First spectroscopy of ¹¹⁰ Zr with MINOS

Abstract : A predicted N=70 subshell closure in ¹¹⁰Zr has long been considered a potential explanation for the disagreement between theory and observed abundances of the heavy elements near mass 130 resulting from the rapid neutron capture process (r-process). The r-process is not well understood, due in part to the uncertainties of the neutron-rich structure evolution mechanisms. A subshell closure in ¹¹⁰Zr, though unlikely, could result from either a tetrahedral or spherical symmetry. Each of these symmetries leaves distinct fingerprints on the low lying level structure, and thus can be discerned with a simple spectroscopy measurement. The MINOS system has been used at the Radioactive Isotope Beam Factory of RIKEN in Japan to perform the first spectroscopy of ¹¹⁰Zr. MINOS, developed at CEA-IRFU, combines a thick proton target with a vertex tracker to allow high resolution spectroscopy of rare nuclei. Low lying states in ¹¹⁰Zr were populated via proton removal on the MI- NOS target, and deexcitation gamma rays detected with the DALI2 scintillator array. Results are consistent with a well deformed nucleus. No evidence is found for a subshell closure at N=70 nor tetrahedral symmetry. A complementary study explores inclusive cross sections for (p,2p) and (p,pn) reactions with neutron rich nuclei. Approximately 60 inclusive cross sections have been measured for single nucleon removal on the MINOS target. The (p,2p) systematics reveal an enhanced cross section to odd-Z daughter nuclei, pointing to the importance of pairing correlations. The (p,pn) cross sections are approximately a factor of 10 larger than the (p,2p) cross sections, randomly distributed around 60 mb. Comparison with semi-classical models suggest that both these systematics can be explained by the important role of pairing correlations in direct reaction systematics for exotic nuclei. Finally, the electric field cage of the MINOS time projection chamber is optimized with electrostatic simulations in view of a future application as a pion tracker for antiproton-nucleus collisions in a new physics program at CERN called PUMA.
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  • HAL Id : tel-02130623, version 2

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Nancy Paul. First spectroscopy of ¹¹⁰ Zr with MINOS. Nuclear Experiment [nucl-ex]. Université Paris-Saclay, 2018. English. ⟨NNT : 2018SACLS547⟩. ⟨tel-02130623v2⟩

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