Seminars in 2011:
Tuesday 29th November 2011
Andrei Andreyev* (University of the West of Scotland, Paisley, UK)
Recent laser spectroscopic studies in the Lead region
The talk will review the results of our recent collaboration experiments aimed
at studies of shape coexistence, beta-delayed fission and laser spectroscopy
in very neutron-deficient Tl [1], Pb [2] and Po [3] isotopes. Experiments were
performed by means of Resonance Ionization with the Laser Ion Source (RILIS) at
ISOLDE(CERN, Switzerland).
The experiments showed that the light Pb isotopes remain essentially spherical [2],
even at and beyond the mid-shell point at N=104 (186Pb). In contrast to this, a much
earlier onset of deformation (as compared to earlier understanding) was observed in
the chain of the light 191-200Po isotopes [3]. The results of the July's 2011
experiment for a long series of Tl isotopes [1] will also be presented.
A very important development of the laser-ionised beams of At isotopes [4] will
also be discussed. This opens up a possibility of a series of experiments with pure
At beams, previously un-accessible for such studies. A first ever measurement of
the ionization potential of the element At, which does not have stable isotopes,
will also be presented.
[1] A. Andreyev, B. Barzakh et al., IS511 experiment at ISOLDE, July 2011
[2] H. De Witte et al., Phys. Rev. Lett. 98, 112502 (2007).
[3] T. E. Cocolios et al, Phys. Rev. Lett., 106, 052503 (2011)
[4] A. Andreyev, V. Fedosseyev et al., Letter of Intent I086 "Development of the
laser-ionization scheme for At isotopes", ISOLDE(CERN), (2010)
* On behalf of Paisley-Leuven-Gatchina- Mainz- Manchester-Liverpool-Geneva-Bratislava
collaboration
Tuesday 8th November 2011
Christian Diget (University of York)
Driving stellar explosions creating chemical elements
How were the chemical elements that we consist of created, and what drives
the impact exploding stars have on our universe? These two questions are central
in our understanding of the universe and for how we look at ourselves in relation
to the history and evolution of the universe. The only way to see the driving
processes for the stellar explosions, however, is through utilising large,
international accelerator facilities. Here, the exotic radioactive nuclei involved
in the reactions are produced and accelerated, and through the use of
state-of-the-art particle-detector arrays the emitted particles in the reactions
are detected. By doing so, the conditions in stellar explosions can be reproduced
on a microscopic scale, determining the reactions that govern the evolution and,
at times, violent death of stars. During the talk, examples of such key nuclear
reactions will be introduced, and measurements of these reactions in the laboratory
will be described.
Monday 7th November 2011
Umesh Garg (University of Notre Dame/GSI Darmstadt)
Nuclear Incompressibility, the Asymmetry Term, and the MEM Effect
The Nuclear Incompressibility parameter is one of three important components
characterizing the nuclear equation of state. It has crucial bearing on diverse
nuclear and astrophysical phenomena, including radii of neutron stars, strength
of supernova collapse, emission of neutrinos in supernova explosions, and collective
flow in medium- and high-energy nuclear collisions. In this talk I will review
current status of the research on direct experimental determination of nuclear
incompressibility via the compressional-mode giant resonances. In particular,
recent measurements on a series of Sn and Cd isotopes have provided an "experimental"
value for the asymmetry term of nuclear incompressibility.
We also find that the GMR centroid energies of the in both Sn and Cd isotopes are
significantly lower than the theoretical predictions, pointing to the role of
superfluidityand the MEM (Mutual Enhancement of Magicity) Effect.
Tuesday 1st November 2011
Hideyuki Sakai (RIKEN)
Present status of RIBF --accelerator and experiments
RIBF is a heavy-ion research laboratory at RIKEN Nishina Center based on complex
accelerator facilities providing beams ranging from polarized deuterons (A=2) to
Uranium (A=238) with the maximum energy of 345 MeV/A. A main scientific goal is to
study nuclear structure and nuclear astrophysics far from the stability line.
Exotic nuclei are produced at RIBF utilizing projectile fragmentation and projectile
fission processes with the BigRIPS. RIBF is equipped with the Zero-Degree
Spectrometer(ZDS) and the high resolution spectrometer SHARAQ. Some of the
highlights in recent study with 48Ca- and U-beams will be introduced in this talk.
Slight emphasis will be placed on the research with SHARAQ by triton and 12Be
beams.
In addition, present status of new instruments under construction, SCRIT and SAMURAI
will be shown. If time allows the present accelerator situation after the massive
earthquake of March 11 will be reported.
Tuesday 25th October 2011
Daniel Pena Arteada (CNRS Orsay, France)
Applications of Relativistic Mean Field Theory: deformed RPA and nuclear structure
under strong magnetic fields
Part I Deformed RPA: The E1 strength is systematically analyzed in very neutron-rich
Sn nuclei, beyond 132Sn until 166Sn, within the Relativistic Quasiparticle Random Phase
Approximation. The great neutron excess favours the appearance of a deformed ground
state for 142-162Sn. The evolution of the low-lying strength in deformed nuclei is
determined by the interplay of two factors, isospin asymmetry and deformation
Part II: Covariant density functional theory is used to study the effect of strong magnetic
fields, up to the limit predicted for neutron stars (for magnetars B~ 10^18G),
on nuclear structure. All new terms in the equation of motion resulting from time
reversal symmetry breaking by the magnetic field and the induced currents, as well
as axial deformation, are taken into account in a self-consistent fashion.
Tuesday 18th October 2011
Ian Jones (University of Southampton)
Gravitational waves from neutron stars and the nuclear equation of state
Neutron stars are ready-made laboratories offering us the prospect of probing
the behaviour of matter at extremes of density, pressure, temperature, gravitational
field strength, and rotation rate. In this talk I will describe how astronomical
observations are enabling us to look inside these objects, allowing us to examine
the nuclear equation of state in regimes inaccessible to terrestrial experimenters.
Tuesday 11th October 2011
Pete Mason (University of Surrey)
Fast timing with LaBr3 detector arrays and measurement of the half-life of the
Iπ=4- intruder state in 34P
The recently developed scintillation material LaBr3 combines excellent timing
properties with high energy resolution (typically 3% at 662 keV). This has led
to interest in its application for the measurement of sub-nanosecond nuclear
half-lives. The properties of LaBr3 detectors and principals of fast-timing are
presented along with an example experiment on the in-beam measurement of the
half-life of the Iπ=4- intruder state in 34P.
34P lies on the neutron-rich side of stability approaching the region of anomalous
nuclear structure know as the "island of inversion". The low-lying Iπ=4- intruder
state in this isotope is associated with excitations across the well-known
N=20 shell gap. Excited states in 34P were populated in the 18O(18O,pn)34P
reaction at the Tandem Accelerator facility in Bucharest and studied with a mixed
array of LaBr3 and HPGe detectors.
Tuesday 4th October 2011
Mike Rubery (AWE, Aldermaston)
Detection of gamma rays at inertial fusion facilities using gas Cherenkov detectors.
Inertial confinement fusion (ICF) is an area of experimental physics involving
the implosion of capsules containing hydrogen isotopes to the required temperatures
and densities for fusion using lasers. Energy from the laser is coupled to the
capsule surface, ablating outer material whilst simultaneously driving shock waves
and material inward to a stagnation region where temperatures, pressures and
confinement are appropriate for fusion. To diagnose the implosion many detectors
are used generally measuring radiation from the capsule as a function of energy,
time or space. This talk will discuss the gas Cherenkov detectors fielded at the
NIF and Omega facilities to record low intensity DT fusion gammas; the purpose
being to report the temporal reaction history and FWHM of the implosion. Benefits
include: thresholding where only gammas exceeding a minimum energy are observable
due to the dielectric properties of the gas, reducing sensitivity to low-energy
background radiation; and preservation of the reaction history structure at large
standoff distances, an issue for particle diagnostics.
Thursday 22nd September 2011
Philip Beeley (Khalifa University of Science Technology and Research, Abu Dhabi)
Following the publication of the UAE's Nuclear Policy in 2008 and the announcement
in December 2009 to purchase four Korean APR 1400 PWR reactors, Khalifa
University has embarked on a fast track programme to establish a nuclear engineering
program to support the nuclear industry and regulator in the UAE. This lecture will
provide an overview of our developments over the past two years and our way forward
for the future.
Tuesday 6th September 2011
Michael Wiescher (Joint Institute for Nuclear Astrophysics & Department of
Physics, University of Notre Dame)
Nuclear Astrophysics Underground
The field of nuclear astrophysics is concerned with the question of energy
production and nucleosynthesis of the elements in quiescent and explosive
stellar environments. Key reactions are charged particle interactions at low energy,
which determine the abundance distribution up to iron and play a critical role
in providing the seed material for the nucleosynthesis of heavier elements.
Charged particle reactions in quiescent stellar burning also determine the lifetime
of the evolutionary burning stages of stars and therefore need to be studied
at the characteristic temperatures of the stellar environment. Because of the
extremely low cross sections of these reactions direct measurements are not available
except for two cases and the determination of stellar reaction rates relies largely
on theoretical extrapolation of existing higher energy data. A number of new methods
have been developed over the last decade to improve the experimental data at low
energies. This includes inverse kinematics techniques using intense heavy ion beams
and high resolution recoil separators. Alternative methods are experiments in
an underground, cosmic ray background free environment. Both approached have
contributed greatly to our understanding of stellar burning. This talk will
summarize some of the critical experiments, which, coupled with the development
of new theoretical methods have addressed questions of energy production,
nucleosynthesis, and neutrino production in stellar hydrogen burning environment.
Also presented will be the status and progress in the design and development of new
or future facilities and methods.
Wednesday 17th August 2011
Qiang Zhao (Institute for High Energy Physics (IHEP), Chinese Academy of Sciences)
Charmonium physics
This talk will be a general review of the physics of charmonium
spectroscopy. The
discovery of the J/psi meson (and hence confirmation of the charm quark) in 1974
has been one of the most important successes of quantum chromodynamics (QCD).
Professor Zhao will discuss present interest in this highly topical area based on the
feature that this is an interplay between perturbative and non-perturbative QCD
scenarios.
Thursday 4th August 2011
Takashi Nakamura (Tokyo Institute of Technology, Ookayama, Tokyo)
Breakup reactions to probe nuclear structure at the limit of stability
Breakup reactions at intermediate/high energies have played important roles in
investigating nuclear structure at the stability limit. In this talk, I would like to
characterize the Coulomb and nuclear breakup reactions to probe the weakly-
bound halo states as well as unbound states. The topics I focus are the recent
inclusive breakup measurements of carbon and neon isotopes [1] at about
230 MeV/nucleon at RIBF, RIKEN. I also would like to talk about the study
of 13Be unbound states [2]. Finally, I introduce the project "SAMURAI" at RIBF,
which will be used for further studying the structures of neutron-drip line nuclei
via breakup reactions.
[1] T. Nakamura et al., Phys. Rev. Lett. 103, 262501 (2009).
[2] Y.Kondo, TN et al., Phys. Lett. B 690, 245 (2010).
Tuesday 24th May 2011 (slides)
Marianne Dufour (IN2P3-CNRS/Universite de Strasbourg)
Microscopic cluster model. Applications in reactions of astrophysical interest
and in light nucleus physics
During this talk, general aspects of microscopic cluster models based on the combination of
the Generator-Coordinate-Method and of the R-matrix method will be presented [1, 2]. Such
frameworks present numerous advantages. They provides an unified description of bound and
scattering states. Antisymmetrization between all nucleons, good quantum numbers and boundary
conditions are exactly treated.
Microscopic cluster models are widely used in nuclear astrophysics where measurements
in laboratories are in general impossible at stellar energy. They are also widely applied to
describe broad states in light nuclei such as molecular ones where an exact treatment of the
asymptotic behaviour of the wave-functions is necessary. Our purposes will be illustrated by
recent examples such as the 12C(alpha,gamma )16O E2 cross section[3], the existence of a
molecular band in the 12Be nucleus, the physics of exotic light nuclei such as the 16B nucleus
[4] and the recent research of condensate states in 12C and 16O [5].
1. P. Descouvemont, and D. Baye, Rep. Prog. Phys. 73, 036301 (2010).
2. P. Descouvemont, and M. Dufour, Microscopic cluster model,
to be published in Lecture Note in Physics, Springer (2011), Ed. C. Beck.
3. M. Dufour, and P. Descouvemont, Phys. Rev. C78, 015808 (2008).
4. M. Dufour, and P. Descouvemont, Phys. Lett. B 237 (2011).
5. R. Lazauskas, and M. Dufour, in preparation.
Friday 20th May 2011 (slides)
Wim Dickhoff (Washington University, St. Louis, USA)
New developments using Green s function methods linking nuclear
structure and reactions on the way to the drip lines
The present understanding of proton properties near the Fermi energy for stable
closed-shell nuclei has relied on data from the (e,e'p) reaction.
Hadronic tools to extract such spectroscopic information have been hampered by
the lack of a consistent reaction description that provides unambiguous and
undisputed results. The dispersive optical model (DOM), originally conceived by
Claude Mahaux, provides a unified description of both elastic nucleon scattering
and structure information related to single-particle properties below the
Fermi energy and may be used to overcome this important problem. Its efficacy
is illustrated by a recent extension of the method to groups of isotopes or
isotones establishing the nucleon asymmetry dependence of the DOM potentials.
Based on the extracted asymmetry dependence, it is possible to predict the
nucleon properties in more exotic nuclei.
Several investigations related to and extensions of the DOM are reported:
- the role of non-locality in describing data below the Fermi energy
- properties of valence protons in exotic Sn nuclei
- insights that are provided by ab initio calculations of the nucleon
self-energy emphasizing the coupling to low-lying collective excitations
- insights into the quality of ab initio optical potentials at positive energy
calculated for finite nuclei
Tuesday 17th May 2011 (slides)
Ian Thompson (LLNL, Livermore, USA)
Coupled-channels Neutron Reactions
Microscopic calculations of the reaction cross-section for nucleon-nucleus
scattering have been performed by explicitly coupling the elastic channel to
all the particle-hole (p-h) excitation states in the target and to all
relevant pickup channels. The results of such calculations were compared to
predictions of a well-established optical potential and with experimental
data, reaching very good agreement. Couplings between inelastic states were
found to be not significant, while the inclusion of couplings to pickup
channels was an important contribution to the absorption. For the first
time, calculations of excitations account for all of the observed reaction
cross-sections, at least for incident energies above 10 MeV.
These channel couplings should generate all the imaginary components
of the neutron optical potential, which summarizes the overall effects
of non-elastic channels on the elastic wave function. Strictly, this
optical potential is non-local, and energy and L-dependent. This
dependence is shown, along with equivalent local potentials.
Thursday 12th May 2011
Bertram Blank (CEN Bordeaux-Gradignan)
Weak interaction studies with exotic nuclei
Studies performed in the frame work of the weak-interaction standard model can
use the atomic nucleus as a laboratory. In our experiments, we studied the
super-allowed beta decay and the mirror beta decay of nuclei to determine the
reduced transition strength ft which depends on the decay heat of the
radioactive decay, the so-called Q value, on the branching ratio of a
particular decay branch, the total beta-decay half-life of the nucleus, and,
for the mirror decays, on the Fermi-to-Gamow-Teller ratio. After a few small
corrections, the vector-current coupling constant of the weak interaction and
the Vud element of the CKM quark-mixing matrix can be determined.
In the talk, I will present the state of the art of the subject and describe
our contribution in the past as well as in the future this domain of research.
Tuesday 10th May 2011 (slides)
Stephane Goriely
(Institut d'Astronomie et d'Astrophysique, Universite Libre de Bruxelles)
The r-process nucleosynthesis: nuclear and astrophysics challenges
About half of the nuclei heavier than iron observed in nature are produced by the so-called
rapid neutron capture process, or r-process, of nucleosynthesis. The identification of the astro-
physics site and the specific conditions in which the r-process takes place remains, however,
one of the still-unsolved mysteries of modern astrophysics. Another underlying difficulty
associated with our understanding of the r-process concerns the uncertainties in the predictions
of nuclear properties for the few thousands exotic neutron-rich nuclei involved in the r-process
and for which essentially no experimental data exist.
The present contribution emphasizes some important future challenges faced by nuclear
physics in this problem, particularly in the determination of the nuclear structure properties
of exotic neutron-rich nuclei as well
as their radiative neutron capture rates and their
fission probabilities. These quantities are particularly relevant to
determine the composition of the
matter resulting from the r-process. Both the astrophysics and the nuclear physics difficulties
are critically reviewed with a special attention paid to the r-process taking place during the
decompression of neutron star matter.
Tuesday 29th March 2011
Carlo Barbieri (University of Surrey)
Perspectives for Ab-Initio Theory in Mid-Mass Isotopes
Ab-initio calculations--starting from the sole knowledge of a realistic nuclear
force--aim at eventually achieving parameter-free predictions of nuclear
properties. These pose strong requirements on quantum many-body theory.
Recent breakthroughs in the theory of nuclear interactions and computational
many-body physics have opened the way to unprecedented studies of closed-shell
nuclei in the medium mass region. In these cases, ground state and
spectroscopic properties can now be calculated up to masses of A=56. However,
closed shells represent just a small fraction of the exotic isotopes available
in Nature. New developments (based on calculations of Gorkov-Green's functions
and self-energies) will allow to push back current limitations in two main
frontiers: open-shell systems and reactions.
Monday
21st March
2011
Makito Oi (Senshu University, Tokyo)
Physics of high-K isomers with Pfaffian
Thanks to the newly developed Storage Ring in GSI, the study of high-K isomers
has entered a new chapter. An advantage of SR is to be able to measure
unexpectedly long-lived isomers, on the contrary to the conventional
technique by measuring time-of-flight with gating. Existence of long-life
high-K isomers in the neutron-rich and heavy-mass region implies a new
possibility in interpreting the r-process nucleosynthesis in supernova
explosions, particularly in the N=126 waiting points. The r-process path
can be disturbed by the presence of long-lived isomers. The theoretical
tools required for this new investigation is the quantization technique of
many-body HFB states, so as to calculate transition probabilities.
Recently, new mathematical approaches were pointed out to be very effective
in the quantization: Pfaffian, Fermion coherent states, and Grassmann numbers.
With these new powerful "weapons", I will show my plan how to clear this new
level of a many-body "game".
Tuesday 15th March 2011
Jac Caggiano (LLNL, Livermore, USA)
A first look at dt neutron spectra using the 20 meter neutron time-of-flight
systems at NIF
Tuesday 8th March 2011
David Evans (University of Birmingham)
Results from the ALICE Experiment at the CERN LHC:
The ALICE experiment was designed to study the strong interaction and,
in particular, the quark-gluon plasma. Although designed to cope with the
extreme conditions of heavy-ion collisions at the LHC, ALICE is also well
suited to studying the event characteristics of proton collisions.
The current status and latest results from both proton-proton and lead-lead
collisions will be presented.
Tuesday 1st March 2011 (slides)
Pierre Capel (Helmholtz-Institut Mainz, Institut fur Kernphysik of the Johannes
Gutenberg-Universitat Mainz)
Ratio of angular distributions, a new tool to study halo nuclei.
Halo nuclei are light neutron-rich nuclei that exhibit a strongly clusterised
structure: they can be viewed as a core that contains most of the nucleons,
to which one or two neutrons are loosely-bound. Owing to their low separation
energy, these neutrons tunnel far from the classically-allowed region and form
a sort of halo around the core. This exotic nuclear structure is the subject
of many experimental and theoretical studies. During this seminar, I will
present a new way of extracting information about the halo structure using
angular distributions for elastic scattering and break-up.
Tuesday 22nd February 2011 (slides)
Nikolay Minkov (Institute of Nuclear Research and Nuclear Energy,
Bulgarian Academy of Sciences)
High-K isomers as probes of octupole collectivity in heavy nuclei
The influence of the octupole deformation on the structure of high-K isomeric
states in the region of heavy even-even actinide nuclei is studied [1] through
a reflection asymmetric deformed shell model (DSM). Two-quasiparticle states
with high-K values are constructed by taking into account the pairing effect
through a DSM + BCS procedure with constant pairing interaction. The behaviour of
two-quasiparticle energies and magnetic dipole moments of K^pi=6+, 6-
and 8- configurations, applicable to mass numbers in the range A=234-252,
was examined over a wide range of quadrupole and octupole deformations.
A pronounced sensitivity of the magnetic moments to the octupole deformation
is found. The result suggests a possibly important role for high-K isomers
in determining the degree of octupole deformation in heavy actinide nuclei.
[1] P. M. Walker and N. Minkov, High-K isomers as probes of octupole
collectivity in heavy nuclei, Phys. Lett. B 694, 119
Tuesday 15th February 2011
Stefan Lalkovski ((University of Sofia)
Isomeric decays in the neutron-rich Ag isotopes
Two experiments, focused on the nuclear structure below the N=82 shell gap
[Ju07, Ca09, Na10, Go09] and the nuclear shapes of the neutron-rich A~110
nuclei [Br10], have been carried out during the RISING Stopped beam campaign
at GSI. The exotic neutron-rich nuclei were produced in relativistic fission of 238U
and fragmentation of 136Xe. The nuclei were analyzed with the GSI FRagment
Separator and subsequently implanted into a passive stopper. The isomer-delayed
gamma-rays were detected by 105 HPGe detectors.
The present work extends the above isomeric studies towards the neutron-rich
silver isotopes, where new microsecond isomers have been observed. The
123,125Ag isomers, previously observed in [St09], are confirmed. Extended
level schemes will be presented and discussed.
[Ju07] A. Jungclaus et al., Phys. Rev. Lett. 99 (2007) 132501-1
[Ca09] L. Caceres et al., Phys. Rev. C79 (2009) 011301-1
[Na10] F. Naqvi et al., Phys. Rev. C82 (2010) 034323-1
[Go09] M. Gorska et al., Phys. Lett. B672 (2009) 313
[Br10] A. Bruce et al., Phys. Rev. C82 (2010) 044312
[St09] I. Stefanescu et al., Eur. Phys. J. A42 (2009) 407
Tuesday 25th January 2011
Simon Brown (University of Surrey)
Neutron Shell Breaking in Neutron-Rich Neon Isotopes
In the region of the of the sd shell, it is known that the magic number N = 20 does
not exist far from stability [1] and recent experiments have indicated the existence
of a new shell closure at N = 16 in neutron-rich nuclei [2,3]. This shell migration
has been attributed in part to the monopole shift of the neutron d3/2 energy,
which lies between the s1/2 orbital and the pf shell [4].
An excellent way to probe this evolution is to measure the strength of single-particle
states in isotopes where the relevant orbitals are empty apart from the probe
neutron. This removes many effects of the interactions between neutrons.
In the present work, this is pursued by measuring proton angular distributions
in (d,p) transfer reactions producing states in 27Ne. A 9.8A MeV 26Ne beam
produced by the SPIRAL facility at GANIL bombarded a 1 mgcm^2 CD2 target.
Measurements of the protons, gamma-rays and the heavy recoil particles were
utilised to identify states in 27Ne whether they were bound, unbound or bound
but isomeric. The results are compared to shell model calculations and their
structural implications are discussed.
[1] C. Detraz et al, Physical Review C 19, 164 (1979)
[2] M. Stanoiu et al, Physical Review C 69, 034312 (2004)
[3] A. Obertelli et al, Physical Review C 71, 024304 (2005)
[4] T. Otsuka et al, Phys. Rev. Lett. 105 032501 (2010)
Monday 17th January 2011 (slides)
Adam Garnsworthy (TRIUMF)
Gamma-ray Spectroscopy at TRIUMF-ISAC
The ISotope Separator and Accelerator (ISAC) facility at TRIUMF, Vancouver,
Canada employs up to 100 microamps of 500 MeV protons impinging on various
spallation/fragmentation targets to produce some of the highest-intensity ISOL
radioactive beams in the world. Mass-separated radioactive beams are delivered to
experimental facilities such as the 8pi spectrometer in ISAC I, or post-accelerated
up to 10 MeV/u and delivered to ISAC II experiments such as the TRIUMF-ISAC
Gamma-Ray Escape-Suppressed Spectrometer (TIGRESS). The Gamma-Ray
Spectroscopy Group at ISAC perform investigations of Nuclear Structure and
Astrophysics as well as fundamental Interaction studies utilizing both beta-decay
with the 8pi and nuclear reactions using TIGRESS. I will present an overview of
the facility and experimental capabilities as well as highlight some of the recent
experimental results.
Wednesday 12th - Thursday 13th January 2011 at University of Brighton
PRESPEC Decay Physics Workshop
(programme)Held at: Creativity Suite of the Cockcroft building at the Moulsecoomb site of the
University of Brighton
Organisers: Alison Bruce (Brighton), Paddy Regan (Surrey)