Fri·Apr 18, 2025Friday·April 18, 2025

1. 01*

   Precision mass measurements around ${}^{84}$Mo rule out ZrNb cycle formation in the rapid proton-capture process at type I X-ray bursts

   S. Kimura · M. Wada · C.Y. Fu · N. Fukuda🇯🇵 · Y. Hirayama · D.S. Hou · S. Iimura · H. Ishiyama · Y. Ito🇯🇵 · S. Kubono🇯🇵 · K. Kusaka · S. Michimasa🇯🇵 and 18 other authors

   The rapid proton-capture ($rp$-) process is one of the primary, explosive thermonuclear burning processes that drive type I X-ray bursts. A possible termination of the $rp$-process at around ${}^{84}$Mo was previously suggested by the formation of a ZrNb cycle. We report here precision mass measurements at around ${}^{84}$Mo, which have concluded the possibility of the cycle. The experiment was conducted using the multi-reflection time-of-flight spectrograph at RIKEN RI Beam Factory, and the masses of ${}^{79}$Y, ${}^{83}$Nb, ${}^{84}$Mo, ${}^{88}$Ru, and an isomer in ${}^{78}$Y were measured. For ${}^{84}$Mo, and ${}^{88}$Ru, and the isomeric state of ${}^{78}$Y, their masses are experimentally determined for the first time with uncertainties of $\delta m\approx 20keV/{\mathrm{c}}^2$. The mass precision of ${}^{79}$Y and ${}^{83}$Nb is improved to $13keV/{\mathrm{c}}^2$ and $9.6keV/{\mathrm{c}}^2$, respectively. The new $\alpha$-separation energy of ${}^{84}$Mo, 1.434(83) MeV, unambiguously rules out the possibility of forming the ZrNb cycle. The X-ray burst simulation with the new masses shows that our measurements effectively remove the large final abundance uncertainties in the $A=80-90$ mass region. The new mass values improve the prediction power for the composition of the nuclear ashes in X-ray bursts.

   nucl-exastro-ph.HEnucl-thPRL(2025)·6 citations
2. 02*

   High-Density Ultracold Neutron Source for Low-Energy Particle Physics Experiments

   Skyler Degenkolb🇩🇪 · Estelle Chanel🇫🇷 · Simon Baudoin🇫🇷 · Marie-Hélène Baurand🇫🇷 · Douglas H. Beck🇺🇸 · Juliette Blé🇫🇷 · Eric Bourgeat-Lami🇫🇷 · Zeus Castillo🇫🇷 · Peter Fierlinger🇩🇪 · Hanno Filter-Pieler🇫🇷 · Maurits van der Grinten🇬🇧 · Thomas Hepworth🇨🇦 and 10 other authors

   SuperSUN, a new superthermal source of ultracold neutrons (UCN) at the Institut Laue-Langevin, exploits inelastic scattering of neutrons in isotopically pure superfluid ${}^4$He at temperatures below $0.6$K. For the first time, continuous operation with an intense broad-spectrum cold neutron beam is demonstrated over 60 days. We observe continuous UCN extraction rates of $21000$s${}^{-1}$, and storage in the source with saturated density $273$cm${}^{-3}$. The low-energy $\text{in-situ}$ UCN spectrum is alterable via accumulation and holding delays, opening new possibilities in fundamental and applied physics.

   ↳ physics.ins-dethep-exnucl-ex5 citations
3. 03*

   Rapidity scan with DCCI at LHC energy

   Shin-ei Fujii🇯🇵 · Yasuki Tachibana🇯🇵 · Tetsufumi Hirano🇯🇵

   We extend the dynamical core-corona initialization (DCCI2) model to include the baryon number evolution in the entire system created in high-energy heavy-ion collisions. Introducing the source term for the baryon number, we describe the early-stage equilibration and later-stage hydrodynamic evolution of the baryon number throughout the system from midrapidity to forward rapidity. Through numerical simulations with this extended model, we show that extremely large baryon chemical potentials are realized in forward rapidity regions at the LHC energy and are comparable to those of the BES energies. Moreover, we show that fluctuations of baryon chemical potentials are large and, consequently, negative baryon chemical potential regions appear at midrapidity.

   ↳ nucl-thhep-phnucl-exJ.Subatomic Part.Cosmol.(2026)·1 citation

* 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.