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 e lectrolyte (2 mt) was optimized in order to produce thin isotopically enric hed (e.g., Cr-50) hard chromium layers on gold backings for use as targets in charged particle irradiations at accelerators. Deposition parameters wer e systematically investigated. The enriched chromium layers achieve a thick ness of about 6 mu m after 10 min of electrolysis. The; chromium contents o f both the deposit and the electrolyte were determined via W-photometric Cr -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. Gravimetr ically determined deposition yields, especially for long deposition times, were found to differ significantly from the photometrically determined yiel ds. The kinetics of development of the disturbing Cr-III content in the ele ctrolyte was investigated using high performance liquid chromatography-base d ion-chromatography. The trivalent species was found to accumulate, reachi ng an absolute maximum of about 10% after 15 min. A chemical pathway is des cribed to produce and to reprocess the hexavalent electrolyte. (C) 1999 The Electrochemical Society. S0013-4651(99)01-063-0. All rights reserved.