97A.6A  Optional retirement benefits.
  In lieu of the retirement benefits otherwise provided upon service retirement for members of the system and the members’ beneficiaries, members may elect to receive an optional retirement benefit during the member’s lifetime and have the optional retirement benefit, or a designated fraction of the optional retirement benefit, continued and paid to the member’s beneficiary after the member’s death and during the lifetime of the beneficiary.
  The member shall make the election request in writing to the board of trustees at the time of the member’s service retirement. The election is subject to the approval of the board of trustees. If the member is married, the election of an option under this section requires the written acknowledgment of the member’s spouse.
  A member’s optional retirement benefits shall be the actuarial equivalent of the amount of the retirement benefits payable to the member and the member’s beneficiaries under the service retirement provisions of this chapter. The actuarial equivalent shall be based on the mortality and interest assumptions set out in section 97A.5.
  If the member dies without a beneficiary prior to receipt in benefits of an amount equal to the total amount remaining to the member’s credit at the time of separation from service, the election is void.
  If the member dies with a beneficiary and the beneficiary subsequently dies prior to receipt in retirement benefits by both the member and the beneficiary of an amount equal to the total amount remaining to the member’s credit at the time of separation from service, the election remains valid.
  For the purpose of this section, “beneficiary” means a spouse, child, or a dependent parent.
90 Acts, ch 1240, §10