Material Studies to Reduce the Tritium Memory Effect in BIXS Analytic Systems

Beta-induced X-ray spectrometry (BIXS) is a promising method for activity monitoring of tritiated gas species. BIXS systems measure bremsstrahlung and characteristic X-rays generated by interactions of beta decay electrons with surfaces within the measurement chamber. BIXS and other highly sensitive methods such as ionization counting are limited in accuracy by the tritium memory effect, a preconditioning dependent background signal caused by the sorption of tritium on surfaces. In this work, different surface materials have been investigated aiming at reducing the tritium memory effect while providing a high bremsstrahlung yield. A modular BIXS setup was developed that allows the consecutive investigation of different measurement cells utilizing the same detector while protecting it from contamination during cell exchanges. An uncoated stainless steel cell was compared to cells coated with Au, Ir, Ti-W, Ti-Au-Al, and Ti-Au-Cu layer systems. The sample cells were repeatedly exposed to 1100 Pa of molecular tritium. The development of the resulting memory effect was measured during the evacuation between consecutive exposures. Additionally, the background signal decay was investigated in a long-term measurement after the last exposure. In this presentation, the measurement results of the relative tritium memory effect from various surfaces will be shown. The lowest memory effect was measured for the gold-coated sample cell, reaching a background signal equal to (0.83 ± 0.14)% of the signal during exposure after a total dosage of 21.33 × 10⁴ Pa h.