Amounts deducted and withheld from the basic pay of a participant under this section for pay periods after the first day of the first pay period beginning after the day on which the participant completes 35 years of creditable service computed under sections
2081 and
2082 of this title (excluding service credit for unused sick leave under section
2031
(a)(2) of this title) shall accrue interest. Such interest shall accrue at the rate of 3 percent a year through December 31, 1984, and thereafter at the rate computed under section
8334
(e) of title
5, and shall be compounded annually from the date on which the amount is so deducted and withheld until the date of the participant’s retirement or death.