Seminars in 2017:

In-ring applications of UHV-compatible charged particle detectors

Storage rings offer a range of opportunities for nuclear physics research. High resolution

studies of nuclear reactions producing low-energy  charged particles require in-ring

UHV-compatible detectors. The  design, development and operation of such detectors is

challenging. Examples of such detectors and experiments will be discussed and plans for

an advanced, UHV-compatible silicon strip detector array for CRYRING will be presented.

disciplines

During the last decades we have witnessed a tremendous development in our capabilities

of solving scientific problems through scientific computing, that is, using computers, advanced

numerical algorithms, symbolic computations as well as standard analytical tools to solve and

analyze problems in science. Computing forms now an integrated and central part of essentially

all aspects of modern scientific studies, from basic research to industrial and societal applications.

In this talk I will show how computing can be introduced and integrated in a seamless way in

basic physics, mathematics and other science  courses and how computing can aid students in

gaining deeper insights about the scientific process as well as letting the students get a better

understanding of physics and the pertinent forces and laws of motion. Many on the results

reported in this talk are based on almost two decades of initiatives at integrating computing in

science education at the University of Oslo, Norway as well as recent work at Michigan State

University, USA. The research initiatives pertaining to the presentation are to a large extent

supported by the recently established Norwegian center of excellence in education, the Center

for Computing in Science Education, see http://www.mn.uio.no/ccse/english/ for more

information.

droplets [1-4]. In these experiments we use the strong 18 tesla magnetic field of a superconducting

magnet to suspend cm-sized droplets by diamagnetic levitation. Using this technique the force of

gravity is balanced at the molecular level so that the drops are weightless. The equilibrium shape

of the droplets changes as we spin them up: they deform from spherical to peanut-shaped and

eventually break apart.  I will discuss recent experiments showing the effect of electric charge

on the equilibrium shapes and fission modes of a spinning droplet [1]. In addition, I will also

present the results of experiments to manufacture wax models of spinning drops that reproduce

the curious shapes of tektites---small stones formed in asteroid impacts [2].
[1] L.Liao and R. J. A. Hill, Phys. Rev. Lett. 119, 114501 (2017)
[2] K. A. Baldwin, Samuel L. Butler, R.J.A. Hill Sci. Rep., 5, 7660 (2015).
[3] R. J. A. Hill, L. Eaves, Appl. Phys. Lett., 100, 114106 (2012).
[4] R. J. A. Hill, L. Eaves, Phys. Rev. Lett., 101, 234501 (2008).

of nuclei especially in the medium-heavy and heavy mass region.  I will discuss an application

of the Adiabatic Time Dependent Hartree-Fock-Bogolyubov (ATDHFB) theory to describe

low-energy quadrupole collective excitations in even-even nuclei.  The theory makes it possible

to calculate energy levels of excited states and electromagnetic transition probabilities based

solely on the microscopic input.  In most presented cases theoretical results were obtained

using the Skyrme-like energy functionals.  I will also mention some open questions, e.g. 

to be used in the energy density functional (EDF) theory with specific assumptions for defining

a power counting. So far this procedure is developed through the evaluation of the equation of

state (EOS) of symmetric and pure neutron matter and is evaluated up to next-to-leading order

in the beyond mean–field scheme. Counter terms are introduced to absorb the divergences

present in beyond mean–field diagrams, which contain also parameters which do not contribute

to the EOS of matter and may eventually be determined through future adjustments to properties

of some selected finite nuclei. Our work serves as a simple starting point for constructing a

well–defined power counting within the EDF framework.

in recent years as a tool to extract information from exotic nuclei, thanks to the availability

of exotic beams with which to perform these reactions in inverse kinematics.  These reactions

are expected to be sensitive to deeper parts of the removed-nucleon wave function than

knockout reactions with heavier targets, so they are expected to give complementary information

to these reactions, regarding the single-particle properties of stable and exotic nuclei. Of particular

interest is the study of the so-called Borromean nuclei,  three-body systems all  of  whose  two-body 

subsystems  are  unbound.   The  removal  of  a  nucleon  from  Borromean nuclei results in an

unbound residual nucleus, whose properties can be reconstructed from the products of its decay

following the (p; pN) reaction.
In this work we use an extension to the Transfer to the Continuum [1] formalism to study (p; pN)

reactions,  focusing  our  interest  on  Borromean  nuclei,  and  the  energy  distributions for the

two-body unbound residual nucleus.  A participant-spectator model is assumed when treating

the reaction mechanism and an expansion in a transformed harmonic oscillator basis is performed

to calculate the ground state of the Borromean nucleus.  Results have already been published for

the naming rights for the elements 113,115,117 and 118 to groups at the FLNR and at

RIKEN [1–4].  For nuclei beyond the region of fermium-rutherfordium the liquid drop fission

barrier vanishes.  They owe their existence solely to quantum mechanics effects what

makes them an ideal laboratory to study the strong nuclear interaction by in-beam

methods as well as decay spectroscopy after separation [5].
While in-beam spectroscopy gives access to nuclear structure at higher spins like e.g. 

rotational bands [6], decay spectroscopy after separation of these deformed nuclei in the

region Z=100-112 and N=152-162 provides direct links to the next heavier spherical closed

shell nuclei, by investigating single particle levels [7]. A particularly interesting feature are

meta-stable states due to nuclear deformation, so-called K isomers. Following the trend

of vanishing deformation, they can be used to trace the spherical superheavy nuclei (SHN)

and to locate the island of stability [8].
Improved experimental means like new high intensity accelerators,  efficient in-flight separators

and spectrometers, and highly efficient detection systems with fast electronics are the essential

ingredients for the success of the field.  The new SPIRAL2 facility and, in particular, the

separator-spectrometer setup S3 [9, 10] presently under construction at the accelerator laboratory

GANIL in Caen, France, will offer great perspectives for the field [8]. An overview of the recent

achievements and future perspectives for the field of SHN research will be given.
[1]  Yu.Ts. Oganessian et al., Nucl. Phys. A944, 62 (2015).
[2]  K. Morita et al., J. Phys. Soc. Jpn.73, 2593 (2004).
[3]  P.J. Carol et al., Pure and Applied Chemistry 88, 139153 (2016).
[4]  P.J. Carol et al., Pure and Applied Chemistry 88, 155160 (2016).
[5]  D. Ackermann and Ch. Theisen, Phys. Scripta 92, 083002 (2017).
[6]  Ch. Theisen et al., Nucl. Phys. A944, 333 (2015).
[7]  M. Asai et al., Nucl. Phys. A944, 308 (2015).
[8]  D. Ackermann, Nucl. Phys. A944, 376 (2015).
[9]  The Scientific Objectives of the SPIRAL2 Project, Livre Blanc SPIRAL 2, GANIL (2004).
[10]  F. Dechery et al., Eur. Phys. J. A51, 66 (2015).

Electromagnetic beams - neutron stars, new particles and John Virgo trick shots
Recent results and plans for the Edinburgh research programme at JLAB and MAMI will be

presented. This will include our work to elucidate the nature of the narrow "d*" resonance  in

the np system  - which is a hexaquark candidate. New experiments at the upgraded JLAB

will give precise information on the hyperon-nucleon interaction, information crucial for neutron

star properties and hypernuclei. A first look at the potential to reach highly neutron rich nuclei

different steps that led to a promising extension, the so-called N3LO interaction. In particular, I will

show that the general form of the interaction can be deduced from gauge invariance and that the

problem of instabilities observed in calculations can be treated through the linear response theory.

Furthermore, I will present some interesting features of this interaction and compare it to the other

popular finite-range interactions. 

interface between nuclear physics, atomic physics and plasma physics. The most obvious

phenomenon is the excitation of the nucleus by interaction with the plasma components, namely

electrons and photons. Several processes have been identified: photon absorption, inelastic

electron scattering, nuclear excitation by electron capture (NEEC) and nuclear excitation by

electron transition (NEET). This last process occurs when an electron transits from an outer

shell to an inner shell and the transition energy is close enough to the nuclear transition energy.

Whenever these resonant conditions are met, NEET is usually the most efficient process and

so is the object of many studies. However these resonant conditions are heavily dependent on

the electronic configurations of the atom which in turn depend on the plasma conditions.

During this seminar, I will make an overview of the various nuclear excitation processes in plasma.

I will then focus on NEET and explain why the Relativistic Average Atom Model (RAAM) description

of the atom, which is relevant enough for the other processes, cannot be used with NEET. Therefore

we developed a new original method trying to combine the quickness of RAAM and the precision of

Detailed Configuration Accounting methods. It aims at selecting all relevant atomic configurations

from which electron transitions will most closely match the nuclear transition energy and evaluate

atomic transition energies between real atomic configurations while still using some fast RAAM

features. Finally I will detail how through a statistical approach we are able to somehow overcome

the difficulty of the necessarily limited precision (at least for our needs) of even the current best

Tuesday 2nd May 2017

sensitivity of the sub-barrier fusion probability to the structure of the colliding nuclei will be

presented as well as a very recent experimental study showing that, at extreme sub-barrier

energies, a surprising dependence of the process on fundamental properties of nuclear

matter is found, such as its incompressibility, or Pauli repulsion effects.

In this energy region, nuclear fusion is strongly connected with astrophysics, as it is an

essential step for the synthesis of the chemical elements in stars. In this context, we will

discuss experimental investigations in light heavy-ion systems for which resonances have

been observed at the Coulomb barrier and may persist at deep sub-barrier energies. In

particular we will discuss a recent 12C+12C fusion experiment performed in Orsay (France)

at the Andromede facility. This experiment is taking advantage of the particle-gamma

coincidence technique by using large solid angle silicon strip detectors from the STELLA

project combined with up to 36 LaBr3(Ce) scintillators from the high efficiency FATIMA

Tuesday 25th April 2017

Studies at A=31 for nuclear astrophysics and nuclear structure

In this talk, I will discuss two experiments exploring nuclei relevant for nuclear astrophysics

and nuclear structure at A=31. Firstly, we have recently studied the 30P(p,g)31S reaction

using the d(30P,n)31S reaction as a surrogate [1]. The 30P(p,g)31S reaction rate is one of

the most prominent nuclear physics uncertainties in models of oxygen-neon nova explosions.

We performed the first measurements of key resonance strengths for this reaction employing

GRETINA detector array at NSCL for detecting gamma rays from the states populated in

31S. The results clearly indicate the dominance of a single 3/2- resonance state at 196 keV

in the region of nova burning T≈0.10–0.17 GK. 31S is also a member of the T=3/2 isospin

quartet at A=31. For this quartet, we have performed the first high-precision mass measurement

of 31Cl [2] with the JYFLTRAP Penning trap in order to study the isobaric multiplet mass

equation (IMME). The results indicate a breakdown of the quadratic form of the IMME, which

cannot be explained only by the isospin mixing in 31S [3]. The more precise mass of 31Cl is

also relevant for constraining the conditions for 30S being a waiting point in the rapid proton

capture process.

[1] A. Kankainen, P.J. Woods, et al.,  http://doi.org/10.1016/j.physletb.2017.01.084.

[2] A. Kankainen et al., Phys. Rev. C 93, 041304(R) (2016).

[3] M.B. Bennett et al., Phys. Rev. C 93, 064310 (2016).

tool to describe nuclear structure phenomena. I will discuss the concept of CDCF and particularly

why Lorentz invariance should be taken seriously in this context. Then, I will show several very

Coulomb and nuclear effects in breakup and reaction cross sections. The breakup of the projectile

is simulated by a finite number of square integrable wave functions. First we show that the scattering

matrices can be split in a nuclear term, and in a Coulomb term. This decomposition is based on the

Lippmann-Schwinger equation, and requires the scattering wave functions. We present two different

methods to separate both effects.
Then, we apply this separation to breakup and reaction cross sections of 7Li+208Pb. We show that

there is a large ambiguity in defining the 'Coulomb' and 'nuclear' breakup cross sections, since both

techniques, although providing the same total breakup cross sections, strongly differ for the individual

components. We suggest a third method which could be efficiently used to address convergence

Tuesday 21st February 2017

identical particles with the same charge, then excited states in mirror nuclei would have identical

excitation energies. In reality, the pp-, nn- and np-interactions are not identical which leads to small

differences in excitation energy of states of order of 10s of keV. These small differences provide

important insights into the details of the nuclear force. For T=1 isospin triplets, it is possible to

construct mirror energy differences (MED) - the difference between excitation energies in the

Tz= -1 and +1 nuclei, and triplet energy differences (TED) which incorporate the differences

between excitation energies in all three systems. For TED, which are isotensor energy differences,

the single-particle contributions cancel. Since contributions involving Coulomb effects are readily

calculable, TED are particularly sensitive to additional terms such as isospin non-conserving (INC)

components. It has been shown that such a component is necessary to reproduce the experimental

TED in the the f7/2 shell. The question raised is whether such components are needed in different

mass regions and whether they have a similar magnitude.

The study of TED has been pushed to higher masses through the first study of the excited states

of the Tz = -1 nuclei, 66Se, 70Kr and 74Sr. The states were identified using the technique of

recoil-beta-tagging (RBT). The nuclei were produced with cross-sections of around 100 nb in

40Ca(28Si,2n), 40Ca(32S,2n) and 40Ca(36Ar,2n) reactions at the University of Jyvaskyla. The

residues were separated from scattered beam using the RITU recoil separator and implanted into

a double-sided silicon strip detector (DSSD) at the focal plane. The residues were tagged on the

basis of their subsequent decay through the detection of high-energy beta particles using the DSSD

and either a planar germanium detector or plastic scintillator as an effective DE-E telescope. To

discriminate these exotic proton-rich nuclei, a veto detector comprising a box of CsI scintillators

around the target position was used to improve separation of the 2n evaporation channel. The

TED obtained for A=66, 70 and 74 have been compared with shell model calculations using the

JUN45 interaction. In order to reproduce the observed TED, it is necessary in both cases to

incorporate an INC component as in the f7/2 shell. This points to the universal nature of the INC

contribution and to it having a similar magnitude irrespective of the orbitals involved.

Tuesday 14th February 2017

Interplay of experiment and theory in the quest to understand the nuclear force
Understanding the nature of the nuclear force that binds protons and neutrons into nuclei

continues to be one of the main research frontiers of nuclear science. Key to this understanding

is the productive interplay between experiment and theory. In this talk I will discuss how

experiments on exotic nuclei have recently advanced our understanding of the nuclear

many-body problem focusing on my work along these lines. On the theory frontier, a paradigm

shift is currently taking place and theory is switching from phenomenology to a chiral-EFT

description reflecting the symmetries of QCD. Testing and refining these new approaches

require high-quality data on key experimental observables. I will present recent results and