Mon·Nov 2, 2015Monday·November 2, 2015

1. 01*

   Photoproduction of ${\pi }^0$-pairs off protons and off neutrons

   M. Dieterle🇨🇭 · M. Oberle🇨🇭 · J. Ahrens🇩🇪 · J.R.M. Annand🇬🇧 · H.J. Arends🇩🇪 · K. Bantawa🇺🇸 · P.A. Bartolome🇩🇪 · R. Beck🇩🇪 · V. Bekrenev🇷🇺 · H. Berghäuser🇩🇪 · A. Braghieri🇮🇹 · D. Branford🇬🇧 and 62 other authors

   Total cross sections, angular distributions, and invariant-mass distributions have been measured for the photoproduction of ${\pi }^0{\pi }^0$ pairs off free protons and off nucleons bound in the deuteron. The experiments were performed at the MAMI accelerator facility in Mainz using the Glasgow photon tagging spectrometer and the Crystal Ball/TAPS detector. The accelerator delivered electron beams of 1508 and 1557~MeV, which produced bremsstrahlung in thin radiator foils. The tagged photon beam covered energies up to 1400~MeV. The data from the free proton target are in good agreement with previous measurements and were only used to test the analysis procedures. The results for differential cross sections (angular distributions and invariant-mass distributions) for free and quasi-free protons are almost identical in shape, but differ in absolute magnitude up to 15\%. Thus, moderate final-state interaction effects are present. The data for quasi-free neutrons are similar to the proton data in the second resonance region (final state invariant masses up to $\approx$1550~MeV), where both reactions are dominated by the $N(1520)3/2^{-}\to \Delta (1232)3/2^{+}\pi$ decay. At higher energies, angular and invariant-mass distributions are different. A simple analysis of the shapes of the invariant-mass distributions in the third resonance region is consistent with strong contributions of an $N^{\star }\to N\sigma$ decay for the proton, while the reaction is dominated by a sequential decay via a $\Delta \pi$ intermediate state for the neutron. The data are compared to predictions from the Two-Pion-MAID model and the Bonn-Gatchina coupled channel analysis.

   nucl-exEPJA(2015)·29 citations
2. 02*

   Neutron capture and the antineutrino yield from nuclear reactors

   Patrick Huber🇺🇸 · Patrick Jaffke🇺🇸

   We identify a new, flux-dependent correction to the antineutrino spectrum as produced in nuclear reactors. The abundance of certain nuclides, whose decay chains produce antineutrinos above the threshold for inverse beta decay, has a nonlinear dependence on the neutron flux, unlike the vast majority of antineutrino producing nuclides, whose decay rate is directly related to the fission rate. We have identified four of these so-called nonlinear nuclides and determined that they result in an antineutrino excess at low-energies below 3.2MeV, dependent on the reactor thermal neutron flux. We develop an analytic model for the size of the correction and compare it to the results of detailed reactor simulations for various real existing reactors, spanning 3 orders of magnitude in neutron flux. In a typical pressurized water reactor the resulting correction can reach 0.9% of the low energy flux which is comparable in size to other, known low-energy corrections from spent nuclear fuel and the non-equilibrium correction. For naval reactors the nonlinear correction may reach the 10% level.

   ↳ hep-phhep-exnucl-exnucl-thPRL(2016)·27 citations
3. 03*

   Characteristics of a thermal neutrons scintillation detector with the [ZnS(Ag)+${}^6$LiF] at different conditions of measurements

   V.V. Alekseenko · I.R. Barabanov🇷🇺 · R.A. Etezov · Yu.M. Gavrilyuk🇷🇺 · A.M. Gangapshev🇷🇺 · A.M. Gezhaev · V.V. Kazalov🇷🇺 · A.Kh. Khokonov · V.V. Kuzminov🇷🇺 · S.I. Panasenko🇺🇦 · S.S. Ratkevich🇺🇦

   A construction of a thermal neutron testing detector with a thin [ZnS(Ag)+${}^6$LiF] scintillator is described. Results of an investigation of sources of the detector pulse origin and the pulse features in a ground and underground conditions are presented. Measurements of the scintillator own background, registration efficiency and a neutron flux at different objects of the BNO INR RAS were performed. The results are compared with the ones measured by the ${}^3$He proportional counter.

   ↳ physics.ins-detnucl-ex0 citations

* Reconstructed cohort: no mailing for this day survives in the archive. Papers are grouped by their submission times and arXiv's announcement cut-off, assuming announcement without delay; positions follow identifier order. Validated at ~91% exact-day agreement against the archived era.