30 research outputs found
Mass measurements towards doubly magic Ni-78 : Hydrodynamics versus nuclear mass contribution in core-collapse supernovae
We report the first high-precision mass measurements of the neutron-rich nuclei Ni-74,Ni-75 and the clearly identified ground state of Cu-76, along with a more precise mass-excess value of Cu-78, performed with the double Penning trap JYFLTRAP at the Ion Guide Isotope Separator On-Line (IGISOL) facility. These new results lead to a quantitative estimation of the quenching for the N = 50 neutron shell gap. The impact of this shell quenching on core-collapse supernova dynamics is specifically tested using a dedicated statistical equilibrium approach that allows a variation of the mass model independent of the other microphysical inputs. We conclude that the impact of nuclear masses is strong when implemented using a fixed trajectory as in the previous studies, but the effect is substantially reduced when implemented self-consistently in the simulation. (C) 2022 The Authors. Published by Elsevier B.V.Peer reviewe
STRASSE: A Silicon Tracker for Quasi-free Scattering Measurements at the RIBF
STRASSE (Silicon Tracker for RAdioactive nuclei Studies at SAMURAI
Experiments) is a new detection system under construction for quasi-free
scattering (QFS) measurements at 200-250 MeV/nucleon at the RIBF facility of
the RIKEN Nishina Center. It consists of a charged-particle silicon tracker
coupled with a dedicated thick liquid hydrogen target (up to 150-mm long) in a
compact geometry to fit inside large scintillator or germanium arrays. Its
design was optimized for two types of studies using QFS: missing-mass
measurements and in-flight prompt -ray spectroscopy. This article
describes (i) the resolution requirements needed to go beyond the sensitivity
of existing systems for these two types of measurements, (ii) the conceptual
design of the system using detailed simulations of the setup and (iii) its
complete technical implementation and challenges. The final tracker aims at a
sub-mm reaction vertex resolution and is expected to reach a missing-mass
resolution below 2 MeV in for reactions when combined with
the CsI(Na) CATANA array.Comment: 25 pages, 29 figure
Narrow resonances in the continuum of the unbound nucleus F
The structure of the unbound F nucleus is investigated using the inverse kinematics resonant scattering of a radioactive O beam impinging on a CH target. The analysis of H(O,p)O and H(O,2p)N reactions allowed the confirmation of the previously observed narrow resonance, near the two-proton decay threshold, and the identification of two new narrow 5/2 and 3/2 resonances. The newly observed levels decay by 1p emission to the ground of O, and by sequential 2p emission to the ground state (g.s.) of N via the resonance of O. Gamow shell model (GSM) analysis of the experimental data suggests that the wave functions of the 5/2 and 3/2 resonances may be collectivized by the continuum coupling to nearby 2p- and 1p- decay channels. The observed excitation function H(O,p)O and resonance spectrum in F are well reproduced in the unified framework of the GSM
Overview and performance of the 2023 MUGAST@LISE campaign at GANIL
International audienceMUGAST is a state-of-the-art silicon array combining trapezoidal and square shaped double-sided silicon strip detectors (DSSD) to four MUST2 telescopes. Coupled to a γ-ray spectrometer, the excellent angular coverage and compacity of the MUGAST array make it an ideal tool for the study of transfer reactions. It is a first step toward the development of the new generation of silicon arrays using pulse shape analysis (PSA) for particle identification, such as the future GRIT array developed by our collaboration. In recent years, MUGAST has been widely used at GANIL. First with the AGATA γ-ray spectrometer and the VAMOS large acceptance spectrometer for the study of ISOL beams from the SPIRAL1 facility. It is now coupled with twelve EXOGAM clovers and to a new zero degree detection system at the end of the LISE fragmentation beamline
Long-sought isomer turns out to be the ground state of Cu
International audienceIsomers close to the doubly magic nucleus Ni (, ) provide essential information on the shell evolution and shape coexistence far from stability. The existence of a long-lived isomeric state in Cu has been debated for a long time. We have performed high-precision mass measurements of Cu with the JYFLTRAP double Penning trap mass spectrometer at the Ion Guide Isotope Separator On-Line facility and confirm the existence of such a isomeric state with an excitation energy keV. Based on the ratio of detected ground- and isomeric-state ions as a function of time, we show that the isomer is the shorter-living state previously considered as the ground state of Cu. The result can potentially change the conclusions made in previous works related to the spin-parity and charge radius of the Cu ground state. Additionally, the new Cu reaction -value has an impact on the astrophysical rapid neutron-capture process
Evaluation of the reaction rate using the transfer reaction
International audienceBackground: A recent sensitivity study has shown that the K35(p,γ)Ca36 reaction is one of the ten (p,γ) reaction rates that could significantly impact the shape of the calculated x-ray burst light curve. Its reaction rate used up to now in type I x-ray burst calculations was estimated using an old measurement for the mass of Ca36 and theoretical predictions for the partial decay widths of the first 2+ resonance with arbitrary uncertainties. Purpose: In this work, we propose to reinvestigate the K35(p,γ)Ca36 reaction rate, as well as related uncertainties, by determining the energies and decay branching ratios of Ca36 levels, within the Gamow window of x-ray bursts, in the 0.5 to 2 GK temperature range. Method: These properties were studied by means of the one-neutron pickup transfer reaction Ca37(p,d)Ca36 in inverse kinematics using a radioactive beam of Ca37 at 48 MeV nucleon−1. The experiment was performed at the GANIL facility using the liquid hydrogen target CRYPTA, the MUST2 charged particle detector array for the detection of the light charged particles, and a zero degree detection system for the outgoing heavy recoil nuclei. Results: The atomic mass of Ca36 is confirmed and new resonances have been proposed together with their proton decay branching ratios. This spectroscopic information, used in combination with very recent theoretical predictions for the γ-decay width, were used to calculate the K35(p,γ)Ca36 reaction rate. The recommended rate of the present work was obtained within a uncertainty factor of 2 at 1σ. This is consistent with the previous estimate in the x-ray burst temperature range. A large increase of the reaction rate was found at higher temperatures due to two newly discovered resonances. Conclusions: The K35(p,γ)Ca36 thermonuclear reaction rate is now well constrained by the present work in a broad range of temperatures covering those relevant to type I x-ray bursts. Our results show that the K35(p,γ)Ca36 reaction does not affect the shape of the x-ray burst light curve, and that it can be removed from the list of the few influential proton radiative captures reactions having a strong impact on the light curve
N=16 magicity revealed at the proton drip-line through the study of 35Ca
International audienceThe last proton bound calcium isotope Ca has been studied for the first time, using the Ca()Ca two neutron transfer reaction. The radioactive Ca nuclei, produced by the LISE spectrometer at GANIL, interacted with the protons of the liquid hydrogen target CRYPTA, to produce tritons that were detected in the MUST2 detector array, in coincidence with the heavy residues Ca or Ar. The atomic mass of Ca and the energy of its first 3/2 state are reported. A large gap of 4.61(11) MeV is deduced from the mass measurement, which together with other measured properties, makes Ca a doubly-magic nucleus. The shell gaps in Ca and O are of similar amplitude, at both edges of the valley of stability. This feature is discussed in terms of nuclear forces involved, within state-of-the-art shell model calculations. Even though the global agreement with data is quite convincing, the calculations underestimate the size of the gap in 36Ca by 840(110) keV
The structure of Ca under the Coulomb magnifying glass
Detailed spectroscopy of the neutron-deficient nucleus Ca was obtained up to 9 MeV using the Ca(,)Ca and the Ca(,)Ca transfer reactions. The radioactive nuclei, produced by the LISE spectrometer at GANIL, interacted with the protons of the liquid Hydrogen target CRYPTA, to produce light ejectiles (the deuteron or triton ) that were detected in the MUST2 detector array, in coincidence with the heavy residues %identified by a zero degree detection system. %States have been measured up to 9 MeV. Our main findings are: i) a similar shift in energy for the 1 and 2 states by about -250 keV, as compared to the mirror nucleus S, ii) the discovery of an intruder 0 state at 2.83(13) MeV, which appears below the first 2 state, in contradiction with the situation in S, and iii) a tentative 0 state at 4.83(17) MeV, proposed to exhibit a bubble structure with two neutron vacancies in the 2s orbit. The inversion between the 0 and 2 states is due to the large mirror energy difference (MED) of -516(130) keV for the former. This feature is reproduced by Shell Model (SM) calculations, using the - valence space, predicting an almost pure intruder nature for the 0 state, with two protons (neutrons) being excited across the =20 magic closure in Ca (S). This mirror system has the largest MEDs ever observed, if one excludes the few cases induced by the effect of the continuum