Mon·Jun 23, 2025Monday·June 23, 2025

1. 01*

   Search for the in-situ production of ${}^{77}$Ge in the GERDA neutrinoless double-beta decay experiment

   M. Agostini🇬🇧 · A. Alexander🇬🇧 · G. Araujo🇨🇭 · A.M. Bakalyarov🇷🇺 · M. Balata🇮🇹 · I. Barabanov🇷🇺 · L. Baudis🇨🇭 · C. Bauer🇩🇪 · S. Belogurov🇷🇺 · A. Bettini🇮🇹 · L. Bezrukov🇷🇺 · V. Biancacci🇮🇹 and 99 other authors

   The beta decay of ${}^{77}$Ge and ${}^{77\mathrm{m}}$Ge, both produced by neutron capture on ${}^{76}$Ge, is a potential background for Germanium based neutrinoless double-beta decay search experiments such as GERDA or the LEGEND experiment. In this work we present a search for ${}^{77}$Ge decays in the full GERDA Phase II data set. A delayed coincidence method was employed to identify the decay of ${}^{77}$Ge via the isomeric state of ${}^{77}$As (9/2${}^{+}$, 475 keV, $T_{1/2}=114\mu$s, ${}^{77\mathrm{m}}$As). New digital signal processing methods were employed to select and analyze pile-up signals. No signal was observed, and an upper limit on the production rate of was set at $<0.216$ nuc/(kg$\cdot$yr) (90% CL). This corresponds to a total production rate of ${}^{77}$Ge and ${}^{77\mathrm{m}}$Ge of $<0.38$ nuc/(kg$\cdot$ yr) (90% CL), assuming equal production rates. A previous Monte Carlo study predicted a value for in-situ ${}^{77}$Ge and ${}^{77\mathrm{m}}$Ge production of (0.21$\pm$0.07) nuc/(kg$\cdot$yr), a prediction that is now further corroborated by our experimental limit. Moreover, tagging the isomeric state of ${}^{77\mathrm{m}}$As can be utilised to further suppress the ${}^{77}$Ge background. Considering the similar experimental configurations of LEGEND-1000 and GERDA, the cosmogenic background in LEGEND-1000 at LNGS is estimated to remain at a sub-dominant level.

   nucl-exastro-ph.IMEPJC(2025)·0 citations
2. 02*

   New measurement of ${}^{50}$Cr and ${}^{53}$Cr (n,$\gamma$) cross sections at n_TOF: a call for chromium nuclear data revision

   P. Pérez-Maroto · C. Guerrero · A. Casanovas · B. Fernández · E. Mendoza · V. Alcayne · J. Lerendegui-Marco · C. Domingo-Pardo · J. M. Quesada · R. Capote · the n_TOF Collaboration

   ${}^{50}$Cr and ${}^{53}$Cr are very relevant in criticality safety benchmarks related to nuclear reactors. The discrepancies of up to 30% between the neutron capture cross section evaluations have an important effect on the $k_{eff}$ and $k_{\infty }$ in criticality benchmarks particularly sensitive to chromium. In this work, the ${}^{50,53}$Cr(n,$\gamma$) cross sections are to be determined between 1 and 100 keV with an 8-10% accuracy following the requirements of the NEA High Priority Request List (HPRL) to solve the current discrepancies. We have measured these reactions by the time-of-flight technique at the EAR1 experimental area of the n_TOF facility, using an array of four C${}_6$D${}_6$ detectors with very low neutron sensitivity. The highly-enriched samples used are significantly thinner than in previous measurements, thus minimizing the multiple-scattering effects. We have produced, and analysed with the R-matrix analysis code SAMMY, capture yields featuring 33 resonances of ${}^{50}$Cr and 51 of ${}^{53}$Cr with an accuracy between 5% and 9%, hence fulfilling the requirements made by the NEA. The differential and integral cross sections have been compared to previous data and evaluations. The new measured ${}^{50,53}$Cr(n,$\gamma$) cross sections provide a valuable input for upcoming evaluations, which are deemed necessary given that the results presented herein do not support the increase in both cross sections proposed in the recent INDEN evaluation.

   nucl-exEPJA(2026)·0 citations
3. 03*

   An unusual type-I X-ray burst from the neutron star X-ray binary IGR J17591-2342: a double-photospheric-radius-expansion burst?

   Sudip Bhattacharyya🇮🇳 · Akshay Singh · Andrea Sanna🇮🇹

   Type-I X-ray bursts observed from neutron stars originate from intermittent unstable thermonuclear burning of accreted matter on these stars. Such bursts, particularly those reaching the Eddington luminosity and having a temporary photospheric radius-expansion due to radiation pressure, provide a testbed to study nuclear fusion processes in intense radiation, gravity, and magnetic fields. Here, we investigate time-resolved spectroscopic properties of a type-I burst from the accretion-powered millisecond X-ray pulsar IGR J17591-2342. Our basic spectral model includes an absorbed blackbody to describe the burst emission and an absorbed power law to represent the non-burst emission. The blackbody normalisation shows two consecutive humps aligned with blackbody temperature dips during the burst. Such an unusual behaviour could imply two consecutive photospheric radius-expansion events during the same burst or a systematic metallicity evolution in the neutron star atmosphere. However, our spectral analysis suggests the latter option is less likely to be happening for IGR J17591-2342. The novel former option implies that sufficient fuel survived after the first photospheric radius-expansion event to power a second similar event a few seconds later, challenging the current theoretical understanding. If confirmed, the double photospheric radius-expansion event observed in IGR J17591-2342 suggests the possibility of avoiding photospheric expansion at luminosities exceeding Eddington. Mechanisms such as temporary enhancement of the magnetic field by convection and confinement of the plasma could be invoked to explain the peculiar behaviour of the source.

   ↳ astro-ph.HEnucl-exnucl-thAstron.Astrophys.(2025)·0 citations
4. 04*

   Analysis of Atomic Charge State and Atomic Number for VAMOS++ Magnetic Spectrometer using Deep Neural Networks and Fractionally Labelled Events

   M. Rejmund🇫🇷 · A. Lemasson🇫🇷

   The VAMOS++ magnetic spectrometer is a multi-parametric system that integrates ion optical magnetic elements with a multi-detector stack. The magnetic elements, along with the tracking and timing detectors and the trajectory reconstruction method, provide the analysis of the magnetic rigidity, the trajectory length between the beam interaction point and the focal plane of the spectrometer, and the related velocity and mass-over-charge ratio. The segmented ionization chamber provides the energy measurements necessary to analyze the atomic charge state and atomic number. However, this analysis critically suffers from inherent limitations due to the variable thickness and non-uniformity of the entrance window of the ionization chamber and other detector imperfections. Conventionally, this meticulous, detailed analysis is exceptionally tedious, often requiring several months to complete. We present a novel method utilizing deep neural networks, trained on an experimental dataset with only a small fraction of precisely labeled events for the lowest and best-resolved atomic charge states or numbers. This innovative approach enables the networks to autonomously and accurately classify the remaining events. This method drastically accelerates the acquisition of high-resolution atomic charge state and atomic number spectra, reducing analysis time from months to mere hours. Crucially, by discarding human bias, this approach ensures standardized, optimal, and reproducible results with unprecedented efficiency.

   ↳ physics.ins-detcs.LGnucl-exphysics.atom-ph+1JINST(2025)·2 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.