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15. Structures and properties of magnetic molecular charge-transfer salts

Author

Martin, Lee

Subjects
530.41, SUPERCONDUCTORS, MAGNETIC FIELDS, COOPER PAIRS, CHARGE-EXCHANGE REACTIONS, SALTS
Abstract

The superconducting state may be destroyed by magnetic fields which unpair the electrons of a Cooper pair of superconducting charge carriers. This occurs whether the field is applied externally or arises internally from magnetic moments within the material under investigation. However, there is evidence to suggest that S = 1 Cooper pairs can exist in strong magnetic fields. Both magnetic and conducting properties within a lattice may be combined through the synthesis of charge transfer salts which contain organic donor molecules and magnetic counter-ions. With this molecular approach, structural complexities can be invoked which would not be achievable via conventional solid state synthesis. With the above criteria in mind, this thesis reports a series of molecular charge-transfer salts of the organic donor molecule BEDT-TTF, bis(ethylenedithio)tetrathiafulvalene, with anionic tris(oxalato)-mtetallate(III) and (IV) complexes. The structures of these compounds consist of segregated layers containing BEDT-TTF interleaved with layers containing the oxalato complex. Narrow conduction bands are formed by frontier orbital overlap in the BEDT-TTF layers, while localised spins may be introduced in the anionic layers. Several structures in the series (BEDT-TTF)x[AM(C2O4)3].C 6H5CN, where A = H3O+, NH 4+ or K+ and M = Cr3+, Fe3+ Co3+, (x = 4) or Ge4+ (x = 2) have been characterised by X-ray diffraction. The tris(oxalato)-metallate anion can exist in two enantiomeric forms. This thesis shows how the packing of these two enantiomers determines the arrangement of the BEDT-TTF molecules in the organic layer, and thus the conducting properties. It details the synthesis, structure and physical properties of this series of charge-transfer salts. Synthesis is by conventional electrocrystallisation techniques and physical characterisation includes measurement of transport, magnetic susceptibility, polarised infrared reflectivity, circular dichroism, Raman, epr, and ultraviolet spectroscopies. Electronic band structure calculations have also been performed on selected materials.

Published
1999

17. Neutrino–nuclear responses for astro-neutrinos, single beta decays and double beta decays.

Author

Ejiri, H., Suhonen, J., and Zuber, K.

Subjects
*NEUTRINO interactions, *DOUBLE beta decay, *BETA decay
Abstract

Abstract Neutrino–nuclear responses associated with astro-neutrinos, single beta decays and double beta decays are crucial in studies of neutrino properties of interest for astro-particle physics. The present report reviews briefly recent studies of the neutrino–nuclear responses from both experimental and theoretical points of view in order to obtain a consistent understanding of the many facets of the neutrino–nuclear responses. Subjects discussed in this review include (i) experimental studies of neutrino–nuclear responses by means of single beta decays, charge-exchange nuclear reactions, muon- photon- and neutrino–nuclear reactions, and nucleon-transfer reactions, (ii) implications of and discussions on neutrino–nuclear responses for single beta decays, for astro-neutrinos, and for astro-neutrino nucleosynthesis, (iii) theoretical aspects of neutrino–nuclear responses for beta and double beta decays, for nuclear muon capture and for neutrino–nucleus scattering, and (iv) critical discussions on nucleonic and non-nucleonic spin–isospin correlations and renormalization (quenching or enhancement) effects on the axial weak coupling. Remarks are given on perspectives of experimental and theoretical studies of the neutrino–nuclear responses and on future experiments of double beta decays. [ABSTRACT FROM AUTHOR]

Published
2019
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23. Value of the Axial-Vector Coupling Strength in β and ββ Decays: A Review

Author

Jouni T. Suhonen

Subjects
double beta decays, Gamow-Teller beta decays, forbidden beta decays, axial-vector coupling strength, beta spectra, charge-exchange reactions, Physics, QC1-999
Abstract

In this review the quenching of the weak axial-vector coupling strength, gA, is discussed in nuclear β and double-β decays. On one hand, the nuclear-medium and nuclear many-body effects are separated, and on the other hand the quenching is discussed from the points of view of different many-body methods and different β-decay and double-β-decay processes. Both the historical background and the present status are reviewed and contrasted against each other. The theoretical considerations are tied to performed and planned measurements, and possible new measurements are urged, whenever relevant and doable. Relation of the quenching problem to the measurements of charge-exchange reactions and muon-capture rates is pointed out.

Published
2017
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38. Simulations and analysis tools for charge-exchange (d, 2He) reactions in inverse kinematics with the AT-TPC.

Author

Giraud, S., Zamora, J.C., Zegers, R.G.T., Ayyad, Y., Bazin, D., Mittig, W., Carls, A., DeNudt, M., and Rahman, Z.

Subjects
*KINEMATICS, *COMPUTER software development, *COINCIDENCE
Abstract

Charge-exchange (d ,2He) reactions in inverse kinematics at intermediate energies are a very promising method to investigate the Gamow–Teller transition strength in unstable nuclei. A simulation and analysis software based on the attpcroot package was developed to study this type of reactions with the active-target time projection chamber (AT-TPC). The simulation routines provide a realistic detector response that can be used to understand and benchmark experimental data. Analysis tools and correction routines can be developed and tested from simulations in attpcroot , because they are processed in the same way as the real data. In particular, we study the feasibility of using coincidences with beam-like particles to unambiguously identify the (d ,2He) reaction channel, and to develop a kinematic fitting routine for future applications. More technically, the impact of space-charge effects in the track reconstruction, and a possible correction method are investigated in detail. This analysis and simulation package constitutes an essential part of the software development for the fast-beams program with the AT-TPC. [ABSTRACT FROM AUTHOR]

Published
2023
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43. Digital data acquisition for the Low Energy Neutron Detector Array (LENDA).

Author

Lipschutz, S., Zegers, R.G.T., Hill, J., Liddick, S.N., Noji, S., Prokop, C.J., Scott, M., Solt, M., Sullivan, C., and Tompkins, J.

Subjects
*ACQUISITION of data, *NEUTRON counters, *KINETIC energy, *NUCLEAR reactions, *GAMMA rays
Abstract

A digital data acquisition system (DDAS) has been implemented for the Low Energy Neutron Detector Array (LENDA). LENDA is an array of 24 BC-408 plastic-scintillator bars designed to measure low-energy neutrons with kinetic energies in the range of 100 keV–10 MeV from (p,n)-type charge-exchange reactions. Compared to the previous data acquisition (DAQ) system for LENDA, DDAS offers the possibility to lower the neutron detection threshold, increase the overall neutron-detection efficiency, decrease the dead time of the system, and allow for easy expansion of the array. The system utilized in this work was XIA׳s Digital Gamma Finder Pixie-16 250 MHz digitizers. A detector-limited timing resolution of 400 ps was achieved for a single LENDA bar. Using DDAS, the neutron detection threshold of the system was reduced compared to the previous analog system, now reaching below 100 keV. The new DAQ system was successfully used in a recent charge-exchange experiment using the 16 C(p,n) reaction at the National Superconducting Cyclotron Laboratory (NSCL). [ABSTRACT FROM AUTHOR]

Published
2016
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47. Isovector giant monopole and quadrupole resonances in a Skyrme energy density functional approach with axial symmetry

Author

Kenichi Yoshida

Subjects
Nuclear Theory, Magnetic monopole, FOS: Physical sciences, Collective models, Nuclear Theory (nucl-th), 90 ≤ A ≤ 149, 150 ≤ A ≤ 189, 39 ≤ A ≤ 58, Nuclear Experiment (nucl-ex), Nuclear Experiment, Physics, 20 ≤ A ≤ 38, Isovector, Charge-exchange reactions, Resonance, Nuclear density functional theory Nuclear Physics, Electromagnetic transitions, 59 ≤ A ≤ 89, Giant resonance, Excited state, Quadrupole, Quasiparticle, Atomic physics, Ground state, Collective levels
Abstract

Background: Giant resonance (GR) is a typical collective mode of vibration. The deformation splitting of the isovector (IV) giant dipole resonance is well established. However, the splitting of GRs with other multipolarities is not well understood.Purpose: I explore the IV monopole and quadrupole excitations and attempt to obtain the generic features of IV giant resonances in deformed nuclei by investigating the neutral and charge-exchange channels simultaneously.Method: I employ a nuclear energy-density functional (EDF) method: the Skyrme-Kohn-Sham-Bogoliubov and the quasiparticle random-phase approximation are used to describe the ground state and the transition to excited states.Results: I find the concentration of the monopole strengths in the energy region of the isobaric analog or Gamow-Teller resonance irrespective of nuclear deformation, and the appearance of a high-energy giant resonance composed of the particle-hole configurations of $2\ensuremath{\hbar}{\ensuremath{\omega}}_{0}$ excitation. Splitting of the distribution of the strength occurs in the giant monopole and quadrupole resonances due to deformation. The lower $K$ states of quadrupole resonances appear lower in energy and possess the enhanced strengths in the prolate configuration, and vice versa in the oblate configuration, while the energy ordering depending on $K$ is not clear for the $J=1$ and $J=2$ spin-quadrupole resonances.Conclusions: The deformation splitting occurs generally in the giant monopole and quadrupole resonances. The $K$ dependence of the quadrupole transition strengths is largely understood by the anisotropy of density distribution.

Published
2021

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