Resonances, nuclear-excited

In a Mdssbauer transmission experiment, the absorber containing the stable Mdssbauer isotope is placed between the source and the detector (cf. Fig. 2.6). For the absorber, we assume the same mean energy q between nuclear excited and ground states as for the source, but with an additional intrinsic shift A due to chemical influence. The absorption Une, or resonant absorption cross-section cr( ), has the same Lorentzian shape as the emission line and if we assume also the same half width , cr( ) can be expressed as ([1] in Chap. 1)... 

The recoilless nuclear resonance absorption of y-radiation (Mossbauer effect) has been verified for more than 40 elements, but only some 15 of them are suitable for practical applications [33, 34]. The limiting factors are the lifetime and the energy of the nuclear excited state involved in the Mossbauer transition. The lifetime determines the spectral line width, which should not exceed the hyperfine interaction energies to be observed. The transition energy of the y-quanta determines the recoil energy and thus the resonance effect [34]. 57Fe is by far the most suited and thus the most widely studied Mossbauer-active nuclide, and 57Fe Mossbauer spectroscopy has become a standard technique for the characterisation of SCO compounds of iron. 

PAD (perturbed angular distribution) is a variation of PAC with nuclear excitation by a particle beam from an accelerator. QMS is quasielastic MdBbauer-spectroscopy, QNS is quasielastic neutron spectroscopy. For MOBbauer spectroscopy (MS), perturbed angular correlation (PAC), and /J-nuclear magnetic resonance (/3-NMR), the accessible SE jump frequencies are determined by the life time (rN) of the nuclear states involved in the spectroscopic process. Since NMR is a resonance method, the resonance frequency of the experiment sets the time window. With neutron scattering, the time window is determined by the possible energy resolution of the spectrometer as explained later. 

SOM, soil organic matter HS, humic substances DH, degree of humification HAC, humic acid C FAC, fulvic acid C TEC, total extractable C HR, humification rate HI, humification index NHC, nonhumified C TOC, total organic C HA, humic acid FA, fulvic acids UV-Vis, ultraviolet-visible FT-IR, Fourier transform infrared NMR, nuclear magnetic resonance ESR, electron spin resonance EEM, excitation-emission matrix. 

Fig. 8. Pulse sequences for nuclear quadrupole resonance (NQR) excitation (a) spin-lock-spin-echo (SLSE) (b) phase-alternated spin-lock-spin-echo (PASLSE) (c) spin-lock-inversion-midecho (SLIME) (d) non-phase-alternated pulse sequence (NPAPS) (e) phase-alternated pulse sequence (PAPS). Numbers above the pulses indicate the relative phase of the RF dashed lines represent expected NQR signals.

Figure 1. Schematic illustration of (a) shape and (b) nuclear-excited Feshbach resonances. The symbols 0> and i > designate, respectively, the electronic ground state of the neutral molecule and the NIS (1).

Figure 2 Experimental arrangement for measurements of the Fe nuclear resonance at the Advanced Photon Source (APS). In the standard fill pattern, electron bunches with a duration of 100 ps are separated by 153 ns. X-ray pulses are generated when alternating magnetic fields in the undulator accelerate these electron bunches. The spectral bandwidth of the X-rays is reduced to 1 eV by the heat-load monochromator and to 1 meV by the high-resolution monochromator. At the sample, the flux of the beam is about 10 photons/s. APD indicates the avalanche photodiode used to detect emitted X-rays. The lower right inset illustrates that counting is enabled only for times weU-separated from the X-ray pulse, so that only delayed photon emission resulting from decay of the nuclear excited state contributes to the experimental signal...

As a result of these calculations, it is concluded that the SFg molecule will not bind two electrons to form SF. However, the formation of SF5 in an electronically excited state cannot be dismissed easily. Nuclear-excited Feshbach resonances, in which the kinetic energy of the incident electron is absorbed solely into the nuclear motion of the molecule, occur in the electron attachment process of various molecular species The SF " species studied by Henis and... 

Mabie had a lifetime of about 0,5 ms. A lifetime of 0.03 ms, shorter than the value reported by Henis and Mabie, has been discussed and used for equipment calibrations by Hadjiantoniou, Christophorou and Carter It is conceivable that nuclear-excited Feshbach resonances also may participate in the formation of the SFfi " ion and other doubly-charged negative ions. 

In order to demonstrate the physical significance of asymjjtotic nonadiabatic transitions and especially the aiialj-tical theory developed an application is made to the resonant collisional excitation transfer between atoms. This presents a basic physical problem in the optical line broadening [25]. The theoretical considerations were mad( b( for< [25, 27, 28, 29, 25. 30] and their basic id( a has bec n verified experimentally [31]. These theoretical treatments assumed the impact parameter method and dealt with the time-dependent coupled differenticil equations imder the common nuclear trajectory approximation. At that time the authors could not find any analytical solutions and solved the coupled differential equations numerically. The results of calculations for the various cross sections agree well with each other and also with experiments, confirming the physical significance of the asymptotic type of transitions by the dipole-dipole interaction. 

Table 3 Energy shifts of K- and L-shell electrons in hydrogen-like due to various collective excitations. Upper half The contributions fixim low-lying nuclear states are calculated using experimental energies and transition probabilities [69]. Lower half The contributions from giant resonance states. Excitation energies and corresponding reduced electric transition strengths are again estimated based on empirical formulae. Notations are the same as in Table 2.

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