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1. Beyond-mean-field calculations of allowed and first-forbidden β ⁻ decays of r -process waiting-point nuclei

   https://doi.org/10.1051/epjconf/202226003002  

   Robin, Caroline; Litvinova, Elena; Martínez-Pinedo, Gabriel (January 2022, EPJ Web of Conferences)

   Liu, W.; Wang, Y.; Guo, B.; Tang, X.; Zeng, S. (Ed.)

   β -decay rates of neutron-rich nuclei, in particular those located at neutron shell closures, play a central role in simulations of the heavy-element nucleosynthesis and resulting abundance distributions. We present β -decay half-lives of even-even N = 82 and N = 126 r -process waiting-point nuclei calculated in the approach based on relativistic quasiparticle random phase approximation with quasiparticle-vibration coupling. The calculations include both allowed and first-forbidden transitions. In the N = 82 chain, the quasiparticlevibration coupling has an important impact close to stability, as it increases the contribution of Gamow-Teller modes and improves the agreement with the available data. In the N = 126 chain, we find the decay to proceed dominantly via first-forbidden transitions, even when the coupling to vibrations is included. 

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2. First $\beta$ -Delayed Two-Neutron Spectroscopy of the $r$ -Process Nucleus ${}^{134}\mathrm{In}$ and Observation of the $i_{13/2}$ Single-Particle Neutron State in ${}^{133}\mathrm{Sn}$

   https://doi.org/10.1103/l24v-5m31  

   Dyszel, P; Grzywacz, R; Xu, Z Y; Kitamura, N; Karny, M; Korgul, A; Madurga, M; Neupane, S; Algora, A; Andreyev, A N; et al (October 2025, Physical Review Letters)

   This manuscript reports on the direct observation of a $\beta$-delayed two-neutron emission in a study of ${}^{134}\mathrm{In}$at the ISOLDE Decay Station using neutron spectroscopy. We also report on the first measurement in ${\beta }^{-}$decay of the long-sought $13/2^{+}$excited state in ${}^{133}\mathrm{Sn}$, attributed to be the neutron single-particle $i_{13/2}$orbital. The observation of sequential neutron emission is used to extract the relative population of the $i_{13/2}$state, which was found to be much smaller than the predictions of the statistical model. The experiment was possible because of the innovative use of a neutron array with neutron discrimination and interaction tracking capabilities. This is the first study of the details of the two-neutron emission for a nucleus, which belongs to the $r$-process path. Understanding $\beta$-delayed two-neutron emission probabilities is essential to validate models used in astrophysical $r$-process nucleosynthesis calculations. Observing two-neutron emissions in ${\beta }^{-}$decay paves the way for new experiments to study energy and angular correlations for $\beta$-delayed multineutron emitters. 

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3. Constraining Inputs to Realistic Kilonova Simulations through Comparison to Observed r-process Abundances

   https://doi.org/10.3847/1538-4357/acf3e0  

   Ristić, Marko; Holmbeck, Erika M.; Wollaeger, Ryan T.; Korobkin, Oleg; Champion, Elizabeth; O’Shaughnessy, Richard; Fryer, Chris L.; Fontes, Christopher J.; Mumpower, Matthew R.; Sprouse, Trevor M. (October 2023, The Astrophysical Journal)

   Kilonovae, one source of electromagnetic emission associated with neutron star mergers, are powered by the decay of radioactive isotopes in the neutron-rich merger ejecta. Models for kilonova emission consistent with the electromagnetic counterpart to GW170817 predict characteristic abundance patterns, determined by the relative balance of different types of material in the outflow. Assuming that the observed source is prototypical, this inferred abundance pattern in turn must matchr-process abundances deduced by other means, such as what is observed in the solar system. We report on analysis comparing the input mass-weighted elemental compositions adopted in our radiative transfer simulations to the mass fractions of elements in the Sun, as a practical prototype for the potentially universal abundance signature from neutron star mergers. We characterize the extent to which our parameter inference results depend on our assumed composition for the dynamical and wind ejecta and examine how the new results compare to previous work. We find that a dynamical ejecta composition calculated using the FRDM2012 nuclear mass and FRLDM fission models with extremely neutron-rich ejecta (Y_e= 0.035) along with moderately neutron-rich (Y_e= 0.27) wind ejecta composition yields a wind-to-dynamical mass ratio ofM_w/M_d= 0.47, which best matches the observed AT2017gfo kilonova light curves while also producing the best-matching abundance of neutron capture elements in the solar system, though, allowing for systematics, the ratio may be as high as of order unity. 

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4. Measurement of the cosmogenic neutron yield in Super-Kamiokande with gadolinium loaded water

   M. Shinoki et al. (May 2023, Physical review D Particles and fields)

   Cosmic-ray muons that enter the Super-Kamiokande detector cause hadronic showers due to spallation in water, producing neutrons and radioactive isotopes. These are a major background source for studies of MeV-scale neutrinos and searches for rare events. In 2020, gadolinium was introduced into the ultra-pure water in the Super-Kamiokande detector to improve the detection efficiency of neutrons. In this study, the cosmogenic neutron yield was measured using data acquired during the period after the gadolinium loading. The yield was found to be ð2.76  0.02ðstatÞ  0.19ðsystÞÞ × 10−4 μ−1 g−1 cm2 at an average muon energy 259 GeV at the Super-Kamiokande detector. 

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5. Thermal expansion and phase transformation in the rare earth di-titanate ( R 2 Ti 2 O 7 ) system

   https://doi.org/10.1107/S2052520621004479  

   Hulbert, Benjamin S.; McCormack, Scott J.; Tseng, Kuo-Pin; Kriven, Waltraud M. (June 2021, Acta Crystallographica Section B Structural Science, Crystal Engineering and Materials)

   Characterization of the thermal expansion in the rare earth di-titanates is important for their use in high-temperature structural and dielectric applications. Powder samples of the rare earth di-titanates R 2 Ti 2 O 7 (or R 2 O 3 ·2TiO 2 ), where R = La, Pr, Nd, Sm, Gd, Dy, Er, Yb, Y, which crystallize in either the monoclinic or cubic phases, were synthesized for the first time by the solution-based steric entrapment method. The three-dimensional thermal expansions of these polycrystalline powder samples were measured by in situ synchrotron powder diffraction from 25°C to 1600°C in air, nearly 600°C higher than other in situ thermal expansion studies. The high temperatures in synchrotron experiments were achieved with a quadrupole lamp furnace. Neutron powder diffraction measured the monoclinic phases from 25°C to 1150°C. The La 2 Ti 2 O 7 member of the rare earth di-titanates undergoes a monoclinic to orthorhombic displacive transition on heating, as shown by synchrotron diffraction in air at 885°C (864°C–904°C) and neutron diffraction at 874°C (841°C–894°C). 

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