Auger cascades

From other work on Pb(CH3)4 it is known that an Auger cascade connected with an L or M vacancy in the lead atom leads to the development of a charge of up to -t-17. This results in the total destruction of the molecule through a Coulomb explosion. On the basis of the 4/5 rule and the 14% internal conversion, one can estimate that for Pb(CH3)4 the molecule should remain intact in at least 69% of the decays, corresponding to the transformation ... 

A further complicating factor is that many low-energy y-transitions are converted, that is, their energy is released through the expulsion of one or more atomic electrons. This gives rise to the Auger cascade, which will be described below. 

The process of j3-decay in some respects offers simpler radiochemical consequences than do neutron capture and other reactions, because (a) the nuclear recoil energy is very low and (b) the decay schemes, and thus the probability of Auger cascades, are generally well known. Despite this, no clear mechanisms have been worked out. 

Photochemistry and radiation chemistry of biomolecules in vacuo and in water. Radiolytic products from Auger cascade are interesting from the viewpoint of radiotherapy. The development of irradiation systems is required in which liquid samples can be irradiated with vacuum UV or ultrasoft x-rays of high intensity. 

Recombination at and excitation from deep levels are emphasized. Nonradiative transitions at defect levels—Auger, cascade capture, and multiphonon emission processes—are discussed in detail. Factors to be considered in the analysis of optical cross sections which can give information about the parity of the impurity wave function and thus about the symmetry of a particular center are reviewed. 

The decrease for titania occurs at an unexpectedly low dose. The authors note that the copper X-rays should be highly effective for photoelectric ejection of K electrons from titanium, and that the multiply charged ions resulting from the subsequent Auger cascade may be very effective in reducing the surface area, perhaps simply because of the large energy liberation on neutralization. 

Figures. An illustration of the relaxation of a K-shell core hole in xenon by x-ray fluorescence (L[111]- K) followed by an Auger cascade to produce Xe. ...

These studies later were extended to molecules containing only elements from the first series of the periodic table (Carlson and Krause 1972). For these molecules, with only two electronic shells, an Auger cascade cannot occur. Each K shell vacancy produced by x-ray ionization of a Is electron produces a single Auger event with the total loss of two valence electrons. Additional electrons can be lost in shake-off ionization and double Auger decay, which were estimated to contribute about 20% to the the observed ion yields. 

An upper limit can be set to the duration time of several nuclear processes and their consequences such as Auger cascades in the case of electron capture reactions, or the thermal displacement of atoms from one site to another in a-emitting or Coulombic-excitation processes. The subject has recently been reviewed [20]. 

We have already mentioned that the electron-capture decay is prone to decay after-effects. Comparative experiments were first made with in copper, NalOs, Nal, and Ij matrices [49]. The recoil-free fractions of the last two named proved too small for serious use, whereas the copper matrix is the narrow-line source commonly used for this isotope. The NalOs source gave an emission profile which was complex. An analysis was suggested involving at least two distinct charge states of Te formed by the Auger cascade which follows the electron capture. 

Formally, the Auger effect can be interpreted as a two-step process first an X-ray photon is emitted, which is then absorbed via photoelectric effect in the same atom. The Auger effect may cause further ionization of a given atom and so multiply ionized atoms can be formed in Auger cascades, especially in high-Z atoms. This, in turn, can cause chemical changes, so the Auger effect has an important role in the mechanism of radiochemical reactions. 

In addition to resonant conversion. Auger cascades, and shake-off electrons, there are other secondary mechanisms that can lead to the generation of resonant electrons. Thus, electrons coming from the photoionization of an atom hit by resonant gamma or X-rays originated during the nuclear or atomic relaxation of the Mossbauer isotope (and usually denoted as GPE and XPE, respectively) are also electrons carrying resonant information and, consequently, contribute to the Mossbauer spectrum [4]. 

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