Mon·Jul 5, 2021Monday·July 5, 2021

1. 01*

   Measurements of the electron-helicity asymmetry in the quasi-elastic $\mathrm{A}(\vec{e},e^{\prime }p)$ process

   Tim Kolar · Sebouh J. Paul🇺🇸 · Patrick Achenbach🇩🇪 · Hartmuth Arenhövel · Adi Ashkenazi🇺🇸 · Jure Beričič🇺🇸 · Ralph Böhm🇩🇪 · Damir Bosnar🇭🇷 · Tilen Brecelj🇸🇮 · Ethan Cline🇺🇸 · Erez O. Cohen🇮🇱 · Michael O. Distler🇩🇪 and 34 other authors

   We present measurements of the electron helicity asymmetry in quasi-elastic proton knockout from ${}^2$H and ${}^{12}$C nuclei by polarized electrons. This asymmetry depends on the fifth structure function, is antisymmetric with respect to the scattering plane, and vanishes in the absence of final-state interactions, and thus it provides a sensitive tool for their study. Our kinematics cover the full range in off-coplanarity angle ${\varphi }_{pq}$, with a polar angle ${\theta }_{pq}$ coverage up to about 8 degrees. The missing energy resolution enabled us to determine the asymmetries for knock-out resulting in different states of the residual ${}^{11}$B system. We find that the helicity asymmetry for $p$-shell knockout from ${}^{12}$C depends on the final state of the residual system and is relatively large (up to $\approx 0.16$), especially at low missing momentum. It is considerably smaller (up to $\approx 0.01$) for $s$-shell knockout from both ${}^{12}$C and ${}^2$H. The data for ${}^2$H are in very good agreement with theoretical calculations, while the predictions for ${}^{12}$C exhibit differences with respect to the data.

   nucl-exPLB(2022)·4 citations
2. 02*

   Isovector giant monopole and quadrupole resonances in a Skyrme energy density functional approach with axial symmetry

   Kenichi Yoshida🇯🇵

   [Background] Giant resonance (GR) is a typical collective mode of vibration. The deformation splitting of the isovector (IV) giant dipole resonance is well established. However, the splitting of GRs with other multipolarities is not well understood. [Purpose] I explore the IV monopole and quadrupole excitations and attempt to obtain the generic features of IV giant resonances in deformed nuclei by investigating the neutral and charge-exchange channels simultaneously. [Method] I employ a nuclear energy-density functional (EDF) method: the Skyrme-Kohn-Sham-Bogoliubov and the quasiparticle random-phase approximation are used to describe the ground state and the transition to excited states. [Results] I find the concentration of the monopole strengths in the energy region of the isobaric analog or Gamow-Teller resonance irrespective of nuclear deformation, and the appearance of a high-energy giant resonance composed of the particle-hole configurations of $2\hslash {\omega }_0$ excitation. Splitting of the distribution of the strength occurs in the giant monopole and quadrupole resonances due to deformation. The lower $K$ states of quadrupole resonances appear lower in energy and possess the enhanced strengths in the prolate configuration, and vice versa in the oblate configuration, while the energy ordering depending on $K$ is not clear for the $J=1$ and $J=2$ spin-quadrupole resonances. [Conclusions] The deformation splitting occurs generously in the giant monopole and quadrupole resonances. The $K$-dependence of the quadrupole transition strengths is largely understood by the anisotropy of density distribution.

   ↳ nucl-thnucl-exPRC(2021)·3 citations
3. 03*

   Evaluation of the in-situ Performance of Neutron Detectors based on EJ-426 Scintillator Screens for Spent Fuel Characterization

   Hanno Perrey🇸🇪 · Linus Ros · Mikael Elfman🇸🇪 · Ulrika Bäckström · Per Kristiansson · Anders Sjöland

   The reliable detection of neutrons in a harsh gamma-ray environment is an important aspect of establishing non-destructive methods for the characterization of spent nuclear fuel. In this study, we present results from extended in-situ monitoring of detector systems consisting of commercially available components: EJ-426, a ${}^6$Li-enriched solid-state scintillator material sensitive to thermal neutrons, and two different types of Hamamatsu photomultiplier tubes (PMT). Over the period of eight months, these detectors were operated in close vicinity to spent nuclear fuel stored at the interim storage facility CLAB, Oskarshamn, Sweden. At the measurement position the detectors were continuously exposed to an estimated neutron flux of approx. 280 n/s $\cdot$ cm${}^2$ and a gamma-ray dose rate of approx. 6 Sv/h. Using offline software algorithms, neutron pulses were identified in the data. Over the entire investigated dose range of up to 35 kGr, the detector systems were functioning and were delivering detectable neutron signals. Their performance as measured by the number of identified neutrons degrades down to about 30% of the initial value. Investigations of the irradiated components suggest that this degradation is a result of reduced optical transparency of the involved materials as well as a reduction of PMT gain due to the continuous high currents. Increasing the gain of the PMT through step-ups of the applied high voltage allowed to partially compensate for this loss in detection sensitivity. The integrated neutron fluence during the measurement was experimentally verified to be in the order of $5\cdot 10^9$ n/cm${}^2$. The results were interpreted with the help of MCNP6.2 simulations of the setup and the neutron flux.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.A(2021)·3 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.