Electrical shielding against ionizing radiation?

Hi,

yesterday I re-read the part about shielding in the 75 summer study,
especially with an eye towards ionizing particle radiation.

As you probably know, much of this radiation is kept away from us
by the earths magnetic field. (But still we are punctured by
several of these particles per minute.)

The study considered magnetic shielding, concluded it to be too heavy.

It considered electrical shielding, which would mean to create an electric
field of "10 billion volts". This by itself seemed to be enough to
stop thinking about it. But its not obvious to me.

What's the problem of charging some metal-net or metal-sheet up to 10GV?
In vacuum, of course.