Coulomb excitation, experimental

In addition, Coulomb excitation can be used to populate the Mossbauer levels of I77,i78,i80j j [165-167]. The experimental line width using these sources is only slightly larger than the natural line width (e.g., the thickness corrected line width of Hf in a tantalum foil is in good agreement with the natural line width Texp = 1.90 0.07 mm s T at = 1-99 0.04 mm s [168]). 

Experimental Tests of Boson-Fermion Symmetries and Supersymmetries Using Coulomb Excitation with Heavy Ions... 

Since the lowest levels of even-even nuclei almost always have the same parity as the ground state and spin 2, it is generally assumed that Coulomb excitation in heavy elements is mainly an electric quadrupole process and that the cross section observed experimentally measures the E 2 transition probability. Similar assumptions are made for odd-A nuclei. In the majority of nuclei this assumption is justified. However, as Bjerregaard and Huus have shown, the multipole order can be determined directly by measurements with bombarding particles with different specific charge, e.g., protons and deuterons (or a-particles). They have verified that the multipole order is indeed two for the excitation of the lowest excited states in the even-even wolfram nuclei. 

P) M transitions. The reduced transition probability of the M component, as we have shown above, can be obtained from that of the E 2 component in Coulomb excitation, when the ratio of the components is found from angular distributions, angular correlations of successive y-rays, or from internal conversion measurements. Since this extra information is required there is at present less data available on Ml than on 2 transitions. For Ta the reduced Ml transition probabilities obtained by Stelson and McGowan for the 137kev transition and for the l66kev cascade transition were 0.105 and 0.226 in units of (efll2Mc). From these quantities the square of the difference between the gyromagnetic ratios gQ — gr [see Eq. (77-5)] was found to be 0.20 and 0.28, respectively the difference between the two results, these authors state, is probably not outside experimental errors, and illustrates the experimental difficulties involved in this kind of work. 

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. 

Spectroscopic quadrupole moments can be determined by many experimental methods differential perturbed angular distribution of j rays following nuclear reactions, low temperature nuclear orientation, optical spectroscopy. Coulomb excitation reorientation, different methods of laser spectroscopy, hyperfine spKtting of spectrum lines in inhomogeneous electric field, etc. 

Altogether, we thus see a striking similarity, up to details, between the nuclear and the cluster responses for this clean Coulomb excitation mechanism with the prominent feature that the resonance modes turn out to represent robust, harmonic oscillations. It remains to be seen to what extent this behavior persists in other experimental situations. In the following we focus on heavy-ion collisions and laser-cluster interactions as complementary and widely studied excitation mechanisms. 

In-beam Mossbauer spectroscopy (IBMS) involves online measurement of Mossbauer -Y-radiation emitted from excited atoms produced by nuclear reactions, Coulomb excitation, and radioisotope (Rl) implantation. It provides useful information on local atomic and electronic configurations (i.e., site distributions, dynamic diffusion processes, and unusual chemical states) of extremely dilute atoms during the lifetime of the excited Mossbauer state. Physical and chemical transformations that occur in nonequilibrium and metastable states immediately after nuclear reactions and implantation can be observed in suitable materials. This chapter introduces past and current experimental techniques of in-beam Mossbauer spectroscopy and reviews some recent topics using Mn (T /2 = 85s) nuclei at RIKEN Rl Beam Factory (RIBF) and thermal neutron capture reaction. 

The in-beam Mossbauer technique combining Coulomb-excitation and recoil-implantation, which was described in the Sect. 6.3.1, provides a unique feature for studying the anomalously fast diffusion, i.e., one-by-one measurement Every y-ray emission from Fe follows the implantation process. As a consequence, in the lattice the Fe probe always remains fully isolated from other Fe atoms implanted before, and therefore, the spectrum obtained with this method is completely free from overlapping cascades as well as from clustering of Fe atoms. Both of them would change completely the diffusion properties of Fe atoms. This method, therefore, guarantees an experimental condition under which we can follow a few jumps of Fe atoms immediately after the implantation into anomalously fast diffusion systems, such as a-Zr, Sc, and Pb. 

According to a large number of experimental studies, the most stable phologen-erated species in the lowest excited stales of conjugated chains are electron-hole pairs bound by Coulomb attraction and associated to a local deformation of the backbone, i.e., polaron-excilons [18]. A good insight into the properties of these species can be provided by quantum-chemical calculations our recent theoretical... 

As the number of eigenstates available for coherent coupling increases, the dynamical behavior of the system becomes considerably more complex, and issues such as Coulomb interactions become more important. For example, over how many wells can the wave packet survive, if the holes remain locked in place If the holes become mobile, how will that affect the wave packet and, correspondingly, its controllability The contribution of excitons to the experimental signal must also be included [34], as well as the effects of the superposition of hole states created during the excitation process. These questions are currently under active investigation. 

To decide whether a surface effect is present and, if so which, the experimental spectra shown in Fig. 16 have been corrected for the spectrometer transmission. The secondary electron contribution and the emission from conduction band states have also been subtracted. Comparing this spectrum with calculated multiplet intensities it seems that a contribution from a divalent Am surface resulting in a broad structureless 5f 5f line at 1.8 eV is the most suitable explanation of the measured intensity distribution. Theory also supports this interpretation, since the empty 5f level of bulk Am lies only 0.7 eV above Ep within the unoccupied part of the 6d conduction band (as calculated from the difference of the Coulomb energy Uh and the 5 f -> 5 f excitation energy Any perturbation inducing an increase of Ep by that amount will... 

Samuel and Magee250 were apparently the first to estimate the path length /th and time rth of thermalization of slow electrons. For this purpose they used the classical model of random walks of an electron in a Coulomb field of the parent ion. They assumed that the electron travels the same distance / between each two subsequent collisions and that in each of them it loses the same portion of energy A E. Under such assumptions, for electrons with energy 15 eV and for AE between 0.025 and 0.05 eV, they have obtained Tth 2.83 x 10 14 s and /th = 1.2-1.8 nm. At such short /th a subexcitation electron cannot escape the attraction of the parent ion and in about 10 13 s must be captured by the ion, which results in formation of a neutral molecule in a highly excited state, which later may experience dissociation. However, the experimental data on the yield of free ions indicated that a certain part of electrons nevertheless gets away from the ion far enough to escape recombination. 

The energies of the d-d-excitations in this model are obtained by diagonalizing the matrix of the Hamiltonian constructed in the basis of rid-electronic wave functions (nd is the number of d-electrons). Matrix elements of the Hamiltonian are expressed through the parameters describing the crystal field and those of the Coulomb repulsion of d-electrons, which are Slater-Condon parameters Fk, k = 0,2,4, or the Racah parameters A, B, and C. In the simplest version of the CFT these quantities are considered empirical parameters and determined by fitting the calculated excitation energies to the experimental ones. 

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