We report on spectroscopic information and lifetime measurements in the neutron-rich 135,137,139I isotopes. This is the first lifetime data on iodine isotopes beyond N=82. Excited states were ...populated in fast neutron-induced fission of 238U at the ALTO facility of IJCLab with the LICORNE neutron source and detected using the hybrid ν-ball spectrometer. The level schemes of the 135,137,139I isotopes are revised in terms of excited states with up to maximum spin-parity of (33/2+), populated for the first time in fast neutron-induced fission. We provide first results on the lifetimes of the (9/2+1) and (13/2+1) states in 137I and 139I, and the (17/2+1) state in 137I. In addition, we give upper lifetime limits for the (11/2+1) states in 135−139I, the (15/2+1) state in 137I, the (17/2+1) state in 139I, and reexamine the (29/2+1) state in 137I. The isomeric data in 135I are reinvestigated, such as the previously known (15/2+1) and (23/2−1) isomers with T1/2 of 1.64(14) and 4.6(7) ns, respectively, as obtained in this work. The new spectroscopic information is compared to that from spontaneous or thermal-neutron induced fission and discussed in the context of large scale shell-model (LSSM) calculations for the region beyond 132Sn, indicating the behavior of collectivity for the three valence-proton iodine chain with N=82,84,86.
Abstract
The iThemba Laboratory for Accelerator Based Sciences (iThemba LABS) is a centre of expertise and innovation in the field of nuclear-structure physics and is a leader in several high-impact ...studies. One of the highlights of these nuclear-structure experiments is the study of the broad structure of the IsoVector Giant Dipole Resonance (IVGDR) in the rare-earth region. Proton inelastic scattering experiments with
E
p
= 200 MeV were performed on the even-even Nd isotope chain and
152
Sm at very forward scattering angles including zero degrees with the K600 magnetic spectrometer. The evolution of the shape of the IVGDR in the transition from spherical to deformed nuclei was investigated. One of the goals of this highlighted study was to confirm the
K
-splitting observed in previous photo-absorption measurements from Saclay. Significant discrepancies were found between the direct (γ, xn) data obtained at Saclay and the equivalent photo-absorption cross sections obtained using (p, p′) data from the K600. Furthermore, discrepancies exist for several nuclei between photo-absorption data taken at the Saclay and Livermore laboratories. These discrepancies, possible reasons for them and future investigations will be presented and discussed.
Pygmy Dipole Response in Samarium isotopes Jivan, H; Pellegri, L; Adsley, P. ...
Journal of physics. Conference series,
09/2023, Letnik:
2586, Številka:
1
Journal Article
Recenzirano
Odprti dostop
Abstract
The influence of nuclear shape deformation on the Pygmy Dipole Response (PDR) was investigated using (α,α′γ) scattering on
144
Sm and
154
Sm. Experiments were conducted at iThemba LABS, ...coupling for the first time the K600 magnetic spectrometer with the BaGeL (Ball of Germanium and LaBr detectors) array. Preliminary results showcasing the efficacy of the facility and set-up for performing these 0° scattering experiments to investigate the PDR region are presented.
We present
12
C+
12
C direct fusion measurements with STELLA UKFATIMA, that reach into the region of astrophysics interest relevant to massive stars (
M
⊙
≈ 25) using self-supporting thin rotating ...carbon foils 1. We demonstrate that detecting gammas and light charged particles in coincidence with nanosecond timing is key for effective background reduction achieving reliable measurements in the sub-nanobarn range. We give details about core developments of the detection apparatus as well as the coincidence-analysis procedure of low count statistics. The present data largely follows the phenomenological hindrance interpolation and shows indication for resonant behaviour at the lowest energy explored.
Experiments investigating the fine structure of the IsoScalar Giant Monopole Resonance (ISGMR) of 48Ca were carried out with a 200 MeV alpha inelastic-scattering reaction, using the high ...energy-resolution capability and the zero-degree setup at the K600 magnetic spectrometer of iThemba LABS, Cape Town, South Africa. Considerable fine structure is observed in the energy region of the ISGMR. Characteristic energy scales are extracted from the experimental data by means of a wavelet analysis and compared with the state-of-the-art theoretical calculations within a Skyrme-RPA (random phase approximation) approach using the finite-rank separable approximation with the inclusion of phonon-phonon coupling (PPC). Good agreement was observed between the experimental data and the theoretical predictions.
Among the reactions driving stellar evolution during carbon burning, 12C + 12C fusion provides the key ingredients. This system reveals many resonances, but also regions with suppressed fusion ...cross-sections. The reaction was recently measured by the STELLA collaboration utilizing the gammaparticle coincidence technique for precise cross-section measurements reaching down to the Gamow window of massive stars. From the experimental data, reaction rates were determined by approximating a hindrance parametrization and by adding on top a resonance at the lowest measured energy. The impact of these reaction rates on the evolution of massive stars was explored with models of 12 and 25 M⊙ using the stellar evolution code GENEC, and a detailed study of the resulting nucleosynthesis with a 1454 elements network was performed. The sensitivity of the STELLA experimental cross-sections on the temperature range for C-burning for the stellar models studied were presented. The final abundances and their impacts on stellar evolution were discussed.
The Trojan Horse method relies on performing reactions in a specific kinematic phase space that maximizes contributions of a quasi-free reaction mechanism. The hallmark of this method is that the ...incident particle can be accelerated to high enough energies to overcome the Coulomb barrier of the target, but once inside the target nucleus the relative motion of the clustered nuclei allows the reaction of interest to proceed at energies below this Coulomb Barrier. This method allows the experimentalist to probe reactions that have significance in astrophysics at low reaction energies that would otherwise be impossible due to the vanishing cross section. Traditionally the Trojan Horse method has been applied with the use of silicon detectors to observe the reaction products. In this study we apply the Trojan Horse method to a well studied reaction to examine the potential benefits of using a splitpole magnetic spectrograph to detect one of the reaction products. We have measure the three body 7Li(d,αn)α reaction to constrain the energy 7Li(d,α)α cross section. Measurements were first made using two silicon detectors, and then by replacing one detector with the magnetic spectrograph. The experimental design, limitations, and early results are discussed.
The combination of a magnetic spectrometer and ancillary detectors such as silicon detectors is a powerful tool for the study of nuclear reactions and nuclear structure. This paper discusses the ...recently commissioned silicon array called the "CAKE" which is designed for use with the K600 magnetic spectrometer at iThemba LABS.
The experimental setup STELLA (STELlar LAboratory) is designed for the measurement of deep sub-barrier light heavy ion fusion cross sections. For background suppression the γ-particle coincidence ...technique is used. In this project, LaBr3 detectors from the UK FATIMA (FAst TIMing Array) collaboration are combined with annular silicon strip detectors customized at IPHC-CNRS, Strasbourg, and the setup is located at Andromède, IPN, Orsay. The commissioning of the experimental approach as well as a sub-barrier 12C +12C → 24Mg∗ cross section measurement campaign are carried out.
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