Mon·May 22, 2023Monday·May 22, 2023

1. 01*

   Decay Spectroscopy of ${}^{160}$Eu: Quasiparticle Configurations of Excited States and Structure of $K^{\pi }$=$4^{+}$ Band-heads in ${}^{160}$Gd

   D. Yates · R. Kruecken · I. Dillmann · P.E. Garrett · B. Olaizola · V. Vedia · F.A. Ali · C. Andreoiu · W. Ashfield · G.C. Ball · Z. Beadle · N. Bernier and 36 other authors

   \noindent \textbf{Background:} Detailed spectroscopy of neutron-rich, heavy, deformed nuclei is of broad interest for nuclear astrophysics and nuclear structure. Nuclei in the r-process path and following freeze-out region impact the resulting r-process abundance distribution, and the structure of nuclei midshell in both proton and neutron number helps to understand the evolution of subshell gaps and large deformation in these nuclei. \noindent \textbf{Purpose:} To improve the understanding of the nuclear structure of ${}^{160}$Gd, specifically the $K^{\pi }$=$4^{+}$ bands, as well as study the $\beta$-decay of ${}^{160}$Eu into ${}^{160}$Gd. \noindent \textbf{Methods:} High-statistics decay spectroscopy of ${}^{160}$Gd resulting from the $\beta$-decay of ${}^{160}$Eu was collected using the GRIFFIN spectrometer at the TRIUMF-ISAC facility. \noindent \textbf{Results:} Two new excited states and ten new transitions were observed in ${}^{160}$Gd. The $\beta$-decaying half-lives of the low- and high-spin isomer in ${}^{160}$Eu were determined, and the low-spin state's half-life was measured to be $t_{1/2}=26.0(8)$~s, $\sim$16\% shorter than previous measurements. Lifetimes of the two $K^{\pi }$=$4^{+}$ band-heads in ${}^{160}$Gd were measured for the first time, as well as $\gamma$-$\gamma$ angular correlations and mixing ratios of intense transitions out of those band-heads. \noindent \textbf{Conclusions:} Lifetimes and mixing ratios suggest that the hexadecapole phonon model of the $K^{\pi }$=$4^{+}$ band-heads in ${}^{160}$Gd is preferred over a simple two-state strong mixing scenario, although further theoretical calculations are needed to fully understand these states. Additionally, the 1999.0 keV state in ${}^{160}$Gd heavily populated in $\beta$-decay is shown to have positive parity, which raises questions regarding the structure of the high-spin $\beta$-decaying state in ${}^{160}$Eu.

   nucl-exPRC(2023)·1 citation
2. 02*

   Heavy-ion collision basics

   Dariusz Miśkowiec🇩🇪

   Basic concepts and terminology of relativistic heavy-ion collision physics are introduced and illustrated by experimental results. Most plots are taken from a recent ALICE overview paper arxiv:2211.04384 [nucl-ex].

   nucl-ex0 citations
3. 03*

   The helion charge radius from laser spectroscopy of muonic helium-3 ions

   The CREMA Collaboration: Karsten Schuhmann🇨🇭 · Luis M. P. Fernandes🇵🇹 · François Nez🇫🇷 · Marwan Abdou Ahmed🇩🇪 · Fernando D. Amaro🇵🇹 · Pedro Amaro🇧🇷 · François Biraben🇫🇷 · Tzu-Ling Chen🇹🇼 · Daniel S. Covita🇵🇹 · Andreas J. Dax🇨🇭 · Marc Diepold🇩🇪 · Beatrice Franke🇩🇪 and 27 other authors

   Hydrogen-like light muonic ions, in which one negative muon replaces all the electrons, are extremely sensitive probes of nuclear structure, because the large muon mass increases tremendously the wave function overlap with the nucleus. Using pulsed laser spectroscopy we have measured three 2S-2P transitions in the muonic helium-3 ion (${\mu }^3$He${}^{+}$), an ion formed by a negative muon and bare helium-3 nucleus. This allowed us to extract the Lamb shift $E(2P_{1/2}-2S_{1/2})=1258.598(48{)}^{\exp }(3{)}^{\mathrm{theo}}$ meV, the 2P fine structure splitting $E_{\mathrm{FS}}^{\exp }=144.958(114)$ meV, and the 2S-hyperfine splitting (HFS) $E_{\mathrm{HFS}}^{\exp }=-166.495(104{)}^{\exp }(3{)}^{\mathrm{theo}}$ meV in ${\mu }^3$He${}^{+}$. Comparing these measurements to theory we determine the rms charge radius of the helion (${}^3$He nucleus) to be $r_h$ = 1.97007(94) fm. This radius represents a benchmark for few nucleon theories and opens the way for precision tests in ${}^3$He atoms and ${}^3$He-ions. This radius is in good agreement with the value from elastic electron scattering, but a factor 15 more accurate. Combining our Lamb shift measurement with our earlier one in ${\mu }^4$He${}^{+}$ we obtain $r_h^2-r_{\alpha }^2=1.0636(6{)}^{\exp }(30{)}^{\mathrm{theo}}$ fm${}^2$ to be compared to results from the isotope shift measurements in regular He atoms, which are however affected by long-standing tensions. By comparing $E_{\mathrm{HFS}}^{\exp }$ with theory we also obtain the two-photon-exchange contribution (including higher orders) which is another important benchmark for ab-initio few-nucleon theories aiming at understanding the magnetic and current structure of light nuclei.

   ↳ physics.atom-phnucl-ex25 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.