The widow's annuity and widow's prior service annuity for the wife of an employee who withdraws after service of 10 or more years before age 50, and later attains such age and dies while out of service, shall be fixed as of her age at the time the employee becomes age 50. She shall receive annuity, from the date of the employee's death, of such amount as can be provided on a reversionary annuity basis from the following sums accumulated to his credit on the date the annuity was fixed:
40 ILCS 5/6-135