The fine structure of the IsoVector Giant Dipole Resonance (IVGDR) in the doubly-magic nuclei 40,48Ca observed in inelastic proton scattering experiments under 0∘ is used to investigate the role of ...different mechanisms contributing to the IVGDR decay width. Characteristic energy scales are extracted from the fine structure by means of wavelet analysis. The experimental scales are compared to different theoretical approaches allowing for the inclusion of complex configurations beyond the mean-field level. Calculations are performed in the framework of RPA and beyond-RPA in a relativistic approach based on an effective meson-exchange interaction, with the UCOM effective interaction and, for the first time, with realistic two- plus three-nucleon interactions from chiral effective field theory employing the in-medium similarity renormalization group. All models highlight the role of Landau fragmentation for the damping of the IVGDR, while the differences in the coupling strength between one particle-one hole (1p-1h) and two particle-two hole (2p-2h) correlated (relativistic) and non-correlated (non-relativistic) configurations lead to very different pictures of the importance of the spreading width resulting in wavelet scales being a sensitive measure of their interplay. The relativistic approach with particle-vibration coupling, in particular, shows impressive agreement with the number and absolute values of the scales extracted from the experimental data.
Proton inelastic scattering experiments at energy Ep=200 MeV and a spectrometer scattering angle of 0° were performed on 144,146,148,150Nd and 152Sm exciting the IsoVector Giant Dipole Resonance ...(IVGDR). Comparison with results from photo-absorption experiments reveals a shift of resonance maxima towards higher energies for vibrational and transitional nuclei. The extracted photo-absorption cross sections in the most deformed nuclei, 150Nd and 152Sm, exhibit a pronounced asymmetry rather than a distinct double-hump structure expected as a signature of K-splitting. This behaviour may be related to the proximity of these nuclei to the critical point of the phase shape transition from vibrators to rotors with a soft quadrupole deformation potential. Self-consistent random-phase approximation (RPA) calculations using the SLy6 Skyrme force provide a relevant description of the IVGDR shapes deduced from the present data.
Abstract
Extensive experimental investigations into understanding the fine structure of giant resonances in nuclei across the periodic table have been carried out in recent years using the ...state-of-the-art K600 magnetic spectrometer of iThemba LABS, Cape Town, South Africa. Based on the established results in comparison to various theoretical calculations, it has been found that the fine structure observed in different giant resonances, namely Isoscalar Giant Quadrupole Resonance (ISGQR), Isovector Giant Dipole Resonance (IVGDR) and Isoscalar Giant Monopole Resonance (ISGMR), in light nuclei such as
40
Ca,
28
Si and
27
Al is dominated by Landau damping although signatures for the role of the spreading width are also found. In this report, characteristic energy scales extracted in light nuclei are compared with the state-of-the-art theoretical calculations, while the fine structures results obtained are compared using semblance analysis to search for possible signatures of common fragmentation patterns induced by Landau damping and coupling to 2p-2h states obtained from different giant resonances.
We report on the optical and structural properties of plastic scintillators irradiated with neutron beams produced by the IBR-2 reactor of the Frank Laboratory of Neutron Physics in JINR, Dubna. Blue ...UPS-923A and green plastic scintillators were irradiated with neutron fluence ranging from 1013 to 1017 n/cm2. Discolouring in the plastic scintillators was observed after irradiation. The effects of radiation damage on the optical and structural properties of the samples were characterized by conducting light yield, light transmission, light fluorescence and Raman spectroscopy studies. The results showed that neutron radiation induced damage in the material. The disappearance of the Raman peak features in green scintillators at frequencies of 1165.8, 1574.7 and 1651.2 cm−1 revealed significant structural alterations due to neutron bombardment. Losses in fluorescence intensity, light yield and light transmission in the plastic scintillators were observed.
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.
The year 2022 has been scheduled to see an upgrade of the Large Hadron Collider (LHC), in order to increase its instantaneous luminosity. The High Luminosity LHC, also referred to as the upgrade ...Phase-II, means an inevitable complete re-design of the read-out electronics in the Tile Calorimeter (TileCal) of the A Toroidal LHC Apparatus (ATLAS) detector. Here, the new read-out architecture is expected to have the front-end electronics transmit fully digitized information of the detector to the back-end electronics system. Fully digitized signals will allow more sophisticated reconstruction algorithms which will contribute to the required improved triggers at high pile-up. In Phase II, the current Mobile Drawer Integrity ChecKing (MobiDICK) test-bench will be replaced by the next generation test-bench for the TileCal superdrawers, the new Prometeo (A Portable ReadOut ModulE for Tilecal ElectrOnics). Prometeo is a portable, high-throughput electronic system for full certification of the front-end electronics of the ATLAS TileCal. It is designed to interface to the fast links and perform a series of tests on the data to assess the certification of the electronics. The Prometeo's prototype is being assembled by the University of the Witwatersrand and installed at CERN for further developing, tuning and tests. This article describes the overall design of the new Prometeo, and how it fits into the TileCal electronics upgrade.
.
A survey of the fine structure of the Isovector Giant Dipole Resonance (IVGDR) was performed, using the recently commissioned Zero-degree Facility of the K600 magnetic spectrometer at iThemba LABS. ...Inelastic proton scattering at an incident energy of 200MeV was measured on
27
Al ,
40
Ca ,
56
Fe ,
58
Ni and
208
Pb . A high energy-resolution (
Δ
E
≃
40
keV FWHM) could be achieved after utilising faint-beam and dispersion-matching techniques. A considerable fine structure is observed in the energy region of the IVGDR and characteristic energy scales are extracted from the experimental data by means of a wavelet analysis. The comparison with Quasiparticle-Phonon Model (QPM) calculations provides insight into the relevance of different giant resonance decay mechanisms. Photoabsorption cross sections derived from the data assuming a dominance of relativistic Coulomb excitation are in fair agreement with previous work using real photons.
The setup and experimental techniques for measurements of zero-degree inelastic scattering and reactions involving light ions with the K=600 magnetic spectrometer at iThemba LABS are described. ...Measurements were performed for inelastic proton scattering at an incident energy of 200
MeV for targets ranging from
27Al to
208Pb. An energy-resolution of 45
keV (FWHM) was achieved by utilizing the faint-beam dispersion-matching technique. A background subtraction procedure was applied and allowed for the extraction of excitation energy spectra with low background. Measurements of the (p,t) reaction at zero degrees for
E
p
=100 and 200
MeV benefited from the difference in magnetic rigidity between the reaction products and the beam particles, resulting in background-free spectra with an excitation energy-resolution of 32 and 48
keV (FWHM), respectively, and a scattering angle resolution of 0.55° (FWHM). The addition of Double Sided Silicon Strip Detectors (DSSSD) at backward scattering angles allowed for coincident measurements of particle-decay of states excited in the (p,t) reaction at
E
p
=
200
MeV
.
PDF
