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Papers by Ian Thompson

Physics Letters B, 2007

The neutron spectroscopic factor S n of the 7 He ground state is extracted from an R-matrix analy... more The neutron spectroscopic factor S n of the 7 He ground state is extracted from an R-matrix analysis of a recent measurement of the 7 Li(d, 2 He) 7 He reaction with good energy resolution. The width extracted from a deconvolution of the spectrum is Γ = 183(22) keV (full width at half maximum, FWHM). The result S n = 0.64(9) is slightly larger than predictions of recent 'ab initio' Green's function Monte Carlo and fermionic molecular dynamics calculations.

A New Era of Nuclear Structure Physics - Proceedings of the International Symposium, 2004

Physical Review C, 2002

Longitudinal momentum distributions of 7 Be fragments following the dissociation of 8 B on heavy,... more Longitudinal momentum distributions of 7 Be fragments following the dissociation of 8 B on heavy, highly charged target nuclei show forward-aft asymmetries, the result of interference of electric quadrupole (E2) transitions with the dominant E1 excitation process. These asymmetries can therefore be used to gain insight into the E2 contributions to the breakup process. To assess the sensitivity of these E2 interference terms to the assumed reaction mechanism, in particular, the role of higher-order coupling effects at medium energies, coupled discretized continuum channels ͑CDCC͒ calculations are carried out for 8 B breakup at 44 and 81 MeV/nucleon on heavy targets. The effects of higher-order processes due to both Coulomb and nuclear breakup mechanisms can be estimated. In line with earlier work we find that the asymmetries produced by the calculations are reduced when including the higher-order couplings, reflecting an effective quenching of the E2 contributions. The full CDCC calculations show less asymmetry than the available experimental data, suggesting that the structure or reaction model now contains insufficient E2 strength. This contrasts with the results of lowest-order reaction theories that conclude that the 8 B model E2 amplitudes are too large.

The nucleus ^178Hf^m2, with a 16+ isomeric state at 2.46 MeV of a half-life of 31 years, has been... more The nucleus ^178Hf^m2, with a 16+ isomeric state at 2.46 MeV of a half-life of 31 years, has been proposed as a means of storing energy. Many attempts have been made to determine whether this energy can be released by low-energy X-rays, but few unambiguous experimental results have been found: for a review see [1]. Neutrons have been also proposed

Physical Review C, 1999

Analyses using simplified coupled-channels models have been unable to describe the shape of the p... more Analyses using simplified coupled-channels models have been unable to describe the shape of the previously measured fusion barrier distribution for the doubly magic 16 O+ 208 Pb system. This problem was investigated by remeasuring the fission excitation function for 16 O+ 208 Pb with improved accuracy and performing more exact coupled-channels calculations, avoiding the constant-coupling and first-order coupling approximations often used in simplified analyses. Couplings to the single-and 2-phonon states of 208 Pb, correctly taking into account the excitation energy and the phonon character of these states, particle transfers, and the effects of varying the diffuseness of the nuclear potential, were all explored. However, in contrast to other recent analyses of precise fusion data, no satisfactory simultaneous description of the shape of the experimental barrier distribution and the fusion cross-sections for 16 O+ 208 Pb was obtained.

Few-Body Systems, 2010

The 18 C spectrum has been studied in a three body n + n + 16 C model that includes deformation a... more The 18 C spectrum has been studied in a three body n + n + 16 C model that includes deformation and the 2 + excitation of the 16 C core as well as Pauli projection of forbidden states. The 16 C − n interaction employed in this study has been fitted to reproduce the experimental spectrum of 17 C. The calculations show that two neutron separation energy in 18 C in consistent with three-body structure of this nucleus and predict more states bound with respect to three-body decay. The comparison of their position to known excited states in 18 C is discussed. These calculations suggest also that a few states may exist in astrophysically relevant region between the 17 C + n and 16 C + 2n decay thresholds. The most important of them is 1 − as it can give a large E1 resonant contribution to 17 C(n, γ) 18 C neutron capture. The calculations also suggest that a virtual s-wave state may exist above the 17 C+n threshold that can give rise to non-negligible M1 contributions to the 17 C(n, γ) 18 C reaction rate. The presence of these states in the 18 C spectrum can lead to an increased 17 C(n, γ) 18 C reaction rate, which can significantly influence the abundances of uranium and thorium synthesized in the r-process in the supernovae explosions.

Physical Review C, 2004

Inelastic scattering of 11 Li on proton targets at energy of 68 MeV/ nucleon has been studied in ... more Inelastic scattering of 11 Li on proton targets at energy of 68 MeV/ nucleon has been studied in the microscopic four-body distorted-wave model. The ground state and three-body continuum excitations of 11 Li were calculated in the 9 Li+ n + n cluster model using the method of hyperspherical harmonics. The theory describes the experimental data well and clarifies contributions from the three-body monopole resonance in 11 Li and from its soft dipole excitation. Various aspects of the 11 Li excitations and their nature are discussed in terms of correlation plots.

Compound-Nuclear Reactions, 2020

Journal of Physics: Conference Series, 2011

A theory of partial fusion is used to calculate the competition between escape (breakup) and abso... more A theory of partial fusion is used to calculate the competition between escape (breakup) and absorption (compound-nucleus production) following a deuteron-induced transfer of one neutron to a heavy nucleus at energies above the neutron escape threshold. Preliminary calculations are shown to yield excellent results for the competition between neutron absorption and neutron escape when deposited on actinides at energies up to 3 MeV.

Journal of Physics G: Nuclear and Particle Physics, 2020

This white paper reports on the discussions of the 2018 Facility for Rare Isotope Beams Theory Al... more This white paper reports on the discussions of the 2018 Facility for Rare Isotope Beams Theory Alliance (FRIB-TA) topical program ‘From bound states to the continuum: Connecting bound state calculations with scattering and reaction theory’. One of the biggest and most important frontiers in nuclear theory today is to construct better and stronger bridges between bound state calculations and calculations in the continuum, especially scattering and reaction theory, as well as teasing out the influence of the continuum on states near threshold. This is particularly challenging as many-body structure calculations typically use a bound state basis, while reaction calculations more commonly utilize few-body continuum approaches. The many-body bound state and few-body continuum methods use different language and emphasize different properties. To build better foundations for these bridges, we present an overview of several bound state and continuum methods and, where possible, point to cur...

Recently, the first example of two-neutron decay from the ground state of an unbound nucleus, ^16... more Recently, the first example of two-neutron decay from the ground state of an unbound nucleus, ^16Be, was seen. Three-body methods are ideal for exactly treating the degrees of freedom important for these decays. Using a basis expansion over hyperspherical harmonics and the hyperspherical R-matrix method, we construct a realistic model of ^16Be in order to investigate its decay mode and the role of the two-neutron interaction. The neutron-^14Be interaction is constrained using shell model predictions. We obtain a ground state for ^16Be that is over-bound by approximately 1 MeV with a width of approximately 0.23 MeV. This suggests, that for such systems, the three-body force needs to be repulsive.

Submitted for the DNP06 Meeting of The American Physical Society Reaction Mechanisms for (d,p) on... more Submitted for the DNP06 Meeting of The American Physical Society Reaction Mechanisms for (d,p) on Exotic Nuclei NEIL SUMMERS, Rutgers University, FILOMENA NUNES, NSCL/MSU, IAN THOMPSON, Surrey University / LLNL-Transfer reactions are typically analyzed using DWBA reaction theory. The structure of the exotic nuclei of affects the (d,p) cross section through overlaps of the relevant many body wave functions. In standard DWBA theory this overlap is approximated by a single particle wave function, where the core is considered inert. Then the cross section is scaled by the spectroscopic factor. Transfer to excited states and even continuum states for weakly bound nuclei can also be considered. This "standard" reaction theory neglects many things. On top of multi-step effects which can be investigated using a coupled channels approach, the single particle nature of the final states and the assumption that the core is inert are two approximations that can now be examined using an extension of the coupled channels approach called XCDCC (eXtended Continuum Discretized Coupled Channels). We use XCDCC to study Be10(d,p)Be11 and Be11(p,d)Be10 reactions and the effects of couplings. We examine the continuum states of Be11 where we can now model resonances built on excited core components. We compare our results with various sets of data and draw general conclusion important for (p,d) and (d,p) reactions.

Our understanding of halo nuclei has so far relied on high-energy scattering and reactions, but a... more Our understanding of halo nuclei has so far relied on high-energy scattering and reactions, but a number of uncertainties remain. I discuss in general terms the new range of observables which will be measured by experiments around the Coulomb barrier, and how some details of the reaction mechanisms still need to be clarified.

Recently, much philosophical work has emphasized the importance of dispositions for realistic ana... more Recently, much philosophical work has emphasized the importance of dispositions for realistic analyses of causal processes in both physics and psychology. This is partly because of the attractiveness of the thesis of dispositional essentialism, which holds that all existing things have irreducible causal powers, and such views are advocated in (Bird, 2004; Cartwright, 1983; Chakravartty, 2003; Elder, 1994; Ellis, 2000, 2001; Ellis and Lierse, 1994; Fetzer, 1977; Harré and Madden, 1975; McKitrick, 2003; Molnar, 2004; Mumford, 1995, 1998; Shoemaker, 1984; Swoyer, 1982 and Thompson, 1988). The thesis opposes the views of (Ryle, 1949: ch. 5) who sees dispositions as merely ‘inference tickets’ or ‘promises’, and (Armstrong, 1969) who sees them as derived from universal laws combined with non-dispositional properties. (Mumford, 2005) articulates a common aspect of dispositional essentialism, to imagine how the concept of universal laws could be rather replaced by talk of specific objects ...

EPJ Web of Conferences

Recently, the first example of two-neutron decay from the ground state of an unbound nucleus, 16 ... more Recently, the first example of two-neutron decay from the ground state of an unbound nucleus, 16 Be, was seen (A. Spyrou, et. al., Phys. Rev. Lett. 108 102501 (2012)). Three-body methods are ideal for exactly treating the degrees of freedom important for these decays. Using a basis expansion over hyperspherical harmonics and the hyperspherical R-matrix method, we construct a realistic model of 16 Be in order to investigate its decay mode and the role of the two-neutron interaction. The neutron-14 Be interaction is constrained using shell model predictions. We obtain a ground state for 16 Be that is under-bound by approximately 0.7 MeV with a width of approximately 0.17 MeV. For such a system, an attractive three-body force must be included to reproduce the experimental ground state energy.

Probabilities, Causes and Propensities in Physics, 2010

ABSTRACT

Energy correlations in transitions from the bound state to the three-body continuum of Borromean ... more Energy correlations in transitions from the bound state to the three-body continuum of Borromean halo nuclei are considered. A core+n+n three-body cluster model which reproduces experimentally known properties of ^6He and ^11Li has been used to study low-lying resonances and soft modes. The analysis of the correlated responses in ^6He shows that in the case of the narrow three-body 2^+1