This paper illustrates the principle of the Doppler-shift attenuation method (DSAM) using particle-γ coincidences, a method for determining lifetimes of excited nuclear levels in the range of few femtoseconds up to one picosecond. The coincident detection holds several advantages towards conventional DSAM experiments, such as the elimination of background and feeding transitions. Using the experimental data on 94 Zr, the concept of the (p,p’γ) DSAM analysis is presented. Additional experimental results are highlighted.

The lifetimes of the first 2(+) excited states of Po-212,Po-210 were measured in two transfer reactions Pb-208(C-12, Be-8)Po-212 and Pb-208(C-12, Be-10)Po-210 by the Recoil Distance Doppler Shift (RDDS) method and by the Doppler Shift Attenuation method (DSAM), respectively. The derived absolute B(E2) values of 2.6(3) W.u. for Po-212 and 1.83(28) W.u. for Po-210 indicate low collectivity. It is shown that the properties of the yrast 2(1)(+), 4(1)(+), 6(1)(+) and 8(1)(+) states in both nuclei cannot be described consistently in the framework of nuclear shell models. It is also demonstrated in the case of Po-210 that Quasi-particle Phonon Model (QPM) calculations cannot overcome this problem thus indicating the existence of a peculiarity which is neglected in both theoretical approaches.

The E2/M1 multipole mixing ratio delta(1 -> 2) of the 1(sc)(+)-> 2(1)(+) gamma- ray decay in Gd-156 and hence the isovector E2 transition rate of the scissors mode of a well-deformed rotational nucleus has been measured for the first time. It has been obtained from the angular distribution of an artificial quasimonochromatic linearly polarized gamma-ray beam of energy 3.07(6) MeV scattered inelastically off an isotopically highly enriched Gd-156 target. The data yield first direct support for the deformation dependence of effective proton and neutron quadrupole boson charges in the framework of algebraic nuclear models. First evidence for a low-lying J(pi) = 2(+) member of the rotational band of states on top of the 1(+) band head is obtained, too, indicating a significant signature splitting in the K = 1 scissors mode rotational band.

The lifetime of the ${2}_{1}^{+}$ state of $^{212}\mathrm{Po}$ was measured in the $^{208}\mathrm{Pb}$($^{12}\mathrm{C},^{8}\mathrm{Be}$)$^{212}\mathrm{Po}$ transfer reaction by $\ensuremath{\gamma}$-ray spectroscopy employing the recoil distance Doppler shift (RDDS) method. The derived absolute $B(E2)$ value of 2.6(3) W.u. indicates a low collectivity and contradicts previous claims of $\ensuremath{\alpha}$-cluster components in the structure of the ${2}_{1}^{+}$ state. It is demonstrated that a consistent description of the properties of the ${2}_{1}^{+}\ensuremath{-}{4}_{1}^{+}\ensuremath{-}{6}_{1}^{+}\ensuremath{-}{8}_{1}^{+}$ sequence in $^{212}\mathrm{Po}$ cannot be achieved in the framework of a single-$j$ shell-model calculation, either. This puzzle is traced to the properties of the seniority-2 configurations in $^{210}\mathrm{Pb}$ and $^{210}\mathrm{Po}$.

The lifetime of the 2(1)(+) state of Po-212 was measured in the Pb-208(C-12, Be-8)Po-212 transfer reaction by gamma-ray spectroscopy employing the recoil distance Doppler shift (RDDS) method. The derived absolute B(E2) value of 2.6(3) W.u. indicates a low collectivity and contradicts previous claims of alpha-cluster components in the structure of the 2(1)(+) state. It is demonstrated that a consistent description of the properties of the 2(1)(+)-4(1)(+)-6(1)(+)-8(1)(+) sequence in Po-212 cannot be achieved in the framework of a single-j shell-model calculation, either. This puzzle is traced to the properties of the seniority-2 configurations in Pb-210 and Po-210.

. The lifetimes of the 2^+_1 , the 2^+_2 and the 3^-_1 states of 210 Po have been measured in the 208 Pb( 12 C, 10 Be) 210 Po transfer reaction by the Doppler-shift attenuation method. The result for the lifetime of the 2^+_1 state is about three times shorter than the adopted value. However, the new value still does not allow for a consistent description of the properties of the yrast 2^+_1 , 4^+_1 , 6^+_1 , and 8^+_1 states of 210 Po in the framework of nuclear shell models. Quasi-particle Phonon Model (QPM) calculations also cannot overcome this problem thus indicating the existence of a peculiarity which is neglected in both theoretical approaches.

The nucleosynthesis of elements beyond iron is dominated by neutron captures in the s and r processes. However, 32 stable, proton-rich isotopes cannot be formed during those processes, because they are shielded from the s-process flow and r-process beta-decay chains. These nuclei are attributed to the p and rp process. For all those processes, current research in nuclear astrophysics addresses the need for more precise reaction data involving radioactive isotopes. Depending on the particular reaction, direct or inverse kinematics, forward or time-reversed direction are investigated to determine or at least to constrain the desired reaction cross sections. The Facility for Antiproton and Ion Research (FAIR) will offer unique, unprecedented opportunities to investigate many of the important reactions. The high yield of radioactive isotopes, even far away from the valley of stability, allows the investigation of isotopes involved in processes as exotic as the r or rp processes.

The decay properties of the Pygmy Dipole Resonance (PDR) have been investigated in the semi-magic N=82 nucleus 140Ce using a novel combination of nuclear resonance fluorescence and γ–γ coincidence techniques. Branching ratios for transitions to low-lying excited states are determined in a direct and model-independent way both for individual excited states and for excitation energy intervals. Comparison of the experimental results to microscopic calculations in the quasi-particle phonon model exhibits an excellent agreement, supporting the observation that the Pygmy Dipole Resonance couples to the ground state as well as to low-lying excited states. A 10% mixing of the PDR and the [21+×PDR] is extracted.

In this work we present the results from two experiments dedicated to search for quadrupolecollective isovector valence-shell excitation, the states with so-called mixed proton-neutron symmetry (MSS), in nuclei around the doubly magic nucleus 208Pb. 212Po was studied in an α-transfer reaction. 204Hg was studied in an inverse kinematics Coulomb excitation reaction on a carbon target. Both experiments provide indications for existence of one-phonon MSSs. Those are the first experimentally identified MSSs in the mass A ≈ 208 region.

We present the results from an experiment dedicated to search for quadrupole-collective isovector valence-shell excitations, states with so-called mixed proton-neutron symmetry (MSS), of $^{212}\mathrm{Po}$. This nucleus was studied in an $\ensuremath{\alpha}\text{-transfer}$ reaction. The lifetimes of two short-lived excited states, candidates for the one-phonon MSS, were determined by utilizing the Doppler shift attenuation method. The experimental results are in qualitative agreement with a simple $\text{single-}j$ shell model calculation, which, together with the observed lack of quadrupole collectivity, indicates that the isovector nature of low-lying states is a property of the leading single-particle valence shell configuration.

V. Derya,1,* N. Tsoneva,2,3,4 T. Aumann,5 M. Bhike,6 J. Endres,1 M. Gooden,6 A. Hennig,1 J. Isaak,2,7 H. Lenske,3 B. Löher,7 N. Pietralla,5 D. Savran,7 W. Tornow,6,8 V. Werner,5 and A. Zilges1 1Institut für Kernphysik, Universität zu Köln, 50937 Köln, Germany 2Frankfurt Institute for Advanced Studies (FIAS), 60438 Frankfurt am Main, Germany 3Institut für Theoretische Physik, Universität Gießen, 35392 Gießen, Germany 4Institute for Nuclear Research and Nuclear Energy, 1784 Sofia, Bulgaria 5Institut für Kernphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany 6Department of Physics, Duke University, Durham, North Carolina 27708, USA 7GSI Helmholtzzentrum für Schwerionenforschung GmbH, 64291 Darmstadt, Germany 8Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA (Received 27 January 2016; published 10 March 2016)

We present the results from an experiment dedicated to search for quadrupole-collective isovector valence-shell excitations, states with so-called mixed proton-neutron symmetry (MSS), of Po-212. This nucleus was studied in an a-transfer reaction. The lifetimes of two short-lived excited states, candidates for the one-phonon MSS, were determined by utilizing the Doppler shift attenuation method. The experimental results are in qualitative agreement with a simple single-j shell model calculation, which, together with the observed lack of quadrupole collectivity, indicates that the isovector nature of low-lying states is a property of the leading single-particle valence shell configuration.

Excited states with intermediate and high spins in $^{33}\mathrm{P}$ and $^{33}\mathrm{S}$ have been populated using the $^{26}\mathrm{Mg}(^{13}\mathrm{C},np\ensuremath{\alpha})$ and $^{26}\mathrm{Mg}(^{13}\mathrm{C},2n\ensuremath{\alpha})$ fusion-evaporation reactions. The level schemes of both nuclei have been considerably extended. Utilizing $\ensuremath{\gamma}\ensuremath{\gamma}$ angular correlations the spin-parity assignment of the new excited states in $^{33}\mathrm{P}$ has been investigated. The experimentally determined results from both nuclei were compared to $0\ensuremath{\hbar}\ensuremath{\omega}$ and $1\ensuremath{\hbar}\ensuremath{\omega}$ truncated p-sd-pf shell-model calculations utilizing the PSDPF interaction, showing a very good agreement between experiment and theory.

Background: Two-phonon excitations originating from the coupling of two collective one-phonon states are of great interest in nuclear structure physics. One possibility to generate low-lying E1 excitations is the coupling of quadrupole and octupole phonons. Purpose: In this work, the γ-decay behavior of candidates for the (2_1^+⊗ 3_1^-)_1^- state in the doubly-magic nucleus ^40Ca and in the heavier and semi-magic nucleus ^140Ce is investigated. Methods: (γ⃗,γ') experiments have been carried out at the High Intensity γ-ray Source (HIγS) facility in combination with the high-efficiency γ-ray spectroscopy setup γ^3 consisting of HPGe and LaBr_3 detectors. The setup enables the acquisition of γ-γ coincidence data and, hence, the detection of direct decay paths. Results: In addition to the known ground-state decays, for ^40Ca the decay into the 3^-_1 state was observed, while for ^140Ce the direct decays into the 2^+_1 and the 0^+_2 state were detected. The experimentally deduced transition strengths and excitation energies are compared to theoretical calculations in the framework of EDF theory plus QPM approach and systematically analyzed for N=82 isotones. In addition, negative parities for two J=1 states in ^44Ca were deduced simultaneously. Conclusions: The experimental findings together with the theoretical calculations support the two-phonon character of the 1^-_1 excitation in the light-to-medium-mass nucleus ^40Ca as well as in the stable even-even N=82 nuclei.

In this work we present an experiment dedicated to searching for quarupole- collective isovector valence-shell excitation — the states with so-called mixed proton-neutron symmetry (MSSs), in the nucleus 212Po. The states of interest were populated and studied by an α-transfer reaction. The experiment provides indication for existence of one-phonon MSS in the nucleus 212Po which is the first experimentally identified MSS in the region around double magic nucleus 208Pb.

Excited states with intermediate and high spins in P-33 and S-33 have been populated using the Mg-26(C-13, np alpha) and Mg-26(C-13,2n alpha) fusion-evaporation reactions. The level schemes of both nuclei have been considerably extended. Utilizing gamma gamma angular correlations the spin-parity assignment of the new excited states in P-33 has been investigated. The experimentally determined results from both nuclei were compared to 0 (h) over bar omega and 1 (h) over bar omega truncated p-sd-pf shell-model calculations utilizing the PSDPF interaction, showing a very good agreement between experiment and theory.