Electrolytic preparation of isotopically enriched hard chromium layers on gold backings for nuclear reaction studies

Batch electrodeposition based on very dilute (0.14 M) hexavalent chromium electrolyte (2 mL) was optimized in order to produce thin isotopically enriched (e.g., exp 50 Cr) hard chromium layers on gold backings for use as targets in charged particle irradiations at accelerators. Deposition parameters were systematically investigated. The enriched chromium layers achieve a thickness of about 6 mu m after 10 min of electrolysis. The chromium contents of both the deposit and the electrolyte were determined via UV-photometric Cr exp VI analysis in acid media. A pH range between 1 and 4 gives an absorption plateau for the two peaks at 257 and 348 nm of acid chromate, thus allowing a precise chromium determination without an exact pH adjustment. Gravimetrically determined deposition yields, especially for long deposition times, were found to differ significantly from the photometrically determined yields. The kinetics of development of the disturbing Cr exp III content in the electrolyte was investigated using high performance liquid chromatography-based ion-chromatography. The trivalent species was found to accumulate, reaching an absolute maximum of about 10% after 15 min. A chemical pathway is described to produce and to reprocess the hexavalent electrolyte.