This involved, amongst other things, research into more efficient phosphors. In the middle nineties, the Japanese examined some of these efficient light-activated phosphors for use outside of lamps. As a side benefit, this phosphor is moisture resistant, and UV light resistant. The X-rays are shielded by using leaded glass or leaded acrylic resin as a crystal. Also, sapphire crystals cannot be leaded.
Manufacturers do it because it is so cheap.
The last U. S. high neutron flux reactor at Savannah River was shut down in 1988. Medical isotopes that must be produced by neutron activation are made in Canada at Chalk River or in Europe. It will not be until the first half of the next decade before there will be a domestic source of high flux neutrons. The patent was applied for in 1978 and granted in 1981. This fell to mb-microtec.