Paul Stevenson

Dr Paul Stevenson


Reader
MA (Oxon) MSc (Open) DPhil (Oxon)

Academic and research departments

Department of Physics.

Biography

Areas of specialism

Nuclear Physics; Theoretical Physics; Computational Physics

University roles and responsibilities

  • MPhys Research Year Coordinator
  • Head of Nuclear Theory Group

My qualifications

1999
D.Phil, Nuclear Physics
University of Oxford

My publications

Publications

Avgoulea M, Gangrsky YP, Marinova KP, Zemlyanoi SG, Fritzsche S, Iablonskyi D, Barbieri C, Simpson EC, Stevenson PD, Billowes J, Campbell P, Cheal B, Tordoff B, Bissell ML, Forest DH, Gardner MD, Tungate G, Huikari J, Nieminen A, Penttila H, Aysto J (2011) Nuclear charge radii and electromagnetic moments of radioactive scandium isotopes and isomers, JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS 38 (2) ARTN 025104 IOP PUBLISHING LTD
Goddard PM, Stevenson PD, Rios A (2014) Cause of the charge radius isotope shift at the N =126 shell gap, EPJ Web of Conferences 66
We discuss the mechanism causing the 'kink' in the charge radius isotope shift at the N = 126 shell closure. The occupation of the 1i11/2 neutron orbital is the decisive factor for reproducing the experimentally observed kink. We investigate whether this orbital is occupied or not by different Skyrme effective interactions as neutrons are added above the shell closure. Our results demonstrate that several factors can cause an appreciable occupation of the 1i11/2 neutron orbital, including the magnitude of the spin-orbit field, and the isoscalar effective mass of the Skyrme interaction. The symmetry energy of the effective interaction has little influence upon its ability to reproduce the kink. © Owned by the authors, published by EDP Sciences, 2014.
Godbeer AD, Al-Khalili JS, Stevenson PD (2015) Modelling proton tunnelling in the adenine-thymine base pair., Phys Chem Chem Phys 17 (19) pp. 13034-13044
The energies of the canonical (standard, amino-keto) and tautomeric (non-standard, imino-enol) charge-neutral forms of the adenine-thymine base pair (A-T and A*-T*, respectively) are calculated using density functional theory. The reaction pathway is then computed using a transition state search to provide the asymmetric double-well potential minima along with the barrier height and shape, which are combined to create the potential energy surface using a polynomial fit. The influence of quantum tunnelling on proton transfer within a base pair H-bond (modelled as the DFT deduced double-well potential) is then investigated by solving the time-dependent master equation for the density matrix. The effect on a quantum system by its surrounding water molecules is explored via the inclusion of a dissipative Lindblad term in the master equation, in which the environment is modelled as a heat bath of harmonic oscillators. It is found that quantum tunnelling, due to transitions to higher energy eigenstates with significant amplitudes in the shallow (tautomeric) side of the potential, is unlikely to be a significant mechanism for the creation of adenine-thymine tautomers within DNA, with thermally assisted coupling of the environment only able to boost the tunnelling probability to a maximum of 2 × 10(-9). This is barely increased for different choices of the starting wave function or when the geometry of the potential energy surface is varied.
Kaur M, Behera BR, Singh G, Singh V, Madhavan N, Muralithar S, Nath S, Gehlot J, Mohanto G, Mukul I, Siwal D, Thakur M, Kapoor K, Sharma P, Banerjee T, Jhingan A, Varughese T, Bala I, Nayak BK, Saxena A, Chatterjee MB, Stevenson PD (2016) Probing dynamics of fusion reactions through cross-section and spin distribution measurement, EPJ Web of Conferences 117 EDP Sciences
Present work aims to explicate the effect of entrance channel mass asymmetry on fusion dynamics for the Compound Nucleus 80Sr populated through two different channels, 16O+64Zn and 32S+48Ti, using cross-section and spin distribution measurements as probes. The evaporation spectra studies for these systems, reported earlier indicate the presence of dynamical effects for mass symmetric 32S+48Ti system. The CCDEF and TDHF calculations have been performed for both the systems and an attempt has been made to explain the reported deviations in the ±-particle spectrum for the mass symmetric system.
Almehed D, Stevenson PD (2005) Isoscalar and isovector giant monopole resonances using TDHF, EXOTIC NUCLEAR SYSTEMS 802 pp. 305-308 AMER INST PHYSICS
Joss DT, Darby IG, Page RD, Uusitalo J, Eeckhaudt S, Grahn T, Greenlees PT, Jones PM, Julin R, Juutinen S, Ketelhut S, Leino M, Leppanen A-P, Nyman M, Pakarinen J, Rahkila P, Saren J, Scholey C, Steer A, Cannon AJ, Stevenson PD, Al-Khalili JS, Erturk S, Venhart M, Gall B, Hadinia B, Simpson J (2006) Probing the limit of nuclear existence: Proton emission from Re-159, PHYSICS LETTERS B 641 (1) pp. 34-37 ELSEVIER SCIENCE BV
Al-Khalili JS, Stevenson PD (2008) Simulating the Quantum Zeno and Anti-Zeno Effects During Position Measurements, ADVANCED SCIENCE LETTERS 1 (1) pp. 140-144 AMER SCIENTIFIC PUBLISHERS
Goddard P, Stevenson P, Rios A (2015) Fission dynamics within time-dependent Hartree-Fock: Deformation-induced fission, PHYSICAL REVIEW C 92 (5) ARTN 054610 AMER PHYSICAL SOC
Stevenson PD, Rikovska Stone J, Miller JC, Koncewicz R, Strayer MR (2003) Nuclear matter and neutron star properties calculated with the Skyrme interaction, Phys. Rev. C 68 034324
The effective Skyrme interaction has been used extensively in mean-field models for several decades and many different parametrizations of the interaction have been proposed. All of these give similar agreement with the experimental observables of nuclear ground states as well as with the properties of infinite symmetric nuclear matter at the saturation density n0. However, when applied over a wider range of densities (up to
Nomura K, Otsuka T, Rodriguez-Guzman R, Robledo LM, Sarriguren P, Regan PH, Stevenson PD, Podolyak Z (2011) Spectroscopic calculations of the low-lying structure in exotic Os and W isotopes, PHYSICAL REVIEW C 83 (5) ARTN 054303 AMER PHYSICAL SOC
Centelles M, Patra SK, Roca-Maza X, Sharma BK, Stevenson PD, Vinas X (2010) The influence of the symmetry energy on the giant monopole resonance of neutron-rich nuclei analyzed in Thomas-Fermi theory, JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS 37 (7) ARTN 075107 IOP PUBLISHING LTD
Orce JN, Bruce AM, Emmanouilidis A, Wheldon C, Xu FR, Walker PM, Caamano M, Podolyak Z, El-Masri H, Stevenson PD, Byrne AP, Dracoulis GD, Hazel JC, Kibedi T, Cullen DM (2003) Interplay between K-isomerism and gamma-softness in Xe-128, ACTA PHYSICA POLONICA B 34 (4) pp. 2253-2256 ACTA PHYSICA POLONICA B, JAGELLONIAN UNIV, INST PHYSICS
Sharma BK, Patra SK, Gupta RK, Shukla A, Arumugam P, Stevenson PD, Greiner W (2006) Reaction cross-sections for light nuclei on C-12 using relativistic mean field formalism, JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS 32 (11) pp. 2089-2097 IOP PUBLISHING LTD
Rath AK, Stevenson RD, Regan PH, Xu FR, Walker RM (2003) Self-consistent description of dysprosium isotopes in the doubly midshell region, PHYSICAL REVIEW C 68 (4) ARTN 044315 AMERICAN PHYSICAL SOC
Mason PJR, Podolyak Z, Arginean NM, Regan PH, Alexander T, Algora A, Alharbi T, Bowry M, Britton R, Bucurescu D, Bruce AM, Bunce M, Cata-Danil G, Cata-Danil I, Cooper N, Deleanu D, Delion D, Filipescu D, Gelletly W, Glodariu T, Gheorghe I, Ghita D, Ilie G, Ivanova D, Kisyov S, Lalkovski S, Lica R, Liddick SN, Marginean R, Mihai C, Mulholland K, Negret A, Nita CR, Rice S, Roberts OJ, Sava T, Smith JF, Soederstroem P-A, Stevenson PD, Stroe L, Toma S, Townsley C, Werner V, Wilson E, Wood RT, Zamfir NV, Zhekova M (2012) Li-7-Induced Reactions for Fast-Timing With LaBr3:Ce Detectors, NUCLEAR STRUCTURE AND DYNAMICS '12 1491 pp. 93-96 AMER INST PHYSICS
Goddard PM, Cooper N, Werner V, Rusev G, Stevenson PD, Rios A, Bernards C, Chakraborty A, Crider BP, Glorius J, Ilieva RS, Kelley JH, Kwan E, Peters EE, Pietralla N, Raut R, Romig C, Savran D, Schnorrenberger L, Smith MK, Sonnabend K, Tonchev AP, Tornow W, Yates SW (2013) Dipole response of $^76$Se above 4 MeV, Phys. Rev. C 88 (6) pp. 064308-064308 American Physical Society
The dipole response of 76 34 Se in the energy range from 4 to 9 MeV has been analyzed using a (³ × ,³ 2 ) polarized photon scattering technique, performed at the High Intensity ³ -Ray Source facility at Triangle Universities Nuclear Laboratory, to complement previous work performed using unpolarized photons. The results of this work offer both an enhanced sensitivity scan of the dipole response and an unambiguous determination of the parities of the observed J=1 states. The dipole response is found to be dominated by E1 excitations, and can reasonably be attributed to a pygmy dipole resonance. Evidence is presented to suggest that a significant amount of directly unobserved excitation strength is present in the region, due to unobserved branching transitions in the decays of resonantly excited states. The dipole response of the region is underestimated when considering only ground state decay branches. We investigate the electric dipole response theoretically, performing calculations in a three-dimensional (3D) Cartesian-basis time-dependent Skyrme-Hartree-Fock framework.
Antonov AN, Gaidarov MK, Ivanov MV, Kadrev DN, Aïche M, Barreau G, Czajkowski S, Jurado B, Belier G, Chatillon A, Granier T, Taieb J, Doré D, Letourneau A, Ridikas D, Dupont E, Berthoumieux E, Panebianco S, Farget F, Schmitt C, Audouin L, Khan E, Tassan-Got L, Aumann T, Beller P, Boretzky K, Dolinskii A, Egelhof P, Emling H, Franzke B, Geissel H, Kelic-Heil A, Kester O, Kurz N, Litvinov Y, Münzenberg G, Nolden F, Schmidt K-H, Scheidenberger C, Simon H, Steck M, Weick H, Enders J, Pietralla N, Richter A, Schrieder G, Zilges A, Distler MO, Merkel H, Müller U, Junghans AR, Lenske H, Fujiwara M, Suda T, Kato S, Adachi T, Hamieh S, Harakeh MN, Kalantar-Nayestanaki N, Wörtche H, Berg GPA, Koop IA, Logatchov PV, Otboev AV, Parkhomchuk VV, Shatilov DN, Shatunov PY, Shatunov YM, Shiyankov SV, Shvartz DI, Skrinsky AN, Chulkov LV, Danilin BV, Korsheninnikov AA, Kuzmin EA, Ogloblin AA, Volkov VA, Grishkin Y, Lisin VP, Mushkarenkov AN, Nedorezov V, Polonski AL, Rudnev NV, Turinge AA, Artukh A, Avdeichikov V, Ershov SN, Fomichev A, Golovkov M, Gorshkov AV, Grigorenko L, Klygin S, Krupko S, Meshkov IN, Rodin A, Sereda Y, Seleznev I, Sidorchuk S, Syresin E, Stepantsov S, Ter-Akopian G, Teterev Y, Vorontsov AN, Kamerdzhiev SP, Litvinova EV, Karataglidis S, Alvarez Rodriguez R, Borge MJG, Fernandez Ramirez C, Garrido E, Sarriguren P, Vignote JR, Fraile Prieto LM, Lopez Herraiz J, Moya de Guerra E, Udias-Moinelo J, Amaro Soriano JE, Lallena Rojo AM, Caballero JA, Johansson HT, Jonson B, Nilsson T, Nyman G, Zhukov M, Golubev P, Rudolph D, Hencken K, Jourdan J, Krusche B, Rauscher T, Kiselev D, Trautmann D, Al-Khalili J, Catford W, Johnson R, Stevenson PD, Barton C, Jenkins D, Lemmon R, Chartier M, Cullen D, Bertulani CA, Heinz A (2011) The electron-ion scattering experiment ELISe at the International Facility for Antiproton and Ion Research (FAIR)- A conceptual design study, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 637 (1) pp. 60-76
Caamano M, Walker PM, Regan PH, Pfutzner M, Podolyak Z, Gerl J, Hellstrom M, Mayet P, Mineva MN, Aprahamian A, Benlliure J, Bruce AM, Butler PA, Gil DC, Cullen DM, Doring J, Enqvist T, Fox C, Narro JG, Geissel H, Gelletly W, Giovinazzo J, Gorska M, Grawe H, Grzywacz R, Kleinbohl A, Korten W, Lewitowicz M, Lucas R, Mach H, O'Leary CD, De Oliveira F, Pearson CJ, Rejmund F, Rejmund M, Sawicka M, Schaffner H, Schlegel C, Schmidt K, Schmidt KH, Stevenson PD, Theisen C, Vives F, Warner DD, Wheldon C, Wollersheim HJ, Wooding S, Xu F, Yordanov O (2005) Isomers in neutron-rich A approximate to 190 nuclides from Pb-208 fragmentation, EUROPEAN PHYSICAL JOURNAL A 23 (2) pp. 201-215 SPRINGER
Reinhard PG, Stevenson PD, Almehed D, Maruhn JA, Strayer MR (2006) Role of boundary conditions in dynamic studies of nuclear giant resonances and collisions, PHYSICAL REVIEW E 73 (3) ARTN 036709 AMERICAN PHYSICAL SOC
Antonov AN, Gaidarov MK, Ivanov MV, Kadrev DN, Aïche M, Barreau G, Czajkowski S, Jurado B, Belier G, Chatillon A, Granier T, Taieb J, Doré D, Letourneau A, Ridikas D, Dupont E, Berthoumieux E, Panebianco S, Farget F, Schmitt C, Audouin L, Khan E, Tassan-Got L, Aumann T, Beller P, Boretzky K, Dolinskii A, Egelhof P, Emling H, Franzke B, Geissel H, Kelic-Heil A, Kester O, Kurz N, Litvinov Y, Münzenberg G, Nolden F, Schmidt K-H, Scheidenberger C, Simon H, Steck M, Weick H, Enders J, Pietralla N, Richter A, Schrieder G, Zilges A, Distler MO, Merkel H, Müller U, Junghans AR, Lenske H, Fujiwara M, Suda T, Kato S, Adachi T, Hamieh S, Harakeh MN, Kalantar-Nayestanaki N, Wörtche H, Berg GPA, Koop IA, Logatchov PV, Otboev AV, Parkhomchuk VV, Shatilov DN, Shatunov PY, Shatunov YM, Shiyankov SV, Shvartz DI, Skrinsky AN, Chulkov LV, Danilin BV, Korsheninnikov AA, Kuzmin EA, Ogloblin AA, Volkov VA, Grishkin Y, Lisin VP, Mushkarenkov AN, Nedorezov V, Polonski AL, Rudnev NV, Turinge AA, Artukh A, Avdeichikov V, Ershov SN, Fomichev A, Golovkov M, Gorshkov AV, Grigorenko L, Klygin S, Krupko S, Meshkov IN, Rodin A, Sereda Y, Seleznev I, Sidorchuk S, Syresin E, Stepantsov S, Ter-Akopian G, Teterev Y, Vorontsov AN, Kamerdzhiev SP, Litvinova EV, Karataglidis S, Alvarez Rodriguez R, Borge MJG, Fernandez Ramirez C, Garrido E, Sarriguren P, Vignote JR, Fraile Prieto LM, Lopez Herraiz J, Moya De Guerra E, Udias-Moinelo J, Amaro Soriano JE, Lallena Rojo AM, Caballero JA, Johansson HT, Jonson B, Nilsson T, Nyman G, Zhukov M, Golubev P, Rudolph D, Hencken K, Jourdan J, Krusche B, Rauscher T, Kiselev D, Trautmann D, Al-Khalili J, Catford W, Johnson R, Stevenson PD, Barton C, Jenkins D, Lemmon R, Chartier M, Cullen D, Bertulani CA, Heinz A (2011) The electronion scattering experiment ELISe at the International Facility for Antiproton and Ion Research (FAIR) - A conceptual design study, Nuclear Instruments and Methods in Physics Research, Section A: Accelerators, Spectrometers, Detectors and Associated Equipment 637 (1) pp. 60-76
Stevenson PD (2016) Resonances and reactions from mean-field dynamics, INTERNATIONAL CONFERENCE ON NUCLEAR STRUCTURE AND RELATED TOPICS (NSRT15) 107 E D P SCIENCES
We motivate and summarise some recent results in the application of formally exact boundary conditions in nuclear time-dependent Hartree-Fock calculations, making use of Laplace transformations to calculate the values of the wave functions at the boundaries. We have realised the method in the case of giant monopole resonances of spherically-symmetric nuclei, and present strength functions of 16O and 40Ca using a simplified version of the Skyrme force, showing that no artefacts from discretisation occur as contaminatnts © Owned by the authors, published by EDP Sciences, 2014.
This paper deals with the solution of the spherically symmetric
time-dependent Hartree-Fock approximation applied to nuclear giant monopole
resonances in the small amplitude regime. The problem is spatially unbounded as
the resonance state is in the continuum. The practical requirement to perform
the calculation in a finite-sized spatial region yields an artificial boundary,
which is not present physically. The question of how to ensure the boundary
does not interfere with the internal solution, while keeping the overall
calculation time low is studied. Here we propose an absorbing boundary
condition scheme to handle the conflict. The derivation, via a Laplace
transform method, and implementation is described. An inverse Laplace transform
required by the absorbing boundaries is calculated using a method of non-linear
least squares. The accuracy and efficiency of the scheme is tested and results
presented to support the case that they are a effective way of handling the
artificial boundary.
Goddard P, Stevenson P, Rios A (2016) Fission dynamics within time-dependent Hartree-Fock. II. Boost-induced fission, PHYSICAL REVIEW C 93 (1) ARTN 014620 AMER PHYSICAL SOC
Background: Nuclear fission is a complex large-amplitude collective decay mode in heavy nuclei. Microscopic
density functional studies of fission have previously concentrated on adiabatic approaches based on constrained
static calculations ignoring dynamical excitations of the fissioning nucleus and the daughter products.
Purpose: We explore the ability of dynamic mean-field methods to describe induced fission processes, using
quadrupole boosts in the nuclide 240Pu as an example.
Methods: Following upon the work presented in Goddard et al. [Phys. Rev. C 92, 054610 (2015)], quadrupoleconstrained
Hartree-Fock calculations are used to create a potential energy surface. An isomeric state and a state
beyond the second barrier peak are excited by means of instantaneous as well as temporally extended gauge boosts
with quadrupole shapes. The subsequent deexcitation is studied in a time-dependent Hartree-Fock simulation,
with emphasis on fissioned final states. The corresponding fission fragment mass numbers are studied.
Results: In general, the energy deposited by the quadrupole boost is quickly absorbed by the nucleus. In
instantaneous boosts, this leads to fast shape rearrangements and violent dynamics that can ultimately lead to
fission. This is a qualitatively different process than the deformation-induced fission. Boosts induced within a
finite time window excite the system in a relatively gentler way and do induce fission but with a smaller energy
deposition.
Conclusions: The fission products obtained using boost-induced fission in time-dependent Hartree-Fock are
more asymmetric than the fragments obtained in deformation-induced fission or the corresponding adiabatic
approaches.
Grahn T, Stolze S, Joss JT, Page RD, Saygi B, O'Donnell D, Akmali M, Andgren K, Bianco L, Cullen DM, Dewald A, Greenlees PT, Heyde K, Iwasaki H, Jakobsson U, Jones P, Judson DS, Julin R, Juutinen S, Ketelhut S, Leino M, Lumley N, Mason PJR, Moller O, Nomura K, Nyman M, Petts A, Peura P, Pietralla N, Pissulla T, Rahkila P, Sapple PJ, Saren J, Scholey C, Simpson J, Sorri J, Stevenson PD, Uusitalo J, Watkins HV, Wood JL (2016) Excited states and reduced transition probabilities in 168Os, Physical Review C: Nuclear Physics 94 (4)
The level scheme of the neutron-deficient nuclide 168Os has been extended and mean lifetimes of excited states have been measured by the recoil distance Doppler-shift method using the JUROGAM \gamma-ray spectrometer in conjunction with the IKP K\"oln plunger device. The 168Os \gamma rays were measured in delayed coincidence with recoiling fusion-evaporation residues detected at the focal plane of the RITU gas-filled separator. The ratio of reduced transition probabilities B(E2;4_1^+ \rightarrow 2_1^+)/B(E2;2_1^+ \rightarrow 0_1^+) is measured to be 0.34(18), which is very unusual for collective band structures and cannot be reproduced by IBM-2 model calculations based on the SkM* energy-density functional.
Dutra M, Lourenco O, Sa Martins JS, Delfino A, Stone JR, Stevenson PD (2012) Skyrme interaction and nuclear matter constraints, PHYSICAL REVIEW C 85 (3) 035201 American Physical Society
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 ²-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.
Stevenson PD, Broomfield JMA (2010) Testing a Variational Method for Fluctuations, XVIII INTERNATIONAL SCHOOL ON NUCLEAR PHYSICS, NEUTRON PHYSICS AND APPLICATIONS 205 ARTN 012027 IOP PUBLISHING LTD
Al-Dahan N, Regan PH, Podolyák Z, Walker PM, Alkhomashi N, Dracoulis GD, Farrelly G, Benlliure J, Pietri SB, Casten RF, Stevenson PD, Gelletly W, Steer SJ, Garnsworthy AB, Casarejos E, Gerl J, Wollersheim HJ, Grebosz J, Górska M, Kojouharov I, Schaffner H, Algora A, Benzoni G, Blazhev A, Boutachkov P, Bruce AM, Cullen IJ, Denis Bacelar AM, Deo AY, Estevez ME, Fujita Y, Hoischen R, Kumar R, Lalkovski S, Liu Z, Mason PJ, Mihai C, Molina F, Mücher D, Rubio B, Tamii A, Tashenov S, Valiente-Dobón JJ, Woods PJ (2012) Multiple ² - Decaying states in 194Re: Shape evolution in neutron-rich osmium isotopes, Physical Review C - Nuclear Physics 85 (3) 034301 American Physical Society
decays from heavy, neutron-rich nuclei with A
Page RD, Bianco L, Darby IG, Uusitalo J, Joss DT, Grahn T, Herzberg R-D, Pakarinen J, Thomson J, Eeckhaudt S, Greenlees PT, Jones PM, Julin R, Juutinen S, Ketelhut S, Leino M, Leppanen A-P, Nyman M, Rahkila P, Saren J, Scholey C, Steer A, Hornillos MBG, Al-Khalili JS, Cannon AJ, Stevenson PD, Erturk S, Gall B, Hadinia B, Venhart M, Simpson J (2007) alpha decay of Re-159 and proton emission from Ta-155, PHYSICAL REVIEW C 75 (6) ARTN 061302 AMERICAN PHYSICAL SOC
Pardi CI, Stevenson PD (2013) Continuum time-dependent Hartree-Fock method for giant resonances in spherical nuclei, Physical Review C - Nuclear Physics 87 (1) American Physical Society
This paper deals with the solution of the spherically symmetric time-dependent Hartree-Fock approximation applied in the case of nuclear giant monopole resonances in the small and large amplitude regimes. The problem is spatially unbounded as the resonance state is in the continuum. The practical requirement to perform the calculation in a finite-sized spatial region results in a difficulty with the spatial boundary conditions. Here we propose an absorbing boundary condition scheme to handle the conflict. The derivation, via a Laplace transform method, and implementation is described. The accuracy and efficiency of the scheme is tested and the results presented to support the case that they are a effective way of handling the artificial boundary. © 2013 American Physical Society.
Stevenson PD, Fracasso S, Suckling EB (2012) The tensor-kinetic field in nuclear collisions, Journal of Physics: Conference Series 381 1 pp. 012105-012105 Institute of Physics
The role of the tensor terms in the Skyrme interaction is studied for their effect in dynamic calculations where non-zero contributions to the mean-field may arise, even when the starting nucleus, or nuclei are even-even and have no active time-odd potentials in the ground state. We study collisions in the test-bed 16 O- 16 O system, and give a qualitative analysis of the behaviour of the time-odd tensor-kinetic density, which only appears in the mean field Hamiltonian in the presence of the tensor force. We find an axial excitation of this density is induced by a collision.
Stevenson PD (2015) Numerical Calculations of TDHF, In: Iwata Y (eds.), Progress of time-dependent nuclear reaction theory Bentham Science Publishers
We discuss some aspects of implementing the time-dependent Hartree-Fock method in the case of nuclear physics. Topics discussed include implementation of the time-stepping algorithm, considerations involving the ef- fective interaction, and the use (or not) of particular optional terms in the energy density functional, and boundary conditions. Examples of application of the technique to giant resonances and reactions are given, concentrating on issues to do with numerical and conceptual interpretation.
Stevenson PD, Broomfield JMA (2009) A Variational Approach to Mass Fluctuations, NUCLEAR STRUCTURE AND DYNAMICS '09 1165 pp. 177-180 AMER INST PHYSICS
Maruhn JA, Reinhard P-G, Stevenson PD, Umar AS (2014) The TDHF code Sky3D, Computer Physics Communications 185 (7) pp. 2195-2216 Elsevier
The nuclear mean-field model based on Skyrme forces or related density functionals has found widespread application to the description of nuclear ground states, collective vibrational excitations, and heavy-ion collisions. The code Sky3D solves the static or dynamic equations on a three-dimensional Cartesian mesh with isolated or periodic boundary conditions and no further symmetry assumptions. Pairing can be included in the BCS approximation for the static case. The code is implemented with a view to allow easy modifications for including additional physics or special analysis of the results. © 2014 Elsevier B.V. All rights reserved.
Caamaño M, Walker PM, Regan PH, Pfützner M, Podolyák Z, Gerl J, Hellström M, Mayet P, Mineva MN, Aprahamian A, Benlliure J, Bruce AM, Butler PA, Cortina Gil D, Cullen DM, Döring J, Enqvist T, Fox C, Garcés Narro J, Geissel H, Gelletly W, Giovinazzo J, Górska M, Grawe H, Grzywacz R, Kleinböhl A, Korten W, Lewitowicz M, Lucas R, Mach H, O'Leary CD, De Oliveira F, Pearson CJ, Rejmund F, Rejmund M, Sawicka M, Schaffner H, Schlegel C, Schmidt K, Schmidt KH, Stevenson PD, Theisen C, Vivès F, Warner DD, Wheldon C, Wollersheim HJ, Wooding S, Xu F, Yordanov O (2005) Isomers in neutron-rich A H 190 nuclides from 208Pb fragmentation, European Physical Journal A 23 (2) pp. 201-215
Relativistic projectile fragmentation of 208Pb has been used to produce isomers in neutron-rich, A H 190 nuclides. A forward-focusing spectrometer provided ion-by-ion mass and charge identification. The detection of ³-rays emitted by stopped ions has led to the assignment of isomers in 188Ta, 190W, 192Re, 193Re, 195Os, 197Ir, 198Ir, 200Pt, 201Pt, 202Pt and 203Au, with half-lives ranging from approximately 10 ns to 1 ms. Tentative isomer information has been found also for 174Er, 175Er, 185Hf, 191Re, 194Re and 199Ir. In most cases, time-correlated, singles ³-ray events provided the first spectroscopic data on excited states for each nuclide. In 200Pt and 201Pt, the assignments are supported by ³-³ coincidences. Isomeric ratios provide additional information, such as half-life and transition energy constraints in particular cases. The level structures of the platinum isotopes are discussed, and comparisons are made with isomer systematics. © Società, Italiana, di Fisica/Springer-Verlag 2004.
Regan PH, Alkhomashi N, Al-Dahan N, PodolyÁk Z, Pietri SB, Steer SJ, Garnsworthy AB, Suckling EB, Stevenson PD, Farrelly G, Cullen IJ, Gelletly W, Walker PM, Benlliure J, Morales AI, Casajeros E, Estevez ME, Gerl J, GÓrska M, Wollersheim HJ, Boutachkov P, Tashenov S, Kojouharov I, Schaffner H, Kurz N, Kumar R, Rubio B, Algora A, Molina F, Grebosz J, Benzoni G, MÜcher D, Bruce AM, Bacelar AMD, Lalkovski S, Fujita Y, Tamii A, Hoischen R, Liu Z, Woods PJ, Mihai C, Valiente-DobÓn JJ (2008) First results with the rising active stopper, International Journal of Modern Physics E 17 (SUPPL. 1) pp. 8-20
Stevenson PD, Broomfield JMA (2009) Mass distributions in a variational model, REVISTA MEXICANA DE FISICA 55 (2) pp. 114-118 SOC MEXICANA FISICA
Xu FR, Pei JC, Stevenson PD (2006) Deformed halo nuclei in mean-field approach, AIP Conference Proceedings 865 pp. 96-100
The halo properties of the odd light nuclei have been studied with the deformed Skyrme-Hartree-Fock model, in which the blocking effect of the odd nucleon is taken into account. For nuclei near drip lines, the pairing was treated in the frame of Lipkin-Nogami method, using a volume-surface mixing paring interaction. The 1/2+ state in 11Be was calculated to have a very large soft deformation. The origin of deformed halo structures was discussed. © 2006 American Institute of Physics.
Bianco L, Page RD, Darby IG, Joss DT, Simpson J, Al-Khalili JJ, Cannon AJ, Cederwall B, Eeckhaudt S, Erturk S, Gall B, Hornillos MBG, Grahn T, Greenlees PT, Hadinia B, Heyde K, Jakobsson U, Jones PM, Julin R, Juutinen S, Ketelhut S, Labiche M, Leino M, Leppanen A-P, Nyman M, O'Donnell D, Paul ES, Petri M, Peura P, Puurunen A, Rahkila P, Ruotsalainen P, Sandzelius M, Sapple PJ, Saren J, Scholey C, Smirnova NA, Steer AN, Stevenson PD, Suckling EB, Thomson J, Uusitalo J, Venhart M (2010) Discovery of W-157 and Os-161, PHYSICS LETTERS B 690 (1) pp. 15-18 ELSEVIER SCIENCE BV
Oi M, Regan PH, Xu FR, Walker PM, Rath AK, Stevenson PD (2002) Cranked-Hartree-Fock-Bogoliubov analysis at the valence maximum: Yrast behaviour of Dy-170(66)104, PROGRESS OF THEORETICAL PHYSICS SUPPLEMENT (146) pp. 609-610 PROGRESS THEORETICAL PHYSICS PUBLICATION OFFICE
Stevenson PD, Fracasso S (2010) Extracting structure information from TDHF, J PHYS G NUCL PARTIC 37 (6) 064030 IOP PUBLISHING LTD
Regan PH, Alkhomashi N, Al-Dahan N, Podolyak Z, Suckling EB, Stevenson PD, Pietri SB, Steer SJ, Garnsworthy AB, Gelletly W, Benlliure J, Morales AI, Gerl J, Gorska M, Wollersheim HJ, Kumar R, Grebosz J, Algora A, Benzoni G, Boutachkov P, Bruce AM, Casarejos E, Cullen IJ, Bacelar AMD, Blazhev A, Estevez ME, Farrelly G, Fujita Y, Hoischen R, Lalkovski S, Liu Z, Kojouharov I, Kurz N, Mihai C, Molina F, Muecher D, Rubio B, Schaffner H, Tashenov S, Tamii A, Dobon JJV, Walker PM, Woods PJ (2009) New Insights into the Structure of Exotic Nuclei Using the RISING Active Stopper, CAPTURE GAMMA-RAY SPECTROSCOPY AND RELATED TOPICS 1090 pp. 122-129 AMER INST PHYSICS
Stevenson PD (2003) Automatic generation of vacuum amplitude many-body perturbation series, International Journal of Modern Physics C 14 (8) pp. 1135-1141
An algorithm and a computer program in Fortran 95 are presented which enumerate the Hugenholtz diagram representation of the many-body perturbation series for the ground state energy with a two-body interaction. The output is in a form suitable for post-processing such as automatic code generation. The result of a particular application, generation of LATEX code to draw the diagrams, is shown.
Maruhn JA, Reinhard P-G, Stevenson PD, Strayer MR (2006) Spin-excitation mechanisms in Skyrme-force time-dependent Hartree-Fock calculations, PHYSICAL REVIEW C 74 (2) ARTN 027601 AMERICAN PHYSICAL SOC
Almehed D, Stevenson PD (2005) Isovector giant monopole resonances in spherical nuclei, Journal of Physics G: Nuclear and Particle Physics 31 (10)
We study isovector giant monopole resonances in spherical nuclei using the time-dependent Hartree-Fock method with different Skyrme forces. The aim of the investigation is to study how, for example, mass number and neutron excess influence the isovector giant monopole resonances and their mixing with isoscalar modes. We also study how nuclear matter properties, such as the asymmetry energy, of different Skyrme forces affect the behaviour of giant resonances. We find isovector and isoscalar modes to be strongly mixed and that there is little correlation between asymmetry energy and isovector resonance energy. © 2005 IOP Publishing Ltd.
Stone JR, Miller JC, Koncewicz R, Stevenson PD, Strayer MR (2003) Nuclear matter and neutron-star properties calculated with the Skyrme interaction, PHYSICAL REVIEW C 68 (3) ARTN 034324
Joss DT, Darby IG, Page RD, Uusitalo J, Eeckhaudt S, Grahn T, Greenlees PT, Jones PM, Julin R, Juutinen S, Ketelhut S, Leino M, Leppänen AP, Nyman M, Pakarinen J, Rahkila P, Sarén J, Scholey C, Steer AN, Al-Khalili JS, Cannon AJ, Stevenson PD, Ertürk S, Gall B, Hadinia B, Venhart M, Simpson J (2007) Discovery of the proton emitting nucleus 159Re, AIP Conference Proceedings 961 pp. 28-33
The observation of the new nuclide 159Re provides important insights into the evolution of single-particle structure in heavy nuclei beyond the proton drip line. The nuclide 159Re was synthesised in the reaction 106Cd(58Ni, p4n) and identified via its proton radioactivity using the RITU gas-filled separator and the GREAT focal-plane spectrometer. Comparisons of the measured proton energy (Ep = 1805±20 keV) and decay half-life (t1/2 = 21±4 ¼s) with values calculated using the WKB method indicate that the proton is emitted from an h11/2 state. The implications of these results for future experimental investigations into even more proton unbound Re isotopes using in-flight separation techniques are considered. © 2007 American Institute of Physics.
Goddard PM, Stevenson PD, Rios A (2013) Charge radius isotope shift across the N=126 shell gap, Physical Review Letters 110 (3) American Physical Society
We revisit the problem of the kink in the charge radius shift of neutron-rich even isotopes near the N=126 shell closure. We show that the ability of a Skyrme force to reproduce the isotope shift is determined by the occupation of the neutron 1i orbital beyond N=126 and the corresponding change it causes to deeply-bound protons orbitals with a principal quantum number of 1. Given the observed position of the single-particle energies, one must either ensure occupation is allowed through correlations, or not demand that the single-particle energies agree with experimental values at the mean-field level. © 2013 American Physical Society.
Walker PM, Lalkovski S, Stevenson PD (2010) Configuration dependence of K-forbidden transition rates from three-quasiparticle isomers, PHYSICAL REVIEW C 81 (4) ARTN 041304 AMER PHYSICAL SOC
Page RD, Bianco L, Darby IG, Joss DT, Grahn T, Herzberg R-D, Pakarinen J, Thomson J, Uusitalo J, Eeckhaud S, Greenlees PT, Jones PM, Julin R, Juutinen S, Ketelhut S, Leino M, Leppanen A-P, Nyman M, Rahkila P, Saren J, Scholey C, Steer A, Venhart M, Simpson J, Al-Khalili JS, Cannon AJ, Stevenson PD, Erturk S, Gall B, Hadinia B (2007) Probing single-particle structures beyond the proton drip line, PROTON EMITTING NUCLEI AND RELATED TOPICS 961 pp. 137-142 AMER INST PHYSICS
Stevenson PD, Rikovska Stone J, Strayer MR (2002) Mean field calculation of Ne, Mg and Si nuclei at N = 20 with the separable monopole interaction, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 545 (3-4) pp. 291-297
A new model has been developed to study nuclei using many-body perturbation theory with a density dependent separable monopole nucleon-nucleon interaction (SMO) [Phys. Rev. C 63 (2001) 054309; P.D. Stevenson, D.Ph. Thesis, Oxford 1999; Phys. Rev. C 65 (2002) 064312]. The model is in the zeroth order an alternative to mean-field models based on more conventional effective nucleon-nucleon interactions (e.g., Skyrme, Gogny). Results on shapes and related ground state observables are reported for even-even Ne, Mg, and Si nuclei with N
Stevenson PD, Almehed D, Reinhard PG, Maruhn JA (2007) Monopole Giant Resonances and TDHF boundary conditions, Nuclear Physics A 788 (1-4) pp. 343-348
Using time-dependent Hartree-Fock, we induce isoscalar and isovector monopole vibrations and follow the subsequent vibrations of both the same and opposite isospin nature in the N ` Z nucleus 132Sn. By suitable scaling of the proton and neutron parts of the excitation operators, the coupling between the modes is studied, and the approximate normal modes found. Chaotic dynamics are then analysed in the isoscalar giant monopole resonance by using reflecting boundaries in a large space to build up a large number of 0+ states whose spacings are then analysed. A Wigner-like distribution is found. © 2007 Elsevier B.V. All rights reserved.
Stevenson PD, Rios A, Goddard PM (2015) Shapes and Dynamics from the Time-Dependent Mean Field, Bulgarian Journal of Physics 42 (4) pp. 354-361
Explaining observed properties in terms of underlying shape degrees
of freedom is a well?established prism with which to understand atomic nuclei. Self?consistent mean?field models provide one tool to understand nuclear shapes, and their link to other nuclear properties and observables. We present examples of how the time?dependent extension of the mean?field approach can be used in particular to shed light on nuclear shape properties, particularly looking at the giant resonances built on deformed nuclear ground states, and at dynamics in highly-deformed fission isomers. Example calculations are shown of 28Si in the first case, and 240Pu in the latter case.
Shizuma T, Stevenson PD, Walker PM, Toh Y, Hayakawa T, Oshima M, Furuno K, Komatsubar T (2002) High-K negative parity states in Os-184, PHYSICAL REVIEW C 65 (6) ARTN 064310
Sharma BK, Arumugam P, Patra SK, Stevenson PD, Gupta RK, Greiner W (2006) Clustering in superheavy nuclei within the relativistic mean field approach, JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS 32 (1) pp. L1-L9 IOP PUBLISHING LTD
Bianco L, Page RD, Darby IG, Joss DT, Simpson J, Al-Khalili JS, Cannon AJ, Cederwall B, Eeckhaudt S, Ertürk S, Gall B, Hornillos MBG, Grahn T, Greenlees PT, Hadinia B, Heyde K, Jakobsson U, Jones PM, Julin R, Juutinen S, Ketelhut S, Labiche M, Leino M, Leppänen A-P, Nyman M, O'Donnell D, Paul ES, Petri M, Peura P, Puurunen A, Rahkila P, Ruotsalainen P, Sandzelius M, Sapple PJ, Sarén J, Scholey C, Smirnova NA, Steer AN, Stevenson PD, Suckling EB, Thomson J, Uusitalo J, Venhart M (2010) Discovery of 157W and 161Os, Physics Letters, Section B: Nuclear, Elementary Particle and High-Energy Physics 690 (1) pp. 15-18
Suckling EB, Stevenson PD (2010) The effect of the tensor force on the predicted stability of superheavy nuclei, EPL 90 (1) ARTN 12001 EPL ASSOCIATION, EUROPEAN PHYSICAL SOCIETY
Maruhn JA, Reinhard PG, Stevenson PD, Stone JR, Strayer MR (2005) Dipole giant resonances in deformed heavy nuclei, Physical Review C - Nuclear Physics 71 (6)
The spectral distribution of isovector dipole strength is computed using the time-dependent Skyrme-Hartree-Fock method with subsequent spectral analysis. The calculations are done without any imposed symmetry restriction, allowing any nuclear shape to be dealt with. The scheme is used to study the deformation dependence of giant resonances and its interplay with Landau fragmentation (owing to 1ph states). Results are shown for the chain of Nd isotopes, superdeformed Dy152, triaxial Os188, and U238. © 2005 The American Physical Society.
Broomfield JMA, Stevenson PD (2008) Mass dispersions from giant dipole resonances using the Balian-Veneroni variational approach, JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS 35 (9) ARTN 095102 IOP PUBLISHING LTD
Regan PH, Xu FR, Walker PM, Oi M, Rath AK, Stevenson PD (2002) Structure of the doubly midshell nucleus Dy-170(66)104, PHYSICAL REVIEW C 65 (3) ARTN 037302 AMERICAN PHYSICAL SOC
Broomfield J, Stevenson P (2009) Mass Distributions Beyond TDHF, FUSION 08 1098 pp. 133-138 AMER INST PHYSICS
Godbeer AD, Al-Khalili JS, Stevenson PD (2014) Environment-induced dephasing versus von Neumann measurements in proton tunneling, Physical Review A - Atomic, Molecular, and Optical Physics 90 (1)
In this work we compare two theoretical approaches to modeling the action of the environment on an open quantum system. It is often assumed that as the temperature of the environment surrounding a quantum system increases, so does the speed of environment-induced dephasing, or decoherence (dynamical noise), and so the efficacy of processes such as quantum tunneling drops. An alternative way of viewing the action of the environment is to consider it as carrying out von Neumann-type measurements that, in the limit of continuous observation, lead to the so-called quantum Zeno effect, whereby the system is never allowed to evolve because its wave function is collapsed to its initial state with overwhelming likelihood. However, it has been established in recent years that under certain conditions quantum processes such as tunneling can actually be enhanced (thermally assisted) when the system couples to its environment, as this allows transitions to higher-energy eigenstates closer to the top of the potential barrier. Here we show that, over a specific temperature range, increasing the temperature of the heat bath to encourage such thermally induced tunneling is equivalent to increasing the frequency of a von Neumann-type measurement on the system by the environment (an anti-Zeno effect). However, this correspondence between these two independent pictures of quantum measurement breaks down above a certain limit: Increasing the frequency of measurement above this limit leads to a reversal from an anti-Zeno to a Zeno effect and the tunneling rate decreases again, whereas raising the temperature further leads to a leveling off in the tunneling probability. © 2014 American Physical Society.
Stevenson PD, Almehed D, Reinhard P-G, Maruhn JA (2007) Monopole Giant Resonances and TDHF boundary conditions, Nuclear Physics A 788 pp. 343-348 Elsevier
Stevenson PD, Suckling EB, Fracasso S, Simmons ED, Umar AS (2015) Role of the Skyrme tensor force in heavy-ion fusion, VI INTERNATIONAL CONFERENCE FUSION14 86 E D P SCIENCES
We make use of the Skyrme e
ff
ective nuclear interaction within the time-dependent Hartree-Fock
framework to assess the e
ff
ect of inclusion of the tensor terms of the Skyrme interaction on the fusion window
of the
16
O?
16
O reaction. We find that the lower fusion threshold, around the barrier, is quite insensitive to
these details of the force, but the higher threshold, above which the nuclei pass through each other, changes by
several MeV between di
ff
erent tensor parametrisations. The results suggest that eventually fusion properties
may become part of the evaluation or fitting process for e
ff
ective nuclear interactions
Pei JC, Xu FR, Stevenson PD (2006) Deformation effects on the structures of N=7 halo nuclei, NUCLEAR PHYSICS A 765 (1-2) pp. 29-38 ELSEVIER SCIENCE BV
Fracasso S, Suckling EB, Stevenson PD (2012) Unrestricted Skyrme-tensor time-dependent Hartree-Fock model and its application to the nuclear response from spherical to triaxial nuclei, Physical Review C - Nuclear Physics 86 (4)
The nuclear time-dependent Hartree-Fock model formulated in three-dimensional space, based on the full standard Skyrme energy density functional complemented with the tensor force, is presented. Full self-consistency is achieved by the model. The application to the isovector giant dipole resonance is discussed in the linear limit, ranging from spherical nuclei (16O and 120Sn) to systems displaying axial or triaxial deformation (24Mg, 28Si, 178Os, 190W and 238U). Particular attention is paid to the spin-dependent terms from the central sector of the functional, recently included together with the tensor. They turn out to be capable of producing a qualitative change on the strength distribution in this channel. The effect on the deformation properties is also discussed. The quantitative effects on the linear response are small and, overall, the giant dipole energy remains unaffected. Calculations are compared to predictions from the (quasi)-particle random-phase approximation and experimental data where available, finding good agreement. © 2012 American Physical Society.
Stone JR, Stevenson PD, Strayer MR (2002) At the N=Z line and beyond: HF+BCS mean-field calculations with the separable monopole interaction., ABSTRACTS OF PAPERS OF THE AMERICAN CHEMICAL SOCIETY 224 pp. U92-U92
Gupta RK, Patra SK, Stevenson PD, Beck C, Greiner W (2008) Fission of hyper-hyperdeformed Ni-56: a clustering analysis within mean-field approaches, JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS 35 (7) ARTN 075106 IOP PUBLISHING LTD
AI-Khaffli JS, Cannon AJ, Stevenson PD (2007) The two-potential approach to one-proton emission, PROTON EMITTING NUCLEI AND RELATED TOPICS 961 pp. 66-71 AMER INST PHYSICS
Al-Dahan N, Regan PH, Podolyák Z, Walker PM, Alkhomashi N, Dracoulis GD, Farrelly G, Benlliure J, Pietri SB, Casten RF, Stevenson PD, Gelletly W, Steer SJ, Garnsworthy AB, Casarejos E, Gerl J, Wollersheim HJ, Grebosz J, Górska M, Kojouharov I, Schaffner H, Algora A, Benzoni G, Blazhev A, Boutachkov P, Bruce AM, Cullen IJ, Denis Bacelar AM, Deo AY, Estevez ME, Fujita Y, Hoischen R, Kumar R, Lalkovski S, Liu Z, Mason PJ, Mihai C, Molina F, Mücher D, Rubio B, Tamii A, Tashenov S, Valiente-Dobón JJ, Woods PJ (2012) Multiple ² - Decaying states in 194Re: Shape evolution in neutron-rich osmium isotopes, Physical Review C - Nuclear Physics 85 (3)
² decays from heavy, neutron-rich nuclei with A
Jones GA, Regan PH, Walker PM, Podolyak Z, Stevenson PD, Carpenter MP, Carroll JJ, Chakrawarthy RS, Chowdhury P, Garnsworthy AB, Janssens RVF, Khoo TL, Kondev FG, Lane GJ, Liu Z, Seweryniak D, Thompson NJ, Zhu S, Williams SJ (2007) Identification of a high-spin isomer in (99)Mo, PHYSICAL REVIEW C 76 (4) ARTN 047303 AMER PHYSICAL SOC
Patra SK, Gupta RK, Sharma BK, Stevenson PD, Greiner W (2007) Exotic clustering in heavy and superheavy nuclei within the relativistic and non-relativistic mean field formalisms, JOURNAL OF PHYSICS G-NUCLEAR AND PARTICLE PHYSICS 34 (9) pp. 2073-2090 IOP PUBLISHING LTD
Brine MP, Stevenson PD, Maruhn JA, Reinhard P-G (2006) Dipole response in neutron-rich magnesium, INTERNATIONAL JOURNAL OF MODERN PHYSICS E-NUCLEAR PHYSICS 15 (7) pp. 1417-1423 WORLD SCIENTIFIC PUBL CO PTE LTD
Pei JC, Xu FR, Stevenson PD (2005) Density distributions of superheavy nuclei, Physical Review C - Nuclear Physics 71 (3)
We employed the Skyrme-Hartree-Fock model to investigate the density distributions and their dependence on nuclear shapes and isospins in the superheavy mass region. Different Skyrme forces were used for the calculations with a special comparison to the experimental data in 208Pb. The ground-state deformations, nuclear radii, neutron-skin thicknesses and ±-decay energies were also calculated. Density distributions were discussed with the calculations of single-particle wave functions and shell fillings. Calculations show that deformations have considerable effects on the density distributions, with a detailed discussion on the 292120 nucleus. Earlier predictions of remarkably low central density are not supported when deformation is allowed for. © 2005 The American Physical Society.
Stevenson PD, Brine MP, Podolyak Z, Regan PH, Walker PM, Stone JR (2005) Shape evolution in the neutron-rich tungsten region, PHYSICAL REVIEW C 72 (4) ARTN 047303 AMERICAN PHYSICAL SOC
Stevenson PD, Goddard PM, Stone JR, Dutra M (2013) Do Skyrme forces that fit nuclear matter work well in finite nuclei?, XXXV BRAZILIAN WORKSHOP ON NUCLEAR PHYSICS 1529 pp. 262-268 AMER INST PHYSICS
Orce JN, Bruce AM, Emmanouilidis A, Byrne AP, Dracoulis GD, Kibedi T, Caamano M, El-Masri H, Pearson CJ, Podolyak Z, Stevenson PD, Walker PM, Xu FR, Cullen DM, Wheldon C (2006) Shape-driving effects in the triaxial nucleus, Xe-128, PHYSICAL REVIEW C 74 (3) ARTN 034318 AMERICAN PHYSICAL SOC
Gupta RK, Patra SK, Stevenson PD, Greiner W (2007) A highly neutron-rich cluster and/or a superheavy nucleus in the compound nucleus U-238+U-238: A mean field study, INTERNATIONAL JOURNAL OF MODERN PHYSICS E-NUCLEAR PHYSICS 16 (6) pp. 1721-1732 WORLD SCIENTIFIC PUBL CO PTE LTD
Stevenson PD, Fracasso S, Suckling EB (2012) The tensor-kinetic field in nuclear collisions, RUTHERFORD CENTENNIAL CONFERENCE ON NUCLEAR PHYSICS, 2011 381 IOP PUBLISHING LTD
Stevenson PD, Strayer MR, Rikovska Stone J, Newton WG (2004) Giant resonances from TDHF, International Journal of Modern Physics E 13 (1) pp. 181-185
A method of calculating giant resonance strength functions using Time-Dependent Hartree-Fock techniques is described. An application to isoscalar giant monopole resonances in spherical nuclei is made, thus allowing a comparison between independent 1-, 2- and 3-Dimensional computer codes.
Xu FR, Pei JC, Stevenson PD (2005) Densities of superheavy nuclei at closed shells, Journal of Physics G: Nuclear and Particle Physics 31 (10)
We employed the Skyrme-Hartree-Fock + BCS model to investigate the density distributions of even-even superheavy nuclei around the predicted magic numbers of Z d 114, 120, 126 and N d 172, 184. The central depressions in densities are shown in the heaviest nuclei with Z d 120 and N d 178, which is due to high-j orbits occupied. However, densities become flatter when deformations occur. The superheavy nuclei with N d 180-188 and Z d 126 have no central depressions, due to that low-j orbits become occupied. Shell closures in the superheavy mass region are isospin dependent. © 2005 IOP Publishing Ltd.
Stevenson PD, Almehed D, Reinhard P-G, Maruhn JA (2007) Monopole giant resonances and TDHF boundary conditions, NUCLEAR PHYSICS A 788 pp. 343C-348C ELSEVIER SCIENCE BV
Stevenson PD (2002) Analytic angular momentum coupling coefficient calculators, Computer Physics Communications 147 (3) pp. 853-858
A Java implementation of a suite of programs was described to calculate the angular momentum coupling coefficients analytically. The angular momentum coupling coefficients were found in problems involving quantum mechanical theory of angular momentum. The operating systems under which the program was tested included Netscape 4.75 on Solaris 7 and Internet Explorer 5.5 on Windows NT4.
Maruhn J, Reinhard P, Stevenson P, Umar A (2014) The TDHF code Sky3D, Computer Physics Communications 185 (7) pp. 2195-2216 ELSEVIER SCIENCE BV
The nuclear mean-field model based on Skyrme forces or related density functionals has found widespread application to the description of nuclear ground states, collective vibrational excitations, and heavy-ion collisions. The code Sky3D solves the static or dynamic equations on a three-dimensional Cartesian mesh with isolated or periodic boundary conditions and no further symmetry assumptions. Pairing can be included in the BCS approximation for the static case. The code is implemented with a view to allow easy modifications for including additional physics or special analysis of the results.
Mason P, Podolyak Z, Marginean N, Regan PH, Stevenson PD, Werner V, Alexander T, Algora A, Alharbi T, Bowry M, Britton R, Bruce A, Bucurescu D, Bunce M, Cata-Danil G, Cata-Danil I, Cooper N, Deleanu D, Delion D, Filipescu D, Gelletly W, Ghita D, Gheorghe I, Glodariu T, Ilie G, Ivanova D, Kisyov S, Lalkovski S, Lica R, Liddick S, Marginean R, Mihai C, Mulholland K, Nita C, Negret A, Pascu S, Rice S, Roberts O, Sava T, Smith J, Soederstroem P, Stroe L, Suliman G, Suvaila R, Toma S, Townsley C, Wilson E, Wood RT, Zhekova M, Zhou C (2013) Half-life of the yrast 2(+) state in W-188: Evolution of deformation and collectivity in neutron-rich tungsten isotopes, PHYSICAL REVIEW C 88 (4) 044301 AMER PHYSICAL SOC
The half-life of the yrast I À = 2+ state in the neutron-rich nucleus 188W has been measured using fast-timing
techniques with the HPGe and LaBr3:Ce array at the National Institute of Physics and Nuclear Engineering,
Bucharest. The resulting value of t1/2 = 0.87(12) ns is equivalent to a reduced transition probability of
B(E2; 2+
1 ’ 0+
1 ) = 85(12) W.u. for this transition. The B(E2; 2+
1 ’ 0+
1 ) is compared to neighboring tungsten
isotopes and nuclei in the Hf, Os, and Pt isotopic chains. Woods-Saxon potential energy surface (PES) calculations
have been performed for nuclei in the tungsten isotopic chain and predict prolate deformed minima with rapidly
increasing ³ softness for 184?192W and an oblate minimum for 194W.
Reinhard P, Umar A, Stevenson PD, Piekarewicz, J, Oberacker V, Maruhn J (2016) Sensitivity of the fusion cross section to the density dependence of the symmetry energy, Physical Review C 93 (4) 044618 American Physical Society
Background: The study of the nuclear equation of state (EOS) and the behavior of nuclear matter under extreme conditions is crucial to our understanding of many nuclear and astrophysical phenomena. Nuclear reactions serve as one of the means for studying the EOS. Purpose: It is the aim of this paper to discuss the impact of nuclear fusion on the EOS. This is a timely subject given the expected availability of increasingly exotic beams at rare isotope facilities [A. B. Balantekin et al., Mod. Phys. Lett. A 29, 1430010 (2014)]. In practice, we focus on 48Ca+48Ca fusion. Method: We employ three different approaches to calculate fusion cross sections for a set of energy density functionals with systematically varying nuclear matter properties. Fusion calculations are performed using frozen densities, using a dynamic microscopic method based on density-constrained time-dependent Hartree-Fock (DC-TDHF) approach, as well as direct TDHF study of above barrier cross sections. For these studies, we employ a family of Skyrme parametrizations with systematically varied nuclear matter properties. Results: The folding-potential model provides a reasonable ?rst estimate of cross sections. DC-TDHF, which includes dynamical polarization, reduces the fusion barriers and delivers much better cross sections. Full TDHF near the barrier agrees nicely with DC-TDHF. Most of the Skyrme forces which we used deliver, on the average, fusion cross sections in good agreement with the data. Trying to read off a trend in the results, we ?nd a slight preferenceforforceswhichdeliveraslopeofsymmetryenergyofL H 50MeVthatcorrespondstoaneutron-skin thickness of 48Ca of Rskin = (0.180?0.210) fm. Conclusions: Fusion reactions in the barrier and sub-barrier region can be a tool to study the EOS and the neutron skin of nuclei. The success of the approach will depend on reduced experimental uncertainties of fusion data as well as the development of fusion theories that closely couple to the microscopic structure and dynamics.
Stevenson PD, Suckling E, Fracasso S, Barton MC, Umar A (2016) The Skyrme Tensor Force in Heavy Ion Collisions, Physical Review C 93 054617 American Physical Society
Background: It is generally acknowledged that the time-dependent Hartree-Fock (TDHF) method provides a useful foundation for a fully microscopic many-body theory of low-energy heavy-ion reactions. The TDHF method is also known in nuclear physics in the small amplitude domain, where it provides a useful description of collective states, and is based on the mean-?eld formalism which has been a relatively successful approximation to the nuclear many-body problem. Currently, the TDHF theory is being widely used in the study of fusion excitation functions, ?ssion, deep-inelastic scattering of heavy mass systems, while providing a natural foundation for many other studies. Purpose: With the advancement of computational power it is now possible to undertake TDHF calculations without any symmetry assumptions and incorporate the major strides made by the nuclear structure community in improving the energy density functionals used in these calculations. In particular, time-odd and tensor terms in these functionals are naturally present during the dynamical evolution, while being absent or minimally important for most static calculations. The parameters of these terms are determined by the requirement of Galilean invariance or local gauge invariance but their signi?cance for the reaction dynamics have not been fully studied. This work addresses this question with emphasis on the tensor force. Method: The full version of the Skyrme force, including terms arising only from the Skyrme tensor force, is applied to the study of collisions within a completely symmetry-unrestricted TDHF implementation. Results: We examine the e?ect on upper fusion thresholds with and without the tensor force terms and ?nd an e?ect on the fusion threshold energy of the order several MeV. Details of the distribution of the energy within terms in the energy density functional is also discussed. Conclusions: Terms in the energy density functional linked to the tensor force can play a non-negligible role in dynamic processes in nuclei.
Loebl N, Umar A, Maruhn J, Reinhard P, Stevenson PD, Oberacker V (2012) Single-particle dissipation in a time-dependent Hartree-Fock approach studied from a phase-space perspective, PHYSICAL REVIEW C 86 (2) ARTN 0 AMER PHYSICAL SOC
My research has been focused on time-dependent aspects of nuclear physics both at the mean-field and at the beyond-mean-field level. At the mean field level, the objective of my PhD has been to understand how the introduction of the tensor part of the Skyrme interaction affects heavy ion collisions and giant magnetic resonances, in a self consistent and symmetry unrestricted manner. The introduction of the tensor force redistributes the strength of the giant magnetic resonances within the same energy range. Within the study of heavy ion collisions of 16O+16O the introduction of the tensor decreased the amount of dissipation in the system. At the beyond mean field level, the objective of my PhD was to implement a time dependent density matrix (TDDM) theory, self consistently, without symmetry restrictions using the full Skyrme force. TDDM allows an order by order truncation of the Bogoliubov-Born-ýýGreen-ýýKirkwood-ýýYvon (BBGKY) hierarchy, which relates the evolution of many body densities. If two-body correlations are assumed to dominate the dynamics of the system, the resulting equations incorporate one-particle-one-hole and two-particle-two-hole correlations. A variety of different nuclei below A=40 were chosen to study the formation of correlations for different nuclear ground states. Two body correlations were found to have a noticeable effect on the ground state properties of these nuclei. For example on average 4 - 5 % of the total energy is due to correlations. When time dependent calculations were performed with these correlated nuclei, computational limitations led to problems with conservation laws.
Schuetrumpf B, Reinhard P, Stevenson P, Umar A, Maruhn J (2018) The TDHF code Sky3D version 1.1, Computer Physics Communications 229 pp. 211-213 Elsevier
The nuclear mean-field model based on Skyrme forces or related density functionals has found widespread application to the description of nuclear ground states, collective vibrational excitations, and heavy-ion collisions. The code Sky3D solves the static or dynamic equations on a three-dimensional Cartesian mesh with isolated or periodic boundary conditions and no further symmetry assumptions. Pairing can be included in the BCS approximation for the static case. The code is implemented with a view to allow easy modifications for including additional physics or special analysis of the results.
Stevenson P, Broomfield J (2009) Mass Distributions Beyond TDHF, 133 (2009)

The mass distributions for giant dipole resonances in S-32 and Sn-132 decaying through particle emission and for deep-inelastic collisions between O-16 nuclei have been investigated by implementing the Balian-Vénéroni variational technique based upon a three-dimensional time-dependent Hartree-Fock code with realistic Skyrme interactions. The mass distributions obtained have been sown to be significantly larger than standard TDHF results.

Stevenson P, Brine M, Podolyak Z, Regan P, Walker P, Stone J (2005) Shape Evolution in the Neutron-Rich Tungsten Region, Physical Review C 72 (4)

Recent experimental data on the low-lying states in W-190 show a change in the E(4(1)(+))/E(2(1)(+)) behavior compared to less neutron-rich neigbors. Self-consistent axially-deformed Hartree-Fock calculations, using a separable monopole interaction, of nuclei in the vicinity of W-190 are performed to systematically examine the evolution of ground state quadrupole deformations. It is found that the neutron number N=116 causes a coexistence of oblate and prolate shapes, with a weak dependence on proton number, thereby hindering the development of these isotones as well-deformed rotors.

Jones G, Regan P, Walker P, Podolyak Z, Stevenson P, Carpenter M, Carroll J, Chakrawarthy R, Chowdhury P, Garnsworthy A, Janssens R, Khoo T, Kondev F, Lane G, Liu Z, Seweryniak D, Thompson N, Zhu S, Williams S (2007) Identification of a High-Spin Isomer in Mo-99, Physical Review C 76 (4)

A previously unreported isomer has been identified in Mo-99 at an excitation energy of E-x = 3010 keV, decaying with a half-life of T-1/2 = 8(2) ns. The nucleus of interest was produced following fusion-fission reactions between a thick Al-27 target frame and a Hf-178 beam at a laboratory energy of 1150 MeV. This isomeric state is interpreted as an energetically favored, maximally aligned configuration of nu h (11/2) circle times pi(g (9/2))(2).

Stevenson P, Brine M, Podolyak Z, Regan P, Walker P, Stone J (2005) Shape evolution in the neutron-rich tungsten region, Physical Review C 72 (047303)
Goddard P, Stevenson P, Rios Huguet A (2013) Charge Radius Isotope Shift Across the N=126 Shell Gap, Physical Review Letters 110
We revisit the problem of the kink in the charge radius shift of neutron-rich even isotopes near the N=126 shell closure. We show that the ability of a Skyrme force to reproduce the isotope shift is determined by the occupation of the neutron 1i11/2 orbital beyond N=126 and the corresponding change it causes to deeply-bound protons orbitals with a principal quantum number of 1. Given the observed position of the single-particle energies, one must either ensure occupation is allowed through correlations, or not demand that the single-particle energies agree with experimental values at the mean-field level.
Wen K, Barton M, Rios Huguet A, Stevenson P (2018) Two-body dissipation effect in nuclear fusion reactions, Physical Review C 98 (1) 014603 pp. 014603-1-014603-8 American Physical Society
Friction coefficients for the fusion reaction 16O+16O ’ 32S are extracted based on both the time-dependent Hartree-Fock and the time-dependent density matrix methods. The latter goes beyond the mean-field approximation by taking into account the effect of two-body correlations, but in practical simulations of fusion reactions we find that the total energy is not conserved. We analyze this problem and propose a solution that allows for a clear quantification of dissipative effects in the dynamics. Compared to mean-field simulations, friction coefficients in the density-matrix approach are enhanced by about 20 %. An energy-dependence of the dissipative mechanism is also demonstrated, indicating that two-body collisions are more efficient at generating friction at low incident energies.
Stevenson Paul, Barton Matthew (2018) Low-Energy Heavy-Ion Reactions and the Skyrme Effective Interaction, Progress in Particle and Nuclear Physics Elsevier
The Skyrme effective interaction, with its multitude of parameterisations, along with its implementation
using the static and time-dependent density functional (TDHF) formalism have allowed for a
range of microscopic calculations of low-energy heavy-ion collisions. These calculations allow variation
of the effective interaction along with an interpretation of the results of this variation informed by
a comparison to experimental data. Initial progress in implementing TDHF for heavy-ion collisions
necessarily used many approximations in the geometry or the interaction. Over the last decade or so,
the implementations have overcome all restrictions, and studies have begun to be made where details
of the effective interaction are being probed. This review surveys these studies in low energy heavy-ion
reactions, finding significant effects on observables from the form of the spin-orbit interaction, the use
of the tensor force, and the inclusion of time-odd terms in the density functional.