We have designed, fabricated, and field-tested a new, unique, monostatic, broadband, electromagnetic sensor for subsurface geophysical investigation. The sensing unit consists of a pair of concentric, circular coils that transmit a continuous, broadband, digitally-controlled, electromagnetic waveform. The two transmitter coils, with precisely computed dimensions and placement, create a zone of magnetic cavity (viz., an area with a vanishing primary magnetic flux) at the center of the two coils. A third receiving coil is placed within this magnetic cavity so that it senses only the weak, secondary field returned from the earth and buried targets.This monostatic configuration has many advantages including (1) compact sensor head, (2) a large transmitter moment, (3) high spatial resolution, (4) no spatial distortion of an anomaly common to bistatic sensors, (5) circular symmetry that greatly simplifies mathematical description, and, therefore, (6) simplified forward and inverse modeling processes. Three prototype GEM-3 units have been built and tested at various environmental sites, including those containing unexploded ordnance and land mines.

The exposure characteristics of six polymer resists to 1.5 MeV H+, He+, and O+ ions and to 20 keV electrons were measured. The resists used were polystyrene (PS), polymethyl methacrylate (PMMA), PMMA mixed with 20% of a copolymer of vinyl acetate and vinyl chloride (VMCC), poly(glycidyl methacrylate-co-3-chlorostyrene) (GMC), poly(butene-1-sulfone) (PBS), and a novolac. The deposited energy per unit volume required to expose a resist was found to be a function of the spatial energy dissipation rate of the ion in the resist. This has been accounted for in terms of the nature of the energy distribution around the primary particle track in conjunction with whether the resist requires the activation of a single site or two adjacent sites to produce exposure.

We have measured the superfluid density of 3He liquid confined within the pores of a silver sinter plug. The silver was of nominal 70 nm size, and was packed to 54% of solid density. The mean pore size as measured was ∼200 nm. The plug was mounted on a torsional oscillator, and the superfluid density can be measured by studying the decrease of the resonant period. We have measured the pressure and temperature dependence of the period shift and find that the superfluid density is suppressed to ∼14% at 0 bar and is ∼53% of its bulk value at 29 bar. There is substantial temperature dependence even at the lowest values of T/T c (∼0.25) achieved in these experiments.

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