Tue·Oct 31, 2017Tuesday·October 31, 2017

1. 01*

   Precision Mass Measurements of Neutron-Rich Co Isotopes Beyond N=40

   C. Izzo🇨🇦 · G. Bollen🇺🇸 · M. Brodeur🇺🇸 · M. Eibach🇺🇸 · K. Gulyuz🇺🇸 · J. D. Holt🇨🇦 · J. M. Kelly🇺🇸 · M. Redshaw🇺🇸 · R. Ringle🇺🇸 · R. Sandler🇺🇸 · S. Schwarz🇺🇸 · S. R. Stroberg🇨🇦 and 3 other authors

   The region near Z=28, N=40 is a subject of great interest for nuclear structure studies due to spectroscopic signatures in ${}^{68}$Ni suggesting a subshell closure at N=40. Trends in nuclear masses and their derivatives provide a complementary approach to shell structure investigations via separation energies. Penning trap mass spectrometry has provided precise measurements for a number of nuclei in this region, however a complete picture of the mass surfaces has so far been limited by the large uncertainty remaining for nuclei with N > 40 along the iron and cobalt chains. Here we present the first Penning trap measurements of ${}^{68,69}$Co, performed at the Low-Energy Beam and Ion Trap facility at the National Superconducting Cyclotron Laboratory. In addition, we perform ab initio calculations of ground state and two-neutron separation energies of cobalt isotopes with the valence-space in-medium similarity renormalization group approach based on a particular set of two- and three-nucleon forces which predict saturation in infinite matter. We discuss the importance of these measurements and calculations for understanding the evolution of nuclear structure near ${}^{68}$Ni.

   nucl-exPRC(2018)·15 citations
2. 02*

   An experimental study of the rearrangements of valence protons and neutrons amongst single-particle orbits during double {\beta} decay in 100Mo

   S. J. Freeman🇬🇧 · D. K. Sharp🇬🇧 · S. A. McAllister🇬🇧 · B. P. Kay🇺🇸 · C. M. Deibel🇺🇸 · T. Faestermann🇩🇪 · R. Hertenberger🇩🇪 · A. J. Mitchell🇬🇧 · J. P. Schiffer🇺🇸 · S. V. Szwec🇬🇧 · J. S. Thomas🇬🇧 · H.-F. Wirth🇩🇪

   The rearrangements of protons and neutrons amongst the valence single-particle orbitals during double {\beta} decay of 100Mo have been determined by measuring cross sections in (d,p), (p,d), (3He,{\alpha}) and (3He,d) reactions on 98,100Mo and 100,102Ru targets. The deduced nucleon occupancies reveal significant discrepancies when compared with theoretical calculations; the same calculations have previously been used to determine the nuclear matrix element associated with the decay probability of double {\beta} decay of the 100Mo system.

   nucl-exPRC(2017)·34 citations
3. 03*

   Deep crustal heating by neutrinos from the surface of accreting neutron stars

   F. J. Fattoyev🇺🇸 · Edward F. Brown🇺🇸 · Andrew Cumming · Alex Deibel · C. J. Horowitz🇺🇸 · Bao-An Li🇺🇸 · Zidu Lin🇺🇸

   We present a new mechanism for deep crustal heating in accreting neutron stars. Charged pions (${\pi }^{+}$) are produced in nuclear collisions on the neutron star surface during active accretion and upon decay they provide a flux of neutrinos into the neutron star crust. For massive and/or compact neutron stars, neutrinos deposit $\approx 1\text{–}2\mathrm{MeV}$ of heat per accreted nucleon into the inner crust. The strength of neutrino heating is comparable to the previously known sources of deep crustal heating, such as from pycnonuclear fusion reactions, and is relevant for studies of cooling neutron stars. We model the thermal evolution of a transient neutron star in a low-mass X-ray binary, and in the particular case of the neutron star MXB~1659-29 we show that additional deep crustal heating requires a higher thermal conductivity for the neutron star inner crust. A better knowledge of pion production cross sections near threshold would improve the accuracy of our predictions.

   ↳ astro-ph.HEnucl-exnucl-thPRC(2018)·11 citations
4. 04*

   Two-Proton Radioactivity with 2p halo in light mass nuclei A$=$18$-$34

   G. Saxena🇮🇳 · M. Kumawat🇮🇳 · M. Kaushik · S. K. Jain🇮🇳 · Mamta Aggarwal🇮🇳

   Two-proton radioactivity with 2p halo is reported theoretically in light mass nuclei A $=$ 18-34. We predict ${}^{19}$Mg, ${}^{22}$Si, ${}^{26}$S, ${}^{30}$Ar and ${}^{34}$Ca as promising candidates of ground state 2p-radioactivity with S${}_{2p}$ $<$ 0 and S${}_p$ $>$ 0. Observation of extended tail of spatial charge density distribution, larger charge radius and study of proton single particle states, Fermi energy and the wave functions indicate 2p halo like structure which supports direct 2p emission. The Coulomb and centrifugal barriers in experimentally identified 2p unbound ${}^{22}$Si show a quasi-bound state that ensures enough life time for such experimental probes. Our predictions are in good accord with experimental and other theoretical data available so far.

   ↳ nucl-thnucl-exPLB(2017)·42 citations
5. 05*

   Combined parametrization of the neutron electric form factor and the ${\gamma }^{\ast }N\to \Delta (1232)$ quadrupole form factors

   G. Ramalho🇧🇷

   Models based on $SU(6)$ symmetry breaking and large $N_c$ limit provide relations between the pion cloud contributions to the ${\gamma }^{\ast }N\to \Delta (1232)$ quadrupole form factors, electric ($G_E$) and Coulomb ($G_C$), and the neutron electric form factor $G_{En}$, suggesting that those form factors are dominated by the same physical processes. Those relations are improved in order to satisfy a fundamental constraint between the electric and Coulomb quadrupole form factors in the long wavelength limit, when the photon three-momentum vanishes (Siegert's theorem). Inspired by those relations, we study alternative parametrizations for the neutron electric form factor. The parameters of the new form are then determined by a combined fit to the $G_{En}$ and the ${\gamma }^{\ast }N\to \Delta (1232)$ quadrupole form factor data. We obtain a very good description of the $G_E$ and $G_C$ data when we combine the pion cloud contributions with small valence quark contributions to the ${\gamma }^{\ast }N\to \Delta (1232)$ quadrupole form factors. The best description of the data is obtained when the second momentum of $G_{En}$ is $r_n^4\simeq -0.4$ fm${}^4$. We conclude that the square radii associated with $G_E$ and $G_C$, $r_E^2$ and $r_C^2$, respectively, are large, revealing the long extension of the pion cloud. We conclude also that those square radii are related by $r_E^2-r_C^2=0.6\pm 0.2$ fm${}^2$. The last result is mainly the consequence of the pion cloud effects and Siegert's theorem.

   ↳ hep-phhep-exhep-latnucl-ex+1EPJA(2019)·15 citations
6. 06*

   The extraction of 229Th3+ from a buffer-gas stopping cell

   Lars von der Wense · Benedict Seiferle · Mustapha Laatiaoui🇩🇪 · Peter G. Thirolf

   In the whole landscape of atomic nuclei, ${}^{229}$Th is currently the only known nucleus which could allow for the development of a nuclear-based frequency standard, as it possesses an isomeric state of just 7.6 eV energy above the ground state. The 3+ charge state is of special importance in this context, as Th${}^{3+}$ allows for a simple laser-cooling scheme. Here we emphasize the direct extraction of triply-charged ${}^{229}$Th from a buffer-gas stopping cell. This finding will not only simplify any future approach of ${}^{229}$Th ion cooling, but is also used for thorium-beam purification and in this way provides a powerful tool for the direct identification of the ${}^{229}$Th isomer to ground state nuclear transition.

   ↳ physics.ins-detnucl-exNucl.Instrum.Meth.B(2016)·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.