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Tungsten is the material of choice for plasma facing components in future fusion reactors. During operation, these components receive extreme heat and radiation loads. The radiation and ion infusion from the plasma modify the tungsten lattice, altering its material properties such as the thermal diffusivity. Ion-implantation is a useful proxy for studying neutron irradiation and plasma exposure. However, it gives a thin damaged layer that is difficult to probe using conventional thermal transport measurement techniques. Transient grating spectroscopy (TGS) is a novel tool for measuring the thermal diffusivity and surface acoustic wave (SAW) speed in thin ion-implanted layers. We present new developments of the TGS technique that enable the measurement of large area 2D maps of thermal diffusivity and SAW speed with targeted measurements and accommodating samples with increased roughness. These capabilities are demonstrated by recording large TGS maps of deuterium implanted tungsten, linear friction welded aerospace alloys and high entropy alloys. The results illustrate the ability to view grain microstructure in elastically anisotropic samples, and to detect anomalies, for example due to irradiation and previous measurements. They also point to the possibility of using TGS to quantify grain size at the surface of polycrystalline materials. The thermal diffusivity and SAW speed in tungsten exposed to different fluences of deuterium plasma is studied. Scanning electron microscopy (SEM) shows the formation of surface blisters that have similar morphology for all fluences considered. A significant reduction in thermal diffusivity and SAW speed occurs as a result of plasma exposure. A saturation of the thermal diffusivity reduction with fluence is seen. Deuterium ion flux density appears to play a more important role in thermal diffusivity reduction than total fluence. TGS is used to study the thermal diffusivity of tungsten exposed to different levels of 20 MeV self-ion irradiation. Damage as low as 3.2 x 10⁻⁴ displacements per atom (dpa) causes a measurable reduction in thermal diffusivity. Doses of 0.1 dpa and above, up to 10 dpa, give a degradation of ~55% from the pristine value at room temperature. Using a kinetic theory model, the density of irradiation-induced point defects is estimated based on the measured changes in thermal diffusivity as a function of dose. These predictions are compared with point defect and dislocation loop densities observed in transmission electron microscopy (TEM). Molecular dynamics (MD) predictions are combined with the TEM observations to estimate the density of point defects associated with defect clusters too small to be probed by TEM. When these "invisible" defects are accounted for, the total point defect density agrees well with that estimated from TGS for a range of doses spanning 3 orders of magnitude. Kinetic theory modelling is also used to estimate the thermal diffusivity degradation expected due to TEM-visible and invisible defects. Finely distributed invisible defects appear to play a much more important role in the thermal diffusivity reduction than larger TEM-visible dislocation loops. This work demonstrates the capability of TGS, in conjunction with kinetic theory models, to provide rapid, quantitative insight into defect densities and property evolution in irradiated materials.

In this thesis we develop and systematically analyse models which describe collisional processes involving neutral molybdenum (Mo I), neutral tungsten (W I), singly ionised iron (Fe II), and neutral iron (Fe I). While atomic data for the neutral stages of molybdenum and tungsten finds an important application when investigating the influx of impurities into magnetically confined fusion plasmas, atomic data for the low ion stages of iron facilitates the study of astrophysical plasmas across every corner of the universe. To study the atomic structures of Mo I, W I, and Fe II we make use of sophisticated configuration interaction methods implemented by the well known computer packages GRASP0 and CIV3. In addition, to accurately describe electron and photon collisions with these species we make use of relativistic and semi-relativistic R-matrix scattering methods implemented by the parallel Breit-Pauli R-matrix and Dirac R-matrix codes. We then employ collisional-radiative models, exploiting results from both the atomic structure and R-matrix calculations, to provide us with valuable diagnostic information about the plasma. The underlying theory of these atomic structure, scattering, and collisional-radiative methods will be discussed at length and in particular, we will note significant developments to the Dirac R-matrix codes which were necessary to handle the calculations presented throughout this thesis. Detailed level-resolved atomic structure models for Mo I, W I, and Fe II will be discussed and energies and radiative transition rates will be presented. Furthermore, results from large scale R-matrix scattering calculations exploring the electron-impact excitation of Mo I, W I and Fe II and the photoionisation of Fe I will also be presented. Alongside our results we will provide extensive com- parisons with existing theoretical calculations and experimental measurements with a particular focus on transitions most relevant for applications to fusion and astrophysical plasmas.

The geology of SW England is characterised by three geological phenomena which include the Permian granite batholith, complex structural geology and a world-class tin-tungsten-copper orefield. At present, interest in exploration for metals such as tungsten and tin is high because of their designation as "critical" to British and European economies. Furthermore, there is renewed interest in geothermal energy production and the potential for metal extraction, such as lithium, from geothermal brines. Many aspects of the resource-rich geology of SW England remain enigmatic, such as the distribution of different granite types, the fault network and the potential for mineralisation at depth (> 200 m). These three phenomena are intrinsically linked, and are key to finding new metalliferous resources and geothermal energy targets; however, the temperate climate and poor outcrop inland is a significant limitation. High-resolution airborne geophysical data collected over SW England as part of the Tellus South West project (2013-2014) provides a new opportunity to better understand these three geological phenomena. Furthermore, regional geochemical data has also been collected in 2012 as part of the Geochemical Baseline Survey of the Environment (G-BASE). These data have been investigated using machine learning algorithms for integrated data analysis. Machine learning incorporates computer science methods for pattern recognition into statistical analysis to create an objective model. The approach can use supervised or unsupervised algorithms; the former uses a priori data to train algorithms whereas the latter attempts to find natural clusters. These methods are used to generate new models of the granites, structural geology and tungsten prospectivity in the region. Granite classification models attempted to map the distribution of different granite types across the granite batholith. Unsupervised approaches, such as the k-means algorithm, found natural clusters of different granite types using airborne radiometric data and stream-sediment geochemistry, however, clusters were focused on the grouping of thorium-rich and thorium-poor areas. Whilst these showed some similarity to previously described granite types, it was not possible to define all expected granite types. Data from Simons et al. (2016) were used to train a number of supervised algorithms and proved more effective due to their ability to classify non-linearly separable data. The Support Vector Machine algorithm was found to be the most effective classifier, closely followed by Random Forest. A refined geological map of the granite types helps illustrate the potential for occurrences of different granite types that may not be exposed at surface. Unsupervised image segmentation algorithms within an Object-Based Image Analysis framework are applied for regional lineament detection using the high-resolution airborne geophysical data. Data preparation using the Tilt Derivative transform for magnetic, radiometric and LiDAR data was found to generate comparable, normalised input datasets that preserved subtle structural features. Two new stand-alone algorithms are presented that allow the integration of multi-sourced datasets for geological lineament detection. The new lineament datasets derived herein are a significant improvement on pre-existing structural datasets across the region that were either incomplete or subjectively analysed. Tungsten mineralisation is explored for using the Random Forest algorithm to generate a new prospectivity model for the region. The model incorporates high-resolution airborne geophysics and regional geochemistry with the geological lineament data derived in this thesis. Additional data are included on the proximity to granite at surface and at depth (based on gravity modelling by Willis-Richards and Jackson (1989)). Classical prospectivity modelling techniques such as Fuzzy Logic and Weights-of-Evidence, validated using the Receiver Operator Characteristics curve were both found to have accuracies of 0.891. In contrast, the Random Forest model had an accuracy of 0.989. New exploration targets are refined by the derivation of a Confidence Metric which clearly identifies three new areas for follow-up work. Metadata from the Random Forest model has been used to measure variable importance and identify superfluous data which can guide future exploration campaigns. The three geological phenomena are synthesised to demonstrate their relationship where the identification of geological lineaments in granite areas corresponds with highly variable granite distribution which is often found in close proximity to tungsten mineralisation targets. The research therefore enhances our understanding of granite distribution and structural geology with practical applications for mineral exploration. Machine learning is applied widely throughout to stream-line workflows and aid more objective decision-making. Methodologies developed herein are highly applicable to other temperate regions and could assist exploration for tungsten and other metals.

Lithium-ion batteries have transformed energy storage and technological applications. They stand poised to convert transportation from combustion to electric engines. The discharge/charge rate is a key parameter that determines battery power output and recharge time; typically, operation is on the timescale of hours but reducing this would improve existing applications and open up new possibilities. Conventionally, the rate at which a battery can operate has been improved by synthetic strategies to decrease the solid-state diffusion length of lithium ions by decreasing particle sizes down to the nanoscale. In this work, a different approach is taken toward next-generation high-power and fast charging lithium-ion battery electrode materials. The phenomenon of high-rate charge storage without nanostructuring is discovered in niobium oxide and the mechanism is explained in the context of the structure–property relationships of Nb2O5. Three polymorphs, T-Nb2O5, B-Nb2O5, and H-Nb2O5, take bronze-like, rutile-like, and crystallographic shear structures, respectively. The bronze and crystallographic shear compounds, with unique electrochemical properties, can be described as ordered, anion-deficient nonstoichiometric defect structures derived from ReO3. The lessons learned in niobia serve as a platform to identify other compounds with related structural motifs that apparently facilitate high-rate lithium insertion and extraction. This leads to the synthesis, characterisation, and electrochemical evaluation of the even more complicated composition–structure–property relationships in ternary TiO2–Nb2O5 and Nb2O5–WO3 phases. Advanced structural characterisation including multinuclear solid-state nuclear magnetic resonance spectroscopy, density functional theory, X-ray absorption spectroscopy, operando high-rate X-ray diffraction, and neutron diffraction is conducted throughout to understand the evolution of local and long-range atomic structure and changes in electronic states.

This thesis comprises of essentially two parts. The first deals with materials in a fusion reactor and examines how neutron damage affects material in a fusion reactor, with focus on how this is important for plasma damage. The methods used are neutron transport, primary event analysis and molecular dynamics. It found that the neutron damage by 14 MeV neutrons is restricted to back scatter events within the surface (first 20 microns). Molecular dynamics analysis showed that the issue of cascades is heavily dependent on direction of primary event and the energy of such. Statistical analysis was done to provide a standard approach for modelling of damage through neutrons. The second deals with the relaxation of magnetic flux ropes with an emphasis on kink unstable flux ropes. A relaxation model was developed which shows good approximation to simulation results of merging magnetic flux ropes. Subsequently, work was done to establish the physical processes involved in relaxation. This was done by examining magnetohydrodynamic (MHD) simulations of two flux ropes, one unstable and one stable. It was found that there is is a clear distance at which merger does not occur any more. Furthermore, a critical current seems to be a requirement at the edge a stable flux rope.

Tungsten is a candidate material for plasma facing components in the experimental fusion reactor, ITER and the demonstration fusion reactor, DEMO. It has been chosen due to its high melting point, low sputtering yield and resistance to oxidation. However, there are still some issues that need addressing, such as its response to 14 MeV neutrons and helium production, products of the deuterium-tritium reaction that will be used to harness fusion energy. Additionally, the high temperatures of operation are another factor to consider. There is no dedicated materials testing device that can concurrently recreate all the conditions expected in ITER or DEMO. Previous work has focussed on the use of ion beams and linear plasma devices to try and mimic the damage induced from the neutrons and helium. Following from this work, this thesis has focused on three methods in simulating the neutron and helium damage. The three methods used in this project are; helium plasma exposures at fusion relevant temperatures to tungsten and tungsten-rhenium alloys, where rhenium was used to mimic the transmutation induced by neutrons; heavy ion (tungsten and rhenium ions) irradiations in tungsten at 400 °C; and proton irradiations in tungsten at 400 °C and 800 °C. Analysis of the microstructural and micromechanical properties of the exposed samples has been carried out. The effect of rhenium on the formation of a nanostructure (fuzz) in tungsten induced by helium plasma exposures was studied. Rhenium was shown to generally inhibit fuzz formation. Mechanisms by which inhibition could occur were discussed. The most recent literature had suggested that an incubation fluence was required before fuzz growth could occur, but the research in this thesis pointed more towards an alternative incubation time theory. The simultaneous effects of transmutation and displacement cascade damage induced by neutrons were mimicked via irradiations with rhenium ions into tungsten, which were compared to tungsten ion irradiations. The effect on mechanical properties of tungsten was tested using nanoindentation. Up to levels of 40 dpa and 1600 appm, at temperatures of 400 °C, the difference in hardness increase between the two types of irradiations was negligible. Proton irradiations at 400 °C and 800 °C, up to levels of ~2 dpa in the first 2 μm of the samples were explored. The hardness increase observed at 400 °C was much greater than that seen in the heavy ion irradiations, most likely due to the larger volume of irradiated material and the large Bragg peak in the proton irradiated samples. In both the heavy ion and proton irradiated material, higher hardness increases were observed in annealed material, in comparison to an as-received material. Impurity concentrations were observed to be an important issue when carrying out irradiation experiments, particularly at raised temperatures.

In-vessel tungsten components of a future demonstration fusion reactor are likely to be operated in the material's non-ductile regime. Assessment of the components' reliability is not possible with current ductile design codes or through experimental qualification. There is therefore an urgent need for non-ductile assessment procedures. One such approach currently considered is Weibull's weakest link theory, which is based on linear-elastic fracture mechanics and has its origins in ceramics. A full assessment of its validity has been performed, and the challenge of obtaining irradiated material data addressed. Bend tests at the macroscopic scale confirm previous findings that the scatter in strength of pure tungsten follows a two-parameter Weibull distribution, provided the material fractures within its elastic regime. However, tests conducted over a range of specimen sizes reveal the technique's shortcomings in accurately predicting the material's size effect in fracture, questioning its applicability to pure tungsten and also other brittle metallic materials. Fracture strength tests conducted at the micrometre scale through cantilever bending have addressed the challenge of obtaining irradiated material data. An ultra-fine grained self-passivating tungsten alloy, considered as an alternative contender to tungsten for in-vessel components, is shown to fracture within its linear-elastic regime at the microscopic scale. A reliable and repeatable measurement of its strength of approximately 5.9 GPa is obtained. The scatter in measurements is shown to be greater than random errors, and to be described well by a two-parameter Weibull distribution. Cantilever tests conducted over a range of specimen sizes reveal a strong size effect (4.3 - 9.0 GPa), which is accurately predicted by Weibull's weakest link theory. Ion implantations, conducted in the tungsten alloy to mimic neutron induced elastic collision damage, result in a statistically confirmed drop (6 %) in cantilever measured fracture strength at low doses (0.7 dpa), and an increase (9-16 %) at higher doses (7 dpa).The cantilever test technique is therefore suitable for the measurement of ion and neutron irradiation effects on the material's fracture strength. Provided a full validation of Weibull's weakest link theory strength extrapolation from the micro- to macroscopic scale is realised on a future heterogeneity free material batch, irradiated material data obtained from cantilever tests could be used to assess the reliability of in-vessel components fabricated from a self-passivating tungsten alloy, and fill the current gap in non-ductile design assessment procedures.

In this work, new reconstruction and analysis methods were developed for 3D field ion microscopy (FIM) data, motivated by the goal of atomic scale characterisation of radiation damage for fusion applications. A comparative FIM/ atom probe tomography (APT) study of radiation damage in self-implanted tungsten revealed FIM advantages in atomistic crystallographic characterisation, able to identify dislocations, large vacancy clusters, and single vacancies. While the latter is beyond the detection capabilities of APT, larger damage features were observed indirectly in APT data via trajectory aberrations and solute segregation. An automated 3DFIM reconstruction approach was developed to maintain reliable, atomistic, 3D insights into the atomic arrangements and vacancies distribution in ion-implanted tungsten. The new method was utilized for the automated ‘atom-by-atom' reconstruction of thousands of tungsten atoms yielding highly accurate reconstructions of atomically resolved poles but also applied to larger microstructural features such as carbides and a grain boundary, extending across larger portions of the sample. Additional tools were developed to overcome reconstruction challenges arising from the presence of crystal defects and the intrinsic distortion of FIM data. Those were employed for the automated 3D mapping of vacancies in ion-implanted tungsten, analysing their distribution in a volume extending across 50nm into the depth of the sample. The new FIM reconstruction also opened the door for more advanced analyses on FIM data. It was applied to the preliminary studies of the distortion of the reconstructed planes, found to depend on crystallographic orientation, with an increased variance in atomic positions measured in a radial direction to the centre of the poles. Additional analyses followed the subtle displacements in atomic coordinates on consecutive FIM images, to find them affected by the evaporation of atoms from the same plane. The displacements were found to increase with size as the distance to the evaporated atom decreased, and are likely to be the result of a convolution between image gas effects, surface atoms relaxation, and charge re-distribution. These measurements show potential to probe the dynamic nature of the FIM experiment and possibly resolve contributions from the different processes effecting the final image. Finally, APT characterisation was performed on bulk and pre-sharpened needles to determine the effect of sample's geometry on the resulting implantation profiles, and the extent to which pre-sharpened needles could be employed in radiation damage studies. While the ions depth profiles in needles were not found within a good match to SRIM simulations, the damage profiles exhibited closer agreement. Further, the concentration of implanted ions in bulk samples was found significantly higher than in the respective needle implanted samples, with excessive loss found for the light ion implantation.

Tungsten will be a key material for the plasma-facing components in future fusion devices. Its mechanical performance under neutron irradiation will strongly influence the lifetime of these devices. Pure tungsten has been subjected to a variety of irradiating species - tungsten ions, helium ions and fission neutrons - between 500°C and 900°C and the change in mechanical properties measured by micro-mechanical testing methods. Pure tungsten has been ion-irradiated using self-ions and helium ions at 500°C and 800°C. Nanoindentation has been performed on all specimens, and the 800°C specimens have been tested at temperatures up to 750°C using high-temperature nanoindentation. The irradiation temperature has no effect on the hardening of tungsten. Hardening from self-ion irradiation has not saturated by 4.5 dpa with an increase in hardness of 3.3 GPa. The hardening from helium implantation is only 0.73 GPa, and a comparison with literature shows that this hardening only depends on the concentration of the injected helium. The difference is likely due to the much smaller defect size of helium-vacancy clusters when compared to dislocation loops. High-temperature nanoindentation shows that helium-implanted tungsten softens rapidly, with the hardening from the radiation damage becoming negligible above 450°C. Self-ion implanted tungsten does not soften by 650°C, again likely due to the size difference of the defects. Micro-mechanical tests - namely micro-cantilever bending - have been used to investigate the plastic and fracture characteristics of tungsten before and after irradiation. Plastic behaviour is dominated by size effects due to the 3 μm depth of the implanted layers, which makes nanoindentation a better method for investigating radiation damaged layers. In fracture testing, fracture is rarely seen. Using the yield stress to calculate fracture toughness, the hardening from irradiation damage results in an increase in fracture toughness from 2.2 MPa√m to 6.0 MPa√m. The work of deformation at 1% is also increased after irradiation from 7.2 x 10-11 Nm to 2.8 x 10-10 Nm, implying that the implanted damage is not leading to an increase in embrittlement by reducing K1c. Neutron irradiated tungsten also shows an increase in fracture toughness after irradiation from 6.5 MPa√m to 14.5 MPa√m. However, the BDTT increases by ∼ 100°C in poly-crystal tungsten and ∼ 500°C in single-crystal tungsten. The difference in BDTT does not exist in the unimplanted material. The change after irradiation is likely due to the fine (˜ 3 μm) grain size and 900°C irradiation temperature causing a significant amount of the displacement damage to be absorbed at the grain boundaries. The hardness of neutron irradiated and ion irradiated tungsten is very close: 10.4 GPa and 11.2 GPa respectively, demonstrating the ions are likely well-representing the neutron damage in pure tungsten.

The displacement damage induced by primary recoils of fusion neutrons in tungsten and alloys has been studied with self-ion irradiations, followed by damage characterization with electron microscopy. Tungsten and alloys (≤ 5 wt.% Re, Ta, V) were implanted with 2 MeV W+ ions over a dose range of 3.3×1017 - 2.5×1019 W+m-2 at temperatures ranging from 300 to 750°C. Dislocation loops of b = ½<111> (> 60%) and b = <100> were identified, and that ½<111> loops were found more thermally stable. Among loops that were large enough for nature determination, at least 50% were found to be of interstitial type, with larger fractions in high-temperature and high-dose conditions. The diameter of loops did not exceed 20 nm, with the majority being ≤ 5 nm. The loop number density varied between 1022 and 1023 m-3. The effects of ion dose, irradiation temperature, composition and grain orientation on damage microstructure were investigated. In-situ irradiations (150 keV W+ ions) were carried out as a complement to the bulk implantations. Qualitative trends in loop size, geometry and nature with irradiation dose and temperature were similar to bulk irradiated specimens. Also, the dynamics of defects and their effects on the damage evolution were explored. In-situ annealing of irradiated thin foils was performed to investigate the thermal stability of radiation damage in tungsten. The majority of microstructure transformations were completed within 15 min of annealing. However, extended durations did favour the increase of loop size and the fraction of ½<111> loops.

This thesis describes the design, manufacture and characterisation of thick vacuum plasma sprayed tungsten (W) coatings on steel substrates. Fusion is a potentially clean, sustainable, energy source in which nuclear energy is generated via the release of internal energy from nuclei. In order to fuse nuclei the Coulomb barrier must be breached - requiring extreme temperatures or pressures – akin to creating a ‘star in a box’. Tungsten is a promising candidate material for future fusion reactors due to a high sputtering threshold and melting temperature. However, the large coefficient of thermal expansion mismatch with reactor structural steels such as the low activation steel Eurofer’97 is a major manufacturing and in-service problem. A vacuum plasma spraying approach for the manufacture of tungsten and tungsten/steel graded coatings has been developed successfully. The use of graded coatings and highly textured 3D interface surfi-sculpt substrates has been investigated to allow the deposition of thick plasma sprayed tungsten coatings on steel substrates. Finite element models have been developed to understand the residual stresses that develop in W/steel systems and made use of experimental measurements of coating thermal history during manufacture and elastic moduli measured by nano-indentation. For both the graded and surfi-sculpt coating, the models have been used to understand the mechanism of residual stress redistribution and relief in comparison with simple W on steel coatings, particularly by consideration of stored strain energy. In the case of surfi-sculpt W coatings, the patterned substrate gave rise to regular stress concentrating features, and allowed 2mm thick W coatings to be produced reproducibly without delamination. Preliminary through thickness residual stress measurements were compared to model predictions and provided tentative evidence of significant W coating stress relief by regulated coating segmentation.

There is a considerable interest in the use of tungsten oxide in the research and development of new materials and devices, such as gas sensors and as photocatalysts. In order to improve the photocatalytic properties of WO3, its combination with metals which allows the preparation of WMxOy materials are believed to be promising photocatalysts under visible light. The present work deals with the synthesis of homo- and hetero-metallic tungsten alkoxide and amide compounds using the single source precursor approach for potential chemical vapour deposition precursors of mixed-metal oxide films.

The unusual combination of extreme properties possessed by diamond could potentially benefit a wide range of applications. Thus far practical utilisation of this material has remained difficult and consequently limited; natural and synthetic crystals are unsuitable forms for many uses, particularly electronic applications which ideally require large area, single crystal substrates. Emerging CVD methods for the growth of thin film diamond offer a practical alternative; although nucleation on non-diamond substrates during CVD growth is in general poor, recently introduced negative substrate biasing has shown that very high nucleation densities and limited forms of heteroepitaxy can be achieved. However, although development has been rapid many problems remain; in particular, the underlying mechanisms of biased nucleation and growth on non-diamond substrates are not well understood. Furthermore, the successful development of a new material such as CVD diamond relies on a balance between fundamental research and exploitation of its benefits in the form of applications; at present there are only a few such examples for CVD diamond. This thesis addresses these issues by considering the bias enhanced nucleation of CVD diamond on silicon and tungsten substrates together with a study of the acoustic properties of the material. Bias enhanced nucleation and growth of (100) diamond on tungsten substrates has been characterised using secondary electron microscopy and Raman spectroscopy. Optical emission spectroscopy has been used to study the influence of substrate bias on the microwave plasma during diamond nucleation. Surface acoustic wave (SAW) devices have recently emerged as promising near term applications for currently available CVD diamond, however little is known about the propagation of acoustic waves in this material. A detailed study of the influence of film characteristics on acoustic propagation in free standing CVD diamond films has been undertaken using the techniques of laser ultrasonic analysis.

The high spin structure of the nucleus 178W has been studied, at the Australian National University, with the 170Er(13C,5n) reaction at 80 MeV. Many previously unidentified rotational bands are seen based on high-K, 2, 4, 6 and 8-quasiparticle structures, some of which are isomeric. This is the first identification of rotational bands based on 8-quasiparticle states. The excitation energies of the multiquasiparticle bandheads are compared with BCS calculations, including residual interactions. The bands show substantial increases in moments-of-inertia with increasing quasiparticle number. These are examined in terms of pairing blocking. The effect of blocked pairing is also taken into account in the calculation of g-factors, which supports the configuration assignments. The Kpi = 25+, eight-quasiparticle band forms the yrast line from its bandhead upwards. This bandhead is a 220 ns isomer whose decay is strongly hindered, compared to the decay of the four- and six-quasiparticle structures.