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The dipole strength of the $N=50$ nucleus ${}^{86}$Kr was studied in photon-scattering experiments using bremsstrahlung produced with electron beams of energies of 7.9 and 11.2 MeV delivered by the linear accelerator ELBE as well as using quasimonoenergetic and linearly polarized $\ensuremath{\gamma}$ rays of 10 energies within the range from 4.7 to 9.3 MeV delivered by the HI$\ensuremath{\gamma}$S facility. A high-pressure gas target was used. We identified 39 levels up to an excitation energy of 10.1 MeV. Simulations of $\ensuremath{\gamma}$-ray cascades were performed to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section derived in this way up to the neutron-separation energy is combined with the photoabsorption cross section obtained from a $(\ensuremath{\gamma},n)$ experiment at HI$\ensuremath{\gamma}$S. The enhanced $E1$ strength found in the range from 6 to 10 MeV is compared with the ones in the $N$ $=$ 50 isotones ${}^{88}$Sr, ${}^{90}$Zr, and ${}^{92}$Mo and with predictions of calculations within the quasiparticle-phonon model.

The $\ensuremath{\gamma}$-ray strength function is an important input quantity for the determination of the photoreaction rate and the neutron capture rate for astrophysics as well as for nuclear technologies. To test model predictions, the photoabsorption cross section of $^{139}\mathrm{La}$ up to the neutron-separation energy was measured using bremsstrahlung produced at the electron accelerator ELBE of Forschungszentrum Dresden-Rossendorf with an electron beam of $11.5$ MeV kinetic energy. The experimental data were analyzed by applying Monte Carlo simulations of $\ensuremath{\gamma}$-ray cascades to obtain the intensities of the ground-state transitions and their branching ratios. We found a significant enhancement of electric dipole strength in the energy range from $6$ to $10$ MeV that may be related with a pygmy dipole resonance. The present data are combined with photoneutron cross sections for $^{139}\mathrm{La}$ and compared with results of calculations on the basis of a quasiparticle-random-phase approximation using an instantaneous-shape sampling.

Photoactivation measurements on $^{144}\mathrm{Sm}$ have been performed with bremsstrahlung endpoint energies from 10.0 to 15.5 MeV at the bremsstrahlung facility of the superconducting electron accelerator ELBE of Forschungszentrum Dresden-Rossendorf. The measured activation yield for the $^{144}\mathrm{Sm}$($\ensuremath{\gamma},n$) reaction is compared with the calculated yield using cross sections from previous photoneutron experiments. The activation yields measured for all disintegration channels $^{144}\mathrm{Sm}$($\ensuremath{\gamma},n$), ($\ensuremath{\gamma},p$), and ($\ensuremath{\gamma},\ensuremath{\alpha}$) are compared to the yield calculated by using Hauser-Feshbach statistical models. A new parametrization of the photon strength function is presented and the yield simulated by using the modified photon strength parameters is compared to the experimental data.

The dipole response of the doubly magic nuclide $^{208}\mathrm{Pb}$ was studied in photon-scattering experiments at the electron linear accelerator ELBE with bremsstrahlung produced at kinetic electron energies of 9.0 and 15.0 MeV. The present $(\ensuremath{\gamma},{\ensuremath{\gamma}}^{\ensuremath{'}})$ data combined with $(\ensuremath{\gamma},n)$ data from the literature are compared with results of shell-model calculations and calculations using a quasiparticle random-phase approximation. The shell-model calculations including (2p-2h) excitations describe the experimental $E1$ strength well and reproduce the spreading of the giant dipole resonance by applying a small smearing width only.

Excited states with J{sup {pi}}=1{sup +} and 1{sup -} in {sup 26}Mg were studied in a photon-scattering experiment using bremsstrahlung produced by an electron beam of 13.0 MeV kinetic energy provided by the superconducting electron linear accelerator ELBE. We determined the transition strengths from the 1{sup +} and 1{sup -} states to the ground state as well as to low-lying excited states. In addition, we observed a J=1 state at 11.154 MeV, above the neutron-separation energy of 11.093 MeV, and determined its partial {gamma} decay width for the first time.

Photoexcitation of the N=50 nucleus {sup 89}Y has been performed at the bremsstrahlung facility at the superconducting electron accelerator ELBE at electron energies of E{sub e}{sup kin}=9.5 and 13.2 MeV. About 250 levels up to the neutron-separation energy were identified. Statistical methods were applied to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. The photoabsorption cross section derived in this way up to the neutron-separation energy is combined with the photoabsorption cross section obtained from ({gamma}, n) data and provides information about the extension of the giant dipole resonance toward energies below the neutron-separation energy. An enhancement of E1 strength has been found in the range from about 6 to 11 MeV. The experimental photoabsorption cross sections of {sup 89}Y and of the neighboring N=50 isotones {sup 88}Sr and {sup 90}Zr are compared with predictions of the quasiparticle-random-phase approximation.

The dipole response of the N=50 nucleus 90Zr was studied in photon-scattering experiments at the electron linear accelerator ELBE with bremsstrahlung produced at kinetic electron energies of 7.9, 9.0, and 13.2 MeV. We identified 189 levels up to an excitation energy of 12.9 MeV. Statistical methods were applied to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. In this way we derived the photoabsorption cross section up to the neutron-separation energy. This cross section matches well the photoabsorption cross section obtained from (gamma,n) data and thus provides information about the extension of the dipole-strength distribution toward energies below the neutron-separation energy. An enhancement of E1 strength has been found in the range of 6 MeV to 11 MeV. Calculations within the framework of the quasiparticle-phonon model ascribe this strength to a vibration of the excessive neutrons against the N = Z neutron-proton core, giving rise to a pygmy dipole resonance.

The ${}^{197}\mathrm{Au}(\ensuremath{\gamma},n)$ reaction is used as an activation standard for photodisintegration studies on astrophysically relevant nuclei. At the bremsstrahlung facility of the superconducting electron accelerator ELBE (Electron Linear accelerator of high Brilliance and low Emittance) of Forschungszentrum Dresden-Rossendorf, photoactivation measurements on $^{197}\mathrm{Au}$ have been performed with bremsstrahlung endpoint energies from 8.0 to 15.5 MeV. The measured activation yield is compared with previous experiments as well as with calculations using Hauser-Feshbach statistical models. It is shown that the experimental data are best described by a two-Lorentzian parametrization with taking the axial deformation of $^{197}\mathrm{Au}$ into account. The experimental ${}^{197}\mathrm{Au}(\ensuremath{\gamma},n)$ reaction yield measured at ELBE via the photoactivation method is found to be consistent with previous experimental data using photon scattering or neutron detection methods.

Dipole-strength distributions in the nuclides $^{98}\mathrm{Mo}$ and $^{100}\mathrm{Mo}$ up to the neutron-separation energies have been studied in photon-scattering experiments at the bremsstrahlung facility of the Forschungszentrum Dresden-Rossendorf. To determine the dipole-strength distributions up to the neutron-emission thresholds, statistical methods were developed for the analysis of the measured spectra. The measured spectra of scattered photons were corrected for detector response and atomic background by simulations using the code GEANT3. Simulations of $\ensuremath{\gamma}$-ray cascades were performed to correct the intensities of the transitions to the ground state for feeding from higher-lying levels and to determine their branching ratios. The photoabsorption cross sections obtained for $^{98}\mathrm{Mo}$ and $^{100}\mathrm{Mo}$ from the present $(\ensuremath{\gamma},{\ensuremath{\gamma}}^{'})$ experiments are combined with $(\ensuremath{\gamma},n)$ data from literature, resulting in a photoabsorption cross section covering the range from 4 to about 15 MeV of interest for network calculations in nuclear astrophysics. Novel information about the low-energy tail of the giant dipole resonance and its energy dependence is derived. The photoabsorption cross sections deduced from the present photon-scattering experiments are compared with existing data from neutron capture and $^{3}\mathrm{He}$-induced reactions.

The dipole response of the magic $N=50$ nucleus $^{88}\mathrm{Sr}$ was studied in photon-scattering experiments at the electron linear accelerator ELBE with bremsstrahlung produced at kinetic electron energies of 9.0, 13.2, and 16.0 MeV. We identified 160 levels up to an excitation energy of 12 MeV. By using polarized photons linear polarizations of about 50 \ensuremath{\gamma} transitions were measured that enabled parity assignments to the corresponding states. In the energy range of 6--12 MeV we identified only one $M1$ transition; all other transitions have $E1$ character. Thus, $E1$ character was proven for 63% of the total dipole strength of the observed levels in the given energy range. Statistical methods were applied to estimate intensities of inelastic transitions and to correct the intensities of the ground-state transitions for their branching ratios. In this way we derived the photoabsorption cross section up to the neutron-separation energy. This cross section matches well the photoabsorption cross section obtained from $(\ensuremath{\gamma},n)$ data and thus provides information about the extension of the dipole-strength distribution toward energies below the neutron-separation energy. An enhancement of $E1$ strength at 6--11 MeV may be considered as an indication for a pygmy dipole resonance.

The role of nuclear deformation in the photoabsorption cross section in the tail region of the electric giant dipole resonance (GDR) is studied in terms of a deformed oscillator model and a Nilsson-plus-random-phase-approximation model. It is found within the framework of these approaches that extra electric dipole strength is generated at energies below the GDR maximum if the nuclear system is spatially deformed. This is important in the prediction of stellar photodisintegration rates, knowing that an extra strength can affect these rates even below the particle separation energies through the so-called \ensuremath{\gamma} process. Because the nuclear deformation is governed by shell effects, this extra strength does not directly correlate with the neutron excess.

Systematic nuclear resonance fluorescence (NRF) experiments on all nine stable (seven even-even and two odd-mass) Xe isotopes have been performed at the bremsstrahlung facility of the 4.3-MV Stuttgart Dynamitron accelerator. For the first time thin-walled, high-pressure gas targets (about 70 bar) with highly enriched target material were used in NRF experiments. Precise excitation energies, transition strengths, spins, and decay branching ratios were obtained for numerous states, most of them previously unknown. The systematics of the observed $E1$ two-phonon excitations (${2}^{+}\ensuremath{\bigotimes}{3}^{\ensuremath{-}}$) and $M1$ excitations to ${1}^{+}$ mixed-symmetry states in the even-even isotopes are discussed with respect to the new critical point symmetry E(5). The fragmentation of these fundamental dipole excitation modes in the odd-mass isotopes $^{129,131}\mathrm{Xe}$ is shown and discussed. In the even-even nuclei several low-lying $E2$ excitations were observed.

The nuclides {sup 98}Mo and {sup 100}Mo have been studied in photon-scattering experiments by using bremsstrahlung produced from electron beams with kinetic energies from 3.2 to 3.8 MeV. Six electromagnetic dipole transitions in {sup 98}Mo and 19 in {sup 100}Mo were observed for the first time in the energy range from 2 to 4 MeV. A specific feature in the two nuclides is the deexcitation of one state with spin J=1 to the 0{sup +} ground state as well as to the first excited 0{sup +} state, which cannot be explained in standard models. We present a model that allows us to deduce the mixing coefficients for the two 0{sup +} shape-isomeric states from the experimental ratio of the transition strengths from the J=1 state to the 0{sup +} ground state and to the 0{sup +} excited state.

High-spin states in ${}^{90}\mathrm{Y}$ were populated in the ${}^{82}\mathrm{Se}{(}^{11}\mathrm{B},3n)$ reaction at a beam energy of 37 MeV. \ensuremath{\gamma} rays were detected with the spectrometer GASP. The level scheme of ${}^{90}\mathrm{Y}$ was extended up to ${J}^{\ensuremath{\pi}}{=(18}^{+})$ at 9.6 MeV. Mean lifetimes of four levels were determined using the Doppler-shift-attenuation method. The structure of ${}^{90}\mathrm{Y}$ was interpreted in terms of the shell model. The calculations were performed in the model space $\ensuremath{\pi}{(0f}_{5/2}{,1p}_{3/2}{,1p}_{1/2}{,0g}_{9/2})\ensuremath{\nu}{(1p}_{1/2}{,0g}_{9/2}{,1d}_{5/2})$ and in an extended space including the $\ensuremath{\nu}{(0g}_{7/2})$ orbital also. The calculations in the extended model space reveal a correspondence between states in ${}^{90}\mathrm{Y}$ and ${}^{89}\mathrm{Y}.$ Moreover, a combination of the predicted states with ${J}^{\ensuremath{\pi}}g~{14}^{(+)}$ can be found that reproduces the large experimental $B(M1)$ values of up to about 1 Weisskopf unit.

The $^{181}\mathrm{Ta}$ relaxation rate is determined by nuclear acoustic resonance in $\mathrm{Ta}{\mathrm{H}}_{x}$ and $\mathrm{Ta}{\mathrm{D}}_{x}$ ($0.0003l~xl~0.0324$) for temperatures between 100 and 370 K. The nearest-neighbor quadrupolar interaction with the diffusing H or D which is responsible for the relaxation amounts to $\frac{{e}^{2}\mathrm{qQ}}{\ensuremath{\hbar}}=5.4\ifmmode\times\else\texttimes\fi{}{10}^{9} \mathrm{and} 4.7\ifmmode\times\else\texttimes\fi{}{10}^{9}$ ${\mathrm{s}}^{\ensuremath{-}1}$, respectively, i.e., it exceeds by far the Zeeman interaction. The experimental results are discussed with respect to this rather unusual situation and compared with macroscopic diffusion experiments.