X-ray Standards

A new free-air ionization chamber has been built to eventually replace the Wyckoff-Attix chamber, which has been used at NIST as a primary x-ray standard for more than fifty years.

A new free-air ionization chamber has been built to eventually replace the Wyckoff-Attix chamber, which has been used at NIST as a primary x-ray standard for more than fifty years to realize air kerma for x-ray beams of 50 kV to 300 kV. The dimensions and the parallel-plate design of the new chamber are identical to those of the Wyckoff-Attix chamber, but the materials are different. The chamber incorporates a unique guard bar and insulator design, and precision slides facilitate alignment and direct measurement of the air-attenuation correction. The new standard will undergo a full evaluation in a parallel measurement arrangement with the current standard.