Seminars in 2019:
Tuesday 26th
November 2019
Pete Jones (iThemba LABS, Cape Town, South Africa)
using a gamma-ray spectrometer in singles and coincidence mode
Measurements of activity concentration using gamma–gamma coincidence methods are
significantly improved than single measurements in terms of minimizing spectrum background,
summing effects and pulse pile-up. Detection limits can be improved by eliminating the internal
activity in LaBr3:Ce scintillator through gamma-gamma coincidence conditions. An array of
LaBr3:Ce (2" by 2") detectors connected to a Digital Signal Processing system were used for
measurement of natural occurring radioactive materials (NORM) in 1L Marinelli beakers for
particular measurements with U ore and Th ore. A novel method for background reduction
was implemented for the coincident data. Gamma-gamma coincident spectra were generated
by setting software gates on gamma-gamma matrices associated with the U and Th ore
samples, respectively. The results of these measurements will be presented and discussed.
Tuesday 19th
November 2019
Double-folding potentials from chiral EFT applied to non-closed shell nuclei scattering.
I will present the construction and application of double-folding potentials using new two-body
soft local chiral EFT interactions. This approach is benchmarked in 16O-16O scattering, and
extended to describe the scattering of 12C-12C and the fusion of oxygen isotopes relevant
for astrophysics. I will show results for cross sections computed for elastic scattering at
energies up to 1000 MeV, as well as for the astrophysical S factor of the fusion.
Our analysis of these various reaction observables has enabled us to study the impact of
the nucleon-nucleon interaction, the nuclear density and the imaginary potential on the
corresponding cross sections.
Tuesday 12th
November 2019
Preparing the next Decade@Ganil
The GANIL facility presently has a wide range of beams ranging from intense stable and
short-lived Rare isotopic beams (produced by ISOL and fragmentation) using the five cyclotrons,
and a variety of unique and state of art equipment. These are mainly used to study the evolution
of the properties of the quantum many body system, the nucleus, as a function of the three axis
in nuclear physics namely excitation energy, angular momentum and the asymmetry of neutrons
and protons. This is supplemented by a strong program of accelerator based atomic physics,
condensed matter, radiobiology and industrial applications. Presently the facility is being augmented
by very intense beams of neutrons and stable beams from the superconducting Linear accelerator
coupled with new instrumentation,
representing a major upgrade.
We will introduce
the facility along with an overview of the arsenal of tools and their upgrades.
And also discuss in particular the recent upgrade of its ISOL facility (SPIRAL1) and the status
of the commissioning of the superconducting LINAC and associated facilties (SPIRAL2 phase 1).
The talk will highlight and discuss the recent results that illustrate new vistas for searching and
understanding the simple and regular patterns found in the structure of complex nuclei and the
dynamics of colliding nuclei.
Tuesday 5th November 2019
Andreas Ekstrom
(Chalmers Institute of Technology)
How do properties of atomic nuclei depend on the underlying interaction between protons
and neutrons? Recent ab initio computations of nuclei have revealed that theoretical predictions
of nuclear observables are very sensitive to the values of the coupling constants in chiral
Hamiltonian models with two- and three-nucleon forces and it is not clear why certain interaction
models work better than others. I will present a new method that enables fast ab initio computation
of nuclear observables across a domain of relevant coupling constants. This approach will enable
statistical computation and inference in ab initio nuclear theory to help us infer new knowledge
about the nuclear interaction.
Tuesday 29th
October 2019
Nuclear Theory at AWE
This presentation will provide an overview of AWE’s current interests and research in the
field of nuclear theory. Most of our current research in this area is focused on calculations
of neutron-induced interactions on medium-Z nuclei in order to generate new and independent
nuclear data evaluations. These calculations may be supplemented by new experimental
measurements taken at AWE, or elsewhere, and potentially via surrogate reaction studies.
Preliminary investigations into two-neutron transfer reactions have been performed in order
to support surrogate
studies.
The nuclear data evaluations generated will be utilised by in-house users of
neutron transport
codes and hopefully accepted for inclusion in an open source evaluated library. In addition to
describing work performed on the above, future research goals and potential areas of
collaboration will be briefly discussed.
Tuesday 15th
October 2019
Alex Brown (Michigan State University)
Energy-density-functional results for magic nuclei and the
extrapolations to the nuclear matter
equations of
state for neutron stars
I will discuss results from the references below for the applications of
Skyrme energy-density
functionals to properties of doubly-magic nuclei, ab-initio calculations of low-density neutron
matter, and neutron stars. The correlation between the neutron skin and the slope of the neutron
equation of state near a density of 0.10 nucleons/fm^3 discovered in (1,2,3) was extended
to the differences in the charge radii of mirror nuclei (4). Alternatively, when the Skyrme parameters
are constrained by ab-initio calculations of low-density neutron matter, predictions can be made for
the neutron skin and the slope of the neutron equation of state (4). The maximum mass of the
neutron star depends on the neutron effective mass. A value of [m∗n/m](ρ0) = 0.60-0.65 is required
to obtain a maximum neutron star mass of 2.1 solar masses (6). With the constraints to the
low-density neutron matter and neutron star mass, a value of 12.4(1) km is predicted for the radius
of a 1.4 solar mass
neutron star.
1) Neutron Radii in Nuclei and the Neutron Equation of State,
Phys. Rev. Lett. 85, 5296 (2000).
2) Neutron Radii and the Neutron Equation of State in
Relativistic Models, Phys. Rev.
C64, 027302 (2001).
3) Constraints on the Skyrme Equations of State from Properties of Doubly
Magic Nuclei, Phys.
Rev. Lett. 111, 232502 (2013).
4) Constraints on the Skyrme Equations of State from Properties of Doubly
Magic Nuclei and ab
initio Calculations of Low-Density Neutron Matter, Phys. Rev. C 89,
011307(R) (2014).
5) Mirror Charge Radii and the Neutron Equation of State, Phys. Rev. Lett.
119, 122502 (2017).
6) C. Y. Tsang, B. A. Brown, F.J. Fattoyev, W. G. Lynch, and M. B. Tsang,
arXiv:1908.11842v1
Tuesday 1st October 2019
Morten Hjorth-Jensen (Michigan
State University, USA and University of Oslo, Norway)
Machine Learning and quantum mechanical many-body problems
The main aim is to give you a short and pedestrian introduction to how
we can use Machine
Learning methods to solve quantum mechanical many-body problems. And why this could
be of interest. I will focus on the link between variational methods (Variational Monte Carlo
as an example) and so-called Boltzmann machines and how they can be used to solve
many-body problems. I will also show examples on how one can use deep learning methods
in connection with standard many-body methods like Coupled Cluster theory and Similarity
Renormalization Group methods.
Tuesday 9th September 2019
Tomas Rodriguez (Universidad Autonoma de Madrid)
Symmetry conserving configuration mixing methods
to describe nuclear spectra
Experimental excitation energies and transition probabilities of the
atomic nucleus provide
information about its underlying shell structure, deformation, etc., and, eventually, about
the nuclear interactions. To understand better these structural properties we have to
compare with theoretical calculations. During the last two decades beyond-mean-field
techniques using energy density functionals (EDF) have been developed to provide
reliable predictions and physically sound interpretations of nuclear spectra at low
excitation energies. In particular, the so-called symmetry conserving configuration
mixing (SCCM) method based on the Gogny EDF has been used to study the
appearance/degradation of shell closures, shape evolution/mixing/coexistence, etc., in
different regions of the nuclear chart. In this talk I will briefly review the main aspects
of the theoretical framework and I will focus on some recent studies of the quadrupole
and octupole shape evolution in several regions of the nuclear chart.
Monday 2nd - Friday 6th September 2019
24th European Conference on Few-Body Problems in Physics (EFB24)
The European Conference on Few-Body Problems in Physics (EFB24) was held at the
University of Surrey from 2nd to 6th September 2019.
This, the 24th edition of this conference series, has most recently taken place in Aarhus
(2016), Krakow (2013), Salamanca (2010), and Pisa (2007).
The first conference circular is available here
Thursday 8th August 2019
Takaharu Otsuka (RIKEN, Wako Campus, Japan)
Prospects of nuclear structure physics
Prof. Otsuka is well known for Monte Carlo Shell Model calculations, using which he
described nuclear structure phenomena over (almost) all the nuclide chart. This includes
shape coexistence in mercury isotopes, shape evolution and collectivity in neutron-rich
zirconium isotopes, B(E2) in tin isotopes, etc.
Wednesday 24th - Friday 26th July 2019
Workshop: Ab-initio
nuclear theory: from breakthroughs to applications
Workshop program and abstracts are available
here
Tuesday 23rd July 2019
C.A. Bertulani (Texas
A&M University-Commerce)
Neutron Skins, Symmetry Energy, and Neutron Stars
I will present a brief overview on the quest to determine the Equation of State
(EoS) of
neutron stars. Early experimental studies of pygmy resonances in neutron-rich nuclei will
be discussed together with theoretical attempts to develop relationships between the
properties of pygmy resonances and the EoS of neutron stars. Recent efforts to
correlate neutron skins in nuclei and the EoS will also be presented. Focus will be given
to microscopic descriptions of nuclei, how they predict diverse EoS, and how one can
constrain their predictions by comparison with experiments at nuclear facilities and with
astronomical observations [1-4].
[1] C.A. Bertulani,
arXiv:1904.10628 (2019).
[2] Shubhchintak, C.A. Bertulani and T. Aumann, Phys. Lett. B 778, 30 (2018).
[3] T. Aumann, C.A. Bertulani, F. Schindler, S. Typel, Phys. Rev. Lett. 119,
262501 (2017).
[4] C.A. Bertulani and T. Kajino, Prog. Part. Nucl. Phys. 89, 56 (2016).
Tuesday
12th March 2019
First measurements with the ISOLDE Solenoidal Spectrometer - probing single-
particle structure approaching the N=20 "island of inversion" via a measurement
of the 28Mg(d,p)29Mg reaction
The neutron-rich nuclei between Z=8-20 are in an interesting region of the nuclear
chart to study the evolution of single-particle structure, with several identified
phenomena to understand. To start, the N=20 shell closure has been shown to
disappear with a new gap at N=16 emerging in 24O. Whilst in the neutron-rich Si,
Al, Mg, Na and Ne isotopes a region known as the ``island of inversion" appears.
This region is characterized by deformed structures prevalent in the ground and
low-lying excitations, developing as intruder configurations from particle-hole
excitations that appear at lower excitations as shell gaps weaken.
In order to probe the evolution of single-particle structure approaching these
regions the 28Mg(d,p)29Mg reaction has been performed using a 9.5 MeV/u
radioactive ion beam of 28Mg from HIE-ISOLDE. This is the first physics
measurement using the ISOLDE Solenoidal Spectrometer (ISS), used to analyse
the outgoing protons from the reaction. Bound and unbound states have been
identified in the residual N=17 nucleus accounting for the majority of single-particle
strength for the negative-parity f7/2 and p-orbital, the states that arise from cross-
shell excitations. In this talk I will describe the use of the solenoid technique for
measuring direct reactions in inverse kinematics and introduce the ISOLDE Solenoidal
Spectrometer project, giving an update on its current status and future developments.
I will also present the preliminary results from the first physics measurements
mentioned above.
Tuesday
26th February 2019
Extending the limits of laser spectroscopy
This presentation will discuss the recent results and progress by the Collinear resonance
ionization spectroscopy (CRIS) experiment at ISOLDE CERN. During the final year before
LS2 nearly 100 shifts of beam time was taken (more than any other experiment at ISOLDE),
which was used to address many exciting and challenging physics problems. The importance
of these results, in connection with long-standing nuclear structure puzzles in the regions
around 100Sn, 132Sn and 52Ca and their potential impact on nuclear theory will be outlined.
At the end of 2018 the CRIS collaboration began a new and challenging experimental campaign
to study molecular species. This culminated in the first molecular spectroscopy of the radioactive
species RaF as part of the international effort to develop a molecular cooling and trapping
scheme for EDM searches. The preliminary results from this campaign will be presented.
The CRIS technique has applications beyond nuclear physics and can be combined with
existing mass spectrometry tools such as gas chromatography (GC), isotope ratio mass
spectrometry (IRMS) and inductively coupled mass spectrometry (ICP-MS) to efficiently
remove interferences (isobars) which will enhance the mass abundance sensitivity by more
than 3 orders of magnitude. By improving the limit of detection of these techniques beyond
the part per trillion level it becomes possible to detect cosmogenic isotopes in environmental
samples using a “table top” device. This seminar will present progress towards a table top
radiocarbon detection device and commercialization project at the University of Manchester.
Tuesday 12th February 2019
Robin Smith (Sheffield Hallam University)
It’s not you, it’s me: What can we learn from break-up of the 12C
Hoyle state?
The 0+ excited state of 12C at 7.65 MeV is named after Sir Fred
Hoyle, who proposed
its existence in order to account for high stellar abundances of carbon. Aside from this
astrophysical significance, it is thought to possess a curious α-cluster structure. However,
many questions still remain. To what extent can this state be described as three interacting
α-particles, and if so, what geometric configuration do they take – a linear chain, equilateral
triangle or something entirely different altogether? Exotic Efimov- and α-condensate- type
states have also been proposed!
Two recent experiments have tested the validity of these models by
examining the ways
that the Hoyle state decays. By precisely measuring the three α-particles emitted during
the decay in a high statistics experiment, it was possible to differentiate between sequential
(8Be + α) and direct (3α) processes. This talk details the experimental challenges associated
with this measurement along with its implications for the structure of the Hoyle state. The
usefulness of Time Projection Chamber (TPC) detectors for future studies will also be
discussed.
Monday
4th February 2019
High resolution gamma-ray spectrometry using GALILEO array
The GALILEO gamma-ray spectrometer has been constructed at the Legnaro National
Laboratory of INFN (LNL-INFN). It can be coupled to advanced ancillary devices which
allows nuclear structure studies employing the variety of in-beam gamma-ray spectroscopy
methods. Such studies benefit from reactions induced by the intense stable beams delivered
by the Tandem-ALPI-PIAVE accelerator complex and by the radioactive beams which to be
provided by the SPES facility. In the talk I will outline two experiments performed within the
experimental campaigns at GALILEO coupled to the EUCLIDES Si-ball, the Neutron Wall
array. The first one was aimed at spectroscopic studies in A=31 mirror nuclei and the second
one at measurements of lifetimes of excited states in nuclei in the vicinity of 100Sn.
Tuesday
22nd January 2019
Gianluca Colo (INFN, Milano)
Nuclear excitations: density-functional versus many-body approaches
In this talk, I will start with a bird's eye view of the present status of
Density Functional
Theory (DFT) in nuclear physics. In recent years, the functionals that have been developed
have reached a quite high level of sophistication. I will explain the
attempts by our group
for the improvement of these functionals: we aim at understanding on equal
footing both
ground-state and excited-state properties. The focus will be on isospin as well as spin-
isospin excitations of finite nuclei. I will also touch upon isospin symmetry and its breaking.
Finally, a link with the properties of the nuclear equation of state, whose relevance is also
related to the recent new signals from neutron stars, will be established.
In the second part of the talk, I will dwell on the comparison
between DFT and quantum
many-body theory. I will describe our models based on the extension of DFT that take
care of further correlations, I will discuss which observables do call for such extension,
and draw an analogy with the GW-method for electronic systems. In fact, a
stronger
cross-fertilisation between the studies of nucleonic and electronic systems
will be eventually
called for.
Tuesday
15th January 2019
Skyrmions and clustering in light nuclei
It is almost 60 years since Skyrme introduced his model of nuclei as topological solitons
(Skyrmions) in a nonlinear pion theory. I shall review the Skyrme model and discuss some
of the successes and failures of Skyrmions. In particular, I will describe some recent work
that yields improved results for binding energies and clustering in light nuclei, by extending
the standard theory of Skyrmions to include the next lightest subatomic meson particles
traditionally neglected.
Naya and Sutcliffe, PRL 121, 232002 (2018).