To solve the problem of the lack of evidence of a nuclear
disintegration he came up with a 'voltage-multiplying'
circuit that used capacitors (also known as condensers)
to produce a high voltage direct current from a much
lower voltage alternating current. He and Walton erected
a column of five rectifier diodes and capacitors to
produce a DC voltage four times greater than the transformer
in May 1931 the room that Cockcroft and Walton were
using had to be vacated, so they moved to the old Balfour
Library which had a much higher ceiling. With the help
of a £600 grant they could build a generator capable
of around 500-700 kV, which they hoped to be enough
to produce the disintegrations that they had missed
at 300 kV. When the apparatus was completed they continued
looking for gamma rays.