The right of a person to a retirement allowance or to the return of contributions, a retirement allowance itself, any optional allowance or payment on death, or any other right accrued or accruing to any person under this chapter and the moneys of the system are exempted from any state or municipal tax; are exempted from levy and sale, garnishment, attachment, or any other process whatsoever; and shall be unassignable except as otherwise specifically provided for in this chapter.