Applications of laser produced continuum radiation

High density high temperature plasmas produced m the foci of powerful pulsed laser beams have many applications and have been the subject of intensive investigations since high power lasers first became available. The work described in this thesis is iargly concerned with one particular application of laser generated plasmas that of photoabsorption spectroscopy of ionized species. The first chapter provides an introduction to the subject by reviewing the work done to date in this area and the various techniques which have been used to obtain absorption spectra. The usefulness of results obtained from VUV absorption spectra is also dealt with Recent work on the laser produced continuum source and the various applications which the source has found is also reviewed. A detailed description of the experimental method used to create two laser produced plasmas on separate targets and study the resulting absorptfon spectrum which is observed when continuum radiation emitted from one plasma is absorbed by the second plasma is given. New absorption spectra of magnesium aluminium and silicon plasmas are discussed and results are presented for the third fourth and fifth members of the neon-like isoeiectronic sequence Mg Hi Ai IV and Si V. The VUV absorption spectra of these ions have been recorded in the wavelength range 250 - 60A. This is the first recorded observation of absorption features along an extended isoeiectronic sequence. The wavelengths of the principal 2 s 22p 6 XS 0 - 2 s 2 2p sns nd transitions have been measured. Also the autoionizing levels due to inner 2s shell excitation 2s 22p6 1 S 0 - 2s 2p6np1 P 1 have been recorded and wavelengths for these features are given. Many new lines particularly in the spectra of aluminium and silicon plasmas are reported in this work for the first time. Extensive atomic structure calculations have been carried out In an attempt to assign these features. Calculations have also been carried out for the autoionizing levels of the neon-like sequence from Na II to Si V. The Xenon isoeiectronic sequence has also been studied m absorption and results are presented for the absorption spectrum of a lanthanum plasma. The 4d photoabsorption spectrum of La IV has been recorded for the first time in this work and this spectrum is discussed in terms of the previously observed 4d photoabsorption spectrum of Ba III. Progress on the evaluation of neutron scintillating glasses as new detector materials for the VUV spectral region is reported m Appendix 1 "I his application of laser produced conlinua is discussed and tentative results for cerium doped glass scintillators are presented. in Appendix 2 computer programs written over the course of this work are described. Examples of input and output data are given

XUV photoabsorption studies along extended isoelectronic sequences using a dual laser produced plasma techniques

Hot dense plasmas produced when the output of powerful pulsed laser systems are focused onto targets located in vacuum have been the subject of extensive study for a number of years. Such plasmas have found applications both as intense sources of continuum radiation in the XUV and as a versatile source of ionic species. In the work reported here the above properties of the laser produced plasma were exploited and enabled many new photoabsorption spectra of ionic species to be recorded in the XUV region. Using a dual laser produced plasma technique the XUV radiation emitted from laser plasmas created on the surface of a high Z material was used to backlight a second laser plasma and carry out ionic photoabsorption studies at wavelengths below 300A. An extensive examination of a number of isoelectronic sequences was undertaken. XUV photoabsorption studies were carried out on members of the neon, sodium, argon, krypton, bromine, selenium and xenon sequences. Absorption along the neon like sequence was extended to the fifth member, Si V. We report here the first unambiguous photoabsorption spectrum of the neon like A1 ion showing the principal outer shell transitions together with 2s inner shell autoionizing features. Detailed XUV photoabsorption spectra of the Si4+ ion are reported here for the first time, excitations involving an inner 2s electron were classified and m the case of the 2s-»3p transition found to be an example of forced autoionization. An intensity anomaly in the Beutler Fano line shape of the 2s->3p member of the autoionizing series 4 in Si was studied with varying plasma conditions. Absorption studies along the sodium isoelectronic sequence have resulted in the classification of new lines arising from transitions to core excited autoionizing 2 3 levels in the A1 and Si ions, transitions from ground and excited states were observed. XUV photoabsorption spectra of plasmas formed on targets of elements following argon (scandium and titanium) in the periodic table were found to be of a complex nature and to contain contributions from a number of different ion stages. Elements following krypton were also studied. Absorption spectra of laser produced plasmas formed on targets of strontium, yttrium and zirconium were recorded. The strontium and yttrium work resulted m 3d->4p transitions being observed m a number of ion stages for the first time. Work along the xenon sequence was found to be in 2 agreement with previous Ba observations Absorption studies along the sequence were extended to the fifth member Ce4+. An extensive analysis of the 4d photoabsorption spectrum of La was carried out and revealed that the 4d-»4f transition, expected to be the strongest was not observed. The interpretation of the spectrum showed that the feature possessed a large autoionization width and was not present m the experimental spectrum. The analysis further confirmed 2 that the 4f wave function m Ba is only partially collapsed. The work reported here has clearly shown the dual laser produced plasma technique to be a powerful and versatile method for recording XUV photoabsorption spectra of ionized species

Rise and fall of the 4d¹⁰→4d⁹4f resonance in the Xe isoelectronic sequence

The extreme ultraviolet photoabsorption spectrum of a laser-produced lanthanum plasma has been recorded and found to contain a number of discrete features in the 130-eV region. These have been analyzed as 4d10→4d9nf,np transitions in La3+. We show that the 4f transition, which is expected to be the strongest, is not in evidence. The reason is that this resonance, after the collapse of the 4f wave function, has a large autoionization width. We conclude that the 4f orbital in Ba2+ is only partially collapsed, which settles a long-standing discussion of this point

Twenty-three unsolved problems in hydrology (UPH) – a community perspective

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through on-line media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focussed on process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come

Twenty-three unsolved problems in hydrology (UPH) – a community perspective

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through online media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focused on the process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come

Twenty-three unsolved problems in hydrology (UPH) – a community perspective

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through online media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focused on the process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come

Twenty-three unsolved problems in hydrology (UPH) – a community perspective

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through online media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focused on the process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come

Chromium contamination and its risk management in complex environmental settings

Chromium reaches the soil environment through waste disposal emanating from a number of industrial activities, including coal-fired power production, electroplating, leather tanning, timber treatment, pulp production, and mineral ore and petroleum refining. Of the heavy metals, chromium (Cr) is a major pollutant, poses a great threat to flora and fauna and persists for long time. The most abundant species of Cr—Cr(III) and Cr(VI)—have very different properties. The toxicity, mobility, and bioavailability of Cr mainly depend on its speciation. In the natural environment, Cr(III) is most immobile, less soluble and stable, whereas Cr(VI) is highly mobile, soluble and bioavailable. Redox reactions play an important role in the interconversion of Cr(VI) and Cr(III). As our awareness of the rising toxicity of Cr increases, it is necessary to develop new and advanced strategies to mitigate this toxicity in the environment. Several physicochemical methods have been developed but these techniques are expensive and are not readily applicable to large contaminated zones. This chapter provides an overview of the concepts of Cr biogeochemistry, bioavailability and integrated risk management. The physicochemical factors, speciation and toxicity have been discussed with special emphasis on the remediation methods due to the complex reactions associated with Cr toxicity mitigation. Furthermore, this study identified systematically the future needs for understanding Cr biogeochemistry and low-cost remediation methods

Twenty-three unsolved problems in hydrology (UPH)–a community perspective

This paper is the outcome of a community initiative to identify major unsolved scientific problems in hydrology motivated by a need for stronger harmonisation of research efforts. The procedure involved a public consultation through online media, followed by two workshops through which a large number of potential science questions were collated, prioritised, and synthesised. In spite of the diversity of the participants (230 scientists in total), the process revealed much about community priorities and the state of our science: a preference for continuity in research questions rather than radical departures or redirections from past and current work. Questions remain focused on the process-based understanding of hydrological variability and causality at all space and time scales. Increased attention to environmental change drives a new emphasis on understanding how change propagates across interfaces within the hydrological system and across disciplinary boundaries. In particular, the expansion of the human footprint raises a new set of questions related to human interactions with nature and water cycle feedbacks in the context of complex water management problems. We hope that this reflection and synthesis of the 23 unsolved problems in hydrology will help guide research efforts for some years to come