lying metastable level called an isomer. 

The scattering of protons by He is of particular interest because the proton should enter a -state if the compound nucleus Li is formed. This nucleus is unstable in its ground state [defined by reactions such as against disinte-... 

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