6.—(1) This Regulation shall apply in relation to the use of—
(a)any radioactive substance which has an activity in excess of 0.002 of a microcurie per gram, or
(b)any apparatus in which electrons are accelerated by a potential difference of at least 5 kilovolts other than—
(i)a television receiving set, or
(ii)an apparatus designed primarily to produce visual images derived from video recordings, closed circuit television equipment or the output of a computer.
(2) No such substance or apparatus shall be used for the purposes of instruction at a school or further education establishment unless that use is for the time being approved by the Secretary of State; and an approval given for the purposes hereof shall be withdrawn if at any time the Secretary of State is of the opinion that the arrangements made for the health and safety of the pupils and staff at the school or establishment are inadequate.