9 research outputs found
Study of oblate nuclear shapes and shape coexistence in neutron-deficient rare earth isotopes
Search for Na in novae supported by a novel method for measuring femtosecond nuclear lifetimes
Classical novae are thermonuclear explosions in stellar binary systems, and
important sources of Al and Na. While gamma rays from the decay
of the former radioisotope have been observed throughout the Galaxy, Na
remains untraceable. The half-life of Na (2.6 yr) would allow the
observation of its 1.275 MeV gamma-ray line from a cosmic source. However, the
prediction of such an observation requires good knowledge of the nuclear
reactions involved in the production and destruction of this nucleus. The
Na()Mg reaction remains the only source of large
uncertainty about the amount of Na ejected. Its rate is dominated by a
single resonance on the short-lived state at 7785.0(7) keV in Mg. In the
present work, a combined analysis of particle-particle correlations and
velocity-difference profiles is proposed to measure femtosecond nuclear
lifetimes. The application of this novel method to the study of the Mg
states, combining magnetic and highly-segmented tracking gamma-ray
spectrometers, places strong limits on the amount of Na produced in
novae, explains its non-observation to date in gamma rays (flux < 2.5x
ph/(cms)), and constrains its detectability with future space-borne
observatories.Comment: 18 pages, 3 figures, 1 tabl
Conceptual design of the early implementation of the NEutron Detector Array (NEDA) with AGATA
The NEutron Detector Array (NEDA) project aims at the construction of a new high-efficiency compact neutron detector array to be coupled with large (Formula presented.) -ray arrays such as AGATA. The application of NEDA ranges from its use as selective neutron multiplicity filter for fusion-evaporation reaction to a large solid angle neutron tagging device. In the present work, possible configurations for the NEDA coupled with the Neutron Wall for the early implementation with AGATA has been simulated, using Monte Carlo techniques, in order to evaluate their performance figures. The goal of this early NEDA implementation is to improve, with respect to previous instruments, efficiency and capability to select multiplicity for fusion-evaporation reaction channels in which 1, 2 or 3 neutrons are emitted. Each NEDA detector unit has the shape of a regular hexagonal prism with a volume of about 3.23l and it is filled with the EJ301 liquid scintillator, that presents good neutron- (Formula presented.) discrimination properties. The simulations have been performed using a fusion-evaporation event generator that has been validated with a set of experimental data obtained in the 58Ni + 56Fe reaction measured with the Neutron Wall detector array
Analysis of the Response of AGATA Detectors at GSI
In 2012 and 2014 the gamma-ray tracking spectrometer AGATA was operated at the SIS/FRS facility at GSI in Darmstadt, Germany. The performance of the array is discussed, outlining some important aspects of the offline data processing and analysis. Relying on the data obtained from measurements with standard gamma-ray sources, a first estimate of the photopeak efficiency and peak-to-total (P/T) is presented
N=50 core excited states studied in the 4696Pd50 nucleus
The four-proton hole Pd-96 neighbor of the doubly-magic Sn-100 nucleus was studied in-beam, using a fusion-evaporation reaction of a Ni-58 beam on a Sc-45 target. States of Pd-96 were established up to an excitation energy of 9707 keV. A core-excited odd-parity isomer with T-1/2 = 37.7(1.1) ns was identified. Shell model calculations were performed in four different model spaces. Even-parity states of Pd-96 are very well reproduced in large-scale shell model (LSSM) calculations in which excitations are allowed of up to five g(9/2) protons and neutrons across the N = Z = 50 gap, to the g(7/2), d(5/2), d(3/2), and s(1/2) orbitals. The odd-parity isomer can be only qualitatively interpreted though, employing calculation in the full fpg shell model space, with just one particle-hole core excitation
Search for Na in novae supported by a novel method for measuring femtosecond nuclear lifetimes
Classical novae are thermonuclear explosions in stellar binary systems, and important sources of Al and Na. While γ rays from the decay of the former radioisotope have been observed through-out the Galaxy, Na remains untraceable. The half-life of Na (2.6 yr) would allow the observation of its 1.275 MeV γ-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of the nuclear reactions involved in the production and destruction of this nucleus. The Na(p, γ)Mg reaction remains the only source of large uncertainty about the amount of Na ejected. Its rate is dominated by a single reso- nance on the short-lived state at 7785.0(7) keV in Mg. In the present work, a combined analysis of particle-particle correlations and velocity-difference profiles is proposed to measure femtosecond nuclear lifetimes. The application of this novel method to the study of the Mg states, combining magnetic and highly-segmented tracking γ -ray spectrometers, places strong limits on the amount of Na produced in novae, explains its non-observation to date in γ rays (flux < 2.5×10 ph.cm s), and constrains its detectability with future space-borne observatories
Search for 22Na in novae supported by a novel method for measuring femtosecond nuclear lifetimes
Abstract Classical novae are thermonuclear explosions in stellar binary systems, and important sources of 26Al and 22Na. While γ rays from the decay of the former radioisotope have been observed throughout the Galaxy, 22Na remains untraceable. Its half-life (2.6 yr) would allow the observation of its 1.275 MeV γ-ray line from a cosmic source. However, the prediction of such an observation requires good knowledge of its nucleosynthesis. The 22Na(p, γ)23Mg reaction remains the only source of large uncertainty about the amount of 22Na ejected. Its rate is dominated by a single resonance on the short-lived state at 7785.0(7) keV in 23Mg. Here, we propose a combined analysis of particle-particle correlations and velocity-difference profiles to measure femtosecond nuclear lifetimes. The application of this method to the study of the 23Mg states, places strong limits on the amount of 22Na produced in novae and constrains its detectability with future space-borne observatories
Physics opportunities with the Advanced Gamma Tracking Array : AGATA
New physics opportunities are opening up by the Advanced Gamma Tracking Array, AGATA, as it evolves to the full 4 pi instrument. AGATA is a high-resolution gamma -ray spectrometer, solely built from highly segmented high-purity Ge detectors, capable of measuring gamma rays from a few tens of keV to beyond 10 MeV, with unprecedented efficiency, excellent position resolution for individual gamma -ray interactions, and very high count-rate capability. As a travelling detector AGATA will be employed at all major current and near-future European research facilities delivering stable and radioactive ion beams
Pseudospin Symmetry and Microscopic Origin of Shape Coexistence in the Ni-78 Region : A Hint from Lifetime Measurements
Lifetime measurements of excited states of the light N = 52 isotones Kr-88, Se-86, and Ge-84 have been performed, using the recoil distance Doppler shift method and VAMOS and AGATA spectrometers for particle identification and gamma spectroscopy, respectively. The reduced electric quadrupole transition probabilities B(E2; 2(+)-> 0(+)) and B(E2; 4(+)-> 2(+)) were obtained for the first time for the hard-to-reach 84Ge. While the B(E2; 2(+)-> 0(+) ) values of Kr-88, Se-86 saturate the maximum quadrupole collectivity offered by the natural valence (3s, 2d, 1g(7/2), 1h(11/2)) space of an inert Ni-78 core, the value obtained for Ge-84 largely exceeds it, suggesting that shape coexistence phenomena, previously reported at N less than or similar to 49, extend beyond N = 50. The onset of collectivity at Z = 32 is understood as due to a pseudo-SU(3) organization of the proton single-particle sequence reflecting a clear manifestation of pseudospin symmetry. It is realized that the latter provides actually reliable guidance for understanding the observed proton and neutron single particle structure in the whole medium-mass region, from Ni to Sn, pointing towards the important role of the isovector-vector rho field in shell-structure evolution