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 the provisions of this chapter, and the monies of the system are exempted from state or municipal tax, except the taxes imposed pursuant to Chapters 7, 15, and 16 of Title 12, and exempted from levy and sale, garnishment, attachment, or any other process and are unassignable except as otherwise provided in this chapter.