Electron internal conversion

In addition to the possible multipolarities discussed in the previous sections, internal-conversion electrons can be produced by an EO transition, in which no spin is carried off by the transition. Because the y-rays must carry off at least one unit of angular momentum, or spin, there are no y-rays associated with an EO transition, and the corresponding internal-conversion coefficients are infinite. The most common EO transitions are between levels with J = = where the other multipolarities caimot contribute. However, EO transitions can also occur mixed with other multipolarities whenever... 

The particle notation is j3 for electrons from j3 -decay, e for internal-conversion electrons, and IB for photons from internal bremsstrahlung. Ref 15. 

Internal Conversion—Process in which a gamma ray knocks an electron out of the same atom from which the gamma ray was emitted. The ratio of the number of internal conversion electrons to the number of gamma quanta emitted in the de-excitation of the nucleus is called the "conversion ratio."... 

Transition, Isomeric—The process by which a nuclide decays to an isomeric nuclide (i.e., one of the same mass number and atomic number) of lower quantum energy. Isomeric transitions (often abbreviated I.T.) proceed by gamma ray and/or internal conversion electron emission. 

Internal-conversion electrons, 21 309 Internal-conversion process, 21 300, 306-309... 

Internal conversion (IC) is a competing process to 7-ray decay and occurs when an excited nucleus interacts electromagnetically with an orbital electron and ejects it. This transfer of the nuclear excitation energy to the electron occurs radiationlessly (without the emission of a photon). The energy of the internal conversion electron, Eic, is given by... 

Thus, if a transition has transition = 0.412 MeV, you would expect to see the spectrum of emitted internal conversion electrons shown in Figure 9.5. Note the different lines corresponding to the ejection of electrons from the K, L, and M shells. The nucleus will interact more readily with the K electrons than with the L electrons,... 

Figure 9.5 Kinetic energy spectrum of internal conversion electrons for a 412-keV nuclear transition in 198Hg. Superimposed on this spectrum is the accompanying spectrum of (i particles from the [1 decay that feeds the excited state. The peaks labeled K, L, and M represent conversion of electrons with principal quantum numbers of 1, 2, or 3, respectively. (From Marmier and Sheldon, 1969, p. 332.) Copyright Academic Press. Reprinted by permission of Elsevier.

Most often the transmission mode is found to be the most convenient in Mossbauer spectroscopy, i.e., the y radiation passes from the source through the absorber, and the attenuation of the primary beam is measured at the various Doppler velocities. However, there are a number of cases where a "scattering geometry may be advantageous (SO). The basis for this geometry lies in those processes that take place after resonant absorption of y radiation by the Mossbauer isotope. Specifically, after excitation the Mossbauer isotope may reemit the y ray, or it may decay by emission of internal conversion electrons and X rays [with the probability of internal conversion equal to a/(l + a)]. 

A. Internal Conversion Electronic Relaxation in Substituted Benzenes... 

By electron capture (e) or internal conversion, electrons are taken away from inner orbitals and the vacancies are filled with electrons from outer orbitals with resulting emission of characteristic X rays. Electrons may also be emitted by an internal photoeffect. Finally, at least one electron is missing, and this may also cause breaking of the chemical bond. As electron capture leads also to a change of the atomic number (Z = Z — 1), it is not possible to distinguish the effects due to the capture of an electron from those that are caused by the change of Z. In internal conversion, however, the atomic number is not changed, and the chemical effects observed in this... 

A process alternative to isomeric transition is called internal conversion (IC). In some cases, the y-energy is absorbed by a K-shell (inner) electron. This electron is ejected out with lower energy. This ejected electron is the internal conversion electron, and the process is called internal conversion. Some diagnostic and therapeutic radionuclides with corresponding half lives are given below. 

Gd is also known to generate Auger and internal conversion electrons efficiently by irradiation with a neutron beam. Based on this, an increase of the local concentration of Gd should enhance the properties for tumor cell detection, and Gd neutron capture therapy could be more efficient. For this purpose, a novel water-soluble PAMAM-based dendrimers terminated with DPTA extremities covered with 254 Gd atoms were prepared with excellent results [69]. 

Preliminary results from the on-line separation of At from molten ThF4,LiF in the 600 MeV C.E.R.N. synchrotron have been reported by Ravn et a/. The energies and intensities of y-rays and internal-conversion electrons from the electron capture and from the particle decay of "At have been measured. The rates of exchange of iodine and astatine species between submonolayers on Pt and aqueous solution have been compared. ... 

Although the conventional experimental technique uses a transmission g ibmetry and a scintillation or proportional counter, spectra have also been recorded using counting of the internal conversion electrons in a doublelens /S-spectrometer [21] the source and absorber matrices were j8-tin. 

Sometimes the excitation energy of the nucleus is given to an atomic electron instead of being released in the form of a photon. This type of nuclear transition is called internal conversion (IC), and the ejected atomic electron is called an internal conversion electron. 

Therefore, a nucleus that undergoes internal conversion is a source of groups of monoenergetic electrons with energies given by Eqs. 3.37. A typical internal conversion electron spectrum is shown in Fig. 3.6. The two peaks correspond to K and L electrons. The diagram on the right (Fig. 3.6) shows the transition... 

Detection of internal conversion electrons. Radioisotopes emitting internal conversion (IC) electrons also emit gammas and X-rays. The use of a single detector to count electrons will record not only IC electrons but also Compton electrons produced in the detector by the gammas. To eliminate the Compton electrons, one can utilize the X-rays that are emitted simultaneously with the IC electrons. Thus, a second detector is added for X-rays and the counting system... 

Figure 13.8 The internal conversion electron spectrum obtained with a plastic scintillator. The solid line was obtained using Eq. 13.10 (from Ref. 20).

Once an electron is ejected from an atomic orbital due to internal conversion, electron capture, or some other process involved in radioactive decay, a vacancy is created in the electron shell which can be filled in several ways. Electrons from higher energy orbitals can occupy the vacancy. The difference in the binding raergy of the two shells involved in the transition will be emitted from the atom as X-rays. This process is called fluorescent radiation. 

The magnetic components can also be obtained by measurements of internal conversion electrons. Experimental methods of measurement of internal conversion electrons produced by Coulomb excitation have been developed by Huus and Bjerregaard and used by them to study the rare earth nuclei in some detail 2. This method has the advantage that the composition of a mixed y-ray can be determined from the magnitude of the conversion coefficient or from the KjL ratios, although it is still necessary to know the relative intensities of the transitions between the various states. 

It should be noted that for a number of radionuclides the Qp values are more restrictive than those of the earlier Q system. These lower Qp values are primarily associated with radionuclides which emit internal conversion electrons. 

As an alternative to y-ray emission, an excited nuclear state can also lose its energy by internal conversion electron emission. In this parallel process, the energy of the excited state is transferred directly to an electron of the atomic shell, without previous y-ray emission. The energy of internal conversion electrons depends on the nuclear transition energy and also on the ionization energy of the K, L, M,... electrons. 

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