The photodissociation of the deuteron is a key reaction in Big Bang nucleosynthesis, but is only sparsely measured in the relevant energy range. To determine the cross section of the d(gamma,n)p reaction we used pulsed bremsstrahlung and measured the time-of-flight of the neutrons. In this article, we describe how the efficiency of the neutron detectors was experimentally determined and how the modification of the neutron spectrum by parts of the experimental setup was simulated and corrected.

The dipole strength in the nucleus Pt-196 was investigated using two different experimental methods. The photon spectrum from the deexcitation of a state after cold neutron capture in Pt-195 is influenced by the dipole strength and nuclear level density in Pt-196 as is the gamma-ray spectrum from photon scattering on Pt-196. In a combined analysis of data from the research reactor in Budapest and the bremsstrahlung facility at the ELBE accelerator in Dresden, the GEANT4 code was used to calculate detector response and efficiency. Also the influence of non-nuclear scattered photons was determined and allows us to take into account the continuum of unresolved states. The statistical code gamma DEX was used to estimate branching ratios and compare simulated and experimental spectra. Using information from both experiments it was possible to obtain a temperature parameter of 600 keV for the constant temperature level density model. For the dipole strength a small extra strength over the tail of the giant dipole resonance in the region below the neutron separation energy was found. DOI: 10.1103/PhysRevC.87.044306

The dipole strength function and the nuclear level density of the compound nucleus Se-78 were studied in a combined analysis of a cold neutron capture experiment on Se-77 performed at the research reactor in Budapest and a photon-scattering experiment on Se-78 performed at the electron linear accelerator ELBE with bremsstrahlung produced at a kinetic electron energy of 11.5 MeV. In the combined analysis we developed the extreme statistical code gamma DEX for the simulation of radiative cascade deexcitations occurring in neutron capture and photon scattering. Comparisons of experimental and simulated neutron capture spectra allow us to estimate a temperature of T = 900 keV for the level density according to the constant-temperature model for Se-78. Using gamma DEX, we were also able to estimate ground-state branching ratios and intensities of inelastic transitions for states in Se-78 excited via photon scattering. In this way, we derived the photoabsorption cross section from 4 MeV up to the neutron separation energy from the measured photon-scattering data. The results obtained match the photoabsorption cross section derived from (gamma, n) measurements and show an enhancement of dipole strength around 9 MeV.

The electromagnetic dipole strength of the nucleus Ba-136 has been investigated. Two measurements were performed with electron energies of 7.0 and 11.4 MeV at the bremsstrahlung facility at the ELBE accelerator of the Helmholtz-Zentrum Dresden-Rossendorf. Photon scattering experiments on the same nucleus have been performed at the high-intensity gamma-ray source (HI gamma S) facility of the Triangle Universities Nuclear Laboratory between 4.7 and 9.3 MeV. The GEANT4 code has been used to determine detector response and non-nuclear scattered events. Thus it is possible to account for the dipole strength in the quasicontinuum of unresolvable transitions. A statistical code was used to simulate inelastic transitions and to determine the branching ratios of transitions to the ground state. The resulting photoabsorption cross section is compared to quasiparticle random-phase approximation and relativistic quasiparticle time blocking approximation calculations.

Intense positron sources require the pair production process for the positron generation. In case a pulsed positron source shall be constructed, a superconducting LINAC-based accelerator allows generating the required final time structure for the electron beam. This simplifies the positron beam construction. The first such setup, the EPOS system (ELBE Positron Source) at the Forschungszentrum Dresden-Rossendorf (FZD), is described.

The 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 La-139 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 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 La-139 and compared with results of calculations on the basis of a quasiparticle-random-phase approximation using an instantaneous-shape sampling.

R. Schwengner,1 R. Massarczyk,1,2 B. A. Brown,3 R. Beyer,1 F. Dönau,1 M. Erhard,1,* E. Grosse,1,2 A. R. Junghans,1 K. Kosev,1 C. Nair,1,† G. Rusev,1,‡ K. D. Schilling,1 and A. Wagner1 1Institut für Strahlenphysik, Forschungszentrum Dresden-Rossendorf, D-01314 Dresden, Germany 2Institut für Kernund Teilchenphysik, Technische Universität Dresden, D-01062 Dresden, Germany 3National Superconducting Cyclotron Laboratory, Michigan State University, East Lansing, Michigan 48824, USA (Received 9 March 2010; revised manuscript received 6 April 2010; published 21 May 2010)

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.

Photoactivation measurements on Sm-144 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 Sm-144(gamma,n) reaction is compared with the calculated yield using cross sections from previous photoneutron experiments. The activation yields measured for all disintegration channels Sm-144(gamma,n), (gamma,p), and (gamma,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.

A. Makinaga,1,* R. Schwengner,2 G. Rusev,3 F. Dönau,2 S. Frauendorf,2,4 D. Bemmerer,2 R. Beyer,2 P. Crespo,2,† M. Erhard,2,‡ A. R. Junghans,2 J. Klug,2,§ K. Kosev,2 C. Nair,2,‖ K. D. Schilling,2 and A. Wagner2 1Department of Physics, Konan University, Okamoto 8-9-1, Higashinada, Kobe 658-8501, Japan 2Institut für Strahlenphysik, Forschungszentrum Dresden-Rossendorf, D-01314 Dresden, Germany 3Department of Physics, Duke University, and Triangle Universities Nuclear Laboratory, Durham, North Carolina 27708, USA 4Department of Physics, University of Notre Dame, Notre Dame, Indiana 46556, USA (Received 4 June 2010; published 16 August 2010)

In explosive nucleosynthesis temperatures are high enough for photodisintegration reactions to occur, e.g. leading to the production of p-process nuclei. I n order to understand the reaction rates of element production and element disruption we start ed an experimental program at the new bremsstrahlung facility of the superconducting electr on accelerator ELBE of FZ DresdenRossendorf. The bremsstrahlung facility and the detector s etup are designed such that the scattering of photons from nuclei and the photodisintegration o f uclei around the particle separation energies can be studied under optimized background conditi s. In activation measurements with bremsstrahlung at end-point energy from 10.0 to 16.5 MeV ( γ,p), (γ,n) and (γ,α) reactions of 92,100Mo have been studied. Our activation yields can be described within a factor 2-3 or better with calculations using the cross sections from recent Haus er-Feshbach models.

This paper focuses on the evaluation of a microchannel-plate photomultiplier tube (MCP-PMT) as a candidate detector, suitable for positron lifetime studies. Several properties of MCP-PMTs, such as their fast time response, compact size, low susceptibility to magnetic fields, relatively high gain and the low power consumption make them attractive for positron lifetime spectroscopy. The preliminary tests were performed with a 85001-501 Burle PlanaconTM photomultiplier tube assembly. Initial measurements were conducted with a pulsed Picosecond Injection Laser (PiLas) system. The engineering sample of the 85001 exhibits a transit-time-spread (TTS) of 110ps (FWHM). Further timing experiments showing the suitability of the device as Cherenkov detector are presented. For the first time, a conventional positron lifetime spectrum of a Cz-Si probe measured with a spectrometer, where an MCP-PMT detector is included, has been demonstrated.

The dipole response of the doubly magic nuclide Pb-208 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 (gamma,gamma') data combined with (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.

Two methods based on bremsstrahlung were applied to the stable even Mo isotopes for the experimental determination of the photon strength function covering the high excitation energy range above 4 MeV with its increasing level density. Photon scattering was used up to the neutron separation energies S-n and data up to the maximum of the isovector giant resonance (GDR) were obtained by photoactivation. After a proper correction for multistep processes the observed quasicontinuous spectra of scattered photons show a remarkably good match to the photon strengths derived from nuclear photoeffect data obtained previously by neutron detection and corrected in absolute scale by using the new activation results. The combined data form an excellent basis to derive a shape dependence of the E1 strength in the even Mo isotopes with increasing deviation from the N = 50 neutron shell (i.e., with the impact of quadrupole deformation and triaxiality). The wide energy coverage of the data allows for a stringent assessment of the dipole sum rule and a test of a novel parametrization developed previously which is based on it. This parametrization for the electric dipole strength function in nuclei with A > 80 deviates significantly from prescriptions generally used previously. In astrophysical network calculations it may help to quantify the role the p-process plays in cosmic nucleosynthesis. It also has impact on the accurate analysis of neutron capture data of importance for future nuclear energy systems and waste transmutation.

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.