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Öğe Accessing tens-to-hundreds femtoseconds nuclear state lifetimes with low-energy binary heavy-ion reactions(Springer, 2021) Ciemala, M.; Ziliani, S.; Crespi, F. C. L.; Leoni, S.; Fornal, B.; Maj, A.; Bednarczyk, P.A novel Monte Carlo technique has been developed to determine lifetimes of excited states in the tens-to-hundreds femtoseconds range in products of low-energy heavy-ion binary reactions, with complex velocity distributions. The method is based on a detailed study of Doppler-broadened gamma-ray lineshapes. Its relevance is demonstrated in connection with the 18O(7.0MeV/u)+181Ta experiment, performed at GANIL with the AGATA+VAMOS+PARIS setup, to study neutron-rich O, C, N, ... nuclei. Excited states in O-17 and O-19, with known lifetimes, are used to validate the method over the similar to 20-400fs lifetime-sensitivity range. Emphasis is given to the unprecedented position resolution provided by gamma-tracking arrays, which turns out to be essential for reaching the required accuracy in Doppler-shift correction. The technique is anticipated to be an important tool for lifetime investigations in exotic neutron-rich nuclei, produced with intense ISOL-type beams.Öğe Complete set of bound negative-parity states in the neutron-rich nucleus 18N(Amer Physical Soc, 2021) Ziliani, S.; Ciemala, M.; Crespi, F. C. L.; Leoni, S.; Fornal, B.; Suzuki, T.; Otsuka, T.High-resolution. -ray spectroscopy of N-18 is performed with the Advanced GAmma Tracking Array, following deep-inelastic processes induced by an O-18 beam on a Ta-181 target. Six states are newly identified, which together with the three known excitations exhaust all negative-parity excited states expected in N-18 below the neutron threshold. Spin and parities are proposed for all located states on the basis of decay branchings and comparison with large-scale shell-model calculations performed in the p-sd space, with the YSOX interaction. Of particular interest is the location of the 0(1)(-) and 1(2)(-) excitations, which provide strong constrains for cross-shell p-sd matrix elements based on realistic interactions and help to simultaneously reproduce the ground and first-excited states in N-16 and N-18, for the first time. Understanding the N-18 structure may also have significant impact on neutron-capture cross-section calculations in r-process modeling including light neutron-rich nuclei.Öğe DETERMINATION OF LIFETIMES OF EXCITED STATES IN NEUTRON-RICH O-20 ISOTOPE FROM EXPERIMENT WITH THE AGATA plus PARIS plus VAMOS SETUP(JAGIELLONIAN UNIV PRESS, 2019) Ciemala, M.; Ziliani, S.; Crespi, F.; Leoni, S.; Fornal, B.; Maj, A.; Beckers, M.An experiment aiming at measuring lifetimes of the second 2(+) excited states in neutron-rich C and O isotopes was recently performed at the GANIL laboratory, in France. In these nuclei, recent ab initio calculations provide a detailed description of the nuclear excited states, predicting a strong sensitivity of the electromagnetic transition probabilities to the details of the nucleon-nucleon interactions, especially in connection with the role played by the three-body (NNN) forces. Thus, the measurement of 2(+) states lifetimes in this region will be a stringent test of the importance of including the NNN forces in describing the electromagnetic properties of selected nuclear states. This contribution reports on the status of the experimental analysis for the case of lifetimes in O-20.Öğe Lifetime analysis of short-lived states in 17N(Soc Italiana Fisica, 2021) Ziliani, S.; Ciemala, M.; Crespi, F. C. L.; Leoni, S.; Fornal, B.; Maj, A.; Bednarczyk, P.A recent extension of the Doppler-shift attenuation method to measure short lifetimes of states populated in low-energy binary reactions is applied to the case of N-17. The reliability of the technique is confirmed by measuring the lifetime of the 5515 keV 3/2(-) state, which is depopulated by two different gamma rays. The method is used to measure the lifetime of the 5170 keV (9/2(+)) state in the same nucleus. Comparisons with large-scale shell-model predictions are given as well.Öğe SHORT-RANGE LIFETIME MEASUREMENTS FOR DEEP-INELASTIC REACTION PRODUCTS: THE 19O TEST CASE(Jagiellonian Univ Press, 2020) Ciemala, M.; Ziliani, S.; Crespi, F.; Leoni, S.; Fornal, B.; Maj, A.; Bednarczyk, P.An experiment, aiming at measuring lifetimes of excited states in neutron-rich C and O isotopes, was performed at the GANIL laboratory with the use of the AGATA segmented HPGe tracking array, coupled to the PARIS scintillator array and to the VAMOS++ magnetic spectrometer. The nuclei of interest were populated in transfer and deep-inelastic processes induced by an O-18 beam at 126 MeV (7.0 MeV/u) on a Ta-181 target. This paper contains a brief description of a novel implementation of a Monte-Carlo technique, which allowed us to obtain excited states lifetimes in the range from tens to hundreds femtoseconds for a reaction with complex initial velocity distribution, making use of the Doppler-shift attenuation method (DSAM). As a test case, we present here the analysis for two states in O-19: 2371-keV 9/2(+) and 2779-keV 7/2(+), for which lifetimes of tau > 400 fs and tau = 140(-40)(+50) fs were obtained, respectively, in agreement with literature values. This newly developed approach will be essential for short lifetimes measurements in neutron-rich systems, exploiting intense ISOL-type beams, currently under development.Öğe SPECTROSCOPY OF NEUTRON-RICH C, O, N AND F ISOTOPES WITH THE AGATA plus PARIS plus VAMOS SETUP AT GANIL(JAGIELLONIAN UNIV PRESS, 2019) Ziliani, S.; Ciemala, M.; Crespi, F.; Leoni, S.; Fornal, B.; Maj, A.; Beckers, M.Recent ab initio calculations pointed out the importance of the three-body terms of the nuclear interaction, in the description of the structure of n-rich systems. The state lifetimes in light n-rich carbon and oxygen nuclei have been predicted to be sensitive to the three-body terms and, in this context, an experiment, aiming at the measurement of these lifetimes, was performed in GANIL in July 2017 with the AGATA and PARIS arrays coupled to the VAMOS++ magnetic spectrometer. Details on the AGATA preliminary data analysis are presented.Öğe SPECTROSCOPY OF NEUTRON-RICH NITROGEN ISOTOPES WITH AGATA plus PARIS plus VAMOS(Jagiellonian Univ Press, 2020) Ziliani, S.; Ciemala, M.; Crespi, F. C. L.; Leoni, S.; Fornal, B.; Maj, A.; Bednarczyk, P.Excited states of N-17, N-18 and N-19 were investigated through the measurement of gamma rays, following their population via deep-inelastic reactions induced by an O-18 beam (7 MeV/u) on a thick Ta-181 target. The experimental setup comprised the AGATA+PARIS detection system, coupled to the VAMOS++ magnetic spectrometer. In the N-17 nucleus, the analysis of gamma-ray transitions de-exciting two states around 4-5 MeV clearly pointed to discrepancies with the lifetime values reported in literature. Three new gamma rays were observed in N-18 at the energies of 1662.3 (3) keV, 2073.4 (8) keV and 2300.9 (8) keV, and hints for other two new transitions around 1566 keV and 1720 keV were found. In addition, a new transition with energy of 2489.7 (8) keV was observed in N-19.Öğe Testing ab initio nuclear structure in neutron-rich nuclei: Lifetime measurements of second 2+ state in 16C and 20O(Amer Physical Soc, 2020) Ciemala, M.; Ziliani, S.; Crespi, F. C. L.; Leoni, S.; Fornal, B.; Maj, A.; Bednarczyk, P.To test the predictive power of ab initio nuclear structure theory, the lifetime of the second 2(+) state in neutron-rich O-20, tau(2(2)(+)) = 150(-30)(+80) fs, and an estimate for the lifetime of the second 2(+) state in C-16 have been obtained for the first time. The results were achieved via a novel Monte Carlo technique that allowed us to measure nuclear state lifetimes in the tens-to-hundreds of femtoseconds range by analyzing the Doppler-shifted gamma-transition line shapes of products of low-energy transfer and deep-inelastic processes in the reaction O-18 (7.0 MeV/u) + Ta-181. The requested sensitivity could only be reached owing to the excellent performances of the Advanced gamma-Tracking Array AGATA, coupled to the PARIS scintillator array and to the VAMOS++ magnetic spectrometer. The experimental lifetimes agree with predictions of ab initio calculations using two- and three-nucleon interactions, obtained with the valence-space in-medium similarity renormalization group for O-20 and with the no-core shell model for C-16. The present measurement shows the power of electromagnetic observables, determined with high-precision gamma spectroscopy, to assess the quality of first-principles nuclear structure calculations, complementing common benchmarks based on nuclear energies. The proposed experimental approach will be essential for short lifetime measurements in unexplored regions of the nuclear chart, including r-process nuclei, when intense beams, produced by Isotope Separation On-Line (ISOL) techniques, become available.
