A State or local government employee who is given an appointment in a Federal agency for the period of the assignment or who is on detail to a Federal agency and who suffers disability or dies as a result of personal injury sustained while in the performance of his duty during the assignment shall be treated, for the purpose of subchapter I of chapter 81 of this title, as though he were an employee as defined by
section 8101 of this title who had sustained the injury in the performance of duty. When an employee (or his dependents in case of death) entitled by reason of injury or death to benefits under subchapter I of chapter 81 of this title is also entitled to benefits from a State or local government for the same injury or death, he (or his dependents in case of death) shall elect which benefits he will receive. The election shall be made within 1 year after the injury or death, or such further time as the Secretary of Labor may allow for reasonable cause shown. When made, the election is irrevocable unless otherwise provided by law.