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