M. Kempe

Fast neutron inelastic scattering at the nELBE facility

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.

Prototyping a 2m × 0.5m MRPC-based neutron TOF-wall with steel converter plates

A 2 m ? 0.5 m large prototype of an MRPC-based (Multi-gap Resistive Plate Chamber) neutron Time-Of-Flight-wall for detecting relativistic neutrons in an energy range from 200 MeV to 1 GeV was successfully designed and realized. It consists of steel plates which convert neutrons via hadronic interactions into charged particles, followed by a 2 ? 2 gap MRPC-structure to detect the charged particles. Tests were carried out using 30 MeV electrons with an energy close to the minimum of ionization in order to study the properties of the prototype achieving an efficiency larger than 90 % and a time resolution ?t better than 100 ps. For units with an active area of 40 cm ? 20 cm and otherwise the same design, quasi-monochromatic neutrons with a peak energy of 175 MeV were utilized to study their response to relativistic neutrons. Detailed Monte Carlo simulations were performed both for the small and for the large modules to simulate their properties to both neutrons and electrons and to study the performance of the final neutron detector assembly with an area of 2 m ? 2 m for single-neutron and multi-neutron events.

Annihilation Lifetime Spectroscopy Using Positrons from Bremsstrahlung Production

A new type of a positron annihilation lifetime spectroscopy (PALS) system has been set up at the superconducting electron accelerator ELBE [ at Helmholtz-Zentrum Dresden-Rossendorf. In contrast to existing source-based PALS systems, the approach described here makes use of an intense photon beam from electron bremsstrahlung which converts through pair production into positrons inside the sample under study. The article focusses on the production of intense bremsstrahlung using a superconducting electron linear accelerator, the production of positrons inside the sample under study, the efficient detector setup which allows for annihilation lifetime and Doppler-broadening spectroscopy simultaneously. Selected examples of positron annihilation spectroscopy are presented.

Measurement of the photodissociation of the deuteron at energies relevant to Big Bang nucleosynthesis

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.

Response of Multi-strip Multi-gap Resistive Plate Chamber

A prototype of Multi-strip Multi-gap Resistive Plate chamber (MMRPC) with active area 40 cm × 20 cm has been developed at SINP, Kolkata. Detailed response of the developed detector was studied with the pulsed electron beam from ELBE at Helmholtz-Zentrum Dresden-Rossendorf. In this report the response of SINP developed MMRPC with different controlling parameters is described in details. The obtained time resolution (σt) of the detector after slew correction was 91.5 ± 3 ps. Position resolution measured along (σx) and across (σy) the strip was 2.8±0.6 cm and 0.58 cm, respectively. The measured absolute efficiency of the detector for minimum ionizing particle like electron was 95.8±1.3 %. Better timing resolution of the detector can be achieved by restricting the events to a single strip. The response of the detector was mainly in avalanche mode but a few percentage of streamer mode response was also observed. A comparison of the response of these two modes with trigger rate was studied.

EXPERIMENTS WITH NEUTRONS AND PHOTONS AT ELBE

We describe the photo-neutron source at the superconducting electron accelerator ELBE of the Helmholtz-Zentrum Dresden-Rossendorf and present first experiments to determine cross sections of inelastic scattering of neutrons in the MeV range. We discuss analysis and results of photon-scattering experiments using the bremsstrahlung facility at ELBE. A consistent determination of the dipole strength function from the combination of photon scattering and radiative neutron capture is presented.