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The inelastic scattering of fast neutrons from 7Li nuclei was investigated at the nELBE neutron-time-of-flight facility. This process has technological implications in fusion and fission reactors. In the former it could create an intense γ-ray field causing heating and radiation damage, in the latter it could strongly influence the neutron energy spectrum and therefore the neutronics of e.g. novel reactor concepts like the molten salt reactor. Furthermore the γ-ray production cross section of 7Li is a very good case to be used as an alternative for neutron fluence determination to enable relative measurements of neutron-induced reactions. Inelastic neutron scattering on 7Li leads to the production of a 478 keV γ-ray from the first excited state of 7Li. The next higher lying state in this nucleus at 4630 keV already undergoes break up into an α-particle and a triton. The angular distribution of the γ-rays after inelastic neutron scattering is isotropic and has negligible internal conversion. The threshold energy is low enough to be able to cover a large range of neutron energy and the cross section of about 0.2 barn is reasonably high to enable good statistics within a feasible measurement time. At nELBE the photon production cross section was determined by irradiated a disc of LiF with a neutrons of energies ranging from 100 keV to about 10 MeV. The target position was surounded by a setup of 7 LaBr3 scintillation detectors and 4 high-purity germanium detectors to detect the 478 keV de-excitation gamma-rays. A 235U fission chamber was used to determine the incoming neutron flux. All details of the experiment and the data analysis will be explained. The final results will be compared to previous measurement done e.g. at the GELINA facility.

Secondary high-energy neutrons are produced when high-energy particles (of several GeV) interact with matter as it is the case for cosmic radiation impinging on the Earth’s atmosphere, during ion-beam therapy or on shielding at high-energy particle accelerators. Especially, after traversing a large amount of matter, the residual neutron energy spectrum exhibits two energy regions which mainly contribute to the total ambient dose equivalent: around 1 MeV (evaporation peak) and around 100 MeV. Particle detectors and dosemeters used in such a radiation environment need a full characterization which requires measurements in neutron reference radiation fields. Up to 20 MeV in energy such fields are maintained by PTB in Germany, IRSN in France or NPL in United Kingdom. At higher neutron energies the neutron facility at iThemba LABS together with the neutron metrology by PTB provides the possibility to characterize instruments at neutron energies around 100 MeV. This was the aim of the EURADOS campaign in 2011.

To ensure the validity of their national standards, National Metrology Institutes, NMIs, participate regularly in international comparisons. In the area of neutron metrology, Section III of the Consultative Committee for Ionizing Radiation is in charge of the organization of these comparisons. From September 2011 to October 2012, the eleventh key comparison, named CCRI(III)-K11, took place at the AMANDE facility of the LNE-IRSN, in France. Participants from nine NMIs came with their own primary reference instruments, or instruments traceable to primary standards, with the aim of determining the neutron fluence, at 1 m distance from the target in vacuum, per monitor count at four monoenergetic neutron fields: 27 keV, 565 keV, 2.5 MeV and 17 MeV. The key comparison reference values (KCRV) were evaluated as the weighted mean values of the results provided by seven participants. The uncertainties of each KCRV are between 0.9 % and 1.7 %. The degree of equivalence (DoE), defined as the deviation of the result reported by the laboratories for each energy from the corresponding KCRV, and the associated expanded uncertainty are also reported and discussed.

GSI Scientific Report 2013 - GSI Report 2014-1

Normal human Y and inverted Y chromosomes were chosen for physical fluorescence in situ hybridization (FISH) mapping of RBM and DAZ probes for the relative positioning of the RBM and DAZ gene clusters in interval 6 of the human Y chromosome. The inversion breakpoint in Yq11.23 turned out to be distal to the DAZ gene cluster, as the entire DAZ signal appears in the short arm of the inv(Y) chromosome. On the contrary, this inversion breakpoint in Yq11.23 divides the RBM signal cluster, leaving a weaker signal on the long arm while bringing the main RBM signal to the short arm of the inv(Y) chromosome. Thus, it can be concluded that, in contrast to previous claims, part of the RBM gene cluster is located distally to the DAZ gene cluster in deletion interval 6 of the human Y chromosome.

Total neutron cross section measurements at nELBE

The nELBE time of flight facility has become operational at the ELBE superconducting linear accelerator at Forschungszentrum Dresden-Rossendorf. The commissioning started with a beamtime in November 2007 and again in February 2008. With a short flight path of approximately 5 m a 100 kHz repetition rate of the electron beam was used to measure neutron time of flight in the energy range of 0.1 – 10 MeV. The electron beam energy was 25, and 33 MeV with 1-5 A of average electron current. The electron beam intensity was kept low to allow in-beam single particle counting. The beam profile of neutrons and photons was determined with two plastic scintillators mounted on a translation stage. The neutron time of flight spectrum was determined with plastic scintillators with a low detection threshold of ca. 25 keV and with a 235-U fission chamber from PTB, which also allowed to measure the absolute neutron fluence and estimate the background of low energy neutrons. The transmission of the electron beam line was optimized to reduce the bremsstrahlung background not coming from the photo-neutron source. First transmission measurements of total neutron cross sections were made. Beam time at nELBE is available as of now and all potential users are invited to submit proposals for experiments. TAA funding through EFNUDAT can be provided.

Proton recoil detectors for neutron time-of-flight measurements have been developed, which have a good time and position resolution and at the same time a relatively high efficiency for neutrons with kinetic energies of about 30 keV.