Fri·Feb 5, 2021Friday·February 5, 2021

1. 01*

   ${}^{83}\mathrm{Rb}$/${}^{83m}\mathrm{Kr}$ production and cross-section measurement with 3.4 MeV and 20 MeV proton beams

   Dan Zhang🇺🇸 · Yifan Li · Jie Bao🇨🇳 · Changbo Fu🇨🇳 · Mengyun Guan🇨🇳 · Yuan He🇨🇳 · Xiangdong Ji🇺🇸 · Huan Jia🇨🇳 · Yao Li🇨🇳 · Jianglai Liu · Jingkai Xia🇨🇳 · Weixing Xiong🇨🇳 and 3 other authors

   ${}^{83m}\mathrm{Kr}$, with a short lifetime, is an ideal calibration source for liquid xenon or liquid argon detectors. The ${}^{83m}\mathrm{Kr}$ isomer can be generated through the decay of ${}^{83}\mathrm{Rb}$ isotope which is usually produced by proton beams bombarding natural krypton atoms. In this paper, we report a successful production of ${}^{83}\mathrm{Rb}{/}^{83m}\mathrm{Kr}$ with a proton beam energy of 3.4 MeV, and the first measurement of the production rate with such low energy proton beams. Another production attempt is performed using the newly available 20 MeV proton beam in China, and the measured production rate is consistent with previous measurements. The produced ${}^{83m}\mathrm{Kr}$ source has been successfully injected into the PandaX-II liquid xenon detector, yielding enough statistics for detector calibration.

   nucl-exphysics.ins-detPRC(2022)·11 citations
2. 02*

   Unperturbed inverse kinematics nucleon knockout measurements with a 48 GeV/c carbon beam

   M. Patsyuk · J. Kahlbow · G. Laskaris · M. Duer · V. Lenivenko · E.P. Segarra · T. Atovullaev · G. Johansson · T. Aumann · A. Corsi · O. Hen · M. Kapishin and 157 other authors

   From superconductors to atomic nuclei, strongly-interacting many-body systems are ubiquitous in nature. Measuring the microscopic structure of such systems is a formidable challenge, often met by particle knockout scattering experiments. While such measurements are fundamental for mapping the structure of atomic nuclei, their interpretation is often challenged by quantum mechanical initial- and final-state interactions (ISI/FSI) of the incoming and scattered particles. Here we overcome this fundamental limitation by measuring the quasi-free scattering of 48 GeV/c 12C ions from hydrogen. The distribution of single protons is studied by detecting two protons at large angles in coincidence with an intact 11B nucleus. The 11B detection is shown to select the transparent part of the reaction and exclude the otherwise large ISI/FSI that would break the 11B apart. By further detecting residual 10B and 10Be nuclei, we also identified short-range correlated (SRC) nucleon-nucleon pairs, and provide direct experimental evidence for the separation of the pair wave-function from that of the residual many-body nuclear system. All measured reactions are well described by theoretical calculations that do not contain ISI/FSI distortions. Our results thus showcase a new ability to study the short-distance structure of short-lived radioactive atomic nuclei at the forthcoming FAIR and FRIB facilities. These studies will be pivotal for developing a ground-breaking microscopic understanding of the structure and properties of nuclei far from stability and the formation of visible matter in the universe.

   nucl-exnucl-thNat.Phys.(2021)·67 citations
3. 03*

   Measurement of the proton spin structure at long distances

   X. Zheng🇺🇸 · A. Deur🇺🇸 · H. Kang🇰🇷 · S.E. Kuhn🇺🇸 · M. Ripani🇮🇹 · J. Zhang🇺🇸 · K.P. Adhikari🇺🇸 · S. Adhikari🇺🇸 · M.J. Amaryan🇺🇸 · H. Atac🇺🇸 · H. Avakian🇺🇸 · L. Barion🇮🇹 and 139 other authors

   Measuring the spin structure of protons and neutrons tests our understanding of how they arise from quarks and gluons, the fundamental building blocks of nuclear matter. At long distances the coupling constant of the strong interaction becomes large, requiring non-perturbative methods to calculate quantum chromodynamics processes, such as lattice gauge theory or effective field theories. Here we report proton spin structure measurements from scattering a polarized electron beam off polarized protons. The spin-dependent cross-sections were measured at large distances, corresponding to the region of low momentum transfer squared between 0.012 and 1.0 GeV${}^2$. This kinematic range provides unique tests of chiral effective field theory predictions. Our results show that a complete description of the nucleon spin remains elusive, and call for further theoretical works, e.g. in lattice quantum chromodynamics. Finally, our data extrapolated to the photon point agree with the Gerasimov-Drell-Hearn sum rule, a fundamental prediction of quantum field theory that relates the anomalous magnetic moment of the proton to its integrated spin-dependent cross-sections.

   nucl-exhep-exNat.Phys.(2021)·35 citations
4. 04*

   ${}^{229m}$Th isomer from a nuclear model perspective

   Nikolay Minkov🇧🇬 · Adriana Pálffy🇩🇪

   The physical conditions for the emergence of the extremely low-lying nuclear isomer ${}^{229m}$Th at approximately 8 eV are investigated in the framework of our recently proposed nuclear structure model. Our theoretical approach explains the ${}^{229m}$Th-isomer phenomenon as the result of a very fine interplay between collective quadrupole-octupole and single-particle dynamics in the nucleus. We find that the isomeric state can only appear in a rather limited model space of quadrupole-octupole deformations in the single-particle potential, with the octupole deformation being of a crucial importance for its formation. Within this deformation space the model-described quantities exhibit a rather smooth behaviour close to the line of isomer-ground state quasi-degeneracy determined by the crossing of the corresponding single-particle orbitals. Our comprehensive analysis confirms the previous model predictions for reduced transition probabilities and the isomer magnetic moment, while showing a possibility for limited variation in the ground-state magnetic moment theoretical value. These findings prove the reliability of the model and suggest that the same dynamical mechanism could manifest in other actinide nuclei giving a general prescription for the search and exploration of similar isomer phenomena.

   ↳ nucl-thnucl-exPRC(2021)·30 citations
5. 05*

   Measurement of Ac227 Impurity in Ac225 using Decay Energy Spectroscopy

   Aidan D. Tollefson🇺🇸 · Chandler M. Smith🇺🇸 · Matthew H. Carpenter🇺🇸 · Mark P. Croce🇺🇸 · Michael E. Fassbender🇺🇸 · Katrina E. Koehler🇺🇸 · Laura M. Lilley🇺🇸 · Ellen M. O'Brien🇺🇸 · Daniel R. Schmidt🇺🇸 · Benjamin W. Stein🇺🇸 · Joel N. Ullom🇺🇸 · Michael D. Yoho🇺🇸 · David J. Mercer🇺🇸

   225Ac is a valuable medical radionuclide for targeted alpha therapy, but 227Ac is an undesirable byproduct of an accelerator-based synthesis method under investigation. Sufficient detector sensitivity is critical for quantifying the trace impurity of 227Ac, with the 227Ac/225Ac activity ratio predicted to be approximately 0.15% by end-of-bombardment (EOB). Superconducting transition edge sensor (TES) microcalorimeters offer high resolution energy spectroscopy using the normal-to-superconducting phase transition to measure small change in temperature. By embedding 225Ac production samples in a gold foil thermally coupled to a TES microcalorimeter we can measure the decay energies of the radionuclides embedded with high resolution and efficiency. This technique, known as decay energy spectroscopy (DES), collapses several peaks from alpha decays into single Q-value peaks. In practice there are more complex factors in the interpretation of data using DES, which we will discuss herein. Using this technique we measured the EOB 227Ac impurity to be (0.142 +/- 0.005)% for a single production sample. This demonstration has shown that DES can distinguish closely related isotopic features and is a useful tool for quantitative measures.

   ↳ physics.ins-detnucl-exphysics.med-phAppl.Radiat.Isot.(2021)·3 citations
6. 06*

   The Fermi constant from muon decay versus electroweak fits and CKM unitarity

   Andreas Crivellin🇨🇭 · Martin Hoferichter🇨🇭 · Claudio Andrea Manzari🇨🇭

   The Fermi constant ($G_F$) is extremely well measured through the muon lifetime, defining one of the key fundamental parameters in the Standard Model (SM). Therefore, to search for physics beyond the SM (BSM) via $G_F$, the constraining power is determined by the precision of the second-best independent determination of $G_F$. The best alternative extractions of $G_F$ proceed either via the global electroweak (EW) fit or from superallowed $\beta$ decays in combination with the Cabibbo angle measured in kaon, $\tau$, or $D$ decays. Both variants display some tension with $G_F$ from muon decay, albeit in opposite directions, reflecting the known tensions within the EW fit and hints for the apparent violation of CKM unitarity, respectively. We investigate how BSM physics could bring the three determinations of $G_F$ into agreement using SM effective field theory and comment on future perspectives.

   ↳ hep-phhep-exhep-latnucl-ex+1PRL(2021)·77 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.