Explore the vast range of titles available.

There has been limited research devoted to secondary electron emission (SEE) from nano-materials using rapid and heavy ion bombardment. Here we report a comparison of SEE properties between novel nano-materials with a three-dimensional nano-structure composed of a mostly regular pattern of rods and gold used as a standard material for SEE under bombardment of heavy ions at energies of a few MeV/nucleon. The nano-structured materials show enhanced SEE properties when compared with gold. Results from this work will enable the development of new radiation detectors for science and industry.

Assuming a seniority-conserving interaction, single- j calculations for (j) n configurations with n = 1,..,2j+1 can be performed using a semi-empirical approach, provided that the energies and absolute electromagnetic transition rates are known for the two-particle (hole) nucleus. Using those and the coefficients of fractional parentage, all needed matrix elements for the (j) n configurations can be predicted. At the Cologne Tandem Accelerator of the Institute for Nuclear Physics these relations were tested by measuring lifetimes of excited states in (π9/2) n isotones with N = 50 and N = 126 over the last years. The studies started in the two-proton nucleus 210 Po where the abnormal B(E2:2 1 + → 0 1 + ) value was remeasured, providing important input for the other N = 126 configurations. Then lifetimes of excited states in 211 At were measured using the electronic γ-γ fast timing technique, the Recoil Distance Doppler Shift (RDDS) method, and the Doppler Shift Attenuation (DSA) method. Very good agreement with the analytical single -j calculation is obtained. For N = 50 isotones, we recently started by measuring the previously unknown B(E2:4 1 + → 2 1 + ) value in 92 Mo needed for the prediction of other N = 50 isotones. We also report on experiments on 93 Tc and 94 Ru.

The A = 100 mass region is of special interest due to a rapid shape transition from nearly spherical to strongly deformed shapes by going from neutron number 58 to 60, especially pronounced in the Sr and Zr isotopes. The sudden change of the ground-state deformation can be explained by an evolution of the single particle energies with increased proton and neutron occupation and an additional spin orbital partner interaction which leads to a change of the order of the single particle energies. Another explanation is given by the interplay between normal spherical and well deformed intruder configurations which lead to shape coexistence and sudden inversion of the ground-state configuration at N = 60. To further examine this intricate phenomenon, lifetimes of low-lying excited states in the nuclei 99Zr and 99Nb were determined using the γ-γ fast-timing techniques and an experimental setup consisting of four LaBr3(Ce) detectors. Neutron rich A = 99 fragments were produced in neutron-induced fission and delivered by the LOHENGRIN fission-fragment separator at the Institut Laue-Langevin in Grenoble, France. The experimental results are compared to two different calculations in the framework of the interacting boson-fermion model and discussed in the context of shape transition and shape coexistence.

In this study, the lifetime of the 2 + 1 state of 206 Po was measured by means of the Recoil Distance Doppler Shift method. The determined B ( E 2; 2 + 1 → 0 + 1 ) value shows that the 2 + 1 state of 206 Po is of collective nature. The results were compared with shell-model calculations based on two different effective interactions.

Lifetime measurements with the recoil distance Doppler-shift technique have been performed to determine yrast E2 transition strengths in 178Pt. The experimental data are related to those on neighboring Pt isotopes, especially recent data on 180Pt, and compared to calculations within the interacting boson model and a Hartree-Fock Bogoliubov approach. These models predict prolate deformed ground states in Pt isotopes close to neutron midshell consistent with the experimental findings. Further, evidence was found that the prolate intruder structure observed in neutron-deficient Hg isotopes that is minimum in energy in 182Hg becomes the ground state configuration in 178Pt and neighboring 180Pt with nearly identical transition quadrupole moments. The new data on 178Pt are further discussed in the context of the systematics along the Pt isotopic chain with respect to a possible sharp shape transition towards a weakly deformed or a quasi-vibrational ground state whereas the prolate structure increases in energy in 174,176Pt and becomes an intruder configuration similar to, for example, 180,182Hg.

Lifetimes of excited states of 124Ba were measured by the Recoil Distance Doppler Shift (RDDS) technique. The γ-ray coincidence data were analysed by the Differential Decay Curve method (DDCM). The trend of the experimentally deduced normalized B(E2) values reveals a drop at the 8+1 state, which may be caused by structural changes in the backbending region.

Low-lying yrast states in 204Po and 206Po have been investigated by the γ-γ fast timing technique with LaBr3(Ce) detectors. Excited states of these nuclei were populated in the 197Au(11B,4n) and the 198Pt(12C,4n) fusion-evaporation reactions, respectively, at the FN-Tandem Facility at the University of Cologne. The lifetimes of the 4+1 states in both nuclei were measured, along with an upper limit for the 2+1 state in 204Po. The preliminary results are discussed in the scope of the systematic behavior of the transition strengths between yrast states in polonium isotopes.

Projectile Coulomb excitation experiments were performed at HIE-ISOLDE at CERN with the radioactive ion beams of 140Nd and 142Sm. Ions with an energy of 4:62 MeV/A were impinging on a 1.45 mg/cm2 thick 208Pb target. The γ-rays depopulating the Coulomb-excited states were recorded by the HPGe-array MINIBALL and scattered particles were detected by a double-sided silicon strip detector. Experimental intensities were used for the determination of electromagnetic transition matrix elements. A preliminary result of the B(M1; 2+3 → 2+1) of 140Nd and an upper limit for the case of 142Sm are revealing the main fragments of the proton-neutron mixed-symmetry 2+1;ms states.

Prompt gamma rays of cerium and chlorine were investigated with the FaNGaS (Fast Neutron-induced Gamma-ray Spectrometry) instrument operated at the Heinz Maier-Leibnitz Zentrum (MLZ) in Garching. The gamma radiation was emitted from (n,n’), (n,p) and (n,α) reactions induced by the irradiation of a cerium(III) chloride (CeCl 3 ) sample with a beam of fission neutrons. Additionally, a polyvinylchloride (PVC, (C 2 H 3 Cl) n ) sample was irradiated to verify possible interferences between gamma lines of cerium and chlorine. We identified 87 prompt gamma lines of cerium and chlorine. From these, we assigned 58 lines to the (n,n’) reaction in cerium (one for 136 Ce, 41 for 140 Ce and 16 for 142 Ce), 23 to the (n,n’) reaction in chlorine (15 for 35 Cl and 8 for 37 Cl), 5 lines to the 35 Cl(n,p) 35 S reaction and 1 line to the 35 Cl(n,α) 32 P reaction. We present relative intensities and fast-neutron spectrum-averaged partial cross sections of the aforementioned gamma lines and compare them with available literature data. Identification of new lines and discussion of possible errors adds important value to the literature data found to be consistent with our results. In addition, for a counting time of 12 h we estimate the detection limits for cerium and chlorine as 1 and 2 mg, respectively.

Prompt gamma rays of terbium emitted after (n,nʹγ) inelastic scattering reactions induced by irradiation of a terbium(III) hexahydrate (TbCl 3 ·6H 2 O) sample with a beam of fission neutrons were investigated with the instrument FaNGaS (Fast Neutron-induced Gamma-ray Spectrometry) at an angle of 90° between neutron beam and detector. At sample position, the fast-neutron flux was 1.13 × 10 8  cm −2  s −1 and the neutron beam has an average energy of 2.30 MeV. We identified 124 prompt gamma lines from the 159 Tb(n,nʹγ) 159 Tb reaction. Presence of prompt gamma rays from oxygen and chlorine was used for a concise verification of recently published results. Relative gamma-ray intensities, effective cross sections and fast-neutron spectrum-averaged partial production cross sections of the gamma lines are given including comparisons with available literature data. We found a reasonable agreement and the multitude of unreported lines adds decisive value to nuclear spectroscopy. Additionally, we estimated the detection limit of terbium as 1 mg for a counting time of 12 h.