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