Mon·Jul 8, 2024Monday·July 8, 2024

1. 01*

   Observation of near-scission "polar" and "equatorial" proton emission in heavy-ion induced fission

   Pawan Singh🇮🇳 · Y. K. Gupta🇮🇳 · G. K. Prajapati🇮🇳 · B. N. Joshi🇮🇳 · V. G. Prajapati · N. Sirswal🇮🇳 · K. Ramachandran · A. S. Pradeep🇩🇪 · V. S. Dagre · M. Kumar🇿🇦 · A. Jhingan🇮🇳 · N. Deshmukh🇮🇹 and 4 other authors

   Proton and $\alpha$-particle energy spectra were measured in coincidence with fission fragments at different relative angles in ${}^{16}$O (96 MeV) + ${}^{232}$Th reaction. The multiplicity spectra were analyzed within the framework of a Moving Source Disentangling Analysis (MSDA) to determine contributions from different emission stages. The MSDA conclusively shows ``Near Scission Emission (NSE)" as an essential component in the multiplicity spectra. In contrast to NSE $\alpha$ particles which emit mainly perpendicular (``equatorial emission"), the NSE protons are observed to be emitted perpendicular as well as parallel (``polar emission") to the fission axis with similar intensities ($\sim$20\% for each). Thus, around 40\% of total pre-scission protons are emitted near the scission stage, whereas the same fraction for $\alpha$ particles is only around 10\%. The inevitable presence of ``polar" and ``equatorial" NSE protons in a heavy-ion induced fission has been observed for the first time. Present results open up a new avenue to study the heavy-ion induced fission dynamics.

   nucl-exnucl-thPLB(2024)·6 citations
2. 02*

   Spectroscopy of deeply bound orbitals in neutron-rich Ca isotopes

   P. J. Li🇨🇳 · J. Lee🇨🇳 · P. Doornenbal🇯🇵 · S. Chen🇨🇳 · S. Wang🇨🇳 · A. Obertelli🇩🇪 · Y. Chazono🇯🇵 · J. D. Holt🇨🇦 · B. S. Hu🇨🇦 · K. Ogata🇯🇵 · Y. Utsuno🇯🇵 · K. Yoshida🇯🇵 and 76 other authors

   The calcium isotopes are an ideal system to investigate the evolution of shell structure and magic numbers. Although the properties of surface nucleons in calcium have been well studied, probing the structure of deeply bound nucleons remains a challenge. Here, we report on the first measurement of unbound states in ${}^{53}$Ca and ${}^{55}$Ca, populated from \ts{54,56}Ca($p,pn$) reactions at a beam energy of around 216 MeV/nucleon at the RIKEN Radioactive Isotopes Beam Factory. The resonance properties, partial cross sections, and momentum distributions of these unbound states were analyzed. Orbital angular momentum $l$ assignments were extracted from momentum distributions based on calculations using the distorted wave impulse approximation (DWIA) reaction model. The resonances at excitation energies of 5516(41)\,keV in ${}^{53}$Ca and 6000(250)\,keV in ${}^{55}$Ca indicate a significant $l$\, =\,3 component, providing the first experimental evidence for the $\nu 0f_{7/2}$ single-particle strength of unbound hole states in the neutron-rich Ca isotopes. The observed excitation energies and cross-sections point towards extremely localized and well separated strength distributions, with some fragmentation for the $\nu 0f_{7/2}$ orbital in ${}^{55}$Ca. These results are in good agreement with predictions from shell-model calculations using the effective GXPF1Bs interaction and \textit{ab initio} calculations and diverge markedly from the experimental distributions in the nickel isotones at $Z=28$.

   nucl-exnucl-thPLB(2024)·6 citations
3. 03*

   Probing the equilibration of the QCD matter created in heavy-ion collisions with dileptons

   Xiang-Yu Wu🇨🇦 · Lipei Du🇨🇦 · Charles Gale🇨🇦 · Sangyong Jeon🇨🇦

   A systematic study of intermediate invariant mass dilepton production in Pb+Pb collisions at $\sqrt{s_{NN}}=5.02$ TeV is performed, using next-to-leading-order (NLO) thermal QCD dilepton emission rates with a multistage dynamical approach which includes event-by-event IP-Glasma initial conditions, relativistic viscous fluid dynamics, and a hadronic afterburner. Considering dilepton yield and anisotropic flow, special attention is paid to the out-of-equilibrium aspects, both thermal and chemical, and to the contribution of the Drell-Yan process. The relative contribution of each of those different channels to dilepton observables is calculated and discussed.

   ↳ nucl-thhep-phnucl-exPRC(2024)·23 citations
4. 04*

   Compact Ion Beam System for Fusion Demonstration

   Allan Xi Chen · Nai-Wei Liu · Alexander Gunn · Zhe Su · Benjamin F. Sigal · Matthew Salazar · Nawar Abdalla · James Chen🇺🇸 · Alfred Y. Wong · Qiong Wang

   We demonstrate a compact ion beam device capable of accelerating H${}^{+}$ and D${}^{+}$ ions up to 75keV energy, on to a solid target, with sufficient beam current to study fusion reactions. The ion beam system uses a microwave driven plasma source to generate ions that are accelerated to high energy with a direct current (DC) acceleration structure. The plasma source is driven by pulsed microwaves from a solid-state radiofrequency (RF) amplifier, which is impedance matched to the plasma source chamber at the ISM band frequency (2.4-2.5GHz). The plasma chamber is held at high positive DC potential and is isolated from the impedance matching structure (at ground potential) by a dielectric-filled gap. To facilitate the use of high-energy-particle detectors near the target, the plasma chamber is biased to a high positive voltage, while the target remains grounded. A target loaded with deuterium is used to study D-D fusion and a B${}_4$C or LaB${}_6$ target is used to study p-${}^{11}$B fusion. Detectors include solid-state charged particle detector and a scintillation fast neutron detector. The complete ion beam system can fit on a laboratory table and is a useful tool for teaching undergraduate and graduate students about the physics of fusion.

   ↳ physics.ins-dethep-exnucl-exPhys.Open(2024)·2 citations
5. 05*

   Study of the neutrino-oxygen cross sections of the charged-current reaction 16O(${\bar{\nu }}_e,e^{+}$)16N(0 MeV,$2^{-}$) and the neutral-current reaction 16O($\nu ,\nu$')16O(12.97/12.53 MeV,$2^{-}$), producing high-energy gamma rays

   Makoto Sakuda🇯🇵 · Toshio Suzuki🇯🇵 · Ken'ichiro Nakazato🇯🇵 · Hideyuki Suzuki🇯🇵

   In the previous work, we discussed the cross section and the detection of 4.4-MeV $\gamma$ rays produced in the neutrino neutral-current (NC) reaction ${}^{16}$O($\nu ,{\nu }^{\prime }$)${}^{16}$O(12.97 MeV and 12.53 MeV, $2^{-}$) in a water Cherenkov detector at the low energy below 100 MeV. In this report, we further investigated both the charged-current (CC) reaction ${}^{16}$O(${\bar{\nu }}_e,e^{+}$)${}^{16}$N(0 MeV, $2^{-}$) and the NC reaction${}^{16}$O($\nu ,{\nu }^{\prime }$)${}^{16}$O(12.97 MeV and 12.53 MeV, $2^{-}$), producing high-energy $\gamma$ rays, in which the more solid identification of the reactions can be applied via the coincidence method.

   ↳ nucl-thhep-phnucl-exPTEP(2024)·0 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.