Soft x-ray spectroscopy in atmospheric pressure helium

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Abstract
We report on an environmental chamber, which is attached to a UHV beamline, in which soft x‐ray measurements can be done at atmospheric pressure in helium. X‐ray measurements in air can only be performed at energies above about 3 keV because of the strong absorption of soft x rays by oxygen and nitrogen. However, a low‐Zscatterer such as helium has a long absorption length for soft x rays even at atmospheric pressure. Thus, this new chamber allows soft x‐ray experiments to be performed on samples with physical properties that are incompatible with UHV conditions, e.g., liquid and frozen aqueous solutions, corrosivematerials, etc. A helium‐tight tank has been installed behind the vacuum experimental chamber of the double crystal beamline 3.4 at the Daresbury SRS. The tank is purged with helium at atmospheric pressure and the gas in the tank is isolated from the high vacuum of the rest of the beamline by a thin mylar window which is supported on a capillary array. The tank contains a sample stage, two ionization chambers and a parallel‐plate gas proportional counter for fluorescence detection of dilute samples, which has produced good results on the K edges of Cl, S, and P.

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