On 1852 October 16th British Gold Sovereigns and Half Sovereigns were legalised for use in Ceylon by Proclamation of Queen Victoria. It was revoked by proclamation on 1869 June 18th with the introduction of Decimal curreny for Ceylon.
Note that Shield type Half Sovereigns were Minted in Royal Mint in London, from 1838 to 1885. The coins minted between 1863 and 1880 has the die number on reverse, at the bottom of the coin just above the rose. and known as Type 1B. Other years without die number known as Type 1A. Half Sovereigns minted before 1852 would have been legal tender in Ceylon during the years from 1852 to 1869.
See discussion in Sovereign coin
Ref: The Gold Sovereign. by M. A. Marsh.
1999, Cambridge U.K., 2nd ed. 118pp. Illustr. colour
The Half Sovereign was scanned at 600 dpi and displayed at 300 dpi It was obtained in USA around 2000.