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The aim of this work is to design and build a source for a range of applications, with optimized multilayer structures in order to use the source output as efficiently as possible. The source is built around a Nd:YAG laser with fundamental wavelength 1064 nm, frequency doubled 532 nm (green) and tripled 355 nm, with a pulse length of about 800 ps and a repetition rate up to 50 Hz. The target material is Mylar (C 10 H 8 O 4 ) tape, which is cheap, readily available and has many benefits as explained in this article. A versatile cubic target chamber and a set of computer controlled stage motors are used to allow positioning of the X-ray emission point. A range of measures is used to protect delicate components and optics, including a glass slide between the focusing lens and the target to prevent the lens being coated with debris. A low pressure gas (typically 3-6 mbar) is used inside the chamber as collision of atomic size debris particles with gas molecules reduces their kinetic energy and consequently their adhesion to the surrounding surfaces. The gas used is typically helium or nitrogen, the latter also acting as a spectral filter. Finally, the chamber is continually pumped to ensure that more than 70% of the debris particles are pumped out of the chamber.

Filter samples of atmospheric aerosol were collected daily at a city and a rural site over an extended period. The filters were processed in an environment supersaturated with respect to ice in order to activate ice nuclei. The concentration of nuclei detected at the two sites was compared with reference to the local weather and air-mass trajectories. The city environment generally has a larger ice nucleus concentration than the rural site. However. fluctuations in the concentrations at the two sites are usually in phase. indicating a pre-dominantly common origin. With air-mass trajectories over industrial regions. the nucleus concentration is increased. Local weather has a profound etTect; in particular. rain and snow cause substantial reductions in ice nucleus concentration.

Filter samples of atmospheric aerosol were collected daily at a city and a rural site over an extended period. The filters were processed in an environment supersaturated with respect to ice in order to activate ice nuclei. The concentration of nuclei detected at the two sites was compared with reference to the local weather and air‐mass trajectories. The city environment generally has a larger ice nucleus concentration than the rural site. However, fluctuations in the concentrations at the two sites are usually in phase, indicating a pre‐dominantly common origin. With air‐mass trajectories over industrial regions, the nucleus concentration is increased. Local weather has a profound effect; in particular, rain and snow cause substantial reductions in ice nucleus concentration.

No abstract