[en] For decades, nuclear energy has been a major component of Germany's energy supply. After the Fukushima Daichi incident in 2011, Germany decided in favor of an accelerated nuclear power phase-out, which will be finished with the shutdown of the last power reactor by end of 2022. The present contribution provides an overview of Germany's facilities at the front and back end of the nuclear fuel cycle. This information is complemented with key aspects of associated decommissioning measures. (authors)

No abstract available

[en] Cosmic-ray muons can be used for the non-destructive imaging of spent nuclear fuel in sealed dry storage casks. The scattering data of the muons after traversing provides information on the thereby penetrated materials. Based on these properties, we investigate and discuss the theoretical feasibility of detecting single missing fuel rods in a sealed cask for the first time. We perform simulations of a vertically standing generic cask model loaded with fuel assemblies from a pressurized water reactor and muon detectors placed above and below the cask. By analysing the scattering angles and applying a significance ratio based on the Kolmogorov-Smirnov test statistic we conclude that missing rods can be reliably identified in a reasonable measuring time period depending on their position in the assembly and cask, and on the angular acceptance criterion of the primary, incoming muons. (authors)

[en] Reduced transition strengths expressed by B(E2) values are sensitive signatures to describe collective excitations of atomic nuclei and the evolution of shell structures. Along the N = Z line in the 0f1p shell they provide stringent tests of present shell-model interactions. Recently determined B(E2, 2₁⁺ → 0_g.s.⁺) values for self-conjugate nuclei in the 0f_7/2 shell showed an enhanced collective behavior. The soft shell closure at N = Z = 28 is of particular interest as it has been shown that the doubly-closed shell structure is substantially broken. In order to investigate the interplay between single-particle and collective characters of low-lying states, lifetime measurements employing the Doppler-shift attenuation method (DSAM) were performed at the FN tandem accelerator at the IKP, Cologne. Excited states in ₂₂⁴⁴Ti, ₂₄⁴⁸Cr, ₂₆⁵²Fe, and ₂₈⁵⁶Ni were populated with fusion-evaporation reactions. The emitted γ rays were detected by an array of 11 HPGe detectors. First results on lifetimes and corresponding B(E2) values are presented and discussed.

[en] Reduced transition strengths are sensitive signatures to describe collective excitations of atomic nuclei and the evolution of shell structures. They provide stringent tests of present shell-model interactions in the 0f1p shell along the N=Z line. Recently determined B(E2, 2${}_1^{+}$$\to <!--\; ???\; -->$ 0${}_{g.s.}^{+}$) values for ${}^{44}$Ti showed an enhanced collective behavior which was associated with core excitations from the sd-shell. However, there is a lack of information on precise values along the negative parity band in this nucleus. These states arise from a strong interplay between sd- and pf-shell orbitals and allow for refined tests of cross-shell contributions. In order to investigate the single-particle and collective characters of low-lying states, lifetime measurements employing the Recoil-Distance Doppler Shift (RDDS) and the Doppler-Shift Attenuation Method (DSAM) were performed at the FN tandem accelerator at the IKP, Cologne. Excited states in ${}^{44}$Ti were populated with a ${}^{40}$Ca(${}^6$Li,pn)${}^{44}$Ti fusion-evaporation reaction. The emitted $\mathrm{\gamma <!--\; ??\; -->}$ rays were detected by an array of 11 HPGe detectors. First lifetime results will be presented and compared to shell-model calculations including multi particle-hole cross-shell excitations.

No abstract available

[en] Lifetimes of excited states in the neutron-deficient nucleus ⁶¹Zn were measured employing the Recoil-Distance Doppler-Shift (RDDS) and the Fast-Timing Method at the University of Cologne. The nucleus of interest was populated as an evaporation residue in ⁴⁰Ca(²⁴Mg,n2p)⁶¹Zn and ⁵⁸Ni(α,n)⁶¹Zn reactions at 67 MeV and 19 MeV, respectively. Five lifetimes are measured for the first time, including the 5/2^- → 3/2^- transition depopulating the 124-keV isomer. Short lifetimes from the RDDS analysis are corrected for Doppler-Shift Attentuation (DSA) effects in the stopper foil. Ambiguous results from previous measurements were resolved. The obtained lifetimes are compared to predictions from different sets of shell-model calculations.

[en] Reduced transition strengths expressed with B(E2) values are sensitive signatures to describe collective excitations of atomic nuclei and are indispensable to understand nuclear shell structures. Along the N=Z line in the 1f_7_/_2 shell they provide stringent tests of recent shell-model interactions. So far, B(E2, 2_1"+ → 0_g_._s_."+) values for the self-conjugate "4"4_2_2Ti,"4"8_2_4Cr,"5"2_2_6Fe isotopes are known only with considerable errors. Recoil Distance Doppler-Shift (RDDS) experiments were performed employing the Cologne coincidence plunger device to measure lifetimes with high precision in order to deduce model-independent B(E2) values. Excited states in the nuclei of interest were populated with fusion-evaporation reactions. γ rays were detected by an array of 12 HPGe detectors. Precise B(E2, 2_1"+ → 0_g_._s_."+) values are measured to be 204"+"1"6_-_1_4 e"2fm"4, 262 ± 3 e"2fm"4, and 269 ± 8 e"2fm"4 for "4"4Ti, "4"8Cr, and "5"2Fe, respectively. The results are compared to recent shell-model calculations on the basis of GX1A interaction. While the excitation energies are reproduced quite well, the B(E2) values show considerable differences.

[en] Lifetimes of excited states in the neutron-deficient nucleus ⁶¹Zn were measured employing the Recoil-Distance Doppler-Shift (RDDS) and the Fast-Timing Method in fusion-evaporation reactions at the University of Cologne. Five lifetimes were measured for the first time, including the 5/2^- → 3/2^- transition depopulating the 124-keV isomer. Short lifetimes from the RDDS analysis were corrected for Doppler-Shift Attentuation (DSA) effects in the stopper foil. Ambiguous results from previous measurements were resolved. The obtained lifetimes are compared to predictions from different sets of shell-model calculations in the f_p, f_5/2pg_9/2, and multishell fp-g_9/2d_5/2 model spaces. The inclusion of cross-shell excitation into the 1d_5/2 orbital is found to be decisive for the description of collectivity in the first excited positive-parity band.

[en] The lifetimes of low-lying transitions in ¹³⁸Gd have been measured using the recoil-distance Doppler-shift technique. The resultant reduced transition probabilities have been compared to X(5) critical-point calculations to assess the potential 'phase-transitional' behaviour of ¹³⁸Gd. The X(5) symmetry describes the first order 'phase transition' between sphericity, U(5) and an axially deformed nuclear shape, SU(3). Although a high degree of correspondence is observed between the experimental and theoretical excitation energies, the large uncertainties of the experimental B(E2) values cannot preclude contributions from either vibrational or rotational modes of excitation. In order to further examine the nature of low-lying states in ¹³⁸Gd, ongoing work is aiming to derive solutions to the Bohr Hamiltonian using a more general potential that is not restricted to the X(5) critical point. These results, in parallel to more extensive IBM-1 calculations, will eventually be compared to the experimental results to more accurately locate ¹³⁸Gd along the U(5) − SU(3) arm of the structure triangle.