['< sod > this new research has dramatically also increased the quantity of positrons that experimentalists can produce. physicists working at the [ [ lawrence livermore national laboratory ] ] in california often have used a short, thin ultra - intense laser to irradiate a millimetre - thick gold target and produce more than than 100 billion positrons. < ref > < ref eod > < sod > physicists at the [ [ lawrence livermore national laboratory ] ] in california have used a short, ultra - intense laser to continuously irradiate a millimetre - thick gold target and produce more than another 100 billion positrons. < br ref > < eod >']