Spin Distribution for the ’t Hooft–Polyakov Monopole in the Geometric Theory of Defects

Recently the ’t Hooft–Polyakov monopole solutions in Yang–Mills theory were given new physical interpretation in the geometric theory of defects describing the continuous distribution of dislocations and disclinations in elastic media. It means that the ’t Hooft–Polyakov monopole can be seen, probably, in solids. To this end we need to compute the corresponding spin distribution on lattice sites of crystals. The paper describes one of the possible spin distributions. The Bogomol’nyi–Prasad–Sommerfield solution is considered as an example.

Isomer yields in nuclear fission

The generation of angular momentum in the fission process is still an open question. To shed light on this topic, we started a series of measurements at the IGISOL-JYFLTRAP facility in Finland. Highprecision measurements of isomeric yield ratios (IYR) are performed with a Penning trap, partly with the aim to extract average root-mean-square (rms) quantities of fragment spin distributions. The newly installed Phase-Imaging Ion-Cyclotron Resonance (PI-ICR) technique allows the separation of masses down to tens of keV, which is suffcient to disentangle many isomers. In this paper, we first summarize the previous measurements on the neutron and proton-induced fission of uranium and thorium, e.g. the odd cadmium and indium isotopes (119 ≤ A ≤ 127). The measurements revealed systematic trends as function of mass number, which stimulated further exploration. A recent measurement was performed at IGISIOL and several new IYR data will soon be published, for the first time. Secondly, we employ the TALYS nuclear-reaction code to model one of the newly measured isomer yields. Detailed GEF and TALYS calculations are discussed for the fragment angular momentum distribution in 134I.

Geometries and Terahertz Motions Driving Quintet Multiexcitons and Ultimate Triplet-Triplet Dissociations via the Intramolecular Singlet-Fissions

Importance of vibronic effects has been highlighted for the singlet-fission (SF) that convert one high-energy singlet exciton into doubled triplet excitons, as strongly correlated multiexcitons. However, molecular mechanisms of spin conversion processes and ultimate de-couplings in the multiexcitons are poorly understood. We have analyzed geometries and exchange couplings of the photoinduced multiexcitons in the pentacene dimers bridged by a phenylene at ortho and meta positions [denoted as <i>o</i>-(Pc)₂ and <i>m</i>-(Pc)₂] by simulations of the time-resolved electron paramagnetic resonance spectra. We clarified that terahertz molecular conformation dynamics plays a role on the spin conversion from the singlet strongly coupled multiexcitons ¹(TT) to the quintet state ⁵(TT). The strongly coupled ⁵(TT) multiexcitons are revealed to possess entirely planar conformations stabilized by mutually delocalized spin distributions, while the intramolecular de-coupled spin-correlated triplet pairs generated at 1 microsecond are also stabilized by distorted conformations resulting in two separately localized biradical characters.

Geometries and Terahertz Motions Driving Quintet Multiexcitons and Ultimate Triplet-Triplet Dissociations via the Intramolecular Singlet-Fissions

Importance of vibronic effects has been highlighted for the singlet-fission (SF) that convert one high-energy singlet exciton into doubled triplet excitons, as strongly correlated multiexcitons. However, molecular mechanisms of spin conversion processes and ultimate de-couplings in the multiexcitons are poorly understood. We have analyzed geometries and exchange couplings of the photoinduced multiexcitons in the pentacene dimers bridged by a phenylene at ortho and meta positions [denoted as <i>o</i>-(Pc)₂ and <i>m</i>-(Pc)₂] by simulations of the time-resolved electron paramagnetic resonance spectra. We clarified that terahertz molecular conformation dynamics plays a role on the spin conversion from the singlet strongly coupled multiexcitons ¹(TT) to the quintet state ⁵(TT). The strongly coupled ⁵(TT) multiexcitons are revealed to possess entirely planar conformations stabilized by mutually delocalized spin distributions, while the intramolecular de-coupled spin-correlated triplet pairs generated at 1 microsecond are also stabilized by distorted conformations resulting in two separately localized biradical characters.

Employing TALYS to deduce angular momentum rootmean-square values, Jrms, in fission fragments

Fission fragments exhibit large angular momenta J, which constitutes a challenge for fission models to fully explain. Systematic measurements of isomeric yield ratios (IYR) are needed for basic nuclear reaction physics and nuclear applications, especially as a function of mass number and excitation energy. One goal is to improve the current understanding of the angular momentum generation and sharing in the fission process. To do so, one needs to improve the modeling of nuclear de-excitation. In this work, we have used the TALYS nuclear-reaction code to relax excited fission fragments and to extract root-mean-square (rms) values of initial spin distributions, after comparison with experimentally determined IYRs. The method was assessed by a comparative study on 252Cf(sf) and 235U(nth,f). The results show a consistent performance of TALYS, both in comparison to reported literature values and to other fission codes. A few discrepant Jrms values were also found. The discrepant literature values could need a second consideration as they could possibly be caused by outdated models. Our TALYS method will be refined to better comply with contemporary sophisticated models and to reexamine older deduced values in literature.

Measurement of (n, f) and (n, xn) cross sections with surrogate reaction method

Surrogate reaction method is an important approach to overcome the difficulties meet in the direct measurement of neutron induced nuclear reaction. The current existing surrogate reactions generally employ the peripheral reactions such as inelastic excitation and transfer reaction where the involved angular momenta are much larger than the neutron capture reaction, which causes a difficulty in theoretical correction of spin of compound nucleus. We proposed to use capture reaction of light charged particle as the surrogate reaction, thus the spin distributions of compound nucleus in two reactions are quite similar and therefore the spin correction is not strongly desired. Based on this idea, the 239Pu(n, f) and (n, 2n) cross sections were successfully extracted by using 236U(α,, f) and (α, 2n) reactions as the surrogate reactions. The well coincidence of the present results with the data of ENDFB7 within the error bars shows the reliability of the proposed surrogate capture reaction method.

Decay of 160Er* in 16O + 144Nd and 64Ni + 96Zr Fusion Reactions

The population of evaporation residue entry states in the decay of the compound nucleus 160Er*(54 MeV) is investigated in a cross-bombardment employing the reactions 160 + 144Nd and 64Ni + 96Zr. Evaporation residue cross sections and entry state 7-ray fold distributions of the dominant exit channels were obtained for each reaction, using a 4π 7-ray detection system. An entrance-channel dependence of the 7-ray fold distributions of the xn products is observed. This effect is described successfully by the statistical model making use of compound nucleus angular momentum distributions obtained with a fusion model that provides a good description of the bombarding energy dependence of fusion data for both reactions. In accordance with recent findings on the decay of 164Yb*, it is suggested that the observed differences in the population of the dominant exit channels originate from the primary spin distributions rather than a possible dependence of the compound nucleus decay on the formation mode.

Unmodelled clustering methods for gravitational wave populations of compact binary mergers

ABSTRACT The mass and spin distributions of compact binary gravitational-wave sources are currently uncertain due to complicated astrophysics involved in their formation. Multiple sub-populations of compact binaries representing different evolutionary scenarios may be present amongst sources detected by Advanced LIGO and Advanced Virgo. In addition to hierarchical modelling, unmodelled methods can aid in determining the number of sub-populations and their properties. In this paper, we apply Gaussian mixture model clustering to 1000 simulated gravitational-wave compact binary sources from a mixture of five sub-populations. Using both mass and spin as input parameters, we determine how many binary detections are needed to accurately determine the number of sub-populations and their mass and spin distributions. In the most difficult case that we consider, where two sub-populations have identical mass distributions but differ in their spin, which is poorly constrained by gravitational-wave detections, we find that ∼400 detections are needed before we can identify the correct number of sub-populations.