Tue·Apr 24, 2018Tuesday·April 24, 2018

1. 01*

   Experimental $\gamma$-decay strength in ${}^{59,60}$Ni compared with microscopic calculations

   T. Renstrøm🇳🇴 · G. M. Tveten🇳🇴 · J. E. Midtbø🇳🇴 · H. Utsunomiya🇯🇵 · O. Achakovskiy · S. Kamerdzhiev · B. Alex Brown🇺🇸 · A. Avdeenkov · T. Ari-izumi🇯🇵 · A. Görgen🇳🇴 · S. M. Grimes🇺🇸 · M. Guttormsen🇳🇴 and 11 other authors

   Nuclear level densities and $\gamma$-ray strength functions have been extracted for ${}^{59,60}\mathrm{Ni}$, using the Oslo method on data sets from the ${}^{60}$Ni(${}^3$He,${}^3$He${}^{\prime }\gamma$)${}^{60}$Ni and ${}^{60}$Ni(${}^3$He,$\alpha \gamma$)${}^{59}$Ni reactions. Above the neutron separation energy, S${}_n$, we have measured the $\gamma$-ray strength functions for ${}^{61}$Ni and ${}^{60}$Ni in photoneutron experiments. The low-energy part of the ${}^{59,60}$Ni $\gamma$-ray strength functions show an increase for decreasing $\gamma$ energies. The experimental $\gamma$-ray strength functions are compared with $M1$ $\gamma$-ray strength functions calculated within the shell model. The $E1$ $\gamma$-ray strength function of ${}^{60}$Ni has been calculated using the QTBA framework. The QTBA calculations describe the data above $E_{\gamma }\approx$ 7 MeV, while the shell-model calculations agree qualitatively with the low energy part of the $\gamma$-ray strength function. Hence, we give a plausible explanation of the observed shape of the $\gamma$-decay strength.

   nucl-ex5 citations
2. 02*

   The gamma-ray strength function of ${}^{89}$Y and ${}^{90}$Y

   G. M. Tveten🇳🇴 · T. Renstrøm🇳🇴 · A. C. Larsen🇳🇴 · H. Utsunomiya🇯🇵 · K. Stopani · S. Belyshev · M. Guttormsen🇳🇴 · T. Ari-izumi🇯🇵 · F. L. Bello Garrote🇳🇴 · D. L. Bleuel🇺🇸 · Y. Byun · T. K. Eriksen🇳🇴 and 17 other authors

   In this work, we present new data on the ${}^{89}$Y($\gamma$,n) cross section studied with a quasi-monochromatic photon beam produced at the NewSUBARU synchrotron radiation facility in Japan contributing torwards resolving a long standing discrepancy between existing measurements of this cross section. Results for $\gamma$-ray strength function below threshold obtained by applying the Oslo method to ${}^{89}$Y($p,p^{\prime }\gamma$)${}^{89}$Y coincidences combined with the ${}^{89}$Y($\gamma$,n) data this providing experimental data for the $\gamma$-ray strength function of ${}^{89}$Y for $\gamma$ energies in the range of $\approx 1.6$ Mev to $\approx$ 20 MeV. A low-energy enhancement is seen for $\gamma$-rays below $\approx 2.5$ MeV. Shell-model calculations indicate that this feature is caused by strong, low-energy $M1$ transitions at high excitation energies. The nuclear level density and $\gamma$-ray strength function have been extracted from ${}^{89}$Y($d,p\gamma$)${}^{90}$Y coincidences using the Oslo method. Using the ($\gamma ,n$) and ($d,p\gamma$) data as experimental constraints, we have calculated the ${}^{89}$Y($n,\gamma$)${}^{90}$Y cross section with the TALYS reaction code. Our results have been compared with directly measured (n,$\gamma$) cross sections and evaluations. The $N=50$ isotope ${}^{89}$Y is an important bottleneck in the s-process and the magnitude of the ${}^{89}$Y(n,$\gamma )$ cross section is key to understanding how s-process stars produce heavy isotopes.

   nucl-ex2 citations
3. 03*

   Photoneutron cross sections for Ni isotopes: Toward understanding $(n,\gamma )$ cross sections relevant to the weak s-process nucleosynthesis

   H. Utsunomiya🇯🇵 · T. Renstrøm🇳🇴 · G. M. Tveten🇳🇴 · S. Goriely🇧🇪 · S. Katayama🇯🇵 · T. Ari-izumi🇯🇵 · D. Takenaka🇯🇵 · D. Symochko🇩🇪 · B. V. Kheswa🇳🇴 · V.W. Ingeberg🇳🇴 · T. Glodariu🇷🇴 · Y.-W. Lui🇺🇸 and 10 other authors

   Photoneutron cross sections were measured for ${}^{58}$Ni, ${}^{60}$Ni, ${}^{61}$Ni, and ${}^{64}$Ni at energies between the one-neutron and two-neutron thresholds using quasi-monochromatic $\gamma$-ray beams produced in laser Compton-scattering at the NewSUBARU synchrotron radiation facility. The new photoneutron data are used to extract the $\gamma$-ray strength function above the neutron threshold complementing the information obtained by the Oslo method below the threshold. We discuss radiative neutron capture cross sections and the Maxwellian-averaged cross sections for Ni isotopes including ${}^{63}$Ni, a branching point nucleus along the weak s-process path. The cross sections are calculated with the experimentally constrained $\gamma$-ray strength functions from the Hartree-Fock-Bogolyubov plus quasi-particle-random phase approximation based on the Gogny D1M interaction for both $E1$ and $M1$ components and supplemented with the $M1$ upbend.

   nucl-exnucl-thPRC(2018)·22 citations
4. 04*

   Reexamine the nuclear chiral geometry from the orientation of the angular momentum

   Q. B. Chen🇩🇪 · J. Meng🇨🇳

   The paradox on the previous interpretation for the nuclear chiral geometry based on the effective angle has been clarified by reexamining the system with the particle-hole configuration $\pi (1h_{11/2}{)}^1\otimes \nu (1h_{11/2}{)}^{-1}$ and rotor with deformation parameter $\gamma =30^{\circ }$. It is found that the paradox is caused by the fact that the angular momentum of the rotor is much smaller than those of the proton and the neutron near the bandhead. Hence, it does not support a chiral rotation interpretation near the bandhead. The nuclear chiral geometry based on the effective angle makes sense only when the angular momentum of the rotor becomes comparable with those of the proton and the neutron at the certain spin region.

   ↳ nucl-thnucl-exPRC(2018)·41 citations
5. 05*

   Electrical conductivity of Hot and Dense QCD matter at RHIC BES energies: A Color String Percolation Approach

   Pragati Sahoo🇮🇳 · Swatantra Kumar Tiwari🇮🇳 · Raghunath Sahoo🇮🇳

   Recently, transport coefficients viz. shear viscosity, electrical conductivity etc. of strongly interacting matter produced in heavy-ion collisions have drawn considerable interest. We study the normalised electrical conductivity (${\sigma }_{\mathrm{el}}$/T) of hot QCD matter as a function of temperature (T) using the Color String Percolation Model (CSPM). We also study the temperature dependence of shear viscosity and its ratio with electrical conductivity for the QCD matter. We compare CSPM estimations with various existing results and lattice Quantum Chromodynamics (lQCD) predictions with (2+1) dynamical flavours. We find that ${\sigma }_{\mathrm{el}}$/T in CSPM has a very weak dependence on the temperature. We compare CSPM results with those obtained in Boltzmann Approach to Multi-Parton Scatterings (BAMPS) model. A good agreement is found between CSPM results and predictions of BAMPS with fixed strong coupling constant.

   ↳ hep-phhep-exnucl-exnucl-thPRD(2018)·21 citations
6. 06*

   Accurate determination of the absolute 3He/4He ratio of a synthesized helium standard gas (Helium Standard of Japan, HESJ): Towards revision of the atmospheric 3He/4He ratio

   Kenji Mishima🇯🇵 · Hirochika Sumino🇯🇵 · Takahito Yamada🇯🇵 · Sei Ieki🇯🇵 · Naoki Nagakura🇯🇵 · Hidetoshi Otono🇯🇵 · Hideyuki Oide🇮🇹

   The helium standard of Japan, referred to as HESJ, is an inter-laboratory standard for the 3He/4He ratio. While the ratio of 3He and 4He of the HESJ was previously determined by a relative comparison to atmospheric helium, the absolute value of the 3He/4He ratio of the HESJ has not been directly determined yet. Therefore, it relies on the early measurements of that of atmospheric helium. The accuracy of the absolute 3He/4He ratios of the atmosphere and other working standards including HESJ is crucial in some applications of helium isotopes, such as tritium-3He dating, surface-exposure age determination based on cosmogenic 3He, and the accurate measurement of the neutron lifetime. In this work, new control samples of helium gases with 3He/4He ratios of 14, 28, and 42 ppm were fabricated with accuracy of 0.25-0.38% using a gas-handling system for a neutron lifetime experiment at Japan Proton Accelerator Research Complex (J-PARC). The relative 3He/4He ratios of these samples and the HESJ were measured using a magnetic-sector-type, single-focusing, noble gas mass spectrometer with a double collector system. As a result, the absolute 3He/4He ratio of the HESJ was determined as 27.36 +/- 0.11 ppm. The atmospheric 3He/4He ratio was determined as 1.340 +/- 0.006 ppm, based on this work.

   ↳ physics.geo-phnucl-ex1 citation
7. 07*

   Matching of transverse momentum dependent distributions at twist-3

   Ignazio Scimemi🇪🇸 · Alexey Vladimirov🇩🇪

   We derive the leading order matching of the quark generated polarized transverse momentum dependent (TMD) distributions onto the collinear functions at small values of the transverse distance. Starting from the very definition of the TMD operator and performing the light-cone operator product expansion up to twist-3 order, we evaluate each distribution directly in position space. We primarily consider the cases of Sivers, Boer-Mulders and worm-gear functions. The effects of the TMD process dependence on the matching are explicitly shown. We also discuss the moments of TMD distributions which can be relevant for lattice calculations.

   ↳ hep-phhep-exhep-latnucl-ex+1EPJC(2018)·47 citations
8. 08*

   Calculation of atomic spectra and transition amplitudes for superheavy element Db (Z=105)

   Bryce G. C. Lackenby🇦🇺 · Vladimir A. Dzuba🇦🇺 · Victor V. Flambaum🇦🇺

   Atomic spectra and other properties of superheavy element dubnium (Db, Z=105) are calculated using recently developed method combining configuration interaction with perturbation theory (the CIPT method, Dzuba et al, Phys. Rev. A, {\bf 95}, 012503 (2017)). These include energy levels for low-lying states of Db and Db~II, electric dipole transition amplitudes from the ground state of Db, isotope shift for these transitions and ionisation potential of Db. Similar calculations for Ta, which is lighter analog of Db, are performed to control the accuracy of the calculations.

   ↳ physics.atom-phnucl-exPRA(2018)·10 citations
9. 09*

   Particle number conserving BCS approach in the relativistic mean field model and its application to ${}^{32-74}$Ca

   Rong An · Lisheng Geng🇨🇳 · Shisheng Zhang🇨🇳 · Lang Liu

   A particle number conserving BCS approach (FBCS) is formulated in the relativistic mean field (RMF) model. It is shown that the so-obtained RMF+FBCS model can describe the weak pairing limit. We calculate the ground-state properties of the calcium isotopes ${}^{32-74}$Ca and compare the results with those obtained from the usual RMF+BCS model. Although the results are quite similar to each other, we observe an interesting phenomenon, i.e., for ${}^{54}$Ca, the FBCS approach can enhance the occupation probability of the $2p_{1/2}$ single particle level and slightly increases its radius, compared with the RMF+BCS model. This leads to an unusual scenario that although ${}^{54}$Ca is more bound with a spherical configuration but the corresponding size is not the most compact one. We anticipate that such a phenomenon might happen for other neutron rich nuclei and should be checked by further more systematic studies.

   ↳ nucl-thnucl-exCPC(2018)·12 citations
10. 10*

    Covariant quark model for the electromagnetic structure of light nucleon resonances

    G. Ramalho🇧🇷

    We present estimates from the covariant spectator quark model for the electromagnetic transition form factors for the resonances $N(1440){\frac{1}{2}}^{+}$, $N(1535){\frac{1}{2}}^{-}$, $N(1520){\frac{3}{2}}^{-}$ and $\Delta (1232){\frac{3}{2}}^{+}$, at intermediate and large square momentum transfer ($Q^2$). The calculations associated to the $N(1440){\frac{1}{2}}^{+}$, $N(1535){\frac{1}{2}}^{-}$ and $N(1520){\frac{3}{2}}^{-}$ states are based exclusively on the parametrizations derived for the nucleon. In the case of the $\Delta (1232){\frac{3}{2}}^{+}$ (isospin 3/2), we use lattice QCD data to estimate the radial structure, and take into account the well known effects associated with the pion cloud dressing of the baryons. Our estimates are based mainly on the valence quark degrees of freedom and are in good agreement with the data for $Q^2>2$ GeV${}^2$, with a few exceptions. The present predictions can be tested in a near future for large $Q^2$ at the Jefferson Lab -- 12 GeV upgrade.

    ↳ hep-phhep-exhep-latnucl-ex+10 citations
11. 11*

    Solid deuterium surface degradation at ultracold neutron sources

    A.Anghel🇨🇭 · T.L.Bailey🇺🇸 · G.Bison🇨🇭 · B.Blau🇨🇭 · L.J.Broussard🇺🇸 · S.M.Clayton🇺🇸 · C.Cude-Woods🇺🇸 · M.Daum🇨🇭 · A.Hawari🇺🇸 · N.Hild🇨🇭 · P.Huffman🇺🇸 · T.M.Ito🇺🇸 and 18 other authors

    Solid deuterium (sD_2) is used as an efficient converter to produce ultracold neutrons (UCN). It is known that the sD_2 must be sufficiently cold, of high purity and mostly in its ortho-state in order to guarantee long lifetimes of UCN in the solid from which they are extracted into vacuum. Also the UCN transparency of the bulk sD_2 material must be high because crystal inhomogeneities limit the mean free path for elastic scattering and reduce the extraction efficiency. Observations at the UCN sources at Paul Scherrer Institute and at Los Alamos National Laboratory consistently show a decrease of the UCN yield with time of operation after initial preparation or later treatment (`conditioning') of the sD_2. We show that, in addition to the quality of the bulk sD_2, the quality of its surface is essential. Our observations and simulations support the view that the surface is deteriorating due to a build-up of D_2 frost-layers under pulsed operation which leads to strong albedo reflections of UCN and subsequent loss. We report results of UCN yield measurements, temperature and pressure behavior of deuterium during source operation and conditioning, and UCN transport simulations. This, together with optical observations of sD_2 frost formation on initially transparent sD_2 in offline studies with pulsed heat input at the North Carolina State University UCN source results in a consistent description of the UCN yield decrease.

    ↳ physics.ins-dethep-exnucl-exEPJA(2018)·29 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.