The second random–phase approximation (SRPA) is an extension of the standard random–phase approximation (RPA) where two particle–two hole (2p2h) configurations are included together with the RPA one particle–one hole (1p1h) configurations. This beyond mean– field model allows for reliable quantitative predictions to describe the widths and the fragmentation of excited states, due to the...
The theoretical description of collective excitations in nuclei with all their facets -- such as giant resonances, low-lying strength, fragmentation, and fine structure -- has been the domain of phenomenological models so far. Only recently, first ab initio methods have been proposed to adress the collective response. These approaches transfer the powerful ab initio tools for ground states and...
Response of atomic nuclei to external fields reveals the occurrence of a variety of modes of excitation, and the quest for unique modes of excitation in exotic nuclei has been a major subject in nuclear physics. The low-energy dipole mode or the pygmy dipole resonance (PDR) has been a central issue for its collectivity and the correlation with the neutron skin thickness.
The isovector (IV)...
"Why are the tin isotopes fluffy?" has remained, for nearly a decade, a fundamental open problem in nuclear structure physics: models which reproduce the isoscalar giant monopole resonance (ISGMR) in the “standard" doubly-closed shell nuclei, $^{90}$Zr, $^{208}$Pb, overestimate, by as much as 1 MeV, the ISGMR energies of the open-shell tin and cadmium nuclei [1-4].
To further elucidate this...
This talk will outline the current state of the analysis investigating proposed rotational bands in 18O. These bands, some of which are expected to have 12C ⦻ 2n ⦻ α or 14C ⦻ α structures, were proposed to exist by previous measurements at the Maier-Leibnitz Laboratory [1]. To determine the absolute α-particle decay widths of those states, we performed an experiment, also at the Maier-Leibnitz...
Time-dependent nuclear density functional theory (TDDFT) is a well-suited tool to describe heavy ion collisions and nuclear vibrations. Here we present a study of nuclear vibrations and reactions focusing on the aspect of nucleonic clustering in the intermediate states.
Nuclear vibrations are studied in 3D computational box without any symmetry assumptions on an equidistant grid. Usually...
Neutron-rich beams are being developed at iThemba LABS to study nuclear structure away from stability. This is also the opportunity of deepening our understanding of astrophysical origin of elements. The interest of using (p,xp) reactions in the production of exotic nuclei, lies in the fact that proton beams have a large penetrating power and can be produced with high intensity. Some...
The shape transition of the IsoVector Giant Dipole Resonance from the spherical $^{142}$Nd to the deformed $^{150}$Nd nuclei in the even-even $^{142-150}$Nd chain was established using proton inelastic scattering at zero degrees. Comparisons were made to previous photo-absorption results obtain at Saclay. Some discrepancies that have implications for astrophysical applications were found. It...
Energies of the Giant Monopole Resonance (GMR) modes and the Giant Quadrupole Resonance (GQR) modes are directly related to the incompressibility of finite nuclear matter (KA) from which the incompressibility of infinite nuclear matter($K_∞$) can be deduced by comparing the experimental data with the theoretical predictions such as fully consistent Random Phase Approximations (RPA).The 20%...
A new approach to studying excited 0$^{+}$ states is being introduced at iThemba LABS. It involves the study of low-lying electric monopole (E0) transitions which proceed via internal conversion (IC) and internal pair formation (IPF). Precise measurement of these processes require use of unique tools and techniques, such as an electron spectrometer. An electron spectrometer is currently under...
Assuming the validity of the Brink-Axel hypothesis, the puzzling low-energy enhancement or up-bend in the photon-strength function of medium-mass nuclides with A ≈ 50 contributes to a substantial induction of the nuclear dipole polarizability in the quasi-continuum region. Revealing shell effects are manifested by drops of polarizability in the ground states of semi-magic nuclei with N = 50,...
Sergej Bassauer$^1$, Peter von Neumann-Cosel$^1$, and Atsushi Tamii$^2$ for the E377 + E422 Collaborations
$^1$Institut für Kernphysik, Technische Universität Darmstadt, 64289 Darmstadt, Germany
$^2$Research Center for Nuclear Physics, Osaka University, Ibaraki, Osaka 567-0047, Japan
Inelastic proton scattering at very forward angles and energies of a few hundred MeV has been...
Previous studies have shown that fine structure in the excitation energy spectra of nuclear giant resonances can be attributed to different physical processes. For example, characteristic energy scales of the fine structure for the Isoscalar Giant Quadrupole Resonance (ISGQR) arise mainly from the collective coupling of the ISGQR to low-lying surface vibrations, while on the other hand it has...
The emergence of low-energy dipole strength in nuclei with neutron excess, named pygmy dipole resonance, has triggered a great deal of experimental and theoretical effort.
Despite of many experimental and theoretical evidences for the close relationship between the pygmy dipole resonance and the neutron skin, there is currently no direct method to experimentally extract the neutron skin...
The last few decades have proved to be quite exciting in the field of nuclear structure physics.High energy-resolution proton inelastic-scattering experiments revealed that giant resonances carry fine structure as a signature of the damping mechanisms involved. For the first time itis now possible to achieve such high energy-resolution measurements with intermediate energy (specifically 200...
The charge (mass) distributions of fission fragments resulting from lowand
high-energy fission of the isotopes of Fm, No, and Rf are studied with the
statistical scission-point fission model. The calculated results are compared
with the available experimental data. The difference between the shapes of
mass and charge yields is explored at different excitation energies.
The odd-odd neutron-deficient 138La is very long-lived but one of the less abundant nuclei in the solar system. It is expected to be one of 35 p-nuclei. Most p-nuclei with A>110 are thought to be produced by photo-disintegration of s- and r-process seed nuclei. However, this photo-disintegration cannot satisfactorily explain the observed abundance of 138La and more exotic processes such as the...
The study of the low lying electric dipole strength is attracting considerable attention, in connection with the possible existence of a new collective mode arising from the oscillation of the N=Z core against the neutron skin in neutron rich nuclei. This is the so called Pygmy Dipole Resonance (PDR). From the experimental point of view it was shown the importance of studying the nature of PDR...
The giant resonance(GR) is a collective mode of nuclei. Our group has researched giant resonances of many kinds of nuclei such as Ca, Zr, Pb with high energy resolution by using Grand Raiden magnetic spectrometer[1]. These days their excitation mechanism, for example sum rule and electric dipole polarizability, is well researched[2]. But the decay mechanism of GRs still has large ambiguity....
Measurements of activity concentration using gamma - gamma coincidence is better than single measurement in terms of minimizing spectrum background, summing effects and pulse pile-up \cite{metwally}. Detection limits can be improved by eliminating the internal activity in $LaBr_3$:Ce scintillator through gamma - gamma coincidence condition \cite{Drescher}. An array of $LaBr_3$:Ce (2" by 2")...
Spin and isospin are unique quantum numbers in nuclei defined as “Finite Many-body System consisting of Two Fermions.” Therefore, Gamow-Teller (GT) excitations caused by the spin-isospin (\sigma \tau) operator are unique in the sense that they can reflect the critical part of nuclear structure as well as nuclear interactions. In addition, they are the most common nuclear weak process in the...
The equation of state (EoS) of nuclear matter not only governs the femto-scale quantum many-body system, namely nuclei, but also plays an important role in the structure of neutron stars and in supernova phenomena. In particular, the EoS of isospin asymmetric nuclear matter attracts much interest from the viewpoint of the existence of heavy neutron stars. The asymmetric term of...
The Legnaro National Laboratories have a long-standing tradition in gamma-ray spectroscopy. They hosted the most recent HPGe arrays, from GASP, one of the first Compton-shielded large HPGe array to AGATA, the first operational tracking array worldwide, that is also planned to be one of the major instrument at the time of the SPES reaccelarated ISOL beams.
In this context, a new resident...
GW170817/SSS17a was an event of the century that opened a new window to
multi-messenger astronomy and nuclear astrophysics. Optical and near-infrared emissions
among many other observables suggest that their total energy release is consistent with
radiative decays of r-process nuclei predicted theoretically although no specific r-process
element was identified. Core-collapse supernovae (both...
The study of alpha-cluster in light nuclei have been well documented with experimental evidence. In the recent experiment performed at iThemba LABS using (p,t) reaction on 22Ne with the K600 magnetic spectrometer, a tentative candidate for 5-alpha cluster state at 22.5 MeV, which is situated at 3.3 MeV above the 5-alpha break-up threshold was found. However, this state could not be accounted...
Investigating the low-lying electric dipole (E1) response referred to as the Pygmy Dipole Resonance (PDR) has garnered a lot of attention in recent years, with both experimental and theoretical studies dedicated to this topic. Within the hydrodynamic model, the PDR has been interpreted as an oscillation of excess neutrons against a proton-neutron saturated core [1,2]. The PDR is of...
The progressive development of the scintillator detectors has made it possible to do perform direct determination of electronic lifetimes. 2” x 2” LaBr3 :(Ce) detectors provide a combination of excellent time resolution and good energy resolution. With these detectors it is possible to undertake direct lifetime measurements of excited nuclear states down down to hundreds of...
The light charged particle evaporation from the compound nucleus and
from the complex fragments in the reactions 32S+100Mo, 121Sb+27Al, 40Ar+
164Dy, and 40Ar+natAg is studied within the dinuclear system model. The
possibility to distinguish the reaction products from different reaction mechanisms
is discussed.
From the comparison of the calculated light charged particle (LCP)...
Magnetic spectrometers have proven to be very useful in the world of experimental nuclear and astrophysics. The focal plane detection system instrumenting these spectrometers is instrumental in their success. A new focal plane detection system is envisaged for the K600 QDD magnetic spectrometer at iThemba LABS in Cape Town, South Africa. The existing focal plane detection system, consisting...
The structure of exotic neutron-rich nuclei is one of the main science drivers in contemporary nuclear physics research. An attention has been devoted to effects of varying the ratio between the proton $Z$ and neutron $N$ numbers on different nuclear structure characteristics of nuclei deviated from their valley of $\beta$-stability. One of the phenomena associated with the change in $N/Z$...
Beside the Giant Dipole Resonance (GDR), many nuclei show the feature of additional low-lying electric dipole (E1) strength below and around the particle separation energies, which is usually denoted as Pygmy Dipole Resonance (PDR) [1]. The existence of the PDR in nearly every studied nucleus and the smooth variation of its properties lead to the assumption that the PDR is a newly discovered...
In recent times, considerable progress has been made in the understanding of isospin nature of the pygmy dipole excitation both experimentally and theoretically. On experimental side, this has been due to advancement of techniques which now make it possible to compare the excitation pattern by probes of different isospin nature [1].
In this conference, we present results of such comparative...
The problem of the nuclear incompressibility is a longstanding one. Deducing the incompressibility of nuclear matter from the compression modes of finite nuclei is not straightforward [1]. Whereas some consensus has been reached that from magic nuclei the value of the incompressibility K should be around 240 MeV, this number comes anyhow from the analysis of isoscalar giant monopole and dipole...
Virtual excitations are responsible for the polarization of atoms and molecules and give rise to the well-known van der Waals forces between two neutral atoms or molecules, which are far enough apart for the overlap between the wave functions to be neglected. In nuclei, electric-dipole virtual excitations via high-lying states in the giant dipole resonance can also polarize the ground and...
Recent developments of the relativistic nuclear field theory on the proton-neutron response and on the finite-temperature formalism will be presented. The general non-perturbative framework, which advances the nuclear response theory beyond the one-loop approximation, is formulated in terms of a closed system of non-linear equations for the two-body Green’s functions. This provides a direct...
Most of the nuclear structure properties of exotic nuclei at the proton drip line can be probed by the observation of proton radioactivity [1,2]. Due to the very small cross sections for their production and quite short half lives, it is the only possibility to gather information about their spectroscopic properties. Therefore, the observation and theoretical interpretation of proton...
In addition to establishing the Majorana nature of neutrinos, obtaining the absolute neutrino mass scale is now the focus of several large-scale neutrinoless double beta decay experiments. The current challenge in determining the neutrino mass accurately depends on the calculation of nuclear matrix elements
(NME's) in the select nuclei where these decays can take place. It is well known that...
Dark matter is currently one of the greatest unsolved mysteries in physics. Recently we have observed an anomaly in the internal e+e- decay of 8Be [1]. It turned out [2] that this could be a first hint for a 17 MeV X-boson (X17), which may connect our visible world with dark matter. The possible relation of the X17 to the dark matter problem as well as the fact that it might explain the...
iThemba LABS has embarked on an extensive renewal and enhancement program with the ultimate aim to provide our users with competitive and state-of-the air research facilities for nuclear physics experiments. During the presentation I will provide an overview of the facilities of the Department of Subatomic Physics at iThemba LABS. In particular, I will focus on the latest developments to...
The study of monopole transitions via excited 0+ states requires the measurement of internal conversion electrons and internal pair formation using an electron spectrometer. Such a spectrometer, consisting of a solenoid magnet transporter and a Si(Li) detector with an array of LaBr3, is undergoing development at iThemba LABS. Performance of the electron spectrometer has been investigated using...
Pairing in highly excited nuclei
Nguyen Dinh Dang
Recent achievements in the study of pairing effects on the properties of highly excited nuclei are discussed. In particular, the nuclear level density and radiative gamma-ray strength function are simultaneously described within a consistent approach based on the exact pairing in good...
This contribution reports of the status of construction and the latest experimental results obtained with use of the novel scintillator based calorimeter named PARIS [1]. Thanks to use of LaBr3-NaI and CeBr3-NaI phoswiches, it is characterized by good energy and timing resolution and efficiency, especially for high energy gamma-rays. Due to this properties it can be used...
The review presents the latest experimental data on the total reaction cross sections (σR) and elastic scattering angular distributions of light weakly bound nuclei 6–9,11Li [1].
A review of papers on the interaction of weakly bound 6-9Li and 11Li nuclei published so far and their analysis shows that there are no experimental data on σR and it is necessary to measure it for Li-isotopes at...
Two solenoid electron spectrometers were donated to iThemba LABS by Orsay in France. These lens spectrometers are currently under refurbishment. They will be used to study higher energy electrons which results from internal conversion (IC) process, a process whereby an atomic nucleus emits an electron instead of γ–ray emission. This process can only occur between two 0+. An emitted electron...
The origin of low-energy E1 strength remains an open issue even in the case of stable nuclei. An important question is whether a collective resonance develops (often called pygmy resonance) and accordingly what mechanisms could generate or hinder it. The answer holds particular relevance for predictions about shell structure, the softness of the symmetry energy, phonon coupling, and broad...
Within the framework of a global microscopic approach, all the nuclear input required for nuclear reaction predictions are being, step by step, derived from a sole nucleon-nucleon effective interaction, namely the D1M Gogny force [1]. Nuclear masses [1], deformations, radial densities and level densities [2] have already been obtained and have shown a rather good agreement with experimental...
In the last years it has become obvious that a combination of different experimental approaches is necessary to understand the structure of electric dipole strengths in atomic nuclei (see, e.g., refs. [1-12]) and to be able compare it to theoretical models. Due to the high level density in the energy region of interest, a selective excitation mechanism selective spectroscopy are key...
I discuss recent progress in quest of spin and spin-isospin excitations by hadron inelastic scatterings, single- and double-charge exchange reactions. One topics is the quenching problem of IS and IV spin excitations. Other topics will be
double Gamow-Teller excitations by double charge-exchange reactions. I will report recent theoretical studies of IS quenching problem in sd-shell nuclei...
I will report on the recent results from the proton scattering experiment with the high-resolution spectrometer at RCNP. The talk will cover the following subjects, the relative weights of which depends on the selected aural presentations of the other collaborators.
1) The electric dipole response of nuclei measured by Coulomb excitation: the electric dipole polarizability and the constraint...
Theoretical calculations of spin and orbital components of the M1 dipole strength in $^{52}$Cr are made using the Skyrme effective interaction in which the full tensor interaction has been included (Barton and Stevenson, 2018). The tensor terms have a substantial effect on the structure of the strength function, with different tensor strengths resulting in enhancement or suppression of...
Recently new experiments using fast radioactive beams and the highly efficient gamma detection arrays AGATA and DALI2 gave new results on the search for new E1 excitations around the threshold in neutron rich isotopes. Results will be presented together with an outlook for forcoming experiments combining different target and arrays.
In order to get quantitative information on neutrino absolute mass scale from the possible measurement of the 0νββ decay half-lives,the knowledge of the Nuclear Matrix Elements (NME) involved in such transitions is mandatory.Interesting studies were performed in the eighties, exploring (+,-) Double Charge Exchange (DCE) reactions on different nuclei with the main aim to unveil features of...
The triple $\alpha$ reaction is one of the most important reactions for
the nucleosynthesis in the universe because it is a doorway reaction
to synthesize heavier elements. An $\alpha$ particle is
captured by $^8$Be, which is a two $\alpha$ resonant state, to form a
triple $\alpha$ resonant state. Most of such triple $\alpha$ resonant
states decay back to 3$\alpha$ particles, but a tiny...
An overview of the 12C(α,γ)16O experiment at the University of Birmingham's MC40 cyclotron is presented in this work.
The experimental set-up was a combination of the existing charged particle expertise and capability of the group and the ability to measure the emitted gamma rays using our new LaBr3 detector array. The motivation for this is to measure or put constraints on the B(E2)s for...
Clustering phenomena are well known in nuclear physics. Nuclear reactions which involve the emission or capture of clusters of nucleons are particularly interesting to investigate the interplay between the nuclear structure and reaction dynamics [1]. Indeed, clusters in nuclear systems can be related to their dynamical formation or their structural presence (pre-formation) in nuclei. While for...
Rare Isotopes located far from the valley of stability bring new insight into
the evolution nuclear structure. Our knowledge on the properties of neutronand
proton-rich nuclei guide our understanding of the state of matter in
extreme neutron-rich systems such as neutron stars and supernovae and
heavy element synthesis. The presentation will outline how radioactive (RI)
beams are allowing us to...
The low energy enhancement (LEE) has a potential of increasing the Maxwellian-Average cross sections (MACS) by up to two orders of magnitude. This theoretically predicted effect is pronounced in the mass region towards the neutron drip line. However, to this date there is no experimental data, which proves or disproves the existence of the low energy enhancement in the neutron rich nuclei....
The rare-earth isotopic chain of Samarium provides an excellent opportunity to systematically investigate the evolution of nuclear structure effects from the near spherical (β2=0.09) 144Sm isotope to the highly-deformed system (β2=0.34) 154Sm. As the nuclear shape changes, statistical properties such as the nuclear level density (NLD) and γ-strength function (γSF) are expected to be affected....
Weak-interaction rates in several nuclear mass regions are studied in scenarios characterized by densities and temperatures of astrophysical interest. The study includes even-even and odd-A nuclei in the pf-shell region, as well as neutron-deficient and neutron-rich medium-mass isotopes. Nuclei in these mass regions are involved in presupernova formations, in the rapid proton and in the...
In the last decade the “laser world” is experiencing a "revolution" leading to a new paradigm in science and technology. Laser intensities have increased by 6 orders of magnitude in the last few years. The power (1015 Watts) concentrated in these extremely short burst of light (10-15s) are such that the laws of optics change in a fundamental way. This allows to access energy domains which have...
Pairing correlations play crucial roles in atomic nuclei and in quantum
many-body physics in general. They are responsible for the odd-even staggering
observed in the binding energy of atomic masses, for the fact that all even nuclei have a
J=0+ ground state, and for their small moment of inertia as compared to a rigid
body. More generally, pairing correlations imply a smoothing of the...
Recently, we proposed a new theoretical method which enables to study nuclear structure and responses in an unified way. This method, named real-time evolution method, utilizes the equation-of-motion of interacting nucleon wave packets. It will be demonstrated that this method is very powerful theoretical tool which beyond the small amplitude approximation (RPA).
As an example of the...
The project focuses on studying the evolution of the N=20 shell gap. The shell gaps have been previously investigated through studies of nuclear levels, using various experimental approaches namely: Coulomb excitation, knockout reactions, transfer reactions and g-factor measurements. In exotic nuclei with an imbalanced number of neutrons and protons, significant modifications of the nuclear...
Inelastic scattering of exotic nuclei on an internal gas-jet target of a storage ring allows for a new access to study giant resonances, applicable also for radioactive nuclei. The differential excitation cross section can be measured down to very small scattering angles in the CM system with high angular resolution, making this approach particularly suited e.g. for the study of giant monopole...
The study of exotic Jacobi shapes in nuclei have attracted much attention in recent times [1-4]. The presence of a distinct low energy component around 10 MeV in the giant dipole resonance (GDR) spectrum, originating from Coriolis splitting in a highly deformed rotating nucleus, can be used as a signature of the Jacobi shape transition. The measurement of high energy γ rays from the decay of...
The exclusive study of light charged particles emission in hot light composite systems is a useful tool to underline possible structure effects on the competition between different reaction mechanisms and, in particular the possible evidence of nuclear clustering effects, which may change the expected decay chain probability. In particular, studying the competition between pre-equilibrium and...
B(E2: 2+→0+) values of neutron-rich even-even carbon isotopes have been
reported up to $^{20}$C and do not only provide important information on the
evolution of the underlying structural mechanism towards the drip line but also
provide critical constraints for theoretical models. The B(E2: 2+→0+) value in
$^{14}$C can be indispensable to advance our understanding of the Carbon
isotopic chain....
A study of the γ-decay of GDR formed in a hot compound nucleus will be held in June 2018 at IPN Orsay with the use of the PARIS + nuBall set-up with 18O on 174Yb reaction. It is a very first experiment in which PARIS detectors will be used for this type of measurement and to fully take advantage of these detectors, they will be placed in a non-standard, wall geometry.
The main goal of the...
The recent measurement of the Neutron Star Merger event by LIGO [1] and subsequent optical measurements have revealed that Neutron star mergers are probably one of the primary sites for the r-process of nucleosynthesis [2]. An important source of uncertainty in the r-process models is the nuclear data input [3], especially important is the neutron capture cross-section which is directly...
An experimental campaign to study heavy-ion induced one- and two-nucleon transfer reactions has been performed at INFN-Laboratori Nazionali del Sud in Catania (Italy). In particular reactions induced by 18O and 20Ne beams at energies above the Coulomb barrier on different target isotopes have been explored with high resolution (both in energy and angle) and in a quite wide angular range...
The Cyclotron Center Bronowice (CCB) is the proton beam facility at the Institute of Nuclear Physics Polish Academy of Sciences Poland which, except proton cancer therapy, offers the possibility of using proton beams for nuclear physics investigations. Among others, the measurement concerning study of collective excitations was performed.
The experiment aimed at investigation of gamma decay of...
The Pygmy Dipole Resonance (PDR), the low energy part of the electric dipole response in nuclei, is particularly relevant to investigate the nuclear structure and for its connections with photodisintegration reaction rates in astrophysical scenarios. Studies on the PDR are currently almost exclusively focused on spherical nuclei. For deformed nuclei, several theoretical and experimental works...
This talk will report recent experimental results from the decay of
carbon-12
and other light nuclei, performed by the group in Birmingham. Using the
MC40 cyclotron
and also experimental facilities across Europe we have pushed the
conventional particle
spectroscopy techniques to the limits, in order to shed light on the
cluster structure
in nuclei.
Last years the toroidal dipole resonance (TDR) attracts a high attention [1-4]. This mode is located at the energy of the pygmy dipole resonance and is believed to form the low-energy part of the isoscalar giant dipole resonance. The TDR is the only known dipole {\it vortical} mode in the family of intrinsic electric excitations.Just TDR perhaps generates the pygmy dipole resonance at the...
At the Extreme Light Infrastructure – Nuclear Physics (ELI-NP) facility, high-power laser pulses together with high-brilliance gamma beams will be the main research tools. The status of the construction of the facility, the expected parameters of the gamma-beam system and the implementation scheme of the different instruments will be reported. The emerging nuclear photonics research program at...
The 14C(p,t)12C reaction was employed to investigate the much-discussed excitation energy region above the Hoyle state: there is evidence that suggests that in addition to the broad 0+ state at 10.3 MeV, an additional 0+ resonance is required at ~8.7 MeV. AMD calculations suggest that the Isoscalar Giant Monopole Resonance (ISGMR) may contribute to this region and suggest two distinct...
Nuclear matter incompressibility (KNM) is an important physical constant, unfortunately it cannot be measured directly. The location of the isoscalar giant monopole resonance (ISGMR) can be directly related to the incompressibility coefficient of nuclear matter (NM) by comparing experimental measurements of EGMR with energies calculated using specific microscopic interactions. This provides...
