Publications by Jirina Stone

Braking index of isolated pulsars

Physical Review D - Particles, Fields, Gravitation and Cosmology 91 (2015)

O Hamil, JR Stone, M Urbanec, G Urbancová

© 2015 American Physical Society. Isolated pulsars are rotating neutron stars with accurately measured angular velocities Ω, and their time derivatives that show unambiguously that the pulsars are slowing down. Although the exact mechanism of the spin-down is a question of detailed debate, the commonly accepted view is that it arises through emission of magnetic dipole radiation (MDR) from a rotating magnetized body. Other processes, including the emission of gravitational radiation, and of relativistic particles (pulsar wind), are also being considered. The calculated energy loss by a rotating pulsar with a constant moment of inertia is assumed proportional to a model dependent power of Ω. This relation leads to the power law Ω=-KΩn where n is called the braking index. The MDR model predicts n exactly equal to 3. Selected observations of isolated pulsars provide rather precise values of n, individually accurate to a few percent or better, in the range 1<n<2.8, which is consistently less than the predictions of the MDR model. In spite of an extensive investigation of various modifications of the MDR model, no satisfactory explanation of observation has been found yet. The aim of this work is to determine the deviation of the value of n from the canonical n=3 for a star with a frequency dependent moment of inertia in the region of frequencies from zero (static spherical star) to the Kepler velocity (onset of mass shedding by a rotating deformed star), in the macroscopic MDR model. For the first time, we use microscopic realistic equations of state (EoS) of the star to determine its behavior and structure. In addition, we examine the effects of the baryonic mass MB of the star, and possible core superfluidity, on the value of the braking index within the MDR model. Four microscopic equations of state are employed as input to two different computational codes that solve Einstein's equations numerically, either exactly or using the perturbative Hartle-Thorne method, to calculate the moment of inertia and other macroscopic properties of rotating neutron stars. The calculations are performed for fixed values of MB (as masses of isolated pulsars are not known) ranging from 1.0-2.2M?, and fixed magnetic dipole moment and inclination angle between the rotational and magnetic field axes. The results are used to solve for the value of the braking index as a function of frequency, and find the effect of the choice of the EoS, MB. The density profile of a star with a given MB is calculated to determine the transition between the crust and the core and used in estimation of the effect of core superfluidity on the braking index. Our results show conclusively that, within the model used in this work, any significant deviation of the braking index away from the value n=3 occurs at frequencies higher than about ten times the frequency of the slow rotating isolated pulsars most accurately measured to date. The rate of change of n with frequency is related to the softness of the EoS and the MB of the star as this controls the degree of departure from sphericity. Change in the moment of inertia in the MDR model alone, even with the more realistic features considered here, cannot explain the observational data on the braking index and other mechanisms have to be sought.

Incompressibility in finite nuclei and nuclear matter

PHYSICAL REVIEW C 89 (2014) ARTN 044316

JR Stone, NJ Stone, SA Moszkowski

Magnetic properties of Hf-177 and Hf-180 in the strong-coupling deformed model

PHYSICAL REVIEW C 89 (2014) ARTN 044309

S Muto, NJ Stone, CR Bingham, JR Stone, PM Walker, G Audi, C Gaulard, U Koester, J Nikolov, K Nishimura, T Ohtsubo, Z Podolyak, L Risegari, GS Simpson, M Veskovic, WB Walters

Erratum: Magnetic dipole moment of the doubly-closed-shell plus one proton nucleus Sc49

Physical Review Letters 110 (2013)

T Ohtsubo, NJ Stone, JR Stone, IS Towner, CR Bingham, C Gaulard, U Köster, S Muto, J Nikolov, K Nishimura, GS Simpson, G Soti, M Veskovic, WB Walters, F Wauters

Exploring the nuclear pasta phase in core-collapse supernova matter

Physical Review Letters 109 (2012)

H Pais, JR Stone

The core-collapse supernova phenomenon, one of the most explosive events in the Universe, presents a challenge to theoretical astrophysics. Of the large variety of forms of matter present in core-collapse supernova, we focus on the transitional region between homogeneous (uniform) and inhomogeneous (pasta) phases. A three-dimensional, finite temperature Skyrme-Hartree-Fock (3D-SHF)+BCS calculation yields, for the first time fully self-consistently, the critical density and temperature of both the onset of the pasta in inhomogeneous matter, consisting of neutron-rich heavy nuclei and a free neutron and electron gas, and its dissolution to a homogeneous neutron, proton, and electron liquid. We also identify density regions for different pasta formations between the two limits. We employ four different forms of the Skyrme interaction, SkM*, SLy4, NRAPR, and SQMC700 and find subtle variations in the low density and high density transitions into and out of the pasta phase. One new stable pasta shape has been identified, in addition to the classic ones, on the grid of densities and temperatures used in this work. Our results are critically compared to recent calculations of pasta formation in the quantum molecular dynamics approach and Thomas-Fermi and coexisting phase approximations to relativistic mean-field models. © 2012 American Physical Society.

Magnetic Dipole Moment of the Doubly-Closed-Shell Plus One Proton Nucleus Sc-49


T Ohtsubo, NJ Stone, JR Stone, IS Towner, CR Bingham, C Gaulard, U Koester, S Muto, J Nikolov, K Nishimura, GS Simpson, G Soti, M Veskovic, WB Walters, F Wauters

Constraints on the symmetry energy and neutron skins from experiments and theory

Physical Review C - Nuclear Physics 86 (2012)

MB Tsang, JR Stone, F Camera, P Danielewicz, S Gandolfi, K Hebeler, CJ Horowitz, J Lee, WG Lynch, Z Kohley, R Lemmon, P Möller, T Murakami, S Riordan, X Roca-Maza, F Sammarruca, AW Steiner, I Vidaña, SJ Yennello

The symmetry energy contribution to the nuclear equation of state impacts various phenomena in nuclear astrophysics, nuclear structure, and nuclear reactions. Its determination is a key objective of contemporary nuclear physics, with consequences for the understanding of dense matter within neutron stars. We examine the results of laboratory experiments that have provided initial constraints on the nuclear symmetry energy and on its density dependence at and somewhat below normal nuclear matter density. Even though some of these constraints have been derived from properties of nuclei while others have been derived from the nuclear response to electroweak and hadronic probes, within experimental uncertainties-they are consistent with each other. We also examine the most frequently used theoretical models that predict the symmetry energy and its slope parameter. By comparing existing constraints on the symmetry pressure to theories, we demonstrate how contributions of three-body forces, which are essential ingredients in neutron matter models, can be determined. © 2012 American Physical Society.

Skyrme interaction and nuclear matter constraints

Physical Review C - Nuclear Physics 85 (2012)

M Dutra, O Lourenço, JS Sá Martins, A Delfino, JR Stone, PD Stevenson

This paper presents a detailed assessment of the ability of the 240 Skyrme interaction parameter sets in the literature to satisfy a series of criteria derived from macroscopic properties of nuclear matter in the vicinity of nuclear saturation density at zero temperature and their density dependence, derived by the liquid-drop model, in experiments with giant resonances and heavy-ion collisions. The objective is to identify those parametrizations which best satisfy the current understanding of the physics of nuclear matter over a wide range of applications. Out of the 240 models, only 16 are shown to satisfy all these constraints. Additional, more microscopic, constraints on the density dependence of the neutron and proton effective mass β-equilibrium matter, Landau parameters of symmetric and pure neutron nuclear matter, and observational data on high- and low-mass cold neutron stars further reduce this number to 5, a very small group of recommended Skyrme parametrizations to be used in future applications of the Skyrme interaction of nuclear-matter-related observables. Full information on partial fulfillment of individual constraints by all Skyrme models considered is given. The results are discussed in terms of the physical interpretation of the Skyrme interaction and the validity of its use in mean-field models. Future work on application of the Skyrme forces, selected on the basis of variables of nuclear matter, in the Hartree-Fock calculation of properties of finite nuclei, is outlined. © 2012 American Physical Society.

In-source laser spectroscopy of Cu-75,Cu-77,Cu-78: Direct evidence for a change in the quasiparticle energy sequence in Cu-75,Cu-77 and an absence of longer-lived isomers in Cu-78

PHYSICAL REVIEW C 84 (2011) ARTN 034320

U Koester, NJ Stone, KT Flanagan, JR Stone, VN Fedosseev, KL Kratz, BA Marsh, T Materna, L Mathieu, PL Molkanov, MD Seliverstov, O Serot, AM Sjodin, YM Volkov

A priori calculations of hyperfine interactions in highly ionized atoms: G-factor measurements on aligned pico-second states populated in nuclear reactions

Hyperfine Interactions 197 (2010) 29-35

NJ Stone, JR Stone, P Jonsson

Calculations of hyperfine interaction strength and life-times of states in highly ionized atoms, using the GRASP atomic structure package, are reported. The calculations aim at providing calibration for Recoil-in-Vacuum nuclear excited state g-factor measurements. The method is outlined and results compared with experiment. Inclusion of decay of higher electronic states is discussed. © 2010 Springer Science+Business Media B.V.

Dark Matter, Neutron Stars, and Strange Quark Matter


MA Perez-Garcia, J Silk, JR Stone

POLAREX - Study of polarized exotic nuclei at millikelvin temperatures


L Risegari, A Astier, G Audi, S Cabaret, C Gaulard, G Georgiev, NJ Stone, JR Stone

Structure of Co-65,Co-67 studied through the beta decay of Fe-65,Fe-67 and a deep- inelastic reaction

PHYSICAL REVIEW C 79 (2009) ARTN 044309

D Pauwels, O Ivanov, N Bree, J Buescher, TE Cocolios, M Huyse, Y Kudryavtsev, R Raabe, M Sawicka, J Van de Walle, P Van Duppen, A Korgul, I Stefanescu, AA Hecht, N Hoteling, A Woehr, WB Walters, R Broda, B Fornal, W Krolas, T Pawlat, J Wrzesinski, MP Carpenter, RVF Janssens, T Lauritsen, D Seweryniak, S Zhu, JR Stone, X Wang

g factors of first 2(+) states of neutron-rich Xe, Ba, and Ce isotopes

PHYSICAL REVIEW C 79 (2009) ARTN 034316

C Goodin, JR Stone, NJ Stone, AV Ramayya, AV Daniel, JH Hamilton, K Li, JK Hwang, GM Ter-Akopian, JO Rasmussen

Nuclear spins and magnetic moments of Cu71,73,75: Inversion of π2p3/2 and π1f5/2 Levels in Cu75

Physical Review Letters 103 (2009)

KT Flanagan, P Vingerhoets, M Avgoulea, J Billowes, ML Bissell, K Blaum, B Cheal, M De Rydt, VN Fedosseev, DH Forest, C Geppert, U Köster, M Kowalska, J Krämer, KL Kratz, A Krieger, E Mané, BA Marsh, T Materna, L Mathieu, PL Molkanov, R Neugart, G Neyens, W Nörtershäuser, MD Seliverstov, O Serot, M Schug, MA Sjoedin, JR Stone, NJ Stone, HH Stroke, G Tungate, DT Yordanov, YM Volkov

We report the first confirmation of the predicted inversion between the π2p3/2 and π1f5/2 nuclear states in the νg9/2 midshell. This was achieved at the ISOLDE facility, by using a combination of in-source laser spectroscopy and collinear laser spectroscopy on the ground states of Cu71,73,75, which measured the nuclear spin and magnetic moments. The obtained values are μ(Cu71)=+2.2747(8)μN, μ(Cu73)=+1.7426(8)μN, and μ(Cu75)=+1.0062(13)μN corresponding to spins I=3/2 for Cu71,73 and I=5/2 for Cu75. The results are in fair agreement with large-scale shell-model calculations. © 2009 The American Physical Society.

Levels above the 19/2(-) isomer in Cu-71: Persistence of the N=40 neutron shell gap

PHYSICAL REVIEW C 79 (2009) ARTN 034319

I Stefanescu, WB Walters, RVF Janssens, N Hoteling, R Broda, MP Carpenter, B Fornal, AA Hecht, W Krolas, T Lauritsen, T Pawlat, D Seweryniak, JR Stone, X Wang, A Woehr, J Wrzesinski, S Zhu

Modeling nuclear "pasta" and the transition to uniform nuclear matter with the 3D Skyrme-Hartree-Fock method at finite temperature: Core-collapse supernovae

Physical Review C - Nuclear Physics 79 (2009)

WG Newton, JR Stone

The first results of a new three-dimensional, finite temperature Skyrme-Hartree-Fock+BCS study of the properties of inhomogeneous nuclear matter at densities and temperatures leading to the transition to uniform nuclear matter are presented. Calculations are carried out in a cubic box representing a unit cell of the locally periodic structure of the matter. A constraint is placed on the two independent components of the quadrupole moment of the neutron density to investigate the dependence of the total energy density of matter on the geometry of the nuclear structure in the unit cell. This approach allows self-consistent modeling of effects such as (i) neutron drip, resulting in a neutron gas external to the nuclear structure; (ii) shell effects of bound and unbound nucleons; (iii) the variety of exotic nuclear shapes that emerge, collectively termed nuclear pasta; and (iv) the dissolution of these structures into uniform nuclear matter as density and/or temperature increase. In Part I of this work the calculation of the properties of inhomogeneous nuclear matter in the core collapse of massive stars is reported. Emphasis is on exploring the effects of the numerical method on the results obtained; notably, the influence of the finite cell size on the nuclear shapes and energy-density obtained. Results for nuclear matter in β equilibrium in cold neutrons stars are the subject of Part II. The calculation of the band structure of unbound neutrons in neutron star matter, yielding thermal conductivity, specific heat, and entrainment parameters, is outlined in Part III. Calculations are performed at baryon number densities of nb=0.04-0.12 fm-3, a proton fraction of yp=0.3 and temperatures in the range 0-7.5 MeV. A wide variety of nuclear shapes are shown to emerge. It is suggested that thermodynamical properties change smoothly in the pasta regime up to the transition to uniform matter; at that transition, thermodynamic properties of the matter vary discontinuously, indicating a phase transition of first or second order. The calculations are carried out using the SkM* Skyrme parametrization; a comparison with calculations using Sly4 at nb=0.08 fm-3, T=0 MeV is made. © 2009 The American Physical Society.

Spectroscopy of exotic <sup>121, 123, 125</sup>Ag produced in fragmentation reactions

European Physical Journal A 42 (2009) 407-413

I Stefanescu, WB Walters, PF Mantica, BA Brown, AD Davies, A Estrade, PT Hosmer, N Hoteling, SN Liddick, WDM Rae, TJ Mertzimekis, F Montes, AC Morton, WF Mueller, M Ouellette, E Pellegrini, P Santi, D Seweryniak, H Schatz, J Shergur, A Stolz, JR Stone, BE Tomlin

Excited states in the neutron-rich 121, 123, 125Ag were studied via the fragmentation of a 136Xe beam at 120MeV/nucleon in a thick 9Be target. The levels in 121Ag were populated in the β decay of 121Pd while those assigned to 123, 125Ag were identified via isomer spectroscopy. The transitions identified in 121Ag are consistent with the γ-rays reported in 117, 119Ag. The newly observed transitions were placed in the level schemes of 123, 125Ag based on the analysis of γ-γ coincidences and the systematics. We attribute the onset of isomerism in the 123, 125Ag isotopes to the drop in energy of the negative-parity levels similar to the 5- state in the even-even Cd cores. The proposed level scheme for 125Ag is well described by the NuShellX shell model calculations. © Societá Italiana di Fisica / Springer-Verlag 2009.

Structure of neutron-rich odd-mass<sup>127,129,131</sup>in populated in the decay of<sup>127,129,131</sup>Cd

Acta Physica Polonica B 40 (2009) 437-446

O Arndt, S Hennrich, N Hoteling, CJ Jost, BE Tomlin, J Shergur, KL Kratz, PF Mantica, BA Brown, RVF Janssens, WB Walters, B Pfeiffer, A Wöhr, S Zhu, R Broda, MP Carpenter, B Fornal, AA Hecht, W Królas, T Lauritsen, T Pawlat, J Pereira, D Seweryniak, I Stefanescu, JR Stone, J Wrzesiński

New level structures are proposed for neutron-rich127,129,131In populated in the decay of127,129,131Cd. No evidence for the presence of 1-particle- 2-hole intruder structures in the neutron-rich In isotopes is observed.

Identification of the g(9/2)-proton bands in the neutron-rich Ga-71,Ga-73,Ga-75,Ga-77 nuclei

PHYSICAL REVIEW C 79 (2009) ARTN 064302

I Stefanescu, WB Walters, RVF Janssens, S Zhu, R Broda, MP Carpenter, CJ Chiara, B Fornal, BP Kay, FG Kondev, W Krolas, T Lauritsen, CJ Lister, EA McCutchan, T Pawlat, D Seweryniak, JR Stone, NJ Stone, J Wrzesinski