117. Mrs. Butlerasked the Minister of Health, as representing the Minister for Science, what was the date on which particles of sufficient radioactivity to kill living cells which come into direct contact with them were first discovered in the fall-out in Great Britain by scientists advising the Government; and what is the size and date of discovery of the largest particle thus observed.
§ Mr. Walker-SmithAll radioactive particles whether arising from natural sources or from nuclear tests are capable in appropriate circumstances of inducing lethal damage to human cells. Particles of measurable size have been detected in fall-out since 1950. Studies have been made in the past of the sizes of particles arising from nuclear tests but it is the total radioactivity from this source which is considered to be of main significance for human health and this is what is now regularly measured.