20 CFR 216.52: Who is eligible for an annuity as a divorced spouse.

To be eligible for a divorced spouse annuity, the employee annuitant must be at least age 62 and the divorced spouse (see § 222.22 of this chapter) must:

(a) Be the divorced wife or husband of an employee;

(b) Stop work for a railroad employer;

(c) Not be entitled to an old-age or disability benefit under the Social Security Act based on a primary insurance amount that is equal to or greater than one-half of the employee's tier I primary insurance amount; and either

(d) Have attained retirement age; or

(e) Have attained age 62 but be under retirement age. The annuity is reduced for each month the spouse is under retirement age at the time the annuity begins.