[en] The relative light yields of NE-213 and LAB-based liquid scintillators to electrons were determined in the electron energy range 5-1600 keV using a combination of monoenergetic photon sources and a Compton spectrometer. The light yield was found to be proportional to energy for both types of scintillator and expected deviations below 100 keV were described successfully applying Birks' law. Digital pulse-shape discrimination in a mixed n-γ field of a ²⁵²Cf source was investigated for LAB+PPO and LAB+PPO+bis-MSB and compared to NE-213. In combination with these two solutes, LAB shows poorer abilities to separate neutron-induced pulses from photon-induced ones.

[en] To improve the properties and performance of thin layers produced by molecular plating as targets for nuclear experiments investigations with lanthanide elements (i.e., natural Nd and ¹⁴⁷Sm-enriched Sm) were carried out. Plating parameters like roughness of the deposition substrate, plating solvent, electrolyte concentration, and applied current density were varied. The influence of each parameter on the properties of the layers was studied by characterizing the deposits. The characterizations showed that nuclear targets perform differently depending on their layer properties. The results obtained from the investigations were applied for the quantitative preparation of homogeneous large-area (i.e., 42 cm²) ²⁴²Pu targets to be used for transmutation-relevant experiments. (author)

[en] Photo-absorption experiment on Ca-40 up to the neutron threshold at 15.6 MeV was measured at the bremsstrahlung facility of γELBE in Helmholtz-Zentrum Dresden Rossendorf. Gamma strength function of Ca-40 which is one of the main component in the human body is basic physical quantity in the radiation treatment. In this study, we performed the precise measurement of gamma-ray transitions from excited Ca-40 to evaluate information related to the nuclear structure. (author)

[en] At the superconducting electron accelerator ELBE at Helmholtz-Zentrum Dresden-Rossendorf the compact neutron time-of-flight facility nELBE has been built. There, neutrons in the kinetic energy region from some tens of keV to a few MeV are produced by means of electrons impinging onto a liquid lead target. The emitted neutron spectrum is well suited for measurements of cross sections of fast-neutron nuclear interactions relevant to the transmutation of nuclear waste. To study inelastic neutron scattering a rather unique double-time-of-flight was developed measuring both emitted particles, i.e., the scattered neutron and the de-excitation photon, in coincidence. By this method the inelastic scattering cross section can be measured with a continuous neutron source without the knowledge of the decay scheme of the sample nucleus. Beside inelastic scattering also transmission experiments to measure the total neutron cross section were performed and for the future neutron fission experiments are under preparation.

[en] 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(γ,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. (paper)

[en] The neutron time of flight facility nELBE, produces fast neutrons in the energy range from 0.1 MeV to 10 MeV by impinging a pulsed relativistic electron beam on a liquid lead circuit. The short beam pulses (about 10 ps) and a small radiator volume give an energy resolution better than 1% at 1 MeV using a short flight path of about 6 m, for neutron TOF measurements. The present neutron source provides 2 - 10⁴ n/cm²*s at the target position using an electron charge of 77 pC and 100 kHz pulse repetition rate. This neutron intensity enables to measure neutron total cross section with a 2%-5% statistical uncertainty within a few days. In February 2008, neutron radiator, plastic detector and data acquisition system were tested by measurements of the neutron total cross section for ¹⁸¹Ta and ²⁷Al. Measurement of ¹⁸¹Ta was chosen because of the lack of high quality data in an energy region below 700 keV. The total neutron cross section for ²⁷Al was measured as a control target, since there exists data for ²⁷Al with high resolution and low statistical error. It appears that in the case of high count rate TOF experiments it is necessary to collect and record dead-time data for each event in order to get correct dead time values for every channel. If dead-time data per event can not be collected by a system, a minimum requirement is to collect conversion dead-time spectra. As it is shown this information is sufficient to analyse data. In our case we managed to reproduce dead-time spectra by building up a dedicated setup. The conversion dead-time distribution was adjusted to the ²⁷Al data., by using this information we obtained total neutron cross section for ¹⁸¹Ta in agreement with measurements

[en] The compact neutron-time-of-flight facility nELBE at the superconducting electron accelerator ELBE of Helmholtz-Zentrum Dresden-Rossendorf is currently being rebuilt. As the neutron radiator consists of a liquid-lead circuit no moderated neutrons are produced and also the background from capture gamma rays is very small. The useful neutron spectrum extends from some tens of keV to about 10 MeV. nELBE is intended to deliver cross section data of fast neutron nuclear interactions e.g. for the transmutation of nuclear waste and an improvement of neutron physical simulations of innovative nuclear systems. The new experimental hall will allow measurements of angular distributions in neutron scattering. Inelastic neutron scattering, e.g. on ⁵⁶Fe, has been studied with a double time-of-flight setup and with photon detectors to measure the gamma rays produced in the process. The neutron total cross sections of Au and Ta were determined in a transmission experiment. (author)

[en] The effect of temperature changes on the light output of LAB based liquid scintillator is investigated in a range from -5 to 30 C with α-particles and electrons in a small scale setup. Two PMTs observe the scintillator liquid inside a cylindrically shaped aluminum cuvette that is heated or cooled and the temperature dependent PMT sensitivity is monitored and corrected. The α-emitting isotopes in dissolved radon gas and in natural Samarium (bound to a LAB solution) excite the liquid scintillator mixtures and changes in light output with temperature variation are observed by fitting light output spectra. Furthermore, also changes in light output by compton electrons, which are generated from external calibration γ-ray sources, is analysed with varying temperature. Assuming a linear behaviour, a combined negative temperature coefficient of (-0.29 ± 0.01)%/ C is found. Considering hints for a particle type dependency, electrons show (-0.17 ± 0.02)%/ C, whereas the temperature dependency seems stronger for α-particles, with (-0.35 ± 0.03)%/ C. Due to a high sampling rate, a pulse shape analysis can be performed and shows an enhanced slow decay component at lower temperatures, pointing to reduced non-radiative triplet state de-excitations. (orig.)

[en] The nELBE beamline at Forschungszentrum Dresden-Rossendorf (FZD) provides intense neutron beams by stopping primary electrons (from a superconducting LINAC) in a liquid lead target, where neutrons are produced by Bremsstrahlung photons via (gamma,n) reactions. With the aim of increasing the neutron yield through the enhancement of the electron beam energy (from the current 40 MeV limit up to 50 MeV), as well as of minimizing several sources of background noise that are presently affecting the measurements, a new neutron beam-line and a new, larger neutron experimental room have been designed. The optimization of the neutron/photon ratio, the minimization of the backscattered radiation from the walls and the possibility to have better experimental conditions are the main advantages of the new design. To optimize the beamline, extensive simulations with the particle interaction and transport code FLUKA have been performed. Starting from the primary electron beam, both the photon and neutron radiation fields have been fully characterized. To have a cross-check of the results, the calculated values of the neutron yields at different energies of the primary beam have been compared both with an independent simulation with the MCNP code and with analytical calculations, obtaining a very satisfactory agreement at the level of few percent. The evaluated radiation fields have been used to optimize the direction of the new neutron beamline, in order to minimize the photon flash contribution. A general overview of the new photo-neutron source, together with all the steps of the optimization study, is here presented and discussed. (authors)

[en] The relative light yields of NE-213 and linear alkyl benzene (LAB) based liquid scintillators from electrons were determined in the electron energy range 13–1600 keV using a combination of monoenergetic γ sources and a Compton spectrometer. The light yield was found to be proportional to energy for both types of scintillator and expected deviations below 100 keV were described successfully applying Birks’ law. A description of the Cherenkov light contribution to the total light yield was achieved for both detectors and is in agreement with the electromagnetic theory of fast particles in matter. Digital pulse-shape discrimination in a mixed n–γ field from a ²⁵²Cf source was investigated for LAB+PPO and LAB+PPO+bis-MSB and compared to NE-213. In combination with these two solutes, LAB shows poorer abilities to separate neutron-induced pulses from γ-induced ones.