An energy tunable continuous 23S1 positronium beam.

We describe the experimental production of a beam of 23S1 positronium (Ps) atoms obtained from charge-exchange collisions between a positron beam and Xe held in a gas cell. The angular divergence of the emitted Ps beam was recorded using two position sensitive detectors located at different distances from the gas cell. The fraction of the Ps beam produced in the 23S1 level was measured via the change in the Ps count rate after driving the 23S1 → 23P2 transition with microwave radiation; with optimal experimental parameters, we estimate that up to 10% of the Ps beam is formed in the 23S1 state.

Precision Microwave Spectroscopy of the Positronium 2 ^{3}S_{1}→2 ^{3}P_{2} Interval.

We report the results of a new measurement of the positronium 2 ^{3}S_{1}→2 ^{3}P_{2} (ν_{2}) interval. Using a modified experimental arrangement we have significantly reduced the effects of microwave reflections, which in previous experiments resulted in shifts and asymmetric line shapes. With the improved apparatus we obtain an experimental value of ν_{2}=8627.

Precision Microwave Spectroscopy of the Positronium n=2 Fine Structure.

We report a new measurement of the positronium (Ps) 2^{3}S_{1}→2^{3}P_{0} interval. Slow Ps atoms, optically excited to the radiatively metastable 2^{3}S_{1} level, flew through a microwave radiation field tuned to drive the transition to the short-lived 2^{3}P_{0} level, which was detected via the time spectrum of subsequent ground state Ps annihilation radiation. After accounting for Zeeman shifts we obtain a transition frequency ν_{0}=18501.

Positron scattering from pyridine.

We present a range of cross section measurements for the low-energy scattering of positrons from pyridine, for incident positron energies of less than 20 eV, as well as the independent atom model with the screening corrected additivity rule including interference effects calculation, of positron scattering from pyridine, with dipole rotational excitations accounted for using the Born approximation. Comparisons are made between the experimental measurements and theoretical calculations. For the positronium formation cross section, we also compare with results from a recent empirical model.

Near-Threshold Ionization of Argon by Positron Impact.

The direct single-ionization cross section for Ar by positron impact has been measured in the region above the first ionization threshold. These measurements are compared to semiclassical calculations which give rise to a power law variation of the cross section in the threshold region. The experimental results appear to be in disagreement with extensions to the Wannier theory applied to positron impact ionization, with a smaller exponent than that calculated by most previous works.

Radiofrequency dosimetry for the Ferris-wheel mouse exposure system.

Numerical and experimental methods were employed to assess the individual and collective dosimetry of mice used in a bioassay on the exposure to pulsed radiofrequency energy at 900 MHz in the Ferris-wheel exposure system (Utteridge et al., Radiat. Res.

Noninvasive measurement of current in the human body for electromagnetic dosimetry.

Minimally perturbing, resistive, nonferrous probes were developed for noninvasively measuring hazardous currents induced in the human body by electromagnetic fields at 1 to 200 MHz. Each probe has a resistive toroidal coil that is placed around the leg or other body member. An electrostatic shield is required to limit capacitive coupling.

Evaluation of heating patterns of microwave interstitial applicators using miniature electric field and fluoroptic temperature probes.

The SAR patterns were determined for four commercially available microwave (915 MHz) interstitial applicators. Values of SAR were determined using a miniature (3 mm diameter) implantable isotropic electric field probe or a custom 0.25 mm diameter fluoroptic temperature probe.

Interstitial microwave hyperthermia applicators having submillimetre diameters.

Using microscopic techniques we have fabricated interstitial hyperthermia applicators having diameters of 0.20, 0.33 and 0.

Preclinical evaluation of submillimeter diameter microwave interstitial hyperthermia applicators.

Ultra miniature coaxial cable has been used, with microscopic techniques, to fabricate interstitial hyperthermia applicators having diameters of 0.20 mm, 0.33 mm, and 0.