Spin-labeling techniques, specifically the use of electron-spin-polarized He(2 3S) metastable atoms coupled with energy-resolved spin analysis of the product electrons, are used to investigate the dynamics of Penning ionization in collisions between He(2 3S) atoms and H2O, SO2, NO, and NO2. The data complement earlier studies of the reaction dynamics based on analysis of the energy distribution of the product electrons and confirm that ionization can occur via a number of different reaction channels. For example, the present results show that in collisions with targets having a positive electron affinity, ionization via the ionic channel is important and that effects due to spin-orbit coupling must be considered. The data also provide evidence that exchange may be important in collisions with open-shell targets.

The rate coefficients for mixing between He(2 P-3(J,MJ)) levels during collisions with ground-state helium atoms and for conversion of He(2 P-3(J)) atoms to He-2(b 3PI(g)) molecules via three-body reactions in helium gas have been investigated over the temperature range 1.6-300 K. The measured rate coefficients for collisionally induced P-state mixing decrease slowly with decreasing temperature, from (1.8 +/- 0.5) X 10(-9) cm3 s-1 at 300 K to (4.5 +/- 0.5) X 10(-10) cm3 s-1 at 4.2 K. The rate coefficients for the production of He-2(b 3PI(g)) molecules via three-body reactions are observed to increase with decreasing temperature and are described by the relation k(p) congruent-to (2.5 + 267T-1) X 10(-32) cm6 s-1. This behavior, which is very different from that noted in earlier studies of the conversion of He(2 S-3(1)) atoms to He-2(a 3SIGMA(u)+) molecules through three-body reactions, suggests that the reaction is not thermally activated.

A magneto-optical trap for He(2{sup 3}S) metastable atoms has been constructed, utilizing superconducting magnetic gradient coils and a Ti:Sapphire ring laser for pumping the helium 2{sup 3}S-2{sup 3}P transition. The He(2{sup 3}S) atoms are produced by a weak rf discharge in helium gas at a temperature of 1.4K. The discharge products flow through a small orifice into the trap cell, where a fraction of the He(2{sup 3}S) atoms are trapped and ground state helium atoms are rapidly cryopumped by zeolite pellets that cover most of the cell bottom. Preliminary experiments suggest that {approximately}10{sup 6} atoms are trapped in a small volume at {approximately}1 mK, with a trap lifetime of 10-100 msec limited by resonantly-enhanced He(2{sup 3}S)-He(2{sup 3}P) Penning reactions. Ultimately, it is estimated that a substantial number of atoms can be held at ultra-low temperature in near-perfect vacuum, in a dc magnetic trap. Measurements of decay times of the trapped atoms should yield rate coefficients in the quantum regime for He(2{sup 3}S)-He(2{sup 3}P) and He(2{sup 3}S)-He(2{sup 3}S) Penning reactions, and perhaps the He(2{sup 3}S) radiative lifetime.

A magneto-optical trap for He(2{sup 3}S) metastable atoms has been constructed, utilizing superconducting magnetic gradient coils and a Ti:Sapphire ring laser for pumping the helium 2{sup 3}S-2{sup 3}P transition. The He(2{sup 3}S) atoms are produced by a weak rf discharge in helium gas at a temperature of 1.4K. The discharge products flow through a small orifice into the trap cell, where a fraction of the He(2{sup 3}S) atoms are trapped and ground state helium atoms are rapidly cryopumped by zeolite pellets that cover most of the cell bottom. Preliminary experiments suggest that {approximately}10{sup 6} atoms are trapped in a small volume at {approximately}1 mK, with a trap lifetime of 10-100 msec limited by resonantly-enhanced He(2{sup 3}S)-He(2{sup 3}P) Penning reactions. Ultimately, it is estimated that a substantial number of atoms can be held at ultra-low temperature in near-perfect vacuum, in a dc magnetic trap. Measurements of decay times of the trapped atoms should yield rate coefficients in the quantum regime for He(2{sup 3}S)-He(2{sup 3}P) and He(2{sup 3}S)-He(2{sup 3}S) Penning reactions, and perhaps the He(2{sup 3}S) radiative lifetime.

Spin-labeling techniques, specifically the use of electron-spin-polarized He(2(3)S) metastable atoms coupled with energy-resolved spin analysis of the product electrons, are used to investigate the dynamics of Penning ionization in collisions involving He(2(3)S) atoms. Results obtained using CO2, CO, Cl2, and O2 target gases are presented that illustrate the capabilities of this approach. In particular, the data for Cl2 and O2 confirm that ionization via ionic channels is important and show that exchange and spin-orbit effects must be considered.

The later history of expanded spherulites (thunder eggs), as disclosed by the minerals found within their central cavities, is interpreted as due to three distinct generations of crystallization. The first, consisting of a lining of chalcedony, was based on residual silica within the cavity after the crystallization of the feldspar‐cristobalite cover. The second, in the shape of chalcedonic plates and associated drusy quartz, was due to the migration of silica from the immediately adjacent lava, aided by the diminution of the internal pressure which had given rise to the expansion of the spherulite. The third followed the introduction from purely external and, possibly distant sources, of solutions bearing quartz (in large quantities), calcite, haematite and (rarely) laumontite.

THE purpose of this note is to direct attention to a concept in soil science for which we propose the term 'pedogenic inertia'. This is the concept that a process in soil formation, once established, may continue in spite of changes in the environment to conditions which apparently are not normally favourable to this process. The argument may be stated as follows.

The Skeleton of the Hexaeoralla.III

The object of this paper is to bring before the notice of those interested a number of examples of spherulitic structures which seem to throw some light on the nature of the processes by which spherulites, lithophysae, and pyromerides are formed.

AbstractTHIS paper describes the occurrence in Queensland of a large mass of limestone of late Palaeozoic age made up almost entirely of the microscopic remains of calcareous algae.

IN view of the diverse opinions held by pedologists as to the occurrence of laterites in extra-tropical regions, I wish to direct attention to what I regard as a true laterite in Southern Queensland.

Over the last few decades geophysics has become firmly established as a vital component of modern exploration programmes for metals and minerals. The new frontier of geophysics is the mine site. Geophysics now offers a means for more cost-effective ore body delineation and rock mass characterisation during resource definition, mine development, and production. Geophysical methods can be divided into two broad categories: logging and imaging. Logging systems record in situ phys- ical properties of the borehole wall rocks, while geophysical imaging techniques can map features at tens or hundreds of metres from the sensors. Imaging methods are predominant in exploration, but logging is well suited to resource definition and mining given the high spatial density of holes and the need for detailed information. Density, natural gamma radia- tion, magnetic susceptibility, and conductivity are the principal in-mine logging parameters because they can be recorded in both dry and water-filled holes. Sonic velocity is the premier geotechnical logging parameter, given its sensitivity to rock strength, stress, porosity, and degree of fracturing. Conventional downhole EM and borehole magnetics are used for near-mine exploration, but the higher resolution offered by seismic, radio imaging, and radar is usually necessary to effectively delineate ore bodies and map structures, or to geo- technically characterise the rock mass and identify hazards. Imaging methods can be applied in open pits, or underground from individual holes, between holes, or from hole to mine opening. Geophysics is already playing an important role in a number of metalliferous mines around the world, especially for ore boundary delineation, delivering benefits measured in millions of dollars per year in some cases. The benefit may be direct, e.g. as savings from substitution of core drilling with percussion drilling plus borehole logging, or it may be indirect, e.g. in the form of reduced dilution arising from a more accurate mine model. There is potential for the role of geophysics to expand into automated geological logging, blasting optimisation, and grade estimation. During resource definition and mine development, an appropriate combination of surface and crosshole imaging and borehole logging sometimes has the potential to delineate and geotechnically characterise the ore and host rocks in three (or four) dimensions. Interpretation of the geophysical data in conjunction with all existing geological and geotechnical information can provide a firmer basis for major design and development decisions. Appropriately applied, geophysics can reduce uncertainty in mine design and production, thereby enhancing safety, lower- ing costs, and increasing revenue. The greatest impediment to expanded use of geophysics at mines, however, is the low level of awareness of geophysics on the part of most mine geologists, engineers, and managers. Integration of geophysics with drilling will be a key innovation during the next ten years, guaranteeing access to all holes, simplifying logistics, and eliminating the delay between drilling and interpretation. Measurement-while-drilling technol- ogy, used in drill performance monitoring, represents a source of geotechnical information. Slimline logging-while-drilling technology for delivery of petrophysical and imaging data is in its infancy. Interfacing geophysical modelling and imaging software with mine modelling systems will expedite integrated interpretation of all data. These developments, in combina- tion with other technologies such as high bandwidth communications, will usher in a new paradigm in mining, character- ised by vastly higher information flows and substantially lower risk factors.