Tue·Mar 29, 2022Tuesday·March 29, 2022

1. 01*

   Experimental study of 13C({\alpha},n)16O reactions in the Majorana Demonstrator calibration data

   MAJORANA Collaboration · I.J. Arnquist · F.T. Avignone III · A.S. Barabash · C.J. Barton · K.H. Bhimani · E. Blalock · B. Bos · M. Busch · M. Buuck · T.S. Caldwell · Y-D. Chan and 46 other authors

   Neutron captures and delayed decays of reaction products are common sources of backgrounds in ultra-rare event searches. In this work, we studied ${}^{13}$C($\alpha ,n{)}^{16}$O reactions induced by $\alpha$-particles emitted within the calibration sources of the \textsc{Majorana Demonstrator}. These sources are thorium-based calibration standards enclosed in carbon-rich materials. The reaction rate was estimated by using the 6129-keV $\gamma$-rays emitted from the excited ${}^{16}$O states that are populated when the incoming $\alpha$-particles exceed the reaction Q-value. Thanks to the excellent energy performance of the \textsc{Demonstrator}'s germanium detectors, these characteristic photons can be clearly observed in the calibration data. Facilitated by \textsc{Geant4} simulations, a comparison between the observed 6129-keV photon rates and predictions by a TALYS-based software was performed. The measurements and predictions were found to be consistent, albeit with large statistical uncertainties. This agreement provides support for background projections from ($\alpha ,n$)-reactions in future double-beta decay search efforts.

   nucl-exhep-exphysics.ins-detPRC(2022)·6 citations
2. 02*

   Numerical calculation of 3-pion Coulomb scattering using scalar QED

   Dhevan Gangadharan🇺🇸

   The Coulomb scattering between three charged pions is shown to be perturbatively calculable using scalar QED for the relative momenta accessible to high-energy experiments of particle collisions. For the triplet relative momenta, $Q_3\gtrsim 50$ MeV/$c$, the calculated three-pion correlation function at $O({\alpha }^2)$ is very similar to the commonly-used triple-product of pair factors -- Riverside approximation. At lower $Q_3$, but above the lowest existing experimental measurement of $\sim 15$ MeV/$c$, terms of $O({\alpha }^3)$ or higher are needed to obtain a convincing description of three-pion Coulomb interactions. This is in contrast to two-pion correlations, for which the known exact solution is shown to be saturated by the lower orders at comparable pair relative momenta.

   ↳ hep-phnucl-exnucl-thPLB(2022)·0 citations
3. 03*

   Improved phenomenological nuclear charge radius formulae with kernel ridge regression

   Jian-Qin Ma · Zhen-Hua Zhang🇨🇳

   The kernel ridge regression (KRR) method with Gaussian kernel is used to improve the description of the nuclear charge radius by several phenomenological formulae. The widely used $A^{1/3}$, $N^{1/3}$ and $Z^{1/3}$ formulae, and their improved versions by considering the isospin dependence are adopted as examples. The parameters in these six formulae are refitted using the Levenberg-Marquardt method, which give better results than the previous ones. The radius for each nucleus is predicted with the KRR network, which is trained with the deviations between experimental and calculated nuclear charge radii. For each formula, the resultant root-mean-square deviations of 884 nuclei with proton number $Z\ge 8$ and neutron number $N\ge 8$ can be reduced to about 0.017~fm after considering the modification of the KRR method. The extrapolation ability of the KRR method for the neutron-rich region is examined carefully and compared with the radial basis function method. It is found that the improved nuclear charge radius formulae by KRR method can avoid the risk of overfitting and have a good extrapolation ability. The influence of the ridge penalty term on the extrapolation ability of the KRR method is also discussed. At last, the nuclear charge radii of several recently observed K and Ca isotopes have been analyzed.

   ↳ nucl-thnucl-exCPC(2022)·39 citations
4. 04*

   Ab initio calculation of the $\beta$-decay from ${}^{11}$Be to a p${+}^{10}$Be resonance

   M. C. Atkinson🇨🇦 · P. Navrátil🇨🇦 · G. Hupin🇫🇷 · K. Kravvaris🇺🇸 · S. Quaglioni🇺🇸

   The exotic $\beta$-delayed proton emission is calculated in ${}^{11}$Be from first principles using chiral two- and three-nucleon forces. To investigate the unexpectedly-large branching ratio measured in [PRL 123, 082501 (2019)] we calculate the proposed $(1/2^{+},1/2)$ proton resonance in ${}^{11}$B using the no-core shell model with continuum. This calculation helps to address whether this enhancement is caused by unknown dark decay modes or an unobserved proton resonance. We report a branching ratio of $b_p=(1.3\pm 0.5)\times 10^{-6}$, suggesting that its unexpectedly-large value is caused by an unobserved proton resonance in ${}^{11}$B.

   ↳ nucl-thnucl-exPRC(2022)·9 citations
5. 05*

   Astrophysical reaction rates with realistic nuclear level densities

   Sangeeta · T. Ghosh · B. Maheshwari🇮🇳 · G. Saxena · B. K. Agrawal🇮🇳

   Realistic nuclear level densities (NLDs) obtained within the spectral distribution method (SDM) are employed to study nuclear processes of astrophysical interest. The merit of SDM lies in the fact that the NLDs corresponding to many body shell model Hamiltonian consisting of residual interaction can be obtained for the full configurational space without recourse to the exact diagnolization of huge matrices. We calculate NLDs and s-wave neutron resonance spacings which agree reasonably well with the available experimental data. By employing these NLDs, we compute reaction cross-sections and astrophysical reaction rates for radiative neutron capture in few Fe-group nuclei, and compare them with experimental data as well as with those obtained with NLDs from phenomenological and microscopic mean-field models. The results obtained for the NLDs from SDM are able to explain the experimental data quite well. These results are of particular importance since the configuration mixing through the residual interaction naturally accounts for the collective excitations. In the mean-field models, the collective effects are included through the vibrational and rotational enhancement factors and their NLDs are further normalized at low energies with neutron resonance data.

   ↳ nucl-thastro-ph.HEastro-ph.SRnucl-exPRC(2022)·12 citations
6. 06*

   Simulating Araponga -- The High-Resolution Diffractometer of Brazilian Multipurpose Reactor

   Alexandre P.S. Souza🇧🇷 · Luiz P. de Oliveira🇧🇷 · Frederico A. Genezini🇧🇷 · Adimir dos Santos

   The Brazilian Multipurpose Reactor (RMB) is a fundamental project that aims to turn Brazil into a self-sufficient country in the production of radioisotopes and radiopharmaceuticals to supply the Unified Health System (SUS) as much as the private institutions. In addition, the RMB project describes other applications as irradiation and testing of nuclear fuels and structural material analysis, for instance. There are many techniques in the project to study structural aspects of materials, where neutron diffraction represents one of the priorities for implementation. This technique will take place mainly on two diffractometers on Thermal Neutron Guide 1 (TG1), namely Araponga, a high-resolution diffractometer, and Flautim, a high-intensity diffractometer. In this work, we study the performance of the Araponga diffractometer through McStas simulations with input produced by the MCNP code of the RMB core. We investigate the neutron flux values considering a state-of-art high-resolution diffractometer, and the results are promising since some simulated scenarios present values compatible with high-intensity devices.

   ↳ physics.ins-detnucl-exnucl-thBrazilian Journal of Radiation Sciences, …·2 citations
7. 07*

   Two-Photon-Exchange effect in $ep\to en{\pi }^{+}$ at small $-t$ with the hadronic model and dispersion relation approach

   Qian-Qian Guo🇨🇳 · Hai-Qing Zhou🇨🇳

   In this work, the two-photon-exchange (TPE) effect in $ep\to en{\pi }^{+}$ at small $-t$ is discussed. In the previous work, the TPE contribution with one $\pi$ intermediate state is estimated numerically within a hadronic model under the pion-dominance approximation. Here we extend the discussion to include one $\rho$ intermediate state. The TPE contribution can be described by one scalar function in the limit $m_e\to 0$, the dispersion relation (DR) satisfied by this scalar function is analysed. The analytic expressions for the imaginary parts of the TPE contributions from one $\pi$ or one $\rho$ intermediate state are given within the hadronic model. Combining these analytic expressions and the DR, the corresponding real parts of the TPE contributions can be estimated easily at any available region. This can help the further experimental analysis to include the TPE contributions in a convenient way. The numeric results show that the TPE correction with one $\rho$ intermediate state is much smaller than that with one $\pi$ intermediate state in the current energy region. These results suggest that the TPE contribution with an elastic state is the main TPE contribution in $ep\to en{\pi }^{+}$ at small $-t$.

   ↳ hep-phhep-exnucl-exnucl-thPRC(2022)·6 citations
8. 08*

   Large-mass, low-threshold sapphire detector for rare event searches

   S. Verma🇺🇸 · S. Maludze🇺🇸 · M. Lee🇺🇸 · M. Chaudhuri🇮🇳 · V. Iyer🇮🇳 · V. K. S. Kashyap🇮🇳 · A. Kubik🇨🇦 · T. Lin🇺🇸 · R. Mahapatra🇺🇸 · N. Mirabolfathi🇺🇸 · N. Mishra🇺🇸 · B. Mohanty🇮🇳 and 3 other authors

   Low mass nuclear recoil dark matter and coherent-elastic-neutrino-nucleus-scattering (CENNS) searches confront similar challenges in choosing ultra-low threshold and large-mass detectors. We report experimental results from the first-of-its-kind 100 g single-crystal sapphire detector design with a diameter of 76 mm and thickness of 4 mm. The detector is designed to be sensitive for low-energy rare interactions with an intention to investigate the low mass region of dark matter phase-space and search for CENNS at the reactor site. Sapphire is a crystal of aluminum oxide (Al2O3) and has been found to be a good candidate for light mass spin-dependent dark matter search experiments due to its lower atomic mass compared to other detector materials such as germanium and silicon. Using the data collected from the test facility at Texas A&M University, we were able to resolve low energy lines from calibration sources and estimated that our newly developed sapphire detector has a baseline recoil energy resolution of 18 eV. These detectors are operated at 0 V with the phonon-assisted detection providing a quenching-free low-threshold operation.

   ↳ physics.ins-dethep-exnucl-exNucl.Instrum.Meth.A(2023)·17 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.