The Senate has become increasingly vocal about alleged Chinese spying at the Los Alamos National Laboratory (see PhysicsWeb 28 May) and has argued for increased security at the nuclear weapons labs. Bethe - who was also in charge of the Manhattan bomb-project's theoretical physics division - and the other authors of the letter point out that ratifying the CTBT would be more likely to increase US security.

They say that any country developing an atomic weapon would still have to test it, and the CTBT is still the best way of observing such a test.

It has been almost two years since the CTBT was submitted for ratification to the Senate. Since then it has come under political fire from Senator Jesse Helms, chairman of the Senate Foreign Relations Committee, who has delayed ratification of the treaty. America and Russia are the last two major nuclear weapon states to ratify the CTBT. Delays in ratifying the CTBT in the Senate has put the treaty in doubt and delayed ratification of START II in Russia. It has also jeopardised negotiations on START III, the next round of disarmament discussions between Russia and the US.