Fri·Aug 11, 2023Friday·August 11, 2023

1. 01*

   Reactor Antineutrino Spectral "Bump": Cumulative Fission Yields of Irradiated U-235 and Pu-239 Measured by HPGe Gamma-Ray Spectroscopy

   Samuel Kim · C.J. Martoff🇺🇸 · Michael Dion · David Glasgow

   Recent measurements of the reactor antineutrino emission show that there exists a spectral excess (the "bump") in the 5-7 MeV region when compared to the Huber-Muller prediction based on the conversion method. Analysis within an alternate prediction technique, the summation method, suggests that the bump could be due to excess contributions from a certain few of the beta-decaying fission products. However, it has been shown that when updated fission yield values are used in the summation method, the predicted excess vanishes. In the present preliminary study, fission yields for nuclides suspected of causing the neutrino spectral bump are investigated using gamma-ray spectroscopy of U-235 and Pu-239 samples freshly irradiated using the High Flux Isotope Reactor. For several of the suspect nuclides, the derived fission yields are consistent with JEFF3.3 fission yield library. The exception is the case of Cs-140 from Pu-239, where the discrepancy between the fitted and expected values suggests a potential error in the fission yield library. This highlights the importance of using accurate nuclear data libraries in the analysis of the reactor antineutrino spectra, and the need for ongoing efforts to improve these libraries.

   nucl-exphysics.ins-det0 citations
2. 02*

   Excitation of the ${}^{229}$Th nucleus by the hole in the inner electronic shells

   M. G. Kozlov🇷🇺 · A. V. Oleynichenko🇷🇺 · D. Budker🇩🇪 · D. A. Glazov · Y. V. Lomachuk · V. M. Shabaev🇷🇺 · A. V. Titov · I. I. Tupitsyn🇷🇺 · A. V. Volotka

   The ${}^{229}$Th nucleus has a long-lived isomeric state $A^{\ast }$ at 8.338(24) eV [Kraemer et al, Nature, \textbf{617}, 706 (2023)]. This state is connected to the ground state by an M1 transition. For a hydrogenlike Th ion in the $1s$ state the hyperfine structure splitting is about 0.7 eV. This means that the hyperfine interaction can mix the nuclear ground state with the isomeric state with a mixing coefficient $\beta$ about 0.03. If the electron is suddenly removed from this system, the nucleus will be left in the mixed state. The probability to find the nucleus in the isomeric state $A^{\ast }$ is equal to ${\beta }^2\sim 10^{-3}$. For the $2s$ state the effect is roughly two orders of magnitude smaller. An atom with a hole in the $1s$ or $2s$ shell is similar to the hydrogenlike atom, only the hole has a short lifetime $\tau$. After the hole is filled, there is a non-zero probability to find the nucleus in the $A^{\ast }$ state. Estimates of this probability are presented along with a discussion of possible experiments on Th-doped xenotime-type orthophosphate crystals and other broad band gap materials.

   ↳ physics.atom-phnucl-exPRA(2024)·3 citations
3. 03*

   Comparing pion production in transport simulations of heavy-ion collisions at $270A$ MeV under controlled conditions

   Jun Xu🇨🇳 · Hermann Wolter🇩🇪 · Maria Colonna🇮🇹 · Mircea Dan Cozma🇷🇴 · Pawel Danielewicz🇺🇸 · Che Ming Ko🇺🇸 · Akira Ono🇯🇵 · ManYee Betty Tsang🇺🇸 · Ying-Xun Zhang🇨🇳 · Hui-Gan Cheng🇨🇳 · Natsumi Ikeno🇯🇵 · Rohit Kumar🇺🇸 and 11 other authors

   Within the TMEP, we present a detailed study of the performance of different transport models in Sn+Sn collisions at $270A$ MeV, and put particular emphasis on the production of pions and $\Delta$ resonances, which have been used as probes of the nuclear symmetry energy. We prescribe a common and rather simple physics model, and follow in detail the results of 4 BUU models and 6 QMD models. The nucleonic evolution of the collision and the nucleonic observables in these codes do not completely converge, but the differences among the codes can be understood as being due to several reasons: the basic differences between BUU and QMD models in the representation of the phase-space distributions, computational differences in the mean-field evaluation, and differences in the adopted strategies for the Pauli blocking in the collision integrals. For pionic observables, we find that a higher maximum density leads to an enhanced pion yield and a reduced ${\pi }^{-}/{\pi }^{+}$ yield ratio, while a more effective Pauli blocking generally leads to a slightly suppressed pion yield and an enhanced ${\pi }^{-}/{\pi }^{+}$ yield ratio. We specifically investigate the effect of the Coulomb force, and find that it increases the total ${\pi }^{-}/{\pi }^{+}$ yield ratio but reduces the ratio at high pion energies, although differences in its implementations do not have a dominating role in the differences among the codes. Taking into account only the results of codes that strictly follow the homework specifications, we find a convergence of the codes in the final charged pion yield ratio to a $1\sigma$ deviation of about $5\%$. However, the uncertainty is expected to be reduced to about $1.6\%$ if the same or similar strategies and ingredients, i.e., an improved Pauli blocking and calculation of the non-linear term in the mean-field potential, are similarly used in all codes.

   ↳ nucl-thnucl-exPRC(2024)·33 citations
4. 04*

   Radiative decay of the sub-threshold $1_1^{-}$ and $2_1^{+}$ states of ${}^{16}$O in cluster effective field theory

   Shung-Ichi Ando🇰🇷

   Radiative decay of the sub-threshold $1_1^{-}$ and $2_1^{+}$ states of ${}^{16}$O is studied in cluster effective field theory. The wave function normalization factors for initial and final states of the radiative decay amplitudes are deduced by using the phase shift data of elastic $\alpha$-${}^{12}$C scattering for $l=0,1,2$, which are related to the asymptotic normalization coefficients of $0_1^{+}$, $1_1^{-}$, $2_1^{+}$ states of ${}^{16}$O for the two-body $\alpha$-${}^{12}$C channel; then only one unfixed parameter remains in each of the radiative decay amplitudes. We fit the parameters to the experimental radiative decay rates and apply the fitted parameters to the study of radiative $\alpha$ capture on ${}^{12}$C, ${}^{12}$C($\alpha$,$\gamma$)${}^{16}$O. The order of magnitude of astrophysical $S$ factors of $E1$ and $E2$ transitions of ${}^{12}$C($\alpha$,$\gamma$)${}^{16}$O is reproduced compared to the experimental data, and we discuss an improvement in the calculation of $S$ factors of ${}^{12}$C($\alpha$,$\gamma$)${}^{16}$O.

   ↳ nucl-thnucl-exPRC(2024)·4 citations
5. 05*

   "QGP Signatures" Revisited

   John W. Harris🇺🇸 · Berndt Müller🇺🇸

   We revisit the graphic table of QCD signatures in our 1996 Annual Reviews article "The Search for the Quark-Gluon Plasma" and assess the progress that has been made since its publication towards providing quantitative evidence for the formation of a quark-gluon plasma in relativistic heavy-ion collisions and its characteristic properties.

   ↳ hep-phnucl-exnucl-thEPJC(2024)·129 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.