HC Deb 22 February 1960 vol 618 c6W
58. Mr. P. Noel-Baker

asked the Secretary of State for Foreign Affairs up to what yield in kilotons nuclear test explosions will be permitted under the present proposals made in Geneva by the United States delegate with the support of Her Majesty's Government.

Mr. R. Allan

Under the American proposals the treaty would begin by prohibiting underground tests down to the lowest limit for which effective control can now be foreseen. This limit would depend on the number of inspections which could be agreed. Assuming a reasonable number of inspections, the United States has suggested a limit of 4.75 on the scale of earthquake magnitude as recorded by instruments of the control system. Soviet and Western scientists have differed about the magnitudes which underground explosions of varying sizes would show on the instruments. Soviet scientists have considered a magnitude of 4.75 to be equivalent to an underground explosion of about two kilotons. The estimate of British and American scientists is nearly twenty kilotons. The purpose of expressing the limit as a magnitude instead of a kiloton yield is to circumvent this difference, which we hope can be resolved, amongst others, by the further research called for in the American proposal.