Seminars in 2015:

Friday 4th December 2015
Umesh Garg (University of Notre Dame)
Quantal Rotation in Nuclei

In this talk, I will present recent results on some novel modes of nuclear motion

—chirality, wobbling, and tidal waves. In our measurements on the nucleus 135Nd,

we observed the first clear evidence for a transition from chiral vibrations to chiral

rotation. More recently, we have discovered the first case of multiple chiral bands

in the nucleus 133Ce.
Wobbling is another phenomenon associated with triaxial nuclei. The concept of

transverse wobbling involves alignment of the odd-particle along the "short" axis

of an odd-A triaxial nucleus. We have observed transverse wobbling bands in the

nucleus 135Pr. This is the first time that wobbling bands have been observed in

a mass region other than A~160 where wobbling bands were first discovered.
The concept of nuclear tidal waves is based on the observation that the yrast

states in a phonon multiplet represent waves that travel over the nuclear surface

akin to tidal waves over the ocean surface. This accounts for the experimental

result that the yrast states in vibrational nuclei have a rotational-like structure for

which a sound theoretical basis, especially at higher spins, has been lacking so

far. In our measurements of B(E2)'s in the yrast band of 102Pd, we have found

consonance with the theoretical expectations.

Tuesday 24th November 2015
Teppei Katori (Queen Mary University of London)
Physics of Neutrino Interaction around 1-10 GeV
Neutrino interaction physics around 1 to 10 GeV shows a dramatic progress in the last 10

years, mainly because this is the most important energy region for neutrino oscillation

experiments. Especially, there is a growing evidence that the nucleon correlations play

an important role for neutrino interaction physics, and hence, neutrino oscillation

measurements. In this talk, I would like to review the neutrino interactions, starting from
quasi-elastic scattering, then baryon resonance, and deep inelastic scattering,
with a special emphasis on both recent theoretical progresses and experimental

measurements.
 

Tuesday 17th November 2015
Dave Cullen (School of Physics and Astronomy, University of Manchester)

Nuclear Lifetime measurements using Differential-Plunger and Fast-Timing techniques
The measurement nuclear-state lifetimes has been used to give information about the

deformation of the nucleus. Nuclear deformation can strongly affect the electromagnetic

and particle-emission transition rates.  The comparison of these transition rates with

theoretical calculations can give important information to nuclear theory.  This is

particularly important for nuclei which lie far from stability where little experimental

information exists. In this talk, I will discuss lifetime measurements for two proton

emitting nuclei of differing deformation. In each case, a particle-rotor model calculation

has been performed to extract nuclear wave functions. These wave functions  have then

been used both in electromagnetic transition-rate calculations to compare with the

experimental lifetime measurements and with proton-emission calculations to compare

with the experimental proton emission rates.   Consistency between these approaches

has allowed the nuclear deformation of 151Lu and 113Cs to be extracted for the first

time. The talk will conclude with some prospects for future lifetime studies.

Wednesday 4th - Thursday 5th November 2015

Tuesday 3rd November 2015
Andrea Idini (University of Jyväskylä, Finland)
Beyond and Before mean field theories: Mean field generators, and many-body

correlations from particle-vibration coupling, will be shown as an effective description

of the nuclear system, in the light of future work to be held in Surrey.
The nucleus is an elusive system to describe in all its degrees of freedom and possible

excitations. Recently development in finite-range momentum-dependent pseudopotentials

will be presented as interesting candidates to explain nuclear structure properties in a

more consistent way, being able to avoid projection divergences, and reproducing the

properties of both particle-hole and pairing channel with the same functional.
On the other hand, beyond mean field theories are necessary to consistently investigate

a number of low-energy observables. Making use of Nambu-Gorkov equation, a propagation

of the Dyson Equation in the HFB basis, the coupling between independent-particles and

collective excitations determine the many-body propagator. In the paradigmatic example

of Sn-120, one and two particle transfer, electromagnetic and multiplet splitting are

calculated in qualitative agreement with the experimental data.
This enables also to investigate the starting assumptions, and find out the mean field,

pairing, and particle-vibration coupling properties that better compare with the experimental

data.

Tuesday 27th October 2015

Naomi Rocco (University "La Sapienza", Roma)
Unified description of lepton-nucleus scattering within the Spectral Function formalism
It has been argued that the large excess of CCQE neutrino-Carbon cross section observed

by the MiniBooNE collaboration may be ascribed to the excitation of two particle-two hole

nuclear final states, not taken into account in Monte Carlo simulations for data analysis.

I will discuss the mechanisms leading to the appearance of these final states, and illustrate

their significance through the results of accurate calculations of the nuclear electromagnetic

response in the transverse channel. Preliminary results of a novel approach, allowing for a

consistent treatment of the amplitudes involving one- and two-nucleon currents in the

kinematical region in which the non relativistic approximation breaks down will be presented.

Tuesday 20th October 2015

Francesco Raimondi (University of Surrey)
Ab initio many-body calculations of single-nucleon transfer reactions with

deuteron projectile
We study one-nucleon transfer reactions with a binary-cluster description of the

nuclear system, where both the projectile and target are described in an ab initio

framework, that is, all the nucleons in the projectile-target system are active

degrees of freedom interacting through a realistic nuclear two-body interaction.

In particular we focus on stripping reactions where a deuteron (d) projectile is

impinging on light nuclei with mass number A > 4.
In my talk I will cover the following topics:
• Brief overview of the no-core shell model/resonating-group method (NCSM/RGM)

[1] and NCSM with continuum (NCSMC) [2] formalisms for the description of

deuteron-nucleus collisions and single-nucleon transfer reactions, presenting in

particular the expressions of the Hamiltonian kernels which drive the dynamics

in both elastic and transfer channel of the two-nucleon projectile scattering;
• Presentation of the results for the reaction of a deuteron impinging on a 7Li

target. The 7Li(d,p)8 Li reaction has been used as calibration reaction in order

to obtain the 7Be target thickness, in connection to relevant 7Be(p,γ)8 B

nucleosynthesis reaction [3, 4]. The mechanism of the (d,p) reaction on 7Li

target is described through the analysis of phase shifts and cross sections,

while energies and spin-parity assignments of the resonant states of the

compound nucleus 9 Be above d-7Li threshold are discussed.

[1] S. Quaglioni and P. Navratil, Phys. Rev. Lett. 101, 092501 (2008).
[2] S. Baroni, P. Navratil and S. Quaglioni, Phys. Rev. C 87, 034326 (2013).
[3] A.J. Elwyn, R.E. Holland, C.N. Davids and W. Ray Jr, Phys. Rev. C25,

     2168 (1982).
[4] B.W. Filippone, A.J. Elwyn, and W. Ray Jr, Phys. Rev. C 25, 2174 (1982).

Tuesday 4th August 2015

Takaharu Otsuka (University of Tokyo and Center for Nuclear Studies (RIKEN))
Dual quantum liquid picture of nuclei

I will first overview briefly the shell evolution in exotic nuclei, and then introduce Type

II shell evolution as a possible driving/supporting force of the shape coexistence. This

will lead us to a picture of dual quantum liquid. Most states of nuclei are in the usual

quantum liquid, where single-particle energies are static and constant within a given

nucleus. There can be another phase of the quantum liquid,  where effective single-

particle energies are changed dynamically due to particular massive particle-hole 

excitations.  I shall sketch such a picture, showing  also recent results from Monte

Carlo Shell Model calculations on medium-heavy nuclei.

Tuesday 16th June 2015

is generated by employing a nonlocal dispersive optical potential capable of simultaneously

reproducing all relevant data above and below the Fermi energy. The introduction of non-locality

in the absorptive potentials yields equivalent elastic differential cross sections as compared to

local versions but changes the absorption profile as a function of angular momentum suggesting

important consequences for the analysis of nuclear reactions. Below the Fermi energy, non-locality

is essential to allow for an accurate representation of particle number and the nuclear charge density.

Spectral properties implied by (e,e’p) and (p,2p) reactions are correctly incorporated, including the

energy distribution of about 10% high-momentum nucleons, as experimentally determined by data

from Jefferson Lab. The relevance of dispersive optical potentials for the analysis of transfer

reactions is also discussed.

density functional theory and provide a unified description of nuclear ground states as well

as low-energy excitations. On the one hand, within the last forty odd years numerous

applications thereof have shown a tremendous success of the approach, which allows for a

correct description of a multitude of nuclear phenomena. On the other hand, recent analyses

indicate that the currently used EDFs have probably reached their limits of accuracy and

extrapolability. The question of whether these can be systematically improved appears to be

the central issue of the present-day investigations in this domain of nuclear-structure physics.

In this talk I will present the status of theoretical developments aiming at improvements of the

present-day nuclear EDF approaches. The main lines of current attempts are in expansions

based on higher-order derivative corrections and/or including three- or four-body terms. Novel

EDFs are often based on zero-range or finite-range pseudo-potentials and may have local,

quasi-local, or non-local character. Some of the new developments have already led to

implementations in numerical codes and preliminary applications to finite nuclei are gradually

becoming available.

functions. Application to 12C+alpha.
I first recall the principle of phase-shift analysis and effective-range expansions for charged-

particle elastic scattering. Then, I show how Padé expansions of effective-range functions

can be used to link properties of sub-threshold bound states, in particular asymptotic

normalization constants, to low-energy elastic-scattering phase shifts. Finally, the method

is applied to the C12+alpha system, of which the importance in nuclear astrophysics is

recalled.

an important observable to test nuclear models that describe collective phenomena.

The available data for E2 transition strengths in even-even nuclei in the region between

neutron-deficient hafnium and platinum isotopes are far from complete. More and precise

data are needed to enhance the picture of structure evolution in this region and to test

state-of-the-art nuclear models. A series of experiments conducted at the Cologne Institute

for Nuclear Physics aims to fill these gaps by measuring yrast state half lives in this region.

For this purpose the fast timing method is employed, using a combination of LaBr scintillator

detectors and an Orange conversion electron spectrometer. The results from the first part

of this campaign, with focus on the Hafnium isotopic chain, are compared to calculations

using the interacting boson model. The Hamiltonian, as well as the effective charge for the

calculation of absolute transition strengths, is determined based on microscopic energy-

density functional calculations. This work shows the importance of a mass-dependent

effective boson charge in the interacting boson model for the description of E2 transition

rates in chains of nuclei. It encourages further studies of the microscopic origin of this

mass dependence.
 

most intriguing themes of nuclear physics. The energy density functional (EDF) framework

allows for a global and reasonable description of ground-state properties and collective

excitations over the whole nuclide chart. Meanwhile, the algebraic theory of interacting

bosons, that is, the interacting boson model (IBM), has been successful in the description

of low-energy collective structure in medium-heavy and heavy nuclei.

To describe spectroscopic properties of nuclei based on a global theory, we have

developed a robust framework constructed by linking microscopic EDF framework to

the IBM. The principal idea is to establish an appropriate mapping between nucleon and

boson systems, and thereby the Hamiltonian of the IBM, that is used for calculating
excitation spectra and transition rates, can be determined for various situations of

low-energy quadrupole and octupole collective states and shape coexistence without

invoking phenomenological adjustment to experiment. In this way, bridge is made over

the gap between the EDF and IBM, implying that the two methodologies can develop
collaboratively. In particular, the new approach opens up the possibilities of accessing

spectroscopy of heavy exotic isotopes, which is one of the declared objectives of RIB

facilities.

We discuss the basic notions of and the relevant examples resulting from this approach.

Tuesday 28th April 2015

for the astrophysical r-process
The β-decay of about 40 neutron-rich nuclei with neutron number N ~ 82 were measured

at the RIBF facility for the elements Ru—Sn, as part of the EURICA project. The new data,

are of significance for both nuclear structure and astrophysics. The unknown evolution of

the N = 82 shell closure is a challenge for nuclear models, and it results in half-life

predictions across the shell gap that are often diverging. Many of the measured nuclei

are located deep into the r-process path predicted by most models. Thus, the new

measurements allow a more reliable comparison between the solar system abundance

pattern and the results of reaction network calculations. This seminar will present the

experiment, and will discuss its results and implications for nuclear models and the

Wednesday 22nd April 2015
Taka Kajino (National Astronomical Observatory of Japan, University of Tokyo)
Quest for the origin of r-process
Both core-collapse supernovae (SNe) and binary neutron-star mergers (NSMs) are

viable candidate sites for the r-process nucleosynthesis.  However, there are controversies

between them.  Although SN models such as neutrino-driven winds or magneto-hydrodynamic

jets can very naturally explain the "universality" of the r-process abundance pattern between

the solar-system and the metal-poor stars, the explosion mechanism is till poorly known

theoretically.  On the other hand, the NSMs could not have arrived very early in the Galactic

evolution to account for the "universality" because of their cosmologically long coalescence

time scale 0.1 Gy≤ τ ≤1000 Gy.  In this talk we will discuss first the importance of nuclear

physics data such as beta-decay half-lives and fission fragment distributions for the

studies of the r-process in both models.  We then try to solve the coalescence time

scale problem in the NSMs by studying the Galactic chemo-dynamical evolution of

the Milky Way in which our SN and NSM models of the r-process are used as the

key inputs.

Tuesday 21st April 2015
Nikolay Minkov (Institute of Nuclear Research and Nuclear Energy, Bulgarian Academy of

Sciences)
Octupole deformations in high-K isomeric states of heavy and superheavy nuclei
We have studied the influence of the quadrupole-octupole deformations on the energy and

magnetic properties of high-K isomeric states in even-even actinide (U, Pu, Cm, Fm, No),

rare-earth (Nd, Sm and Gd) and superheavy (270Ds) nuclei within a deformed shell model

with pairing interaction [1,2,3]. The neutron two-quasiparticle (2qp) isomeric energies and

magnetic dipole moments were calculated over a wide range in the plane of quadrupole

and octupole deformations. We found that in most cases the magnetic moments exhibit a

pronounced sensitivity to the octupole deformation. At the same time the calculations outline

three different groups of nuclei: with pronounced, shallow and missing minima in the 2qp

energy surfaces with respect to the octupole deformation. The result indicates regions of

nuclei with octupole softness as well as with possible octupole deformation in the high-K

isomeric states. Recently similar behaviour of the 2qp isomeric energies in some of the

considered nuclei was independently obtained through configuration-constrained potential-

energy-surface calculations [4]. All these findings show the need of further theoretical analysis

as well as of detailed experimental measurements of magnetic moments in heavy

deformed nuclei.

[1] P. M. Walker and N. Minkov, Phys. Lett. B 694, 119122 (2010).
[2] N. Minkov and P. M. Walker, Eur. Phys. J. A 48: 80 (2012).
[3] N. Minkov and P. M. Walker, Phys. Scripta 89, 054021 (2014).
[4] H. L. Liu and F. R. Xu, Phys Rev C 87, 067304 (2013).
 

Tuesday 24th March 2015

Practice talks: for the IOP Particle, Astroparticle, and Nuclear Physics Groups

Monday 23rd March 2015

Adam Garnsworthy (TRIUMF)
The GRIFFIN Spectrometer for Radioactive Decay Spectroscopy at TRIUMF-ISAC
TRIUMF's Isotope Separator and ACcelerator (ISAC), located in Vancouver, Canada,

is one of the world's most powerful ISOL radioactive beam facilities. Gamma-Ray Infra-

structure for Fundamental Investigations of Nuclei(GRIFFIN) is the new decay spectroscopy

facility for TRIUMF-ISAC, which has been installed during 2014. GRIFFIN is an array of

16 large-volume hyper-pure germanium clover detectors coupled with a suite of ancillary

detector systems and a custom-built digital data acquisition system. The suite of ancillary

detector systems presently includes the SCEPTAR array of plastic scintillators for beta-

tagging, the PACES array of in-vacuum lithium-drifted silicon counters for high-resolution

internal conversion electron spectroscopy and an array of lanthanum bromide scintillators

for fast gamma-ray timing measurements. In 2015, GRIFFIN will be combined with the

DESCANT array of neutron detectors, developed by the University of Guelph and TRIUMF,

to enable studies of beta-delayed neutron emitting nuclei relevant to the astrophysical r-

process. First experiments were successfully performed at the end of 2014 using an

early-implementation of the GRIFFIN facility. GRIFFIN greatly enhances the capabilities

in the nuclear structure, nuclear astrophysics and fundamental symmetries research

programs with stopped radioactive beams available from ISAC and in the future ARIEL.

An overview of the GRIFFIN facility and initial results will be presented.

Thursday 19th - Friday 20th March 2015 at the NPL, Teddington

Workshop on Physics Opportunities Using Arrays of Fast-Timing Gamma-Ray Detectors

The workshop will discuss proposed and existing arrays using LaBr3 or CeBr3 fast-timing

detectors and physics areas of interest and potential experimental programmes using

such detectors and hybrid gamma-ray arrays.

Tuesday 17 March 2015

Identical features of semi-magic seniority isomers and the effective interactions

Large amount of experimental data have been presented in our “Atlas of Nuclear Isomers”,

which lists more than 2450 isomers with a half-life cut-off at 10 ns. It is interesting to find

that the nuclear isomers in the semi - magic chains present almost identical systematics

in excitation energy and half-life. Large scale shell model calculations have been carried

out to decipher their configurations and seniorities, which are able to reproduce the

observed systematics quite well. We, therefore, firmly identify them as seniority isomers,

which show similar features due to the same seniorities, even though different orbitals are

involved. This further becomes a great tool to predict some unknown isomers at the nuclear

extremes, like for the drip-lines, on the basis of the systematics. The long chain of isomers

is  also able to shed light on the nature of effective interactions, particularly in the

neutron/proton-rich regions.

Thursday 26th February 2015

Beatriz Fernandez-Dominguez (​ University of Santiago de Compostella, Spain)

Structure around the island of inversion with single-neutron knockout reactions at GANIL.

Tuesday 27th January 2015

Philip Goddard (University of Surrey)

Fission dynamics using the time-dependent Hartree-Fock method

Fission is perhaps the most extreme nuclear decay process, and since its discovery applications

in weaponry and energy production have received considerable attention, both in the scientific

community and in society in general.

 The theoretical understanding of the process was rapidly developed in the 1930’s, relying upon

macroscopic liquid drop models of the nucleus. Although the description of fission based upon

these models allowed humanity to engineer weapons and reactors, a successful description of

the process using a dynamic, microscopic approach has remained elusive for many decades.

This talk will focus on a recent exploratory study to determine whether Time-dependent Hartree-

Fock, a dynamic many-body theory which describes the nuclear system at the mean-field level,

is suitable to model nuclear fission. I will discuss the strategies and methods used to approach

the problem, and present and compare results to experimental data to verify the potential of such

a method to describe the fission process.

Tuesday 20th January 2015

The energy and structure of dilute hard- and soft-sphere gases is  studied in the framework

of several many-body approaches, for Bose and Fermi statistics. The effects of correlations

on the distribution function, momentum distribution and excitation spectrum are discussed

as a function of the gas parameter. In the case Fermi case, we also investigate the existence

of a ferromagnetic transition showing that our microscopic calculation shifts the transition to

high densities.